Publications by authors named "Alexander Leube"

15 Publications

  • Page 1 of 1

Microsaccadic rate signatures correlate under monocular and binocular stimulation conditions.

J Eye Mov Res 2020 Aug 11;11(4). Epub 2020 Aug 11.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Germany.

Microsaccades are involuntary eye movements occurring naturally during fixation. In this study, microsaccades were investigated under monocularly and binocularly stimulated conditions with respect to their directional distribution and rate signature, that refers to a curve reporting the frequency modulation of microsaccades over time. For monocular stimulation the left eye was covered by an infrared filter. In both stimulation conditions, participants fixated a Gabor patch presented randomly in orientation of 45° or 135° over a wide range of spatial frequencies appearing in the center of a monitor. Considering the microsaccadic directions, this study showed microsaccades to be preferably horizontally oriented in their mean direction, regardless of the spatial characteristics of the grating. Furthermore, this outcome was found to be consistent between both stimulation conditions. Moreover, this study found that the microsaccadic rate signature curve correlates between both stimulation conditions, while the curve given for binocular stimulation was already proposed as a tool for estimation of visual performance in the past. Therefore, this study extends the applicability of microsaccades to clinical use, since parameters as contrast sensitivity, has been measured monocularly in the clinical attitude.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.16910/jemr.13.5.3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8008506PMC
August 2020

Utilizing minicomputer technology for low-cost photorefraction: a feasibility study.

Biomed Opt Express 2020 Nov 7;11(11):6108-6121. Epub 2020 Oct 7.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Elfriede-Aulhorn-Str. 7, Tuebingen, 72076, Germany.

Eccentric photorefraction is an objective technique to determine the refractive errors of the eye. To address the rise in prevalence of visual impairment, especially in rural areas, a minicomputer-based low-cost infrared photorefractor was developed using off-the-shelf hardware components. Clinical validation revealed that the developed infrared photorefractor demonstrated a linear working range between +4.0 D and -6.0 D at 50 cm. Further, measurement of astigmatism from human eye showed absolute error for cylinder of 0.3 D and high correlation for axis assessment. To conclude, feasibility was shown for a low-cost, portable and low-power driven stand-alone device to objectively determine refractive errors, showing potential for screening applications. The developed photorefractor creates a new avenue for telemedicine for ophthalmic measurements.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/BOE.400720DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7687974PMC
November 2020

Advancing Digital Workflows for Refractive Error Measurements.

J Clin Med 2020 Jul 12;9(7). Epub 2020 Jul 12.

Institute for Ophthalmic Research, Center for Ophthalmology, Eberhard Karls University of Tuebingen, Elfriede-Aulhorn-Straße 7, 72076 Tuebingen, Germany.

Advancements in clinical measurement of refractive errors should lead to faster and more reliable measurements of such errors. The study investigated different aspects of advancements and the agreement of the spherocylindrical prescriptions obtained with an objective method of measurement ("Aberrometry" (AR)) and two methods of subjective refinements ("Wavefront Refraction" (WR) and "Standard Refraction" (StdR)). One hundred adults aged 20-78 years participated in the course of the study. Bland-Altman analysis of the right eye measurement of the spherocylindrical refractive error (M) identified mean differences (±95% limits of agreement) between the different types of measurements of +0.36 D (±0.76 D) for WR vs. AR (-test: < 0.001), +0.35 D (± 0.84 D) for StdR vs. AR (-test: < 0.001), and 0.0 D (± 0.65 D) for StdR vs. WR (-test: < 0.001). Monocular visual acuity was 0.0 logMAR in 96% of the tested eyes, when refractive errors were corrected with measurements from AR, indicating that only small differences between the different types of prescriptions are present.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/jcm9072205DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7408987PMC
July 2020

Direct modeling of foveal pit morphology from distortion-corrected OCT images.

Biomed Opt Express 2019 Sep 26;10(9):4815-4824. Epub 2019 Aug 26.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Elfriede-Aulhorn-Str. 7, Tuebingen, 72076, Germany.

Inherent distortions affect the spatial geometry of optical coherence tomography (OCT) images and consequently the foveal pit dimensions. Distortion correction provides an accurate anatomical representation of the retinal shape. A novel approach that automatically extracts foveal pit metrics from distortion-corrected OCT images using a sum of Gaussian function is presented. Foveal width, depth and slope were determined in 292 eyes with low fitting errors and high repeatability. Comparisons to undistorted scans revealed significant differences. To conclude, the internal OCT distortions affect the measurements of the foveal pit with their correction providing further insights into the role of foveal morphology in retinal pathologies and refractive development.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/BOE.10.004815DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6757460PMC
September 2019

Effects of eye rotation and contact lens decentration on horizontal peripheral refraction.

Ophthalmic Physiol Opt 2019 09 3;39(5):370-377. Epub 2019 Sep 3.

Institute of Health & Biomedical Innovation and School of Optometry and Vision Science, Queensland University of Technology, Brisbane, Australia.

Purpose: Peripheral refraction is important in design of myopia control therapies. The aim was to investigate the influence of contact lens decentration associated with eye rotation on peripheral refraction in the horizontal visual field.

Methods: Participants were 10 emmetropes and 10 myopes in good general and ocular health. Right eyes underwent cycloplegic peripheral refraction, using a Grand-Seiko WAM-5500 Autorefractor, in 5° steps to ±35° eccentricities along the horizontal visual field. Targets were fixated using eye rotation only or head rotation only. Refractions were measured without correction and with three types of contact lenses: single vision, a multifocal centre-distance aspheric with +2.50 D add and NaturalVue aspheric. Photographs of eyes during lens wear were taken for each eye rotation. Effects of visual field angle, lens type and test method (head or eye rotation) on vector components of relative peripheral refraction were evaluated using repeated measures anovas. Test method for each visual field angle/lens combination were compared via paired t-tests.

Results: Horizontal decentration ranges across the visual field were 1.2 ± 0.6 mm for single vision and 1.2 ± 0.4 mm for multifocal lenses but smaller at 0.7 ± 0.4 mm for NaturalVue lenses. There were only two significant effects of test method across the visual field angle/lens type combinations (single vision: for emmetropes horizontal/vertical astigmatism component at 35° nasal with mean difference -0.38 D and for myopes spherical equivalent refraction at 20° temporal with mean difference +0.24 D).

Conclusion: Upon eye rotation the contact lenses decentred on the eye, but not enough to affect peripheral refraction. For the types assessed and for the horizontal visual field out to ±35° when measurements were performed with the Grand-Seiko WAM-5500 autorefractor, it is valid to use eye rotations to investigate peripheral refraction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/opo.12641DOI Listing
September 2019

Contrast adaptation appears independent of the longitudinal chromatic aberration of the human eye.

J Opt Soc Am A Opt Image Sci Vis 2019 Apr;36(4):B77-B84

As ocular chromatic aberration was suspected to cue contrast adaptation in human vision, the purpose of this study was to investigate contrast adaptation under monochromatic light conditions. Single and complex frequency adaptation stimuli were used, and monochromatic conditions were achieved using band pass filters with short (470±2  ), medium (530±2  ), and long (630±2  ) transmission wavelengths. Post-adaptational contrast sensitivity was shown to be significantly decreased for all wavelength conditions for the single frequency stimulus. A significant difference of contrast adaptation between short and long wavelengths was found. Consistently, adaptation led to a significant decrease in contrast sensitivity for the complex frequency stimulus. To conclude, contrast adaptation under mesopic illumination occurs independently of the longitudinal chromatic aberration of the eye; it can be inferred that this mechanism can be used to distinguish between the sign of optical defocus in poly- and monochromatic light conditions.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/JOSAA.36.000B77DOI Listing
April 2019

Letter to the Editor.

Authors:
Alexander Leube

Vision Res 2019 09 22;162:43. Epub 2018 Apr 22.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Germany. Electronic address:

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.visres.2018.04.001DOI Listing
September 2019

Individual neural transfer function affects the prediction of subjective depth of focus.

Sci Rep 2018 01 30;8(1):1919. Epub 2018 Jan 30.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Elfriede-Aulhorn-Str. 7, Tuebingen, 72076, Germany.

Attempts to accurately predict the depth of focus (DoF) based on objective metrics have failed so far. We investigated the effect of the individual neural transfer function (iNTF) on the quality of the prediction of the subjective DoF from objective wavefront measures. Subjective DoF was assessed in 22 participants using subjective through focus curves of visual acuity (VA). Objective defocus curves were calculated for visual Strehl metrics of the optical (VSOTFa) and the modulation transfer function as well as the point spread function. DoF was computed for residual lower order aberrations (rLoA) and incorporation of iNTF. Correlations between subjective and objective DoF did not reach significance, when a) standard metrics were used and b) rLoA were considered (r  = 0.33, p  > 0.05). By incorporating the iNTF of the individuals in the calculation of the objective DoF from the VSOTFa metric, a moderate statistically significant correlation was found (r = 0.43, p < 0.01, Pearson). The iNTF of the individual's eye is fundamental for the prediction of subjective DoF using the VSOTFa metric. Individualized predictions could aid future application in the correction of refractive errors like presbyopia using intraocular lenses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-20344-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5790003PMC
January 2018

Self-assessment of refractive errors using a simple optical approach.

Clin Exp Optom 2018 05 21;101(3):386-391. Epub 2018 Jan 21.

Institute for Ophthalmic Research, Eberhard Karls University of Tuebingen, Tuebingen, Germany.

Background: This explorative study investigated procedures for the self-assessment of spherocylindrical refractive errors.

Methods: Eighteen participants with a mean age of 34.0 ± 8.8 years were enrolled. Adjustable Alvarez lenses were mounted in a rotatable ring holder and two procedures were tested for the self-adjustment: (1) rotation of the lens in three meridians: 0°, 60° and 120° and (2) rotation of the optotypes in the same meridians. Starting from maximum positive power, the participants were required to decrease the power of the Alvarez lens until the optotypes (0.0 logMAR) appeared to be clear the first time. Best-corrected visual acuity (BVA) was measured using a psychophysical staircase procedure. Bland-Altmann analysis was carried out in order to calculate the limits of agreement between the self-refraction method and the standard subjective refraction.

Results: Using procedure 1, 77 per cent of the subjects achieved a VA ≥ 0.1 logMAR (6/7.5) and the same was true for 88 per cent of the subjects using procedure 2. Using procedure 1, a significantly worse BVA was found, when compared to subjective refraction (ΔVA = -0.15 logMAR, F  = 7.11, p = 0.046, median test). Analysis of variance (ANOVA) analysis showed a significant influence of the refraction method on the oblique astigmatism component J but not for the spherical equivalent M and the straight astigmatism component J (M: F  = 0.532, p = 0.661; J : F  = 0.056, p = 0.983; J : F  = 13.97, p < 0.001; ANOVA). The limits of agreement for the spherical equivalent error M were ± 1.10 D and ± 1.20 D and for the astigmatic components J ± 0.78 D and ± 0.59 D and for J ± 0.62 D and ± 0.54 D, for procedure 1 and procedure 2, respectively.

Conclusions: Fixed adjustable Alvarez lenses and rotatable stimuli can provide a fast and precise self-assessment method to measure the spherocylindrical error of the eye.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/cxo.12650DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5947140PMC
May 2018

Symmetric visual response to positive and negative induced spherical defocus under monochromatic light conditions.

Vision Res 2018 02 28;143:52-57. Epub 2017 Dec 28.

Institute for Ophthalmic Research, Eberhard Karls University of Tuebingen, Germany; Technology and Innovation, Carl Zeiss Vision International GmbH, Aalen, Germany. Electronic address:

The purpose of the study was to investigate the sign-dependent response to real and simulated spherical defocus on the visual acuity under monochromatic light conditions. The investigation included 15 myopic participants with a mean spherical equivalent error of -2.98 ± 2.17 D. Visual acuity (VA) was tested with and without spherical defocus using the source method (simulated defocus) and the observer method (lens-induced defocus) in a range of ±3.0 D in 1.0 D steps. VA was assessed using Landolt C's, while the threshold was determined with an adaptive staircase procedure. Monochromatic light conditions were achieved using band pass filters with a wavelength of 450 ± 2 nm, 530 ± 2 nm and 630 ± 2 nm. Results showed that the reduction of VA was significantly different under blue lighting conditions, when compared to the green and red light conditions. No significant difference in the reduction of the VA was found between the positive and the negative sign of defocus for all lighting conditions. The agreement for the VA between the source and observer method was significantly dependent on the wavelength as well as on the level of defocus. To conclude, under monochromatic light conditions, myopes show a symmetric sign-dependency regarding the influence of spherical defocus on visual acuity. The observed results indicate that the human visual system is capable of integrating the chromatic differences in refraction to distinguish between the signs of defocus.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.visres.2017.12.003DOI Listing
February 2018

Axis-free correction of astigmatism using bifocal soft contact lenses.

Cont Lens Anterior Eye 2017 Dec 19;40(6):394-400. Epub 2017 Sep 19.

Department of Optometry and Vision Science, Ernst Abbe University of Applied Science Jena, Carl-Zeiss-Promenade 2, 07745 Jena, Germany. Electronic address:

Purpose: Pilot study to investigate the feasibility of an axis-free correction approach of regular astigmatism using soft, bifocal contact lenses (CL).

Methods: The investigation covers an optical simulation and a pilot study for the assessment of visual performance (over refraction OR, monocular visual acuity VA). The power of the two zones was adjusted according to the power of the astigmatic meridians, individually. Subjective performance was assessed in 30 participants with a mean horizontal cylindrical component of J=- 0.65±1.29 D (cylinder from -0.75 to -4.00 DC). OR and VA were measured directly after fitting the CL, after one hour and after 5days (3FUP).

Results: Evaluating the modulation transfer function, CL increased the Strehl ratio by 10% and the transferred spatial frequency was improved from 6.6 cpd to 21.3 cpd. Analysis of Sturm's interval revealed a residual astigmatism of D=0.73 D. OR revealed a statistically significant reduction of spherical error between baseline and all follow up (ΔM=-2.14 D, p<0.001) and between the J from baseline to 3FUP (ΔJ=-0.46 D, p=0.04). Wearing the CL for 5days did not result in a significant difference of VA (ΔVA=+0.01 logMAR, p=0.99).

Conclusion: Axis-free correction of astigmatism using bifocal CL resulted in reasonable performance based on computer simulation. Participants showed no clinically reduced visual acuity or contrast sensitivity. Further clinical studies are needed to show if this approach provides a good alternative to conventional astigmatic correction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.clae.2017.09.002DOI Listing
December 2017

TuebingenCSTest - a useful method to assess the contrast sensitivity function.

Biomed Opt Express 2017 Mar 10;8(3):1477-1487. Epub 2017 Feb 10.

Institute for Ophthalmic Research, Eberhard Karls University Tuebingen, Elfriede-Aulhorn-Straße 7, 72076 Tuebingen, Germany.

Since contrast sensitivity (CS) relies on the accuracy of stimulus presentation, the reliability of the psychophysical procedure and observer's attention, the measurement of the CS-function is critical and therefore, a useful threshold contrast measurement was developed. The Tuebingen Contrast Sensitivity Test (TueCST) includes an adaptive staircase procedure and a 16-bit gray-level resolution. In order to validate the CS measurements with the TueCST, measurements were compared with existing tests by inter-test repeatability, test-retest reliability and time. The novel design enables an accurate presentation of the spatial frequency and higher precision, inter-test repeatability and test-retest reliability compared to other existing tests.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/BOE.8.001477DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5480558PMC
March 2017

Sampling rate influences saccade detection in mobile eye tracking of a reading task.

J Eye Mov Res 2017 Jun 7;10(3). Epub 2017 Jun 7.

Institute for Ophthalmic ResearchUniversity of Tuebingen, Germany.

The purpose of this study was to compare saccade detection characteristics in two mobile eye trackers with different sampling rates in a natural task. Gaze data of 11 participants were recorded in one 60 Hz and one 120 Hz mobile eye tracker and compared directly to the saccades detected by a 1000 HZ stationary tracker while a reading task was performed. Saccades and fixations were detected using a velocity based algorithm and their properties analyzed. Results showed that there was no significant difference in the number of detected fixations but mean fixation durations differed between the 60 Hz mobile and the stationary eye tracker. The 120 Hz mobile eye tracker showed a significant increase in the detection rate of saccades and an improved estimation of the mean saccade duration, compared to the 60 Hz eye tracker. To conclude, for the detection and analysis of fast eye movements, such as saccades, it is better to use a 120 Hz mobile eye tracker.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.16910/jemr.10.3.3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7141092PMC
June 2017

The Influence of Induced Astigmatism on the Depth of Focus.

Optom Vis Sci 2016 10;93(10):1228-34

*MSc †PhD ZEISS Vision Science Lab, Institute for Ophthalmic Research, University of Tuebingen, Tuebingen, Germany (all authors).

Purpose: To evaluate whether an induced astigmatism influences the subjective depth of focus.

Methods: Fifty-one participants aged 18 to 35 years and with a mean spherical equivalent refractive error of -0.51 ± 2.35 DS participated in the study. The accommodation was blocked with three drops of 1% cyclopentolate. Refractive errors were corrected after subjective refraction with a 4-mm artificial pupil. To evaluate the depth of focus (DoF), defocus curves with a spherical range of ±1.5 DS were assessed. The DoF was calculated as the horizontal distance at a threshold level of +0.1 logMAR from the maximum visual acuity (VA). Defocus curves were estimated binocularly during distance (500 cm) and a near vision (40 cm) for two induced axis (ATR in 0° and WTR in 90°) and for a fixed amount of astigmatic defocus of -0.5 DC.

Results: The mean natural DoF was 0.885 ± 0.316 D for far vision and 0.940 ± 0.400 D for near vision. With induced astigmatism, the DoF for far vision was significantly increased to 1.095 ± 0.421 D (p = 0.006, ANOVA) for the WTR astigmatism but not for the ATR astigmatism (1.030 ± 0.395 D; p = 0.164, ANOVA). The induced WTR astigmatism enhanced the DoF for near vision significantly to 1.144 ± 0.338 D (p = 0.04, ANOVA), and DoF with induced ATR astigmatism (0.953 ± 0.318 D) was not significantly different (p = 1.00, ANOVA). ATR-astigmatism reduced VA by +0.08 ± 0.08 logMAR (p < 0.01, t-test).

Conclusions: With an induced WTR astigmatism of -0.5 DC, the DoF can be enhanced in the near viewing distance with a marginal loss in binocular VA. The approach of using induced WTR astigmatism can lead to novel optical treatments for presbyopia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1097/OPX.0000000000000961DOI Listing
October 2016

Steps towards Smarter Solutions in Optometry and Ophthalmology-Inter-Device Agreement of Subjective Methods to Assess the Refractive Errors of the Eye.

Healthcare (Basel) 2016 Jul 13;4(3). Epub 2016 Jul 13.

Institute for Ophthalmic Research, University of Tuebingen, Geschwister-Scholl-Platz, 72074 Tübingen, Germany.

Purpose: To investigate the inter-device agreement and mean differences between a newly developed digital phoropter and the two standard methods (trial frame and manual phoropter).

Methods: Refractive errors of two groups of participants were measured by two examiners (examiner 1 (E1): 36 subjects; examiner 2 (E2): 38 subjects). Refractive errors were assessed using a trial frame, a manual phoropter and a digital phoropter. Inter-device agreement regarding the measurement of refractive errors was analyzed for differences in terms of the power vector components (spherical equivalent (SE) and the cylindrical power vector components J0 and J45) between the used methods. Intraclass correlation coefficients (ICC's) were calculated to evaluate correlations between the used methods.

Results: Analyzing the variances between the three methods for SE, J0 and J45 using a two-way ANOVA showed no significant differences between the methods (SE: p = 0.13, J0: p = 0.58 and J45: p = 0.96) for examiner 1 and for examiner 2 (SE: p = 0.88, J0: p = 0.95 and J45: p = 1). Mean differences and ±95% Limits of Agreement for each pair of inter-device agreement regarding the SE for both examiners were as follows: Trial frame vs. digital phoropter: +0.10 D ± 0.56 D (E1) and +0.19 D ± 0.60 D (E2), manual phoropter vs. trial frame: -0.04 D ± 0.59 D (E1) and -0.12 D ± 0.49 D (E2) and for manual vs. digital phoropter: +0.06 D ± 0.65 D (E1) and +0.08 D ± 0.45 D (E2). ICCs revealed high correlations between all methods for both examiner (p < 0.001). The time to assess the subjective refraction was significantly smaller with the digital phoropter (examiner 1: p < 0.001; examiner 2: p < 0.001).

Conclusion: "All used subjective methods show a good agreement between each other terms of ICC (>0.9). Assessing refractive errors using different subjective methods, results in similar mean differences and 95% limits of agreement, when compared to those reported in studies comparing subjective refraction non-cylcoplegic retinoscopy or autorefraction".
View Article and Find Full Text PDF

Download full-text PDF

Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5041042PMC
http://dx.doi.org/10.3390/healthcare4030041DOI Listing
July 2016