The visual benefits of correcting longitudinal and transverse chromatic aberration.

We describe a system-the Binocular Varichrome and Accommodation Measurement System-that can be used to measure and correct the eye's longitudinal and transverse chromatic aberration (LCA and TCA) and to perform vision tests with custom corrections. We used the system to investigate how LCA and TCA affect visual performance. Specifically, we studied the effects of LCA and TCA on visual acuity, contrast sensitivity, and chromostereopsis. LCA exhibited inter subject variability but followed expected trends compared with previous reports. TCA at the fovea was variable between individuals but with a tendency for the shift at shorter wavelengths to be more temporalward in the visual field in each eye. We found that TCA was generally greater when LCA was corrected. For visual acuity, we found that a measurable benefit was realized only with both LCA and TCA correction unless the TCA was low. For contrast sensitivity, we found that the best sensitivity to a 10-cycle/degree polychromatic grating was attained when LCA and TCA were corrected. Finally, we found that the primary cause of chromostereopsis is the TCA of the eyes.

The effect of a short-wave filtering contact lens on color appearance.

We assessed the effect of a contact lens that filters short-wavelength (SW) visible light on color appearance. These effects were modeled and measured by direct comparison to a clear contact lens. Sixty-one subjects were enrolled, and 58 completed as cohort; 31 were 18 to 39 years old (mean ± SD, 29.6 ± 5.6), 27 were 40 to 65 years old (50.1 ± 8.1). A double-masked contralateral design was used; participants randomly wore a SW-filtering contact lens on one eye and a clear control lens on the other eye. Subjects then mixed three primaries (including a short-wave primary, strongly within the absorbance of the test lens) until a perceived perfect neutral white was achieved with each eye. Color appearance was quantified using chromaticity coordinates measured with a spectral radiometer within a custom-built tricolorimeter. Color vision in natural scenes was simulated using hyperspectral images and cone fundamentals based on a standard observer. Overall, the chromaticity coordinates of matches that were set using the SW-filtering contact lens (n = 58; x = 0.345, y = 0.325, u' = 0.222, v' = 0.470) and clear contact lens (n = 58; x = 0.344, y = 0.325, u' = 0.223, v' = 0.471) were not significantly different, regardless of age group. Simulations indicated that, for natural scenes, the SW-filtering contact lens that was evaluated changes L/(L+M) and S/(L+M) chromatic contrast by no more than -1.4% to +1.1% and -36.9% to +5.0%, respectively. Tricolorimetry was used to measure color appearance in subjects wearing a SW-filtering lens in one eye and a clear lens in the other, and the results indicate that imparting a subtle tint to a contact lens, as in the SW-filtering lens that was evaluated, does not alter color appearance for younger or older subjects. A model of color vision predicted little effect of the lens on chromatic contrast for natural scenes.

Coherence revival multiplexed, buffered swept source optical coherence tomography: 400 kHz imaging with a 100 kHz source.

The effective speed of a swept source optical coherence tomography (SSOCT) imaging system was quadrupled using efficient sweep buffering along with coherence revival and spatial multiplexing. A polarizing beam splitter and fold mirror assembly were used to create a dual spot sample arm with a common objective designed for near-diffraction-limited retinal imaging. Using coherence revival, a variable optical delay line allowed for separate locations within a sample to be simultaneously imaged and frequency encoded by carefully controlling the optical path length of each sample path. This method can be used to efficiently quadruple the imaging speed of any SSOCT system employing a low duty-cycle laser that exhibits coherence revival. The system was used to image the retina of healthy human volunteers.

Theoretical impact of chromatic aberration correction on visual acuity.

It has been known for more than 220 years that the image quality of the human eye is significantly degraded by chromatic aberrations. Recently, it was shown experimentally that correcting chromatic aberrations results in a 0.2- to 0.8-line improvement in visual acuity. Here we ask, is this expected? We developed tools that enable simulations of the optical impact of physiologically relevant amounts of chromatic aberration in real human eyes and combined these with tools that compute the visual acuity of an ideal observer. This allows us to characterize the theoretical impact of chromatic aberration correction on visual acuity. Results indicate a substantive improvement of 0.4- to 2-lines in ideal observer visual acuity with chromatic aberration correction. Ideal observer thresholds benefit significantly more from correction of longitudinal than correction of transverse chromatic aberration. Finally, improvements in ideal observer visual acuity are greater for subjects with less monochromatic aberration, such that subjects with better baseline optical quality benefit most from correction of chromatic aberrations.

Simultaneous swept source optical coherence tomography of the anterior segment and retina using coherence revival.

We report on an implementation of coherence revival-based heterodyne swept source optical coherence tomography that is capable of simultaneously imaging the anterior and posterior eye. A polarization-encoded sample arm was used to efficiently focus orthogonal polarizations on the anterior segment and retina. Depth encoding was achieved using coherence revival, which allows for multiple depths within a sample to be simultaneously imaged and frequency encoded by carefully controlling the optical pathlength of each sample path. This design is a significant step toward whole-eye optical coherence tomography (OCT), which would enable customized ray-traced modeling of patient eyes to improve refractive surgical interventions and eliminate optical artifacts in retinal OCT diagnostics. We demonstrated the feasibility of this system for in vivo imaging by simultaneously acquiring images of the anterior segments and retinas in healthy human volunteers.

Human ocular biometry.

The aim of this study was to examine growth of the human eye globe and cornea from early in gestation to late in adult life. Globe antero-posterior length, horizontal and vertical diameters, corneal horizontal and vertical (white to white) diameters and posterior pole to limbus distances were measured using digital calipers (±0.01 mm) in 541 postmortem eyes. Additional pre- and postnatal data for some of the dimensions were obtained from the literature. All dimensions examined increase rapidly during prenatal development but postnatal growth differs. Growth of globe antero-posterior length, vertical and horizontal diameters as well as corneal vertical and horizontal diameters stops within 1 year after birth. Logistic analysis is consistent with an asymptotic prenatal growth mode and no further growth after its completion around 1 year after birth. Horizontal and vertical globe diameters are the same at all ages but the corneal horizontal diameter is always larger than the vertical diameter. No differences could be detected between males and females in any of the ocular dimensions. Globe and corneal growth take place primarily during the prenatal growth mode and dimensions reach their maxima, shortly after birth. It is suggested that cessation of a growth stimulating signal at birth marks the end of the prenatal growth mode and that the small increases over the next year are due to cells already stimulated. Male and female eyes of the same age have the same globe and cornea dimensions.

A portable, contact animal fundus imaging system based on Rol's GRIN lenses.

OBJECTIVE: To demonstrate a cost-effective, portable, and simple-to-use fundus imaging system for laboratory animals. ANIMALS STUDIED: Albino rats, pigmented mice, albino guinea pigs, and New Zealand white rabbits. PROCEDURE: A contact fundus imaging system was designed and constructed using standard optical and mechanical components: a digital camera, an otoscope, a fiber optic light source, and standard optical lenses and mounts. Digital fundus video and photography of two albino rats, two pigmented mice, two New Zealand white rabbits, and two albino guinea pigs were obtained. For all animals examined, pupils were dilated and local anesthetic was administered. RESULTS: Digital images of the fundus were obtained in all animals. Contrast of retinal vasculature and overall image quality varied from one species to another, as the axial length, ocular optics, and retinal reflectance varied significantly across species. Light intensity and focus were optimized via the light source and lens focusing mount to produce high-quality images for each animal. CONCLUSIONS: The portable, cost-effective contact fundus imaging system was easy to use for fundus examination of laboratory animals.

Multifocal contact lens vision simulated with a clinical binocular simulator.

PURPOSE: The purpose of this study is to compare the binocular visual perception of participants wearing multifocal contact lenses and these same lens designs viewed through a temporal multiplexing visual simulator. METHODS: Visual performance and perceived visual quality at various distances were obtained in 37 participants wearing soft M-CLs and through the SimVis Gekko programmed with the same lenses. In a pilot study (n = 10) visual performance was measured in terms of LogMAR visual acuity (VA) at far (4 m), intermediate (64 cm) and near (40 cm) distances and through-focus VA (TFVA) curves with the simulated M-CLs. In the follow-up study (n = 27), LogMAR VA at far, intermediate and near distances were measured both with the actual and simulated M-CLs. Perceived visual quality was measured in both studies using the Multifocal Acceptance Score (MAS-2EV), and a Participants Reported Outcomes Vision questionnaire. Differences between the metrics obtained with simulated and actual lenses were obtained. RESULTS: Both actual and simulated M-CLs increased depth-of-focus by a similar amount. Mean LogMAR VA differences with actual and simulated M-CLs ranged between 4 and 6 letters (0.08 ± 0.01, 0.12 ± 0.01 and 0.10 ± 0.01, for far, intermediate and near distances, respectively). MAS-2EV average score differences with actual and simulated M-CLs ranged between -1.00 and + 4.25. Average MAS-2EV scores were not correlated significantly with VA. However, MAS-2EV (average and individual scores) were highly correlated to visual quality questionnaire responses (p < 0.005). CONCLUSIONS: A simultaneous vision simulator accurately represented vision with M-CLs both VA at various distances and perceived visual quality, as measured in a clinical setting. The MAS-2EV metric accurately captured participant reported outcomes of standard vision questionnaires. The combination of SimVis Gekko and MAS-2EV has the potential to largely reduce chair time in M-CLs fitting.

Contribution of the crystalline lens gradient refractive index to the accommodation amplitude in non-human primates: in vitro studies.

The purpose of this study was to determine the contribution of the gradient refractive index to the change in lens power in hamadryas baboon and cynomolgus monkey lenses during simulated accommodation in a lens stretcher. Thirty-six monkey lenses (1.4-14.1 years) and twenty-five baboon lenses (1.8-28.0 years) were stretched in discrete steps. At each stretching step, the lens back vertex power was measured and the lens cross-section was imaged with optical coherence tomography. The radii of curvature for the lens anterior and posterior surfaces were calculated for each step. The power of each lens surface was determined using refractive indices of 1.365 for the outer cortex and 1.336 for the aqueous. The gradient contribution was calculated by subtracting the power of the surfaces from the measured lens power. In all lenses, the contribution of the surfaces and gradient increased linearly with the amplitude of accommodation. The gradient contributes on average 65 ± 3% for monkeys and 66 ± 3% for baboons to the total power change during accommodation. When expressed in percent of the total power change, the relative contribution of the gradient remains constant with accommodation and age in both species. These findings are consistent with Gullstrand's intracapsular theory of accommodation.

Optical and Visual Quality With Physical and Visually Simulated Presbyopic Multifocal Contact Lenses.

Purpose: As multifocal contact lenses (MCLs) expand as a solution for presbyopia correction, a better understanding of their optical and visual performance becomes essential. Also, providing subjects with the experience of multifocal vision before contact lens fitting becomes critical, both to systematically test different multifocal designs and to optimize selection in the clinic. In this study, we evaluated the ability of a simultaneous vision visual simulator (SimVis) to represent MCLs. Methods: Through focus (TF) optical and visual quality with a center-near aspheric MCL (low, medium and high near adds) were measured using a multichannel polychromatic Adaptive Optics visual simulator equipped with double-pass, SimVis (temporal multiplexing), and psychophysical channels to allow measurements on-bench and in vivo. On bench TF optical quality of SimVis-simulated MCLs was obtained from double-pass (DP) images and images of an E-stimulus using artificial eyes. Ten presbyopic subjects were fitted with the MCL. Visual acuity (VA) and DP retinal images were measured TF in a 4.00 D range with the MCL on eye, and through SimVis simulations of the same MCLs on the same subjects. Results: TF optical (on bench and in vivo) and visual (in vivo) quality measurements captured the expected broadening of the curves with increasing add. Root mean square difference between real and SimVis-simulated lens was 0.031/0.025 (low add), 0.025/0.015 (medium add), 0.019/0.011 (high add), for TF DP and TF LogMAR VA, respectively. A shape similarity metric shows high statistical values (lag κ = 0), rho = 0.811/0.895 (low add), 0.792/0.944 (medium add), and 0.861/0.915 (high add) for TF DP/LogMAR VA, respectively. Conclusions: MCLs theoretically and effectively expand the depth of focus. A novel simulator, SimVis, captured the through-focus optical and visual performance of the MCL in most of the subjects. Visual simulators allow subjects to experience vision with multifocal lenses prior to testing them on-eye. Translational Relevance: Simultaneous visual simulators allow subjects to experience multifocal vision non-invasively. We demonstrated equivalency between real multifocal contact lenses and SimVis-simulated lenses. The results suggest that SimVis is a suitable technique to aid selection of presbyopic corrections in the contactology practice.

Variations in intraocular lens injector dimensions and corneal incision architecture after cataract surgery.

PURPOSE: To evaluate the differences in intraocular lens (IOL) injectors and to assess the effect of IOL insertion on injector tips and eyes after cataract surgery in a rabbit model. SETTING: Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, Miami, Florida, USA. DESIGN: Experimental study. METHODS: A modified optical comparator was used to measure the tips of 13 IOL injector models to determine the perimeter, tip angle, and cone angle of each. Injectors were analyzed before and after IOL insertion. Surgery was performed on rabbits with 71 IOL injectors of 13 models, and custom gauges were used to determine the incision size before and after surgery. RESULTS: The injector dimensions varied by model; tip diameter, tip angle, and cone angle ranged from 1.44 to 2.12 mm, 29.7 to 66.5 degrees and 0.6 to 10.8 degrees, respectively. The incision size through which surgery was successfully performed also varied by injector model; the initial incision sizes ranged from 2.0 to 2.63 mm. For all injectors, there was wound enlargement after IOL insertion that ranged from a 0.1 to 0.65 mm increase in incision length. CONCLUSIONS: The dimensions and injection systems varied with each IOL injector. All injectors led to postoperative wound stretch after IOL insertion, with no final incision measuring less than 2.0 mm. These findings suggest that the clear cornea incision should have a width corresponding to the injector diameter.

Robotic Remote Controlled Stereo Slit Lamp.

PURPOSE: Our purpose was to develop a robotic remotely operated stereo slit lamp system allowing three-dimensional stereo viewing and recording of the patient's examination via local area network, Internet, and satellite. METHODS: A commercial slit lamp was modified to accept motors and servos to permit control of all optical and mechanical components of the device. The custom graphical user interface with dual high-resolution real-time stereoscopic imaging, control/position indicators, overview video, and audio were transmitted via local area network, Internet, and satellite. Under University of Miami Institutional Review Board authorization, Internet connectivity enabled multiple examiners to simultaneously view and control the slit lamp and to collaboratively discuss diagnosis and treatment options. The remote clinicians used a tablet, laptop, or desktop computer to view and control the slit lamp. RESULTS: The network, Internet, satellite-connected system was controllable from the United States, Europe, and Canada while acquiring high-resolution, real-time video in all subjects. Control of the slit lamp through Ethernet, WiFi, and 4G exhibited total system latencies of 464 ± 58, 483 ± 64, and 870 ± 66 milliseconds when transmitting within the continent, and Ethernet control exhibited a latency of 606 ± 130 milliseconds when transmitting between continents. High- and low-magnification images of healthy volunteers were acquired by a remote clinician. CONCLUSIONS: The robotic remotely operated stereo slit lamp system allows three-dimensional stereo viewing and recording of the patient's examination via local area network, Internet, and satellite. TRANSLATIONAL RELEVANCE: The robotic remotely controlled stereo slit lamp system enables remote examination of human subjects.

Handheld Adaptive Optics Scanning Laser Ophthalmoscope.

Adaptive optics scanning laser ophthalmoscopy (AOSLO) has enabled in vivo visualization and enhanced understanding of retinal structure and function. Current generation AOSLOs have a large footprint and are mainly limited to imaging cooperative adult subjects. To extend the application of AOSLO to new patient populations, we have designed the first portable handheld AOSLO (HAOSLO) system. By incorporating a novel computational wavefront sensorless AO algorithm and custom optics, we have miniaturized our HAOSLO to weigh less than 200 grams. HAOSLO imaged the cones closest to the fovea with a handheld probe in adults and captured the first AO-enhanced image of cones in infants.

Wireless, Web-Based Interactive Control of Optical Coherence Tomography with Mobile Devices.

PURPOSE: Optical coherence tomography (OCT) is widely used in ophthalmology clinics and has potential for more general medical settings and remote diagnostics. In anticipation of remote applications, we developed wireless interactive control of an OCT system using mobile devices. METHODS: A web-based user interface (WebUI) was developed to interact with a handheld OCT system. The WebUI consisted of key OCT displays and controls ported to a webpage using HTML and JavaScript. Client-server relationships were created between the WebUI and the OCT system computer. The WebUI was accessed on a cellular phone mounted to the handheld OCT probe to wirelessly control the OCT system. Twenty subjects were imaged using the WebUI to assess the system. System latency was measured using different connection types (wireless 802.11n only, wireless to remote virtual private network [VPN], and cellular). RESULTS: Using a cellular phone, the WebUI was successfully used to capture posterior eye OCT images in all subjects. Simultaneous interactivity by a remote user on a laptop was also demonstrated. On average, use of the WebUI added only 58, 95, and 170 ms to the system latency using wireless only, wireless to VPN, and cellular connections, respectively. Qualitatively, operator usage was not affected. CONCLUSIONS: Using a WebUI, we demonstrated wireless and remote control of an OCT system with mobile devices. TRANSLATIONAL RELEVANCE: The web and open source software tools used in this project make it possible for any mobile device to potentially control an OCT system through a WebUI. This platform can be a basis for remote, teleophthalmology applications using OCT.

Pupil Tracking for Real-Time Motion Corrected Anterior Segment Optical Coherence Tomography.

Volumetric acquisition with anterior segment optical coherence tomography (ASOCT) is necessary to obtain accurate representations of the tissue structure and to account for asymmetries of the anterior eye anatomy. Additionally, recent interest in imaging of anterior segment vasculature and aqueous humor flow resulted in application of OCT angiography techniques to generate en face and 3D micro-vasculature maps of the anterior segment. Unfortunately, ASOCT structural and vasculature imaging systems do not capture volumes instantaneously and are subject to motion artifacts due to involuntary eye motion that may hinder their accuracy and repeatability. Several groups have demonstrated real-time tracking for motion-compensated in vivo OCT retinal imaging, but these techniques are not applicable in the anterior segment. In this work, we demonstrate a simple and low-cost pupil tracking system integrated into a custom swept-source OCT system for real-time motion-compensated anterior segment volumetric imaging. Pupil oculography hardware coaxial with the swept-source OCT system enabled fast detection and tracking of the pupil centroid. The pupil tracking ASOCT system with a field of view of 15 x 15 mm achieved diffraction-limited imaging over a lateral tracking range of +/- 2.5 mm and was able to correct eye motion at up to 22 Hz. Pupil tracking ASOCT offers a novel real-time motion compensation approach that may facilitate accurate and reproducible anterior segment imaging.

Enhanced volumetric visualization for real time 4D intraoperative ophthalmic swept-source OCT.

Current-generation software for rendering volumetric OCT data sets based on ray casting results in volume visualizations with indistinct tissue features and sub-optimal depth perception. Recent developments in hand-held and microscope-integrated intrasurgical OCT designed for real-time volumetric imaging motivate development of rendering algorithms which are both visually appealing and fast enough to support real time rendering, potentially from multiple viewpoints for stereoscopic visualization. We report on an enhanced, real time, integrated volumetric rendering pipeline which incorporates high performance volumetric median and Gaussian filtering, boundary and feature enhancement, depth encoding, and lighting into a ray casting volume rendering model. We demonstrate this improved model implemented on graphics processing unit (GPU) hardware for real-time volumetric rendering of OCT data during tissue phantom and live human surgical imaging. We show that this rendering produces enhanced 3D visualizations of pathology and intraoperative maneuvers compared to standard ray casting.

Handheld, rapidly switchable, anterior/posterior segment swept source optical coherence tomography probe.

We describe the first handheld, swept source optical coherence tomography (SSOCT) system capable of imaging both the anterior and posterior segments of the eye in rapid succession. A single 2D microelectromechanical systems (MEMS) scanner was utilized for both imaging modes, and the optical paths for each imaging mode were optimized for their respective application using a combination of commercial and custom optics. The system has a working distance of 26.1 mm and a measured axial resolution of 8 µm (in air). In posterior segment mode, the design has a lateral resolution of 9 µm, 7.4 mm imaging depth range (in air), 4.9 mm 6dB fall-off range (in air), and peak sensitivity of 103 dB over a 22° field of view (FOV). In anterior segment mode, the design has a lateral resolution of 24 µm, imaging depth range of 7.4 mm (in air), 6dB fall-off range of 4.5 mm (in air), depth-of-focus of 3.6 mm, and a peak sensitivity of 99 dB over a 17.5 mm FOV. In addition, the probe includes a wide-field iris imaging system to simplify alignment. A fold mirror assembly actuated by a bi-stable rotary solenoid was used to switch between anterior and posterior segment imaging modes, and a miniature motorized translation stage was used to adjust the objective lens position to correct for patient refraction between -12.6 and + 9.9 D. The entire probe weighs less than 630 g with a form factor of 20.3 x 9.5 x 8.8 cm. Healthy volunteers were imaged to illustrate imaging performance.

Pupil tracking optical coherence tomography for precise control of pupil entry position.

To maximize the collection efficiency of back-scattered light, and to minimize aberrations and vignetting, the lateral position of the scan pivot of an optical coherence tomography (OCT) retinal scanner should be imaged to the center of the ocular pupil. Additionally, several retinal structures including Henle's Fiber Layer (HFL) exhibit reflectivities that depend on illumination angle, which can be controlled by varying the pupil entry position of the OCT beam. In this work, we describe an automated method for controlling the lateral pupil entry position in retinal OCT by utilizing pupil tracking in conjunction with a 2D fast steering mirror placed conjugate to the retinal plane. We demonstrate that pupil tracking prevents lateral motion artifacts from impeding desired pupil entry locations, and enables precise pupil entry positioning and therefore control of the illumination angle of incidence at the retinal plane. We use our prototype pupil tracking OCT system to directly visualize the obliquely oriented HFL.

Measurement of Crystalline Lens Volume During Accommodation in a Lens Stretcher.

PURPOSE: To determine if the lens volume changes during accommodation. METHODS: The study used data acquired on 36 cynomolgus monkey lenses that were stretched in a stepwise fashion to simulate disaccommodation. At each step, stretching force and dioptric power were measured and a cross-sectional image of the lens was acquired using an optical coherence tomography system. Images were corrected for refractive distortions and lens volume was calculated assuming rotational symmetry. The average change in lens volume was calculated and the relation between volume change and power change, and between volume change and stretching force, were quantified. Linear regressions of volume-power and volume-force plots were calculated. RESULTS: The mean (± SD) volume in the unstretched (accommodated) state was 97 ± 8 mm3. On average, there was a small but statistically significant (P = 0.002) increase in measured lens volume with stretching. The mean change in lens volume was +0.8 ± 1.3 mm3. The mean volume-power and volume-load slopes were -0.018 ± 0.058 mm3/D and +0.16 ± 0.40 mm3/g. CONCLUSIONS: Lens volume remains effectively constant during accommodation, with changes that are less than 1% on average. This result supports a hypothesis that the change in lens shape with accommodation is accompanied by a redistribution of tissue within the capsular bag without significant compression of the lens contents or fluid exchange through the capsule.

The zonules selectively alter the shape of the lens during accommodation based on the location of their anchorage points.

PURPOSE: To determine the role of anterior and posterior zonular tension on the optomechanical lens response during accommodation simulation. METHODS: Ten eyes from nine hamadryas baboons (4.9 ± 0.7 years) and 20 eyes from 18 cynomolgus monkeys (5.4 ± 0.3 years) were dissected, leaving the lens, zonules, ciliary body, hyaloid membrane, anterior vitreous, and a segmented scleral rim intact. The lens preparation was mounted in a lens stretcher, and the outer scleral shell was displaced radially in a stepwise fashion. The load, lens, and ciliary body diameters, lens power, lens thickness, and the anterior and posterior radius of curvature were measured during stretching. The zonular fibers attached to either the posterior or anterior lens surface were then carefully transected and the experiment was repeated. Zonular transection was confirmed in four eyes via laser scanning confocal microscopy after immunostaining. The effect of zonular transection on the tissue response to stretching was quantified. RESULTS: Without anterior zonules, 48% and 97% of the changes in anterior and posterior radii are retained. Without posterior zonules, 81% and 67% of the changes in anterior and posterior radii are retained. The changes in lens shape were reduced after transecting either the anterior or posterior zonules; however, both surfaces still changed shape. CONCLUSIONS: While either the anterior or posterior zonules alone are capable of changing the shape of both lens surfaces, the anterior zonules have a greater effect on the anterior lens surface, and the posterior zonules have a greater effect on the posterior lens surface.