Publications by authors named "Marco Yu"

73 Publications

Deep-learning-based cardiovascular risk stratification using coronary artery calcium scores predicted from retinal photographs.

Lancet Digit Health 2021 05;3(5):e306-e316

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Ophthalmology and Visual Sciences Academic Clinical Program, Duke-NUS Medical School, Singapore.

Background: Coronary artery calcium (CAC) score is a clinically validated marker of cardiovascular disease risk. We developed and validated a novel cardiovascular risk stratification system based on deep-learning-predicted CAC from retinal photographs.

Methods: We used 216 152 retinal photographs from five datasets from South Korea, Singapore, and the UK to train and validate the algorithms. First, using one dataset from a South Korean health-screening centre, we trained a deep-learning algorithm to predict the probability of the presence of CAC (ie, deep-learning retinal CAC score, RetiCAC). We stratified RetiCAC scores into tertiles and used Cox proportional hazards models to evaluate the ability of RetiCAC to predict cardiovascular events based on external test sets from South Korea, Singapore, and the UK Biobank. We evaluated the incremental values of RetiCAC when added to the Pooled Cohort Equation (PCE) for participants in the UK Biobank.

Findings: RetiCAC outperformed all single clinical parameter models in predicting the presence of CAC (area under the receiver operating characteristic curve of 0·742, 95% CI 0·732-0·753). Among the 527 participants in the South Korean clinical cohort, 33 (6·3%) had cardiovascular events during the 5-year follow-up. When compared with the current CAC risk stratification (0, >0-100, and >100), the three-strata RetiCAC showed comparable prognostic performance with a concordance index of 0·71. In the Singapore population-based cohort (n=8551), 310 (3·6%) participants had fatal cardiovascular events over 10 years, and the three-strata RetiCAC was significantly associated with increased risk of fatal cardiovascular events (hazard ratio [HR] trend 1·33, 95% CI 1·04-1·71). In the UK Biobank (n=47 679), 337 (0·7%) participants had fatal cardiovascular events over 10 years. When added to the PCE, the three-strata RetiCAC improved cardiovascular risk stratification in the intermediate-risk group (HR trend 1·28, 95% CI 1·07-1·54) and borderline-risk group (1·62, 1·04-2·54), and the continuous net reclassification index was 0·261 (95% CI 0·124-0·364).

Interpretation: A deep learning and retinal photograph-derived CAC score is comparable to CT scan-measured CAC in predicting cardiovascular events, and improves on current risk stratification approaches for cardiovascular disease events. These data suggest retinal photograph-based deep learning has the potential to be used as an alternative measure of CAC, especially in low-resource settings.

Funding: Yonsei University College of Medicine; Ministry of Health and Welfare, Korea Institute for Advancement of Technology, South Korea; Agency for Science, Technology, and Research; and National Medical Research Council, Singapore.
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http://dx.doi.org/10.1016/S2589-7500(21)00043-1DOI Listing
May 2021

The global extent of undetected glaucoma in adults: a systematic review and meta-analysis.

Ophthalmology 2021 Apr 15. Epub 2021 Apr 15.

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Yong Loo Lin School of Medicine, National University of Singapore, Singapore; Ophthalmology & Visual Sciences Academic Clinical Program (Eye ACP), Duke-NUS Medical School, Singapore. Electronic address:

Topic: Glaucoma is the leading cause of irreversible blindness despite having good prognosis with early treatment. We evaluated the global extent of undetected glaucoma and the factors associated with it in this systematic review and meta-analysis of population-based epidemiological studies.

Clinical Relevance: Undetected glaucoma increases the risk of vision impairment, which leads to detrimental effects on the quality-of-life and socio-economic well-being of those affected. Detailed information on the extent and factors associated with undetected glaucoma aid in the development of public health interventions.

Methods: We conducted a systematic review and meta-analysis of population-based studies published between January 1, 1990 to June 1, 2020. Article search was conducted in online databases (PubMED, Web-of-Science), grey literatures (opengrey) and non-government organization (NGOs) reports. Our outcome measure was the proportion of glaucoma cases that were undetected previously. Manifest glaucoma included any form of glaucoma reported in the respective study and may include primary-open-angle-glaucoma (POAG), primary-angle-closure-glaucoma (PACG), and/or secondary glaucoma. Undetected glaucoma was defined as glaucoma cases that were undetected prior to diagnosis in the respective study. Random-effect meta-analysis was used to estimate the pooled proportion and factors associated with undetected glaucoma. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines in our study.

Results: We identified 61 articles from 55 population-based studies (N= 189,359 participants; N= 6,949 manifest glaucoma; N= 5,558 undetected glaucoma). Globally, more than half of all glaucoma cases were previously undetected in each geographical region. Regionally, Africa (OR 12.70, 95% CI 4.91, 32.86) and Asia (OR 3.41, 95% CI 1.63, 7.16) had higher odds of undetected glaucoma as compared to Europe. Countries with low human development index (HDI, <0.55) had higher proportion of undetected manifest glaucoma as compared to countries of medium to very high HDI (≥0.55, all P <0.001). In 2020, 43.78 million POAG cases were undetected, of which 76.7% reside in Africa and Asia.

Conclusion: Undetected glaucoma is highly prevalent across diverse communities worldwide, and more common in Africa and Asia. Strategies to improve detection are needed to prevent excess visual disability and blindness due to glaucoma.
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http://dx.doi.org/10.1016/j.ophtha.2021.04.009DOI Listing
April 2021

Utilisation of poor-quality optical coherence tomography scans: adjustment algorithm from the Singapore Epidemiology of Eye Diseases (SEED) study.

Br J Ophthalmol 2021 Feb 15. Epub 2021 Feb 15.

Singapore Eye Research Institute, Singapore

Purpose: To evaluate the effect of signal strength (SS) on optical coherence tomography (OCT) parameters, and devise an algorithm to adjust the effect, when acceptable SS cannot be obtained.

Methods: 5085 individuals (9582 eyes), aged ≥40 years from the Singapore Epidemiology of Eye Diseases population-based study were included. Everyone underwent a standardised ocular examination and imaging with Cirrus HD-OCT. Effect of SS was evaluated using multiple structural breaks linear mixed-effect models. Expected change for increment in SS between 4 and 10 for individual parameter was calculated. Subsequently we devised and evaluated an algorithm to adjust OCT parameters to higher SS.

Results: Average retinal nerve fibre layer (RNFL) thickness showed shift of 4.11 µm from SS of 5 to 6. Above 6, it increased by 1.72 and 3.35 µm to 7 and 8; and by 1.09 µm (per unit increase) above 8 SS. Average ganglion cell-inner plexiform layer (GCIPL) thickness shifted 5.15 µm from SS of 5 to 6. Above 6, increased by 0.94 µm from 7 to 8; and by 0.16 µm (per unit increase) above 8 SS. When compared with reference in an independent test set, the algorithm produced less systemic bias. Algorithm-adjusted average RNFL was 0.549 µm thinner than the reference, while the unadjusted one was 2.841 µm thinner (p<0.001). Algorithm-adjusted and unadjusted average GCIPL was 1.102 µm and 2.228 µm thinner (p<0.001).

Conclusions: OCT parameters can be adjusted for poor SS using an algorithm. This can potentially assist in diagnosis and monitoring of glaucoma when scans with acceptable SS cannot be acquired from patients in clinics.
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http://dx.doi.org/10.1136/bjophthalmol-2020-317756DOI Listing
February 2021

Quantitative OCT angiography of the retinal microvasculature and choriocapillaris in highly myopic eyes with myopic macular degeneration.

Br J Ophthalmol 2021 Jan 4. Epub 2021 Jan 4.

Singapore Eye Research Institute, Singapore National Eye Center, Singapore.

Purpose: To quantify retinal and choriocapillaris (CC) microvasculature in highly myopic (HM) eyes with myopic macular degeneration (MMD) using swept-source optical coherence tomography angiography (SS-OCTA).

Methods: 162 HM eyes (spherical equivalent ≤ -6.0 dioptres or axial length (AL) ≥26.5 mm) from 98 participants were enrolled, including 60 eyes (37.0%) with tessellated fundus, 54 eyes (33.3%) with peripapillary diffuse chorioretinal atrophy (PDCA), 27 eyes (16.7%) with macular diffuse chorioretinal atrophy (MDCA) and 21 eyes (13.0%) with patchy or macular atrophy. PLEX Elite 9000 SS-OCTA was performed to obtain perfusion densities (PD) of the superficial and deep retinal capillary plexus, and CC signal voids (number, area and density).

Results: Retinal PD decreased with increasing severity of MMD. Multivariable analysis showed that after adjustment of age and other factors, retinal PD decreased significantly in eyes with longer AL (β≤-0.51, p<0.001) and with an MMD severity of MDCA or worse (β≤-1.63, p<0.001). Reduced retinal PD were significantly associated with worse vision (β≤-0.01, p≤0.04). In terms of CC signal voids, multivariable analysis showed that longer AL (p<0.001), but not MMD severity (p≥0.12) was significantly associated with CC signal void changes in the earliest stage of MMD.

Conclusion: We demonstrate significant OCTA alterations in the retina and CC in HM eyes with varying severities of MMD. In eyes with early-stage PDCA, lower retinal PD and more extensive CC signal voids are predominantly associated with increasing AL. In contrast, in eyes with MDCA or worse, MMD itself was associated with sparser retinal and CC circulation.
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http://dx.doi.org/10.1136/bjophthalmol-2020-317632DOI Listing
January 2021

Progression of Macular Vessel Density in Primary Open-Angle Glaucoma: A Longitudinal Study.

Am J Ophthalmol 2021 03 24;223:259-266. Epub 2020 Oct 24.

Eye Hospital and School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou, Zhejiang, China; National Clinical Research Center for Ocular Diseases, Wenzhou, Zhejiang, China. Electronic address:

Purpose: To evaluate the rate of progression of macular vessel density (mVD) in primary open-angle glaucoma (POAG) and explore the relationship between the progression of mVD and macular ganglion cell-inner plexiform layer (mGCIPL) thickness and parapapillary retinal nerve fiber layer (pRNFL) thickness.

Design: Prospective cohort study.

Methods: In this study, 102 eyes with POAG were followed for 36.6 ± 6.4 months. The rates of progression were estimated by linear models. The agreement of progression detection among the 3 parameters was evaluated with Kappa statistics. The influence of baseline measurements on the rates of progression of mGCIPL thickness, pRNFL thickness, and mVD was investigated by linear mixed modeling. Kaplan-Meier survival analysis was adopted to calculate the survival probabilities.

Results: The respective rate of progression by linear regression was -0.102 ± 0.054 μm/month, -0.160 ± 0.086 μm/month, and -0.199 ± 0.073 %/month for mGCIPL thickness, pRNFL thickness, and mVD. The agreement in detection of progression among them was poor with the Conger's Kappa coefficient of 0.098 (95% confidence interval: -0.025~0.220, P = .116). The significant factors influencing the rate of progression of mVD were baseline mGCIPL thickness, baseline pRNFL thickness, and baseline mVD (P ≤ .001), while baseline mVD was not a significant factor influencing the rates of progression of mGCIPL thickness and pRNFL thickness (P ≥ .659). Also, pRNFL thickness had a better survival probability compared with the other 2 parameters (P = .025).

Conclusions: The mGCIPL thickness, pRNFL thickness, and mVD decreased over time in POAG eyes. The rate of reduction of mVD was significantly influenced by the baseline measurements of mGCIPL thickness, pRNFL thickness, and mVD.
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http://dx.doi.org/10.1016/j.ajo.2020.10.008DOI Listing
March 2021

Prediction of systemic biomarkers from retinal photographs: development and validation of deep-learning algorithms.

Lancet Digit Health 2020 10;2(10):e526-e536

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Ophthalmology and Visual Sciences Academic Clinical Program, Duke-NUS Medical School, Singapore. Electronic address:

Background: The application of deep learning to retinal photographs has yielded promising results in predicting age, sex, blood pressure, and haematological parameters. However, the broader applicability of retinal photograph-based deep learning for predicting other systemic biomarkers and the generalisability of this approach to various populations remains unexplored.

Methods: With use of 236 257 retinal photographs from seven diverse Asian and European cohorts (two health screening centres in South Korea, the Beijing Eye Study, three cohorts in the Singapore Epidemiology of Eye Diseases study, and the UK Biobank), we evaluated the capacities of 47 deep-learning algorithms to predict 47 systemic biomarkers as outcome variables, including demographic factors (age and sex); body composition measurements; blood pressure; haematological parameters; lipid profiles; biochemical measures; biomarkers related to liver function, thyroid function, kidney function, and inflammation; and diabetes. The standard neural network architecture of VGG16 was adopted for model development.

Findings: In addition to previously reported systemic biomarkers, we showed quantification of body composition indices (muscle mass, height, and bodyweight) and creatinine from retinal photographs. Body muscle mass could be predicted with an R of 0·52 (95% CI 0·51-0·53) in the internal test set, and of 0·33 (0·30-0·35) in one external test set with muscle mass measurement available. The R value for the prediction of height was 0·42 (0·40-0·43), of bodyweight was 0·36 (0·34-0·37), and of creatinine was 0·38 (0·37-0·40) in the internal test set. However, the performances were poorer in external test sets (with the lowest performance in the European cohort), with R values ranging between 0·08 and 0·28 for height, 0·04 and 0·19 for bodyweight, and 0·01 and 0·26 for creatinine. Of the 47 systemic biomarkers, 37 could not be predicted well from retinal photographs via deep learning (R≤0·14 across all external test sets).

Interpretation: Our work provides new insights into the potential use of retinal photographs to predict systemic biomarkers, including body composition indices and serum creatinine, using deep learning in populations with a similar ethnic background. Further evaluations are warranted to validate these findings and evaluate the clinical utility of these algorithms.

Funding: Agency for Science, Technology, and Research and National Medical Research Council, Singapore; Korea Institute for Advancement of Technology.
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http://dx.doi.org/10.1016/S2589-7500(20)30216-8DOI Listing
October 2020

Reporting on deep learning algorithms in health care.

Lancet Digit Health 2019 11;1(7):e328-e329

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore; Ophthalmology and Visual Sciences Academic Clinical Program (Eye ACP), Duke-NUS Medical School, Singapore. Electronic address:

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http://dx.doi.org/10.1016/S2589-7500(19)30132-3DOI Listing
November 2019

Anterior chamber angle imaging with swept-source optical coherence tomography: comparison between CASIAII and ANTERION.

Sci Rep 2020 10 30;10(1):18771. Epub 2020 Oct 30.

Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong Eye Hospital, Kowloon, Hong Kong, People's Republic of China.

This study compared the test-retest variabilities and measurement agreement of anterior chamber angle (ACA) dimensions measured by two anterior segment swept-source optical coherence tomography (SS-OCT)-the ANTERION (Heidelberg Engineering, Heidelberg, Germany) and CASIAII (Tomey, Nagoya, Japan). Thirty-eight subjects, 18 patients with primary angle closure and 20 healthy participants with open angles, were included. The mean age was 54.7 ± 15.8 years (range: 26-75 years). One eye of each subject was randomly selected for anterior segment imaging by ANTERION and CASIAII, using the same scan pattern (6 evenly spaced radial scans across the anterior segment for three times) in the same visit. The between- and within-instrument agreement and repeatability coefficients of angle open distance (AOD500), trabecular-iris space area (TISA500), lens vault (LV), scleral spur-scleral spur distance (SSD), anterior chamber depth (ACD), and pupil diameter (PD) were measured. The anterior and posterior boundaries of the cornea, iris, and lens were automatically segmented by the SS-OCT instruments; the scleral spur was manually located by a single masked observer. There were significant differences between ANTERION and CASIAII measurements; the SSD, PD, and ACD were smaller whereas AOD500 and TISA500 were greater in ANTERION compared with CASIAII (P < 0.001). Anterior segment measurements obtained from the two SS-OCT instruments showed strong associations (R ranged between 0.866 and 0.998) although the between-instrument agreement was poor; the spans of 95% limits of between-instrument agreement were ≥ 1.5-folds than the within-instrument agreement for either instrument. Whereas both SS-OCT instruments showed low test-retest measurement variabilities, the repeatability coefficients of AOD500, TISA500, ACD, and PD were slightly smaller for CASIAII than ANTERION (P ≤ 0.012).
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http://dx.doi.org/10.1038/s41598-020-74813-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7603499PMC
October 2020

A deep-learning system for the assessment of cardiovascular disease risk via the measurement of retinal-vessel calibre.

Nat Biomed Eng 2020 Oct 12. Epub 2020 Oct 12.

Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Singapore.

Retinal blood vessels provide information on the risk of cardiovascular disease (CVD). Here, we report the development and validation of deep-learning models for the automated measurement of retinal-vessel calibre in retinal photographs, using diverse multiethnic multicountry datasets that comprise more than 70,000 images. Retinal-vessel calibre measured by the models and by expert human graders showed high agreement, with overall intraclass correlation coefficients of between 0.82 and 0.95. The models performed comparably to or better than expert graders in associations between measurements of retinal-vessel calibre and CVD risk factors, including blood pressure, body-mass index, total cholesterol and glycated-haemoglobin levels. In retrospectively measured prospective datasets from a population-based study, baseline measurements performed by the deep-learning system were associated with incident CVD. Our findings motivate the development of clinically applicable explainable end-to-end deep-learning systems for the prediction of CVD on the basis of the features of retinal vessels in retinal photographs.
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http://dx.doi.org/10.1038/s41551-020-00626-4DOI Listing
October 2020

Six-Year Incidence and Risk Factors of Primary Glaucoma in the Singapore Indian Eye Study.

Ophthalmol Glaucoma 2021 Mar-Apr;4(2):201-208. Epub 2020 Sep 15.

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Republic of Singapore; Duke-NUS, National University of Singapore, Singapore, Republic of Singapore. Electronic address:

Purpose: To determine the 6-year incidence of primary glaucoma and its risk factors in an Indian population in Singapore.

Design: Cohort population-based study.

Participants: Indian adults between 40 and 80 years of age living in Singapore. A total of 3400 participants underwent the baseline examination between 2007 and 2009. Of them, 2200 (response rate, 75.5% of those eligible) participated in the 6-year follow-up visit between 2013 and 2015.

Methods: Standardized examination and investigations were performed, including indentation gonioscopy, intraocular pressure (IOP) measurement, optic disc examination, and static automated perimetry. Glaucoma was defined according to the International Society Geographical and Epidemiological Ophthalmology criteria.

Main Outcome Measures: Incidences of primary open-angle glaucoma (POAG) and primary angle-closure glaucoma (PACG).

Results: The age-standardized incidences of primary glaucoma, POAG, and PACG were 1.68% (95% confidence interval [CI], 1.21%-2.32%), 1.37% (95% CI, 0.94%-1.96%), and 0.32% (95% CI, 0.15%-0.66%), respectively. For eyes with ocular hypertension (n = 45) at baseline, the incidence of POAG was 4.83% (95% CI, 1.24%-17.21%) and for eyes with primary angle closure (n = 14) or suspected primary angle closure (n = 101), the incidence of PACG developing was 1.82% (95% CI, 0.37%-9.68%). Baseline factors associated significantly with risk of primary glaucoma developing included older age (per decade; odds ratio [OR], 1.84; 95% CI, 1.44-2.36; P < 0.001), larger vertical cup-to-disc ratio (per 0.1 unit; OR, 2.78; 95% CI, 2.12-3.64; P < 0.001), and higher IOP (per millimeter of mercury; OR, 1.25; 95% CI, 1.13-1.38; P < 0.001). However, 71 of 85 eyes (84.5%) diagnosed with incident glaucoma had IOP of less than 21 mmHg at the time of examination.

Conclusions: Our study showed that the overall age-standardized incidence of primary glaucoma was 1.68% in an Indian population in Singapore. In our population, the incidence of POAG was only half and the incidence of PACG was similar to the incidence reported by the Chennai Eye Disease Study.
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http://dx.doi.org/10.1016/j.ogla.2020.09.004DOI Listing
September 2020

Evaluation of Primary Angle-Closure Glaucoma Susceptibility Loci for Estimating Angle Closure Disease Severity.

Ophthalmology 2021 Mar 16;128(3):403-409. Epub 2020 Jul 16.

Singapore Eye Research Institute, Singapore National Eye Centre, Singapore, Republic of Singapore; Ophthalmology and Visual Sciences Academic Clinical Program (Eye ACP), DukeNUS Medical School, Singapore, Republic of Singapore; Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.

Purpose: To investigate whether recently identified genetic loci for primary angle-closure glaucoma (PACG) are associated with disease severity.

Design: Case-control study.

Participants: Eight hundred four PACG patients and 943 control participants of Chinese ethnicity from Singapore.

Methods: The 8 PACG-associated single nucleotide polymorphisms (SNPs; rs11024102 at PLEKHA7, rs3753841 at COL11A1, rs1015213 located between PCMTD1 and ST18 on chromosome 8q, rs3816415 at EPDR1, rs1258267 at CHAT, rs736893 at GLIS3, rs7494379 at FERMT2, and rs3739821 mapping in between DPM2 and FAM102A) identified from genome-wide association studies were tested for association with disease severity using logistic regression adjusted for age and gender. A P value of 0.006 was set as significant after Bonferroni correction for testing of 8 loci. We also calculated the weighted genetic risk score (GRS) weighted by the estimated individual SNP effect size on PACG calculated as logarithm of the odds ratio (OR). Disease severity was based on the visual field mean deviation (MD) and classified as early to moderate (MD, >-12 dB) and severe (MD, <-20 dB).

Main Outcome Measures: Association of PACG loci with severe disease.

Results: Of the 804 PACG patients, genotyping data were available for 768 individuals and included 436 with mild-to-moderate PACG and 206 with severe PACG. The PACG patients were significantly older (mean age, 64.3 ± 9.1 years vs. 56.4 ± 8.9 years; P < 0.001) and there were proportionately more women compared with control participants (58.4% vs. 49.0%; P < 0.001). Of the 8 loci investigated, we observed significant evidence of association with severe PACG at 1 SNP, namely rs3816415 in EPDR1 (OR, 2.03; 95% confidence interval [CI], 1.49-2.78; P = 1 × 10). A higher-weighted GRS was associated significantly with severe PACG, with an OR of 3.11 (95% CI, 1.95-4.96) comparing the lowest quartile with the highest quartile.

Conclusions: Our results show that EPDR1 is associated significantly with severe PACG, suggesting that it may predispose patients to more aggressive disease development. Individuals with PACG with a higher GRS were associated with a higher risk of severe PACG.
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http://dx.doi.org/10.1016/j.ophtha.2020.07.027DOI Listing
March 2021

Outcomes and complications in scleral-fixated intraocular lens implantations.

Int Ophthalmol 2020 Nov 1;40(11):2969-2977. Epub 2020 Jul 1.

Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.

Purpose: This study compares outcomes and complications of scleral-fixated intraocular lens implantation between 2 levels of surgeons.

Methods: A retrospective case series of patients undergoing scleral-fixated intraocular lens implantation at Prince of Wales Hospital, Hong Kong, between May 2012 and April 2017 were reviewed. Data collected included age, gender, affected eye, preoperative and postoperative visual acuities, refractive target and outcome, surgeon profile, operative details including method of scleral fixation, intraoperative and postoperative complications and length of follow-up.

Results: Ninety eyes of 90 patients were included for analyses. The mean LogMAR visual acuities were 1.17 ± 0.70 at postoperative week 1, 0.81 ± 0.56 at 1 month, 0.66 ± 0.55 at 3 months, 0.56 ± 0.59 at 6 months, and 0.51 ± 0.60 at 1 year, respectively. After adjusting for age at operation, operative time, axial length, subspecialty of the surgeon and preoperative LogMAR, surgeon seniority was not significantly associated with final visual outcomes. There was no statistically significant difference between the mean improvement in visual acuities between eyes operated by consultants and fellows under direct supervision of a senior surgeon.

Conclusion: Scleral-fixated intraocular lens implantation is safe and effective in improving visual acuity in aphakic adults without capsular support. Under good supervision, fellows were able to produce comparable results compared with experienced specialists.
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http://dx.doi.org/10.1007/s10792-020-01480-8DOI Listing
November 2020

Independent Influence of Parental Myopia on Childhood Myopia in a Dose-Related Manner in 2,055 Trios: The Hong Kong Children Eye Study.

Am J Ophthalmol 2020 10 23;218:199-207. Epub 2020 May 23.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong; Department of Ophthalmology and Visual Sciences, Prince of Wales Hospital, Hong Kong; Hong Kong Eye Hospital, Hong Kong. Electronic address:

Purpose: To determine the effects on childhood myopia of parental myopia, parental education, children's outdoor time, and children's near work.

Design: Population-based cross-sectional study.

Methods: A total of 6,155 subjects in 2,055 family trios (1 child and both parents). Cycloplegic autorefraction was measured for children and noncycloplegic autorefraction for parents. Parental education, children's outdoor time, and near work were collected by questionnaires. Children were categorized into 10 groups based on parental myopia levels. Associations of the above factors with myopia were evaluated by regression analyses. The areas under the receiver operating characteristic curve (AUROCs) for myopia were evaluated.

Results: Mild parental myopia did not increase childhood myopia's risk, but the risk was 11.22-folds when both parents were highly myopic. Higher parental education (Father: OR 1.08, P = .046; Mother: OR 1.11, P = .001) and more reading time of children were risk factors (OR 1.21, P = .044). Reduced odds of myopia were associated with more time spent on outdoor activities (OR 0.78, P = .017). Notably, all these factors became insignificant after adjustment, except for parental myopia. Children with more severe parental myopia spent more time on reading, but less on electronic devices. Parental myopic status alone accounted for 11.82% of myopia variation in children. With age and parental myopia, the AUROC for myopia was 0.731.

Conclusions: Among parental and environmental factors, parental myopia confers, in a dose-related manner, the strongest independent effect on childhood myopia. Therefore children with high risk of myopia can be identified for early prevention, based on parental myopia data.
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http://dx.doi.org/10.1016/j.ajo.2020.05.026DOI Listing
October 2020

Prevalence and Pattern of Geographic Atrophy in Asia: The Asian Eye Epidemiology Consortium.

Ophthalmology 2020 10 25;127(10):1371-1381. Epub 2020 Apr 25.

Medical Research Foundation, Sankara Nethralaya, Chennai, India.

Purpose: Although there have been many population-based studies of age-related macular degeneration (AMD), only limited information is available in Asia on the epidemiology of geographic atrophy (GA). We aimed to determine the prevalence and patterns of GA through an analysis of multiple studies conducted within the Asian Eye Epidemiology Consortium (AEEC).

Design: Cross-sectional meta-analyses.

Participants: A total of 97 213 individuals aged 40 years and older.

Methods: Data from 22 population-based studies from countries belonging to the AEEC were included. In all studies, AMD was defined on the basis of standardized grading systems. Geographic atrophy was defined as an area of pallor in the fundus with visibility of the underlying choroidal blood vessels and sharply defined borders. Random-effects meta-analysis was performed to estimate overall and age-, gender-, and region-specific pooled prevalence of GA.

Main Outcome Measures: Prevalence of GA per 1000 persons.

Results: The mean age was 60.8 ± 10.0 years, and 42 673 (43.9%) were male. Overall, a total of 223 individuals (0.2%) had GA. The pooled overall prevalence of GA was 1.57 per 1000 persons (95% confidence interval [CI], 1.04-2.10), which was 3 times less than that of neovascular AMD of 5.20 per 1000 persons (95% CI, 3.97-6.43). Compared with those aged 50 to 59 years, the prevalence of GA increased from 0.34 per 1000 persons (95% CI, 0.07-0.62) to 2.90 per 1000 persons (95% CI, 1.55-4.25) in those aged ≥70 years. The GA prevalence per 1000 persons was similar between urban (2.22; 95% CI, 1.22-3.23) and rural residents (1.33; 95% CI, 0.70-1.96). Geographic atrophy was more prevalent in South Asia (based on studies from India and Nepal, 3.82 per 1000 persons; 95% CI, 1.72-5.93) compared with East Asia (based on studies from China, Korea, Hong Kong, Taiwan, and Japan, and the Singapore Chinese Eye Study, 0.76 per 1000 persons; 95% CI, 0.31-1.22, P = 0.005).

Conclusions: Geographic atrophy is uncommon in Asian populations compared with those of European ancestry. Even within Asia, geographic differences in GA prevalence were seen. The findings of this meta-analysis suggest that better dissection of risk factors in the Asian population for GA may provide insights into the biological pathways that drive these late-stage manifestations, thus suggesting better targets for prevention.
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http://dx.doi.org/10.1016/j.ophtha.2020.04.019DOI Listing
October 2020

Technical and imaging factors influencing performance of deep learning systems for diabetic retinopathy.

NPJ Digit Med 2020 23;3:40. Epub 2020 Mar 23.

1Singapore Eye Research Institute, Singapore National Eye Center, Singapore, Singapore.

Deep learning (DL) has been shown to be effective in developing diabetic retinopathy (DR) algorithms, possibly tackling financial and manpower challenges hindering implementation of DR screening. However, our systematic review of the literature reveals few studies studied the impact of different factors on these DL algorithms, that are important for clinical deployment in real-world settings. Using 455,491 retinal images, we evaluated two technical and three image-related factors in detection of referable DR. For technical factors, the performances of four DL models (VGGNet, ResNet, DenseNet, Ensemble) and two computational frameworks (Caffe, TensorFlow) were evaluated while for image-related factors, we evaluated image compression levels (reducing image size, 350, 300, 250, 200, 150 KB), number of fields (7-field, 2-field, 1-field) and media clarity (pseudophakic vs phakic). In detection of referable DR, four DL models showed comparable diagnostic performance (AUC 0.936-0.944). To develop the VGGNet model, two computational frameworks had similar AUC (0.936). The DL performance dropped when image size decreased below 250 KB (AUC 0.936, 0.900,  < 0.001). The DL performance performed better when there were increased number of fields (dataset 1: 2-field vs 1-field-AUC 0.936 vs 0.908,  < 0.001; dataset 2: 7-field vs 2-field vs 1-field, AUC 0.949 vs 0.911 vs 0.895). DL performed better in the pseudophakic than phakic eyes (AUC 0.918 vs 0.833,  < 0.001). Various image-related factors play more significant roles than technical factors in determining the diagnostic performance, suggesting the importance of having robust training and testing datasets for DL training and deployment in the real-world settings.
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http://dx.doi.org/10.1038/s41746-020-0247-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7090044PMC
March 2020

Use of Virtual Reality Simulation to Identify Vision-Related Disability in Patients With Glaucoma.

JAMA Ophthalmol 2020 05;138(5):490-498

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, People's Republic of China.

Importance: Clinical assessment of vision-related disability is hampered by the lack of instruments to assess visual performance in real-world situations. Interactive virtual reality (VR) environments displayed in a binocular stereoscopic VR headset have been designed, presumably simulating day-to-day activities to evaluate vision-related disability.

Objective: To investigate the application of VR to identify vision-related disability in patients with glaucoma.

Design, Setting, And Participants: In a cross-sectional study, 98 patients with glaucoma and 50 healthy individuals were consecutively recruited from a university eye clinic; all participants were Chinese. The study was conducted between August 30, 2016, and July 31, 2017; data analysis was performed from December 1, 2017, to October 30, 2018.

Exposures: Measurements of visual acuity, contrast sensitivity, visual field (VF), National Eye Institute 25-item Visual Function Questionnaire Rasch score, and VR disability scores determined from 5 VR simulations: supermarket shopping, stair and city navigations in daytime, and stair and city navigations in nighttime. Duration required to complete the simulation, number of items incorrectly identified, and number of collisions were measured to compute task-specific and overall VR disability scores. Vision-related disability was identified when the VR disability score was outside the normal age-adjusted 95% confidence region.

Main Outcomes And Measures: Virtual reality disability score.

Results: In the 98 patients with glaucoma, mean (SD) age was 49.8 (11.6) years and 60 were men (61.2%); in the 50 healthy individuals, mean (SD) age was 48.3 (14.8) years and 16 were men (32.0%). The patients with glaucoma had different degrees of VF loss (122 eyes [62.2%] had moderate or advanced VF defects). The time required to complete the activities by patients with glaucoma vs healthy individuals was longer by 15.2 seconds (95% CI, 5.5-24.9 seconds) or 34.1% (95% CI, 12.4%-55.7%) for the shopping simulation, 72.8 seconds (95% CI, 23.0-122.6 seconds) or 33.8% (95% CI, 10.7%-56.9%) for the nighttime stair navigation, and 38.1 seconds (95% CI, 10.9-65.2 seconds) or 30.8% (95% CI, 8.8%-52.8%) for the nighttime city navigation. The mean (SD) duration was not significantly different between the glaucoma and healthy groups in daytime stair (203.7 [93.7] vs 192.9 [89.1] seconds, P = .52) and city (118.7 [41.5] vs 117.0 [52.3] seconds, P = .85) navigation. For each decibel decrease in binocular VF sensitivity, the risk of collision increased by 15% in nighttime stair (hazard ratio [HR], 1.15; 95% CI, 1.08-1.22) and city (HR, 1.15; 95% CI, 1.08-1.23) navigations. Fifty-eight patients (59.1%) with glaucoma had vision-related disability in at least 1 simulated daily task; a higher proportion of patients had vision-related disability in nighttime city (27 of 88 [30.7%]) and stair (27 of 90 [30.0%]) navigation than in daytime city (7 of 88 [8.0%]) and stair (19 of 96 [19.8%]) navigation. The overall VR disability score was associated with the National Eye Institute 25-item Visual Function Questionnaire Rasch score (R2 = 0.207).

Conclusions And Relevance: These findings suggest that vision-related disability is associated with lighting condition and task in patients with glaucoma. Virtual reality may allow eye care professionals to understand the patients' perspectives on how visual impairment imparts disability in daily living and provide a new paradigm to augment the assessment of vision-related disability.
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http://dx.doi.org/10.1001/jamaophthalmol.2020.0392DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225912PMC
May 2020

Do we have enough ophthalmologists to manage vision-threatening diabetic retinopathy? A global perspective.

Eye (Lond) 2020 07 28;34(7):1255-1261. Epub 2020 Jan 28.

Singapore Eye Research Institute, Singapore National Eye Centre, The Academia, 20 College Road, Discovery Tower Level 6, Singapore, 169856, Singapore.

We aimed to estimate the supply of ophthalmologists in relation to the global and regional burden of vision-threatening diabetic retinopathy (VTDR). Diabetes mellitus (DM) population data from seven world regions were obtained from the International Diabetes Federation Atlas 2017. A systematic review was performed to include population-, community-based studies that reported country-specific VTDR prevalence. Random effect meta-analysis was then performed to estimate global and regional VTDR prevalence. VTDR prevalence estimates coupled with DM population data were then used to estimate the number of VTDR cases. Global and regional number of ophthalmologists were derived from the International Council of Ophthalmology Report 2015. Fifty studies (17 from Western Pacific [WP], nine North America and Caribbean [NAC], nine Middle East and North Africa [MENA], five Europe, eight South East Asia [SEA], one South and Central America [SACA] and one from Africa) were included. Global VTDR prevalence was 7.26% (95% CI, 6.18-8.32%). Regional VTDR prevalence was 14.35% in Africa, 11.21% in MENA, 10.00% in NAC, 6.32% in Europe, 6.22% in WP, 5.83% in SACA and 2.97% in SEA. Globally, there were 7.16 ophthalmologists per 1000 VTDR patients. Europe had the highest ophthalmologist per 1000 VTDR patient ratio at 18.03 followed by SACA (17.41), while NAC, MENA and Africa had the lowest at 4.90, 4.81 and 0.91 respectively. Across regions, the ophthalmologist densities ranged from 0.91 to 18.03 per 1000 VTDR patients, with NAC, MENA and Africa having less than 5 ophthalmologists per 1000 patients. These findings will aid global and regional policy planning and healthcare resource allocation for VTDR management.
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http://dx.doi.org/10.1038/s41433-020-0776-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7314752PMC
July 2020

High prevalence of myopia in children and their parents in Hong Kong Chinese Population: the Hong Kong Children Eye Study.

Acta Ophthalmol 2020 Jan 24. Epub 2020 Jan 24.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Kowloon, Hong Kong.

Purpose: To determine the myopia prevalence in Hong Kong Chinese children and their parents.

Methods: It was a population-based cross-sectional study. A total of 4257 children aged 6-8 years, and 5880 parents were recruited in the Hong Kong Children Eye Study. Cycloplegic autorefraction was measured for children; and non-cycloplegic autorefraction for parents. Parental educational level, children's outdoor time, and near work were collected by validated questionnaires.

Results: In children aged 6-8 years, 25.0% were myopic, and among them, 12.7% for the 6-year-olds, 24.4% for the 7-year-olds and 36.1% for the 8-year-old. About 0.7% of children aged 8 years were high myopia. In all age groups, boys (their myopia rate: 13.9% at 6 years, 26.7% at 7 years, and 38.3% at 8 years) were more myopic than girls (11.3% at 6 years, 22.0% at 7 years, 33.4% at 8 years). Among parents, 72.2% were myopic (mother, 73.2%; father, 70.7%) and 13.5% high myopia (mother, 12.8%; father, 14.5%). It was observed that prevalence decreased with ages and increased with education level.

Conclusion: There is a strikingly high prevalence of myopia in Hong Kong children aged 6-8, much higher than that of other regions of China. Of note, the prevalence of children was similar to that in 15 years ago. Furthermore, the myopia prevalence of parents is high, and it had already increased in this cohort. Prevention of childhood myopia is important, likewise for visual complications from high myopia in adults.
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http://dx.doi.org/10.1111/aos.14350DOI Listing
January 2020

Diagnostic criteria for detection of retinal nerve fibre layer thickness and neuroretinal rim width abnormalities in glaucoma.

Br J Ophthalmol 2020 02 30;104(2):270-275. Epub 2019 May 30.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China

Background/aims: Although measurements of the Bruch's membrane opening minimum rim width (BMO-MRW) and retinal nerve fibre layer thickness (RNFLT) with optical coherence tomography (OCT) have been widely adopted in the diagnostic evaluation of glaucoma, there is no consensus on the diagnostic criteria to define BMO-MRW and RNFLT abnormalities. This study investigated the sensitivities and specificities of different diagnostic criteria based on the OCT classification reports for detection of glaucoma.

Methods: 340 eyes of 137 patients with glaucoma and 87 healthy individuals, all with axial length ≤26mm, had global and sectoral BMO-MRW and RNFLT measured with Spectralis OCT (Heidelberg Engineering). Six diagnostic criteria were examined: global measurement below the fifth or the first percentile; ≥1 sector measurement below the fifth or the first percentile; superotemporal and/or inferotemporal measurement below the fifth or the first percentile. The sensitivities and specificities of BMO-MRW/RNFLT assessment for detection of glaucoma (eyes with visual field (VF) defects) were compared.

Results: Among the six criteria examined, superotemporal and/or inferotemporal measurement below the fifth percentile showed the highest sensitivities and specificities for glaucoma detection. Abnormal superotemporal and/or inferotemporal RNFLT attained a higher sensitivity than abnormal superotemporal and/or inferotemporal BMO-MRW to detect mild glaucoma (mean VF MD: -3.32±1.59 dB) (97.9% and 88.4%, respectively, p=0.006), and glaucoma (mean VF MD: -9.36±8.31 dB) (98.4% and 93.6%, respectively, p=0.006), at the same specificity (96.1%).

Conclusions: Superotemporal and/or inferotemporal RNFLT/MRW below the fifth percentile yield the best diagnostic performance for glaucoma detection with RNFLT attains higher sensitivities than MRW at the same specificity in eyes without high myopia.
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http://dx.doi.org/10.1136/bjophthalmol-2018-313581DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7025733PMC
February 2020

Accuracy and Precision of Intraocular Lens Calculations Using the New Hill-RBF Version 2.0 in Eyes With High Axial Myopia.

Am J Ophthalmol 2019 09 10;205:66-73. Epub 2019 May 10.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong; Department of Ophthalmology, Hong Kong Sanatorium and Hospital, Hong Kong. Electronic address:

Purpose: To compare the accuracy and precision of the new Hill-RBF version 2.0 (Hill-RBF 2) formula with other formulas (Barrett Universal II, Haigis, Hoffer Q, Holladay 1, and SRK/T) in predicting residual refractive error after phacoemulsification in high axial myopic eyes.

Design: Retrospective case series.

Methods: 127 eyes of 127 patients with axial length (AL) ≥26 mm were included. The refractive prediction error (PE) was calculated as the difference between the postoperative refraction and the refraction predicted by each formula for the intraocular lens (IOL) power actually implanted. Standard deviation (SD) of PE, median absolute PE (MedAE), proportion of eyes within ±0.25, ±0.50, and ±1.00 diopter (D) of PE were compared. A generalized linear model was used to model the mean function and variance function of the PE (indicative of the accuracy and precision) with respect to biometric variables.

Results: The MedAE and SD of Hill-RBF 2 were lower than that of Hoffer Q, Holladay 1, and SRK/T (P ≤ .036) and were comparable to Barrett Universal II and Haigis (P ≥ .077). Hill-RBF 2 had more eyes within ±0.25 D of the intended refraction (76 out of 127 eyes [59.84%]) compared to other formulas (P ≤ .034) except Barrett Universal II (P = .472). AL was associated with the mean function or variance function of the PE for all formulas except Hill-RBF 2.

Conclusions: In this study, the precision of Hill-RBF 2 is comparable to Barret Universal II and Haigis. Unlike the other 5 formulas, its dispersion and the accuracy of the refractive prediction is independent of the AL.
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http://dx.doi.org/10.1016/j.ajo.2019.04.019DOI Listing
September 2019

Repeatability and Agreement of a Swept-Source Optical Coherence Tomography-Based Biometer IOLMaster 700 Versus a Scheimpflug Imaging-Based Biometer AL-Scan in Cataract Patients.

Eye Contact Lens 2020 Jan;46(1):35-45

Department of Ophthalmology and Visual Sciences (T.C.Y.C., K.H.W., F.Y.T., Y.M.W., and C.C.), The Chinese University of Hong Kong, Kowloon, Hong Kong; Hong Kong Eye Hospital (T.C.Y.C.), Kowloon, Hong Kong; and Department of Mathematics and Statistics (M.Y.), Hang Seng Management College, New Territories, Hong Kong.

Purpose: To compare the repeatability and agreement between a swept-source biometer and a Scheimpflug biometer in cataract patients.

Methods: Three consecutive measurements were obtained using a swept-source biometer (IOLMaster 700) and a Scheimpflug biometer (AL-Scan) in 52 eyes of 52 patients. Keratometry, central corneal thickness (CCT), anterior chamber depth (ACD), axial length, and white-to-white (WTW) distance were recorded. Astigmatism values were transformed into vector components of J0 and J45. Intraoperator repeatability was analyzed using intraclass correlation coefficients (ICCs) and reproducibility coefficients (RCs). Agreement of measurements between the two devices was evaluated using the Bland-Altman method.

Results: The IOLMaster 700 showed higher ICCs and lower RCs for the mean keratometry (Km) (P≤0.018), CCT (P≤0.027), and ACD (P≤0.001) measurements, whereas the AL-Scan showed higher ICC and lower RC for the J45 vector component of astigmatism at the 2.4-mm zone (P≤0.034). Both the devices had excellent repeatability (ICC=0.999) in axial length measurement. Systematic differences were found in Km, CCT, ACD, and WTW (P≤0.018) between the devices. The mean difference for Km was -0.196 and -0.144 D measured at the 2.4-mm zone and 3.3-mm zone, respectively. The corresponding mean difference for CCT, ACD, and WTW distance was 14.92 μm, -0.017 mm, and 0.283 mm, respectively. These differences led to a statistically significant but clinically insignificant difference in the prediction of intraocular lens power.

Conclusions: This study showed significant differences in anterior segment measurement repeatability and agreement between a swept-source biometer and a Scheimpflug biometer in eyes with cataract.
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http://dx.doi.org/10.1097/ICL.0000000000000603DOI Listing
January 2020

Limbal ischemia: Reliability of clinical assessment and implications in the management of ocular burns.

Indian J Ophthalmol 2019 Jan;67(1):32-36

Brien Holden Eye Research Center, LV Prasad Eye Institute, Kallam Anji Reddy Campus, Hyderabad, Telangana, India.

Purpose: Limbal ischemia is an important prognostic factor in the management of ocular burns. In this study, we evaluated the reliability of clinically assessing limbal ischemia among ophthalmic professionals.

Methods: This study included 111 ophthalmic professionals who were shown 12 diffuse illumination color slit-lamp photographs of eyes with recent chemical injuries. Respondents were asked whether the photos were assessable and if yes, then to indicate the presence, location, and grade of limbal ischemia in each case. The responses were collected using a standard data collection sheet and the inter-observer agreement was calculated.

Results: All participants responded to every question. Of the 1,332 responses, images were deemed assessable in 1,222 (91.7%) instances. The overall agreement (Fleiss' kappa) for the presence of limbal ischemia and severity of limbal ischemia was 0.106 and 0.139, respectively (P < 0.012). Among the four groups of observers, practicing cornea specialists displayed significantly (P < 0.003) higher kappa values (0.201-0.203) when compared to residents (0.131-0.185), fellows (0.086-0.127), and optometrists (0.077-0.102). All indicated a poor level of inter-rater consistency.

Conclusion: The results indicate that clinical assessment of limbal ischemia is highly subjective and there is lack of reliability even among cornea specialists who regularly manage patients with ocular burns. A non-invasive, standardized, objective, accurate, and reliable modality for ocular surface angiography is desperately needed for proper assessment and prognostication of ocular burns.
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http://dx.doi.org/10.4103/ijo.IJO_945_18DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6324115PMC
January 2019

Moraxella Keratitis: Analysis of Risk Factors, Clinical Characteristics, Management, and Treatment Outcomes.

Am J Ophthalmol 2019 01 8;197:17-22. Epub 2018 Sep 8.

University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA. Electronic address:

Purpose: To analyze the risk factors, clinical characteristics, management, and treatment outcomes of culture-proven cases of Moraxella keratitis at our center.

Design: Retrospective observational case series.

Methods: Thirty-nine culture-proven cases of Moraxella keratitis (39 eyes) diagnosed and treated between January 2003 and April 2018 at the University of Pittsburgh Medical Center were identified and retrospectively reviewed for ocular and systemic risk factors, treatment modalities, and outcomes, as well as for antimicrobial sensitivity and resistance data.

Results: The mean age of the 39 patients was 63.0 (range 4-95 years) with median follow-up time of 170 days. Thirty-four of 39 patients (87.2%) had an ocular risk factor, the most common of which were blepharitis in 12 (30.8%), dry eyes in 12 (30.8%), and history of ocular surgery in 9 (23.1%). History of diabetes mellitus was found in 8 patients (20.5%). Thirty-six of 39 patients (92.3%) received a fluoroquinolone (92.3%) and 30 of 39 (76.7%) received topical fortified antibiotics. Resistance to fluoroquinolones, gentamicin, and tobramycin was seen in 1 patient each, respectively. Four patients (10.3%) required tarsorrhaphy, 6 patients (15.4%) required penetrating keratoplasty, and 1 patient required enucleation. Of the 35 patients for whom visual acuity information was available, 19 (54.3%) were count fingers or worse at most recent follow-up.

Conclusions: Ocular risk factors, especially poor ocular surface, were identified in the vast majority of patients with Moraxella keratitis. Moraxella isolates in our study were susceptible to fluoroquinolones and aminoglycosides. Many patients required surgical intervention and the final visual acuity was often poor.
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http://dx.doi.org/10.1016/j.ajo.2018.08.055DOI Listing
January 2019

Comparison of Corneal Tomography and a New Combined Tomographic Biomechanical Index in Subclinical Keratoconus.

J Refract Surg 2018 Sep;34(9):616-621

Purpose: To investigate and compare the diagnostic ability of corneal tomography and biomechanical and combined parameters for detection of corneal ectasia.

Methods: Consecutive patients with subclinical keratoconus (SCKC) and age-matched controls were included. Only one eye from each patient was selected for analysis. The final D value from the Belin/Ambrósio Enhanced Ectasia Display (BAD) was obtained from the Pentacam (Oculus Optikgeräte, Wetzlar, Germany). The tomographic biomechanical index (TBI) was derived from the Pentacam and Corvis ST (Oculus Optikgeräte). Classification analysis between normal and subclinical keratoconus (SCKC) was evaluated using receiver operating characteristic (ROC) curves. The area under the ROC curve (AUC) and partial AUC (pAUC) with specificity of 80% or greater were compared.

Results: Twenty-three eyes with SCKC and 37 normal eyes were included. All Pentacam-derived parameters (P < .001) and all but two Corvis ST-derived parameters (P < .020) were significantly different between normal and SCKC eyes. A significant difference was found in the final D value (P ≤ .020) and TBI (P ≤ .040) between normal and SCKC eyes. For differentiating normal and SCKC eyes, TBI and BAD final D value demonstrated the highest AUC (0.925 and 0.786, respectively) and pAUC (0.150 and 0.088, respectively). TBI demonstrated 84.4% sensitivity and 82.4% specificity using a cut-off of 0.16. Comparative analysis between these parameters showed that AUC and pAUC of TBI were significantly higher than all parameters from Pentacam (P ≤ .032).

Conclusions: In the current study, combined use of tomographic and biomechanical parameters demonstrated a higher capability in differentiating normal and SCKC eyes when compared to tomographic analysis alone. [J Refract Surg. 2018;34(9):616-621.].
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http://dx.doi.org/10.3928/1081597X-20180705-02DOI Listing
September 2018

Vector analysis of high (≥3 diopters) astigmatism correction using small-incision lenticule extraction and laser in situ keratomileusis.

J Cataract Refract Surg 2018 Jul 13;44(7):802-810. Epub 2018 Jun 13.

From the Department of Ophthalmology and Visual Sciences (Chan, Jhanji), Chinese University of Hong Kong, the Department of Ophthalmology (Chan, Ng), University of Hong Kong, the Department of Mathematics and Statistics (Yu), Hang Seng Management College, and the Hong Kong Laser Eye Center (Cheng), Hong Kong; Tianjin Eye Hospital and Eye Institute (Wang, Zhang), Tianjin, China; the University of Pittsburgh Medical Center (Jhanji), University of Pittsburgh, Pittsburgh, Pennsylvania, USA.

Purpose: To compare the astigmatic correction in high myopic astigmatism between small-incision lenticule extraction and laser in situ keratomileusis (LASIK) using vector analysis.

Setting: Hong Kong Laser Eye Center, Hong Kong.

Design: Retrospective case series.

Methods: Patients who had correction of myopic astigmatism of 3.0 diopters (D) or more and had either small-incision lenticule extraction or femtosecond laser-assisted LASIK were included. Only the left eye was included for analysis. Visual and refractive results were presented and compared between groups.

Results: The study comprised 105 patients (40 eyes in the small-incision lenticule extraction group and 65 eyes in the femtosecond laser-assisted LASIK group.) The mean preoperative manifest cylinder was -3.42 D ± 0.55 (SD) in the small-incision lenticule extraction group and -3.47 ± 0.49 D in the LASIK group (P = .655). At 3 months, there was no significant between-group difference in uncorrected distance visual acuity (P = .915) and manifest spherical equivalent (P = .145). Ninety percent and 95.4% of eyes were within ± 0.5 D of the attempted cylindrical correction for the small-incision lenticule extraction and LASIK group, respectively (P = .423). Vector analysis showed comparable target-induced astigmatism (P = .709), surgically induced astigmatism vector (P = .449), difference vector (P = .335), and magnitude of error (P = .413) between groups. The absolute angle of error was 1.88 ± 2.25 degrees in the small-incision lenticule extraction group and 1.37 ± 1.58 degrees in the LASIK group (P = .217).

Conclusion: Small-incision lenticule extraction offered astigmatic correction comparable to LASIK in eyes with high myopic astigmatism.
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http://dx.doi.org/10.1016/j.jcrs.2018.04.038DOI Listing
July 2018

Longitudinal evaluation of posterior corneal changes after laser in situ keratomileusis in high myopia: a swept-source optical coherence tomography study.

Clin Exp Ophthalmol 2018 09 12;46(7):824-826. Epub 2018 Mar 12.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.

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http://dx.doi.org/10.1111/ceo.13178DOI Listing
September 2018

Comparative evaluation of progression rate in keratoconus before and after collagen crosslinking.

Br J Ophthalmol 2018 08 9;102(8):1109-1113. Epub 2017 Nov 9.

Department of Ophthalmology and Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.

Purpose: To compare the rate of disease progression in keratoconus before and after corneal collagen crosslinking (CXL).

Methods: 145 eyes were followed without CXL (no-CXL group) for a median duration of 31 months whereas 45 eyes were followed up for 41 months before (pre-CXL) and after (post-CXL) accelerated, epithelium-off crosslinking. Progression was defined based on significant slope found in linear mixed effect models against time. Swept-source optical coherence tomography was used for measurement of anterior steep keratometry, anterior flat keratometry (Ant Kf), anterior average keratometry (Ant Avg K); posterior steep keratometry, posteriorflat keratometry (Post Kf), posterior average keratometry (Post Avg K) and corneal thickness.

Results: The patients in pre-CXL group were significantly younger (26.3±5.48 years) compared with the patients in no-CXL group (32.7±10.24 years) (P=0.004). Significant differences were observed during baseline examination for all parameters (P≤0.035) between pre-CXL and no-CXL groups except Ant Cyl and Post Cyl. During observation period, statistically significant differences were noted between pre-CXL and no-CXL groups in the progression rate of Ant Kf, Ant Avg K, Post Kf and Post Avg K (P≤0.045). After CXL, the progression rate in post-CXL group was comparable to that in no-CXL group. All corneal parameters remained stable in no-CXL group throughout the follow-up period.

Conclusions: Serial tomographic examination is useful to document disease progression before and after CXL. In our study, a decrease in progression rate of corneal parameters was noted after CXL. In cases with stable corneal parameters over time, careful monitoring can be considered instead of collagen crosslinking.
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http://dx.doi.org/10.1136/bjophthalmol-2017-311017DOI Listing
August 2018

Corneal backward scattering and higher-order aberrations in children with vernal keratoconjunctivitis and normal topography.

Acta Ophthalmol 2018 May 1;96(3):e327-e333. Epub 2017 Nov 1.

Department of Ophthalmology & Visual Sciences, The Chinese University of Hong Kong, Hong Kong, China.

Purpose: To investigate the corneal backward scattering and higher-order aberrations (HOAs) in children with vernal keratoconjunctivitis (VKC) and normal topography.

Methods: Thirty-six eyes of 22 patients with VKC and 54 eyes of 34 normal subjects were included. All participants had clear cornea, absence of dry eyes and a normal corneal tomography. Scheimpflug imaging was used to measure corneal backward scattering in zones centred on the corneal apex (central 2-mm zone and paracentral 2- to 6-mm zone), and HOAs were compared between VKC and normal control.

Results: The mean age of participants was 12.0 ± 4.1 years in VKC group and 11.2 ± 4.1 years in control group (p = 0.339). There was no significant intergroup difference in mean keratometry, astigmatism and apex pachymetry (p ≥ 0.076). Total corneal backscatter was higher in the VKC group compared to the control group (p ≤ 0.012). Anterior and posterior cornea displayed a higher level of backward scattering in the VKC group (p < 0.001 for anterior; p ≤ 0.048 for posterior). Patients with VKC exhibited higher total HOAs and coma (p ≤ 0.036). There were significant correlations between total anterior HOAs and backward scattering measured at the central (r = 0.500; p = 0.032) and paracentral zones (r = 0.470; p = 0.024) for VKC.

Conclusion: The current study showed optical quality changes in patients with clear corneas and quiescent VKC. An increase in corneal backward scattering and HOAs was noted in patients with VKC as compared to normal patients.
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http://dx.doi.org/10.1111/aos.13566DOI Listing
May 2018

Comparison of Corneal Dynamic and Tomographic Analysis in Normal, Forme Fruste Keratoconic, and Keratoconic Eyes.

J Refract Surg 2017 Sep;33(9):632-638

Purpose: To investigate and compare the diagnostic ability of corneal tomography and dynamic corneal response to differentiate between normal eyes and those with forme fruste keratoconus and keratoconus.

Methods: Corneal tomography was performed using Pentacam (Pentacam HR; Oculus Optikgeräte, Wetzlar, Germany). Corneal deformation response was captured via Corvis ST (Optikgeräte) using a beta version of Corvis software. Classification analysis between normal eyes and eyes with forme fruste keratoconus and between normal and keratoconic eyes was evaluated using receiver operating characteristic curves. The area under the ROC curve (AUC) and partial AUC (pAUC) for each classifying parameter were compared.

Results: Twenty-one patients with forme fruste keratoconus in one eye and clinically evident keratoconus in the fellow eye and 38 normal individuals were recruited. Overall, 21 eyes with forme fruste keratoconus and 18 eyes with keratoconus were compared with 73 normal eyes. The mean age of the participants was comparable between groups. Comparative analysis between Pentacam and Corvis ST parameters showed significantly lower AUC and pAUC for Corvis ST parameters in differentiating keratoconic from normal eyes (P ≥ .049). However, comparable AUC and pAUC was observed between the Corvis Biomechanical Index (AUC = 0.785; pAUC = 0.079) and D value of the Belin/Ambrósio Enhanced Ectasia Display (AUC = 0.757; pAUC = 0.068) (P ≥ .477) for detection of forme fruste keratoconus with sensitivities of 63.2% and 52.6%, given a common specificity of 80.3%.

Conclusions: The current study showed the feasibility of use of non-tomographical parameters obtained from the Corvis ST for differentiating normal eyes and those with forme fruste keratoconus and keratoconus. The diagnostic ability of the Corvis ST was comparable to that of the Pentacam for differentiating normal eyes and eyes with forme fruste keratoconus. [J Refract Surg. 2017;33(9):632-638.].
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http://dx.doi.org/10.3928/1081597X-20170621-09DOI Listing
September 2017