Oxyopia Vision Science Seminars
Oxyopia Seminars (Spring 2015)Oxyopia, the Greek word meaning "acute vision," is the title of the weekly vision science seminars presented at the Indiana University School of Optometry in conjunction with graduate course V765. The seminars serve a twofold purpose in that they:
- stimulate intellectual activity among the faculty, and
- provide a learning environment for graduate students.
Oxyopia presenters are IU School of Optometry faculty members and graduate students as well as visiting lecturers from other departments, universities, research facilities, private practices, industry, etc.
|1/16/2015||Conflict on Wed with BV PEDS|
Wenlin Zhang (30 minutes)
I'm Not Done Yet: Cones in AMD
Glutamine is an essential contributor to the human corneal endothelial ATP pool
There are several common causes of moderate and severe vision impairment (MSVI), which is defined as visual acuity in the better eye lower than 20/60 in Snellen notation and 0.5 on the logMAR scale at presentation. The chief cause of MSVI in industrialized countries outside of Asia is age-related macular degeneration (AMD). In many countries in Asia, degenerative myopia is the chief cause of MSVI, and also among high myopes when the analysis is performed separately, as in the Netherlands. Diabetic retinopathy and glaucoma are also chief causes of vision loss. Given worldwide population aging, preserving sight well into the older ages becomes a priority. The mechanisms that lead to the well-known pathological changes in AMD have been studied both in human pathological tissue and in animal models. Previously, the long-term build-up of debris in Bruch’s membrane, the loss of choriocapillaris, and the death of the retinal pigment epithelial cells have been shown to create a harsh environment for the cone photoreceptors in eyes with AMD. However, even in areas of atrophy as seen with clinical tools, some cone photoreceptors have recently been show to remain. Cones have been shown on histology in eyes with atrophy. We recently showed cones in areas of atrophy with imaging studies performed at high resolution in living eyes. We will discuss how these cones might survive and even function despite the loss of their normal metabolic support. Some cones still functioning, even if poorly, may provide sight. How might these cones be preserved?
Purpose: Glutamine has long been viewed as an essential nutrient in corneal graft storage and corneal endothelial (CE) culture medium. We recently characterized the highly expressed CE membrane protein SLC4A11 as a novel ammonia transporter, suggesting active glutamine metabolism and the net production of ammonia. We hypothesized CE cells can utilize glutamine as an alternative carbon source for ATP production, which potentially is an essential substrate supporting CE Na-K-ATPase and ‘pump’ function.
Method: Enzymes and transporters required for glutamine metabolism were screened by RT-PCR in human CE specimens collected from eye bank tissue. Glutamine consumption in an immortalized human CE cell line was measured by ammonia release into culture medium by colorimetric assay. ATP production by CE in glucose only (5 g/l), glutamine only (4 mM), both or neither substrate was measured by luciferin-luciferase assay in human CE cell lines. All data are expressed as mean ± s.e.m.
Results: We detected the expression of the key enzyme in glutamine metabolism in human CE: phosphate-dependent glutaminase, which catalyzes the first step in glutamine oxidation. Both kidney isoform glutaminase 1 (GLS1) and liver isoform (GLS2) are expressed (GLS1>GLS2). Excitatory Amino Acid Transporter 1-3 (EAAT 1-3), associated with glutamine metabolism, were also detected with expression level EAAT3≈EAAT2>EAAT1. Ammonia release (mM) was dose dependent on glutamine concentration (n=6 at each concentration, 0.1, 0.5, 1, 2, 4 mM) with highest at 4 mM (1.14±0.01) and lowest at 0.1 mM (0.74±0.02) (Independent t-test, p<0.001). Ammonia levels can be fitted against glutamine concentration with the Michaelis–Menten equation (R2=0.918, p<0.0001), and yield a Km of 1.99±0.62 mM (p=0.0034), similar to previously reported glutaminase Km 2~5 mM. ATP production (nmol/106 cells) was highest in glucose and glutamine combined medium (1.10±0.09), slightly lower in glutamine only medium (1.00±0.12), and significantly lower in glucose only (0.52±0.07) and no substrate media (0.34±0.07). (n=23 in each condition, One-way ANOVA, P<0.001).
Conclusion: Human CE can actively use glutamine as an essential carbon source for ATP production through glutaminase. This work could provide insight in optimizing cornea graft storage medium and the pathophysiology caused by mutated ammonia transporter SLC4A11
|1/30/2015||Jason Marsack||An Integrated Approach to Improving Visual Performance in Highly Aberrated Eyes||Brief description/summary abstract of the talk: When considering the development of novel correction strategies for and individual with highly aberrated eyes, two questions we routinely consider are: 1) what goals is the individual trying to achieve with the optical correction and 2) what attributes in an optical correction will best allow the individual to achieve these goals? The underlying premise that ties these two questions together is that patient needs vary and are not simply based on optical or visual performance. Cost, comfort, wear time, complexity of the care regimen and aesthetics are all factors that, along with visual and optical performance, play a role in the patient’s satisfaction with the correction. This presentation describes several research projects related to the development of novel correction strategies for highly aberrated eyes, and considers how each type of correction might meet the varied needs of patients with highly aberrated eyes.|
The sensitivity of vergence eye movements in 5-10 week old infants.
Adaptation of phoria and accommodation in young children
Introduction: Fine motor alignment of the two eyes is required for appropriate binocular experience, yet in adults it appears that binocular processes are responsible for fine motor alignment. There is substantial evidence that infants are not sensitive to retinal disparity (the error-correcting cue for motor alignment) until 3-5 months of age. However, rudimentary eye alignment is possible from birth and matures with age. How then does eye alignment develop in the absence of adult-like binocular processes? Here we investigate the sensitivity of vergence eye movements in 5-10 week old humans to a target moving in depth, while addressing the possible influence of accommodation.
Methods: Young infants (5-10 weeks) and adult controls viewed a naturalistic movie stimulus on a screen that moved sinusoidally in depth at three different amplitudes (1.0, 0.5 and 0.25 MA) at 0.1 Hz. Horizontal eye position and refractive status were measured at 25 Hz. Fast Fourier Transforms were used to determine the amplitude spectra of both vergence and accommodation responses and the frequencies were matched to that of the stimulus. Signal-to-noise ratios (SNRs) were calculated by dividing the response at the stimulus frequency by the mean of the adjacent frequencies.
Results and Discussion: Vergence SNRs were significantly different from 1 (a baseline where signal + noise was no larger than an estimate of noise alone) at even the smallest amplitudes tested suggesting that infants could generate a vergence response to a stimulus moving in depth at 0.25 MA (~30 minutes of disparity) (mean = 2.10; p =0.03). Accommodation responses were only significant for the two larger amplitudes (means = 2.84, 1.47; p = 0.04, 0.03). This indicates that modulation of accommodation alone cannot account for changes in vergence eye position in young infants. Implications for the normal development of eye alignment and future research will be discussed.
Abstract: Young children have a hyperopic refraction and reduced interpupillary distance relative to adults, leading to decreased convergence and increased accommodation demands. These two motor systems are neurally coupled and therefore young children experience an apparent conflict between them. How are young children able to maintain focused and aligned images in the presence of this conflict? Adults demonstrate vergence adaptation to a variety of visual stimuli. In the current study, we found that young children and adults showed heterophoria adaptation to a 2 MA prismatic demand at a 95cm viewing distance. Changes in accommodation responses during the adaptation were significantly smaller than the changes in phoria.
In typically developing children who experience changing visual demands, this adaptation might help maintain eye alignment. Children with hyperopia >+3.50D are under increased risk for developing refractive esotropia. Do they show similar adaptation to induced vergence demands, and could this explain why some of them are able to remain aligned? To better facilitate future testing of high hyperopes wearing spectacles, we are building a computational model of photorefraction to understand issues related to calibration in the presence of the spectacle lenses.
Dynamic network interactions of the human oculomotor system based on intrinsic connectivity
Quantifying the density of Retinal Nerve Fibers (RNF) in SD-OCT enface Images
One of the biggest challenges in neuroscience is to understand how various diverging functions (such as perception, action and cognition) arise from the brain’s fixed structural connections. Neuroimaging studies of the ‘resting’ brain consistently show that in timescales of 10-15 minutes brain structures with known high functional synchrony form distinguishable activation networks, such as the default mode network. White matter tractography studies have identified the structural links between the brain regions within these intrinsic connectivity networks (ICNs). However, synchrony between these brain regions over shorter timescales is not stable. This fluctuation in connectivity manifests as changes in community organization of these ICNs. Since the mental states of the subject are unknown in these resting state experiments, little can be learned about the role and significance of these short-scale modulations in these functional brain networks.
Here, we studied the dynamics in short-scale modulations in connectivity and global functional organization of ICNs during a visually-guided task designed to activate the oculomotor system. Ten subjects, studied on a 3T Siemens Trio MRI scanner and an eye tracker, preformed a battery of 40s long blocks of alternating visually guided oculomotor tasks (fixation, smooth pursuit, saccades and voluntary cued blink conditions). Human and non-human primate oculomotor research has identified a network of cortical and sub-cortical structures involved in the control and execution of numerous subtypes of eye movements. Here, we asked how these structures within these oculomotor networks interact with other known functional networks.
We decomposed our oculomotor task data using independent component analysis to identify and extract the active intrinsic connectivity networks (ICN). Number of structures involved in the control of eye movements, such as the frontal eye fields (FEF), supplemental eye field (SEF) and parietal eye field (PEF) were all part of a single ICN. However, other task activated areas such as lateral frontal eye field (latFEF) and inferior frontal gyrus (IFG) were each identified as separate ICNs. The well-known networks (e.g. the primary vis., higher vis., left executive control network (LECN), RECN, and salience network) were also identified. Utilizing graph analysis, we have studied the modulations of the functional community organization of these ICNs across our different task conditions. Our results showed similar condition-specific modular organizations of the ICNs across subjects. Additionally, most of the ICNs maintained a stable relationship throughout the task block.
Introduction: The principal cells damaged in glaucoma are the retinal ganglion cells. However, due to the microscopic nature of the ganglion cells and their axons, clinical imaging techniques rely on comparatively gross structures such as rim area, retinal nerve fiber layer thickness and the thickness of macular structures to determine the structural integrity of the retinal ganglion cells. The ability of these techniques to quantify the ganglion cell loss is compromised by the non-neural component of the gross structures they measure.
Current imaging techniques present the opportunity to visualize the nerve fiber bundles (formed by the axons) of the retinal ganglion cells. I will be presenting a thresholding technique designed to quantify the density of the fibers in enface images. This technique is formulated to reduce the impact of the non- fiber component in determining ganglion cell loss.
Visual Disturbance and Ocular Irritation in an Experimental Dry Eye Model
Quantifying foveal form birefringence in aging and diabetes
Tear film instability (TFI) is a core mechanism of dry eye (DEWS, 2007), but its connection to dry eye symptoms of ocular irritation and visual disturbance remains poorly understood. In this experimental TFI model, we test the hypothesis that TFI over the pupil decreases optical quality, visual acuity (VA) and stresses the ocular surface, leading to ocular irritation, and that wearing a soft contact lens (CL) partially alters this relationship. We also propose that symptoms of discomfort and blurry vision increase gradually after repeated TFI trials.
Abstract: Polarimetric imaging reveals structures in the eye that cannot otherwise be seen with standard scattered light imaging. It is useful for quantifying changes that occur in the eye’s birefringent tissues, such as the Henle Fiber Layer. The axons of the cone photoreceptors are displaced radially outward from the foveal center in the central macula. The systematic interaction of the form birefringence from these axons and the cornea leads to a characteristic pattern called the macular bow-tie. Using a confocal polarimeter (GDx), we took foveal centered scans with 20 different polarization states for 120 normal subjects, 20 per decade from 20-80 yrs, with an equal number of females and males in each group. We also compared patients with diabetes to age-and gender-matched control subjects. Fifteen diametric measurements, centered on the fovea, encompassing 7.5 deg visual angle were taken for each individual. Data analysis was performed on images computed to include different polarization information. We formed metrics from the mean, standard deviation, and coefficient of variation of birefringence along the diameters. These analyses quantify the loss of birefringence, or the increased variability, due to aging changes to photoreceptors or the effects of diabetes on the retina.
MHz AO-OCT for imaging the microscopic retina
Comparison of cysts in red and green images for diabetic macular edema
Abstract: Image acquisition speed of optical coherence tomography (OCT) remains a fundamental barrier that limits its scientific and clinical utility. Here we demonstrate a novel multi-camera adaptive optics (AO-)OCT system for ophthalmologic use that operates at 1 million A-lines/s at a wavelength of 790 nm with 2.4x2.4x5.3 μm3 3D resolution in retinal tissue. Central to the spectral-domain design is a novel detection channel based on four high-speed spectrometers that receive light sequentially from a 1 × 4 optical switch assembly. Absence of moving parts enables ultra-fast (50ns) and precise switching with low insertion loss (−0.18 dB per channel). This manner of control makes use of all available light in the detection channel and avoids camera dead-time, both critical for imaging at high speeds. Additional benefit in signal-to-noise accrues from the larger numerical aperture afforded by the use of AO and yields retinal images of comparable dynamic range to that of clinical OCT. We validated system performance by a series of experiments that included imaging in both model and human eyes. We demonstrated the performance of our MHz AO-OCT system to capture detailed images of individual retinal nerve fiber bundles and cone photoreceptors. This is the fastest ophthalmic OCT system we know of in the 700 to 915 nm spectral band.
Purpose: To investigate in a population of largely minority eyes whether the red channel image from a color fundus camera better visualizes cysts in diabetic macular edema, as compared to the green channel image alone. In assessing diabetic retinas for clinically significant macular edema, the presence of cysts must be judged with respect to the central macula. Some grading programs use red free images, often derived from green channel images, to enhance visualization of retinal vessel damage. We explored whether using only green channel images lead to reduce detection of cysts.
Methods: We evaluated macular cysts in 13 diabetic patients diagnosed with clinically significant macular edema, age range 33-68 years. Diabetic patients were selected from the screening study of >2000 underserved patients seen at Eastmont Wellness Center, Oakland, CA. Patients underwent photoscreening with a nonmydriatic color fundus camera (Canon Cr-DGi, Tokyo, Japan) and SD-OCT (iVue, Optovue Inc, Fremont, CA). The color fundus images for those patients were transformed into red and green channels to evaluate the appearance of macular cysts in red- channel images and green-channel images. A scale map was used to quantify the region of each cyst and compare it to OCT scans (Adobe Photoshop CS5.1, San Jose, CA). Only cysts touching the central 1 mm around the fixation from the SD-OCT scans were sampled.
Results: The average macular cyst diameter was 124.57 µm (±106.96) and 59.44 µm (±76.6) in red and green channels, respectively. The size of retinal cysts in red channel images was significantly greater than in green channel (p<0.006). Entire cysts could not be seen in 5 eyes in the green channel images.
Conclusions: Our results indicate that the grading of cysts in the central macular might be improved by incorporating red channel images. There are a number of potential factors that could make cysts less visible in the green channel images, including poorer light penetration through to the deeper retinal or macular pigment. Finally, this population includes mostly minority patients who have dark fundi, and therefore darker images.
Uniformity of Accommodation Across the Visual Field
Imaging the retinal pigment epithelium mosaic with AO-OCT
Optical blur due to accommodative error in peripheral vision has been implicated in myopia development and progression. We investigated the uniformity of focusing errors over central retina as a function of accommodation demand in young adult and juvenile subjects.
A laboratory scanning wavefront aberrometer (Wei & Thibos, Opt Express. 2010;18/2:1134-43) uses rotating mirrors to pivot a laser probe beam (850 nm) about the pupil center to place a “retinal beacon” at a random sequence of 37 retinal locations over the central 27° of visual field. For each retinal location, beacon light reflected out of the eye is de-scanned by the same mirrors and then directed to a conventional Shack-Hartmann wavefront sensor for analysis. The visual stimulus was displayed on an achromatic micro-display in a Badal configuration. Aberrations were measured at 8 levels of accommodative demand (1D steps of target vergence starting 1D beyond the estimated far point). Accommodative error is the difference between target vergence and the eye’s refractive state as measured by defocus Zernike coefficient C20 (in diopters).
For most adult subjects, ocular refractive state changed uniformly over the central visual field as the eye accommodated. Visual field maps of accommodative error reveal subtle patterns of deviation on the order of ±0.5 D that are unique to the individual and relatively invariant to changes in accommodative state. Population mean maps for accommodative error are remarkably uniform across the central visual field, indicating the retina of the hypothetical “average eye” is conjugate to a sphere of constant target vergence for all states of accommodation, even though individual eyes might deviate from the mean due to random variations. This result confirms and extends previous work on adults (Mathur, Atchison, & Charman, 2009. J Vis 9, 20 21-11). Similar results were observed also for children. No systematic difference between emmetropic and myopic eyes was evident.
Ocular refractive state changes uniformly over the central visual field as the eye accommodates. Accuracy of accommodation across the visual field is similar to that measured in the fovea. Thus loss of image quality due to accommodative errors, which potentially drives myopia, will be similar across the central retina.
Purpose: The retinal pigment epithelium (RPE) is critical for support and maintenance of photoreceptors. While dysfunction of the RPE underlies numerous retinal pathologies, biomarkers sensitive to early changes in RPE have been elusive. Because such changes start at cellular level, there has been increased interest in targeting the spatial arrangement and distribution of individual RPE cells. To do so in the living human retina is extremely challenging, owing to the lack of intrinsic contrast of RPE, optical waveguiding by the overlying photoreceptors, and blurring by ocular aberrations. In this study, we take advantage of the micron-level 3D resolution afforded by adaptive optics and optical coherence tomography (AO-OCT) to overcome these obstacles in order to visualize RPE cells and investigate their packing geometry.
Methods: Using the Indiana AO-OCT imaging system (λc=790 nm, Δλ=42 nm), volumes of 1°×1° field of view were acquired at 3° and 10° temporal retina in two normal subjects. Volumes were registered, segmented, and RPE en face images extracted. Voronoi analysis was applied to the en face images to determine number of neighbors (NN) and center-to-center nearest neighbor distance (NND) of the RPE cells. 2D power spectra were used to provide additional information about cell spacing.
Results: RPE cell mosaics were resolved in both subjects and retinal eccentricities. Voronoi analysis indicates hexagonal cells (with six NN) are most frequent (>50%) at 3° retinal eccentricity and are of lower frequency (<50%) at 10° retinal eccentricity. NND was 11.4±2.2 μm and 12.8±3.0 μm for subject 1 at 3° and 10° retinal eccentricities respectively, and 12.0±2.0 μm for subject 2 at 3°. Processing of 10° data for subject 2 is ongoing. NND measurements are consistent with the 2D power spectra estimations of 11.9 μm and 12.9 μm of subject 1 (3° and 10°), and 12.7 μm of subject 2 (3°).
Conclusions: AO-OCT imaging permits visualization and quantification of the RPE packing geometry in the living human retina.
Imaging retinal ganglion cells, their axons and transport in experimental models of optic nerve injury: implications for clinical management of glaucoma and other optic neuropathies
Abstract: New insights into glaucoma pathogenesis have arisen over the past decade from the forefront of research on neurodegenerative disease. Neurons possess two, mostly distinct, programs for autonomous self-destruction: the well-characterized pathways of programmed cell death known as apoptosis and the more recently uncovered pathways of axonal self-destruction. Axonal self-destruction is now known to have a role in a wide array of neurodegenerative diseases with subsequent axon loss likely contributing to the neurological symptoms that underlie patient suffering. Evidence has also begun to emerge suggesting that axonal self-destruction mechanisms are active within the anterior visual pathway, along the axons of retinal ganglion cells in experimental models glaucoma. Our recent research has focused on axonopathy in retinal ganglion cells following experimental optic nerve injury in non-human primates and in pigmented rats, including experimental glaucoma, and the ability to detect its manifestations in vivo using scanning laser polarimetry (SLP) and optical coherence tomography (OCT), both common forms of clinical instrumentation, as well as by axonal transport assays. Our findings provide clear evidence that axonopathy manifests at an early stage in well-established models of experimental glaucoma, including axonal cytoskeletal disruption, axonal spheroid formation and failure of axonal transport. We have demonstrated that retinal nerve fiber layer (RNFL) retardance deficits measured by SLP are accompanied by functional loss specific to retinal ganglion cells, and that they begin prior to and progress faster than RNFL thickness loss measured by OCT in experimental injuries including experimental glaucoma. Our findings have important clinical implications as axonal cytoskeletal disruption is thought to be one of the most fundamental pathophysiological events common to many forms of neurodegeneration. Indeed, this early stage abnormality represents an important “tipping point” toward neuronal death because it both reflects and exacerbates failure of axonal transport, long thought to be a critical early pathophysiological deficit in glaucoma. This presentation will review this previously published evidence as well as more recent results from laboratory and clinical studies carried out by our collaborative group of investigators. The implications for clinical management of glaucoma and other optic neuropathies will be discussed.
|3/20/2015||NO OXYOPIA - SPRING BREAK|
|4/3/2015||Nathan Doble||High Resolution Retinal Imaging Using Adaptive Optics||
Adaptive optics (AO) has enabled in vivo imaging of the human retina with unprecedented resolution. By compensating for the deleterious effects of the corneal and lenticular aberrations, AO has allowed for visualization of a variety of retinal cells.
The talk will begin with a brief review of the principle of AO and examples of current AO systems in the laboratory including a flood illuminated fundus camera, a confocal scanning laser ophthalmoscope (SLO) and a combined AO-SLO-OCT system.Results from current projects including imaging of cones and rods, measurement of the pointing of individual cones in both human and animals and novel methods of wavefront measurement will be presented.
|4/10/2015||Mahnaz Shahidi||Retinal Oxygen Delivery and Metabolism Imaging||
Retinal tissue function can be adversely affected by inadequate delivery and/or consumption of oxygen. In fact, derangements in retinal oxygenation are thought to contribute significantly to the development of common vision threatening retinal diseases. However, mechanisms that implicate oxygen in the development of retinal pathologies and impairment of retinal function are not completely understood. Therefore, technologies that allow assessment of oxygen tension in the retinal vasculature and tissue are needed to broaden knowledge of disease pathophysiology, and thereby advance diagnostic and therapeutic procedures. We have developed an optical section phosphorescence lifetime imaging technique that allows depthresolved mapping of retinal vascular oxygen tension and measurement of inner retinal oxygen extraction fraction. Combined with fluorescent microsphere imaging for measurement of retinal blood flow, oxygen delivery by the retinal circulation and global inner retinal oxygen metabolism are derived. These technologies have been applied for assessment of retinal oxygen delivery and metabolism in experimental animal models of retinal ischemia.
The Control of Ocular Alignment During Infancy and Early Childhood
Infants are typically hyperopic while having a reduced interpupillary distance relative to adults. Despite the neural coupling between the two systems, infants must overcome the relatively increased accommodative demand and reduced vergence demand in order to remain aligned and avoid refractive strabismus. Interestingly, the mean age of onset of refractive esotropia is not until two to three years of age, and only a subset of hyperopes develop the deviation. This presentation will explore the control of ocular alignment during infancy and early childhood, specifically examining the role of accommodative performance, heterophoria, vergence ranges and vergence adaptation during this period. The implications for the management of young hyperopes will also be addressed.
|4/24/2015||Nicholas Port||A Rapid Objective Tool for Diagnosing Concussions Utilizing the Involuntary Aspects of Eye Movements||
Critical decisions are made daily about whether to bench athletes who might have suffered mild traumatic brain injury (mTBI). Unfortunately, the low-level, diffuse damage underlying sport-related mTBI has proven difficult to measure, especially on the sidelines where initial decisions must be made quickly. The most widely used tool, beyond self reported symptoms, for diagnosing and tracking sports-related mTBI is the ImPACT test, a neuropsychological battery. This test is not viable as a rapid sidelines test because of its length (30 minutes) and the need for a controlled testing environment. It is also susceptible to motivational factors; one’s performance can be manipulated to increase or decrease the chance of being cleared to play. The ideal instrument for measuring mTBI would be sensitive to low-level diffuse damage, would be easily and rapidly administered on the sidelines after a potentially injurious hit, and would be unaffected by human bias. Based on a body of research documenting the sensitivity of ocularmotor performance (e.g., eye movements such as saccades and smooth pursuit) to mTBI damage, we have built five sideline eye tracker and are currently evaluating its clinical utility as a rapid, objective, and accurate sideline test of sports-related concussion/mTBI. I will present a summary of our new sideline eye tracker which is currently in use with the entire IU athletic department and two local high schools with an enrollment of over 1000 athletes in the study.
Non-‐accommodative treatments for presbyopes
|Presbyopia defines the situation where the eye’s lens loses its ability to change power as it ages. There are three main approaches to treat presbyopia: restoration of accommodation (in the future), or increase the eye’s depth of focus with either multifocal optics or small pupils. In my talk, I will examine the pros and cons of employing small pupils or bifocal/multifocal strategies to improve near vision: Which one is better? One concern about the small pupil strategy is that the gain in near vision achieved from expanded DOF will disappear at low light levels due to reduced retinal illuminance and its accompanying photon noise problems. Will the increased photon noise effects associated with small pupils counteract the beneficial effects of decreased blur? We used computational simulations and psychophysical experiments to answer this question. By incorporating photon noise into our aberrated optical model, we computed polychromatic image quality for a series of pupils ranging from 1mm to 7mm and for a multifocal eye, over a wide range of photopic and mesopic target luminances and for different defocus levels. Psychophysically, we measured the visual acuity, contrast sensitivity, and reading speed for both multifocal and small pupil groups under different light levels in presence of different defocus levels. We compared the modeling data to contrast sensitivity (CS) measures because both are predictably affected by photon noise. In my talk, I will show our results and some recommendations for clinicians who are interested in presbyopic treatment.|
|5/8/2015||NO OXYOPIA - ARVO/FINALS|