Publications by authors named "Omkar Thaware"

3 Publications

  • Page 1 of 1

Accuracy of OCT-derived net corneal astigmatism measurement.

J Cataract Refract Surg 2021 Jul 27. Epub 2021 Jul 27.

Casey Eye Institute and Department of Ophthalmology, Oregon Health and Science University, Portland, Oregon, USA.

Purpose: To assess the repeatability and accuracy of corneal astigmatism measurement with a spectral-domain optical coherence tomography (OCT) system (Avanti, Optovue) and compare them with Scheimpflug imaging (Pentacam HR, Oculus) and swept-source optical biometry (IOLMaster 700, Carl Zeiss Mediatec AG).

Setting: Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA.

Design: Prospective cross-sectional observational study.

Methods: Sixty pseudophakic eyes with monofocal non-toric intraocular lens that previously had refractive surgery were analyzed. To assess accuracy, simulated keratometric (SimK) and net corneal astigmatism, obtained from each device were compared with subjective manifest refraction astigmatism. Repeatability for corneal astigmatism was assessed for OCT and Pentacam HR by the coefficient of repeatability from three repeated measures.

Results: Compared to manifest refraction, SimK readings produced with-the-rule (WTR) astigmatic bias which was reduced for net astigmatism for all the three devices. Except for OCT net astigmatism, all instruments significantly overestimated the magnitude of the astigmatism (linear mixed-effects model (LMM), P < .05). OCT net astigmatism showed the highest accuracy for manifest astigmatism prediction with the smaller 95% confidence ellipse for the mean difference vector. OCT net mean absolute difference was 0.57 D, significantly smaller than that of the other modalities (LMM, P <.05). Net corneal astigmatism measured with OCT showed the best repeatability (coefficient of repeatability = 0.29 D).

Conclusions: OCT has the capability to measure net corneal astigmatism with higher precision and accuracy than Pentacam HR Scheimpflug imaging and IOLMaster 700 swept-source optical biometry in post refractive patients.
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July 2021

Enrichment of Oxygen Concentration Over Simulated Corneal Surface Through Noncontact Oxygen Delivery Device.

J Refract Surg 2020 Sep;36(9):613-616

Purpose: To demonstrate a noncontact device to enrich oxygen concentration during corneal cross-linking (CXL).

Methods: An oxygen delivery device was tested in a laboratory mock-up. The device comprises a clear polycarbonate tube of 14 cm in length and 1.58 cm inner diameter. Compressed oxygen gas is delivered to the tube from a side opening. The oximeter was attached to a sampling tube 3 mm above the apex of a scleral lens that simulates the cornea. The lens was mounted on a mannequin face. During each experimental run, the oximeter reading was recorded manually every 30 seconds for 4.5 minutes after the flow regulator was opened to the preset flow rate. Three flow rates of 0.25, 0.50, and 1 L/min were tested with all three cornea-tube distances of 8, 10, and 14 mm.

Results: The baseline oxygen concentration was 20.9%. The oxygen concentration reached plateau levels after 2 to 3.5 minutes. Oxygen measurements were averaged over the three time points in the plateau phase between 3.5 and 4.5 minutes. Atmospheric oxygen concentration above the simulated cornea was found to be strongly dependent on the oxygen flow rate up to 1 L/min. At the 1 L/min flow rate, 99% concentration was achieved at 8 to 10 mm of cornea-tube distances, and dropped to 90% at 14 mm.

Conclusions: Atmospheric oxygen concentration can be boosted to more than 90% using a noncontact device. This could potentially improve the effectiveness of accelerated CXL by boosting oxygen transport more than fourfold. [J Refract Surg. 2020;36(9):613-616.].
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September 2020

Detection of Nonexudative Choroidal Neovascularization and Progression to Exudative Choroidal Neovascularization Using OCT Angiography.

Ophthalmol Retina 2019 08 21;3(8):629-636. Epub 2019 Mar 21.

Casey Eye Institute, Oregon Health & Science University, Portland, Oregon.

Purpose: To detect nonexudative choroidal neovascularization (CNV) in age-related macular degeneration (AMD) with OCT angiography (OCTA) and determine the risk of exudative CNV developing compared with eyes without nonexudative CNV.

Design: Prospective, longitudinal, observational study.

Participants: Consecutive patients with drusen and pigmentary changes in the study eye and exudative neovascular AMD in the fellow eye.

Methods: In this prospective observational study, participants underwent spectral-domain OCTA (AngioVue; Optovue, Inc, Fremont, CA), clinical examination, and structural OCT at baseline and 6-month intervals for 2 years. OCT angiography images were exported for custom processing to remove projection artifact and calculate CNV vessel area.

Main Outcome Measures: Rate of developing exudation in eyes with and without nonexudative CNV as detected by OCTA on regular follow-up.

Results: Sixty-three study participants were followed up every 6 months and 48 completed the 2-year study. Mean age was 78 years and 60.3% were female. On the baseline visit, 5 eyes (7.9%) were found to have nonexudative CNV by OCTA, and 3 of them demonstrated exudation. Of 58 eyes with a normal OCTA on baseline visit, 5 eyes developed nonexudative CNV during a follow-up visit. All 5 of these nonexudative CNV went on to develop exudation in subsequent visits. Overall, 8 of the 10 eyes with nonexudative CNV developed exudation with a mean time of 8 months and mean CNV area growth rate of 20% per month (P = 0.014, exponential model). Initiation of antiangiogenic treatment halted their growth. In comparison, exudation occurred in only 6 of the 53 eyes (11%) that lacked a precursor nonexudative CNV. Cox proportional hazard analysis showed that having nonexudative CNV detected was associated with an 18.1-fold increase in the rate of exudation subsequently developing (P < 0.0001).

Conclusions: Nonexudative CNV frequently is detected by OCTA in the fellow eyes of those with exudative CNV. These lesions carry a high risk of exudation developing within the first year after detection and could benefit from close monitoring. The high risk of progression may justify prophylactic treatment; further studies are needed.
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August 2019