Alexander Leube

• Phd
• Researcher at Carl Zeiss Vision International GmbH

The Application of the Indentation Test on the Measurement of Modulus of Soft Contact Lens Materials Alexander Leube; Sebastian Marx; Wolfgang Sickenberger Ernst-Abbe University of Applied Sciences Jena, Jena, Germany JenVis Research, Jena, Germany To develop a novel, non-destructive method that evaluates the modulus of common soft contact lens m...

Purpose: The aim of this study is to develop and to test a novel, non-destructive method to evaluate the modulus of common, soft contact lens materials. In course of the development potential confounding factors should be examine. Method: A micro-hardness tester (Fischerscope HM2000) was used the first time to measure the modulus of five different...

Visual impairment is a widespread global health issue that affects millions of people across all ages and backgrounds. Timely intervention is essential for the effective management of eye diseases. Smartphones offer the possibility of continuously recording facial gestures during interaction with the device, whereby changes such as squinting of the...

There is a growing consensus in the global health community that the use of communication technologies will be an essential factor in ensuring universal health coverage of the world’s population. New technologies can only be used profitably if their accuracy is sufficient. Therefore, we explore the feasibility of using Apple’s ARKit technology to a...

Autorefraction is an objective way to determine the refractive error of the eye, without the need for feedback by the patient or a well-educated practitioner. To make refractive measurements more accessible in the background of the growing prevalence of myopia, a compact autorefractor was built, containing only few optical components and relying on...

Purpose: To determine whether accommodative errors in emmetropes and myopes are systematically different, and the effect of using different instruments and metrics. Methods: Seventy-six adults aged 18-27 years comprising 24 emmetropes (spherical equivalent refraction of the dominant eye +0.04 ± 0.03 D) and 52 myopes (-2.73 ± 0.22 D) were include...

Peripheral retinal contrast reduction is suggested as a potential myopia control strategy. However, the underlying mechanism is yet unknown. Therefore, this study investigated the influence of peripheral contrast reduction on central chromatic and achromatic contrast sensitivity (CS). A total of 19 participants were included. Peripheral contrast re...

A novel interferometric instrument for measuring neural transfer function (NTF) of the eye is presented. The device is based on a liquid-crystal-on-silicon spatial light modulator (SLM), which is used to create two laterally separated wavefronts in the pupil plane of the eye that interfere on the retina. The phase mask on the SLM, consisting of two...

Purpose: The purpose of this study is to present a framework to predict visual acuity (VA) based on a convolutional neural network (CNN) and to further to compare PAL designs. Method: A simple two hidden layer CNN was trained to classify the gap orientations of Landolt Cs by combining the feature extraction abilities of a CNN with psychophysical st...

To report eye examinations findings and cost-efficiency of mobile eye and vision care screening in underserved areas in north India. The Aloka Vision Program combines optometrical and ophthalmological screening as mobile eye camps with organized referrals to local eye hospitals. 402 people from urban (N = 191) and rural (N = 211) areas in the distr...

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 ph...

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 refinemen...

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...

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 underwe...

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 Gauss...

Abstract Purpose : Central corneal thickness (CCT) plays an important role in the clinical ophthalmological practice, since the intraocular pressure, planning of refractive surgery procedures and intraocular lens calculations depend on it. Therefore, the current study investigated the agreement and repeatability of a novel optical coherence based b...

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 ( ), medium ( ), and...

Currently available optotypes rely on a resolution task to measure subjective refractive errors, visual acuity and/or contrast sensitivity. In order to further integrate global shape processing, we have investigated the usability of radial frequency (RF) pattern as optotypes to assess the visual acuity (VA) and subjective refraction (SR). Methods:...

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 cu...

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...

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...

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...

Eye tracker (ET) underestimate saccades, whose durations are below 2x the sampling rate of the tracker. The purpose was to investigate the influence of the sampling rate of mobile ET (SMI ETG, 60 Hz and 120 Hz) on the reliability of fixation and saccade detection. Gaze traces of 11 participants were simultaneously recorded be a remote (EyeLink, 100...

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 perfo...

Purpose: The currently used method for radial averaging of the modulation transfer function (MTF) (Thibos, 2004) results in tight fluctuations regarding the outcomes. The purpose of the study was to develop a novel method to average the MTF radially and to evaluate the impact on image quality. Methods: The MTF was calculated from wavefront aberrati...

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 staircas...

Purpose: To evaluate the sign-dependency of spherical defocus on visual acuity and contrast sensitivity in myopes and non-myopes. Methods: 51 participants, 26 myopes and 25 non-myopes, underwent visual acuity testing with and without spherical defocus (±1.5 D in 0.5 D steps) under cycloplegia. Contrast sensitivity (CS) was assessed in n = 5 myopic...

Purpose: To evaluate the sign-dependency of spherical defocus on visual acuity and contrast sensitivity in myopes and non-myopes. Methods: 51 participants, 26 myopes and 25 non-myopes, underwent visual acuity testing with and without spherical defocus (±1.5 D in 0.5 D steps) under cycloplegia. Contrast sensitivity (CS) was assessed in n = 5 myopic...

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...

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 error...

Purpose: To evaluate the best sphero-cylindrical refraction of the human eye using 3-dimensional optimization algorithms regarding wavefront-based visual Strehl metrics and to investigate there correlation to subjective measurements of refractive errors. Methods: 462 eyes of 231 participants with a mean age of 33.1 ± 11.5 years (range: 18 to 78 yea...

Purpose: To evaluate the accuracy of different fitting functions for measured contrast sensitivity assessed with the psychophysical method PSI (Ψ). Methods: Contrast sensitivity was assessed in 7 cyclopleged, fullcorrected participants using an adaptive staircase procedure called PSI (Ψ) method. Sinusoidal grayscale patterns (Gabor patches) were ge...

Purpose: The study compared the depth of focus (DoF) of the human eye, calculated from objective image quality metrics (IQM) and subjectively measured defocus curves. Methods: 40 subjects with a mean age of 24.9±3.2 years and a mean spherical equivalent refractive error of M=-0.54D±2.15D participated and mydrias was assessed using three drops of 1%...