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Birch EE, Duffy KR. Leveraging neural plasticity for the treatment of amblyopia. Surv Ophthalmol 2024; 69:818-832. [PMID: 38763223 PMCID: PMC11380599 DOI: 10.1016/j.survophthal.2024.04.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 04/27/2024] [Accepted: 04/29/2024] [Indexed: 05/21/2024]
Abstract
Amblyopia is a form of visual cortical impairment that arises from abnormal visual experience early in life. Most often, amblyopia is a unilateral visual impairment that can develop as a result of strabismus, anisometropia, or a combination of these conditions that result in discordant binocular experience. Characterized by reduced visual acuity and impaired binocular function, amblyopia places a substantial burden on the developing child. Although frontline treatment with glasses and patching can improve visual acuity, residual amblyopia remains for most children. Newer binocular-based therapies can elicit rapid recovery of visual acuity and may also improve stereoacuity in some children. Nevertheless, for both treatment modalities full recovery is elusive, recurrence of amblyopia is common, and improvements are negligible when treatment is administered at older ages. Insights derived from animal models about the factors that govern neural plasticity have been leveraged to develop innovative treatments for amblyopia. These novel therapies exhibit efficacy to promote recovery, and some are effective even at ages when conventional treatments fail to yield benefit. Approaches for enhancing visual system plasticity and promoting recovery from amblyopia include altering the balance between excitatory and inhibitory mechanisms, reversing the accumulation of proteins that inhibit plasticity, and harnessing the principles of metaplasticity. Although these therapies have exhibited promising results in animal models, their safety and ability to remediate amblyopia need to be evaluated in humans.
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Affiliation(s)
- Eileen E Birch
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation, Dallas, TX, USA; University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Kevin R Duffy
- Department of Psychology and Neuroscience, Dalhousie University, Halifax, NS, Canada
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Van Grootel TJ, Raghavan RT, Kelly JG, Movshon JA, Kiorpes L. Responses to visual motion of neurons in the extrastriate visual cortex of macaque monkeys with experimental amblyopia. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.01.601564. [PMID: 39005459 PMCID: PMC11244960 DOI: 10.1101/2024.07.01.601564] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/16/2024]
Abstract
Amblyopia is a developmental disorder that results from abnormal visual experience in early life. Amblyopia typically reduces visual performance in one eye. We studied the representation of visual motion information in area MT and nearby extrastriate visual areas in two monkeys made amblyopic by creating an artificial strabismus in early life, and in a single age-matched control monkey. Tested monocularly, cortical responses to moving dot patterns, gratings, and plaids were qualitatively normal in awake, fixating amblyopic monkeys, with primarily subtle differences between the eyes. However, the number of binocularly driven neurons was substantially lower than normal; of the neurons driven predominantly by one eye, the great majority responded only to stimuli presented to the fellow eye. The small population driven by the amblyopic eye showed reduced coherence sensitivity and a preference for faster speeds in much the same way as behavioral deficits. We conclude that, while we do find important differences between neurons driven by the two eyes, amblyopia does not lead to a large scale reorganization of visual receptive fields in the dorsal stream when tested through the amblyopic eye, but rather creates a substantial shift in eye preference toward the fellow eye.
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Affiliation(s)
- Tom J Van Grootel
- Center for Neural Science, New York University, New York, NY 10003, USA
| | - R T Raghavan
- Center for Neural Science, New York University, New York, NY 10003, USA
| | - Jenna G Kelly
- Center for Neural Science, New York University, New York, NY 10003, USA
| | - J Anthony Movshon
- Center for Neural Science, New York University, New York, NY 10003, USA
| | - Lynne Kiorpes
- Center for Neural Science, New York University, New York, NY 10003, USA
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Jiang SQ, Chen YR, Liu XY, Zhang JY. Contour integration deficits at high spatial frequencies in children treated for anisometropic amblyopia. Front Neurosci 2023; 17:1160853. [PMID: 37564367 PMCID: PMC10411894 DOI: 10.3389/fnins.2023.1160853] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Accepted: 07/11/2023] [Indexed: 08/12/2023] Open
Abstract
Purpose This study was conducted to reexamine the question of whether children treated for anisometropic amblyopia have contour integration deficits. To do so, we used psychophysical methods that require global contour processing while minimizing the influence of low-level deficits: visibility, shape perception, and positional uncertainty. Methods Thirteen children with anisometropic amblyopia (age: 10.1 ± 1.8 years) and thirteen visually normal children (age: 10.8 ± 2.0 years) participated in this study. The stimuli were closed figures made up of Gabor patches either in noise or on a blank field. The contrast thresholds to detect a circular contour on a blank field, as well as the thresholds of aspect ratio and contour element number to discriminate a circular or elliptical contour in noise, were measured at Gabor spatial frequencies of 1.5, 3, and 6 cpd for amblyopic eyes (AEs), fellow eyes (FEs), and normal control eyes. Visual acuities and contrast sensitivity functions for AEs and FEs and the Randot stereoacuity were measured before testing. Results The AEs showed contrast deficits and degraded shape perception compared to the FEs at higher spatial frequencies (6 cpd). When the influence of abnormal contrast sensitivity and shape perception were minimized, the AEs showed contour integration deficits at spatial frequencies 3 and 6 cpd. These deficits were not related to basic losses in contrast sensitivity and acuity, stereoacuity, and visual crowding. Besides, no significant difference was found between the fellow eyes of the amblyopic children and the normal control eyes in the performance of contour integration. Conclusion After eliminating or compensating for the low-level deficits, children treated for anisometropic amblyopia still show contour integration deficits, primarily at higher spatial frequencies, which might reflect the deficits in global processing caused by amblyopia. Contour integration deficits are likely independent of spatial vision deficits. Refractive correction and/or occlusion therapies may not be sufficient to fully restore contour integration deficits, which indicates the need for the development of clinical treatments to recover these deficits.
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Affiliation(s)
- Shu-Qi Jiang
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, China
| | - Yan-Ru Chen
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, China
| | - Xiang-Yun Liu
- The Affiliated Tengzhou Hospital of Xuzhou Medical University, Tengzhou, Shandong, China
| | - Jun-Yun Zhang
- School of Psychological and Cognitive Sciences and Beijing Key Laboratory of Behavior and Mental Health, Peking University, Beijing, China
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Kelly KR, Jost RM, Hudgins LA, Stager DR, Hunter JS, Beauchamp CL, Dao LM, Birch EE. Slow Binocular Reading in Amblyopic Children Is a Fellow Eye Deficit. Optom Vis Sci 2023; 100:194-200. [PMID: 36715973 PMCID: PMC10245300 DOI: 10.1097/opx.0000000000001995] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
SIGNIFICANCE Amblyopic children read 25% slower than their peers during binocular silent reading. PURPOSE We compared binocular reading to fellow eye reading to determine whether slow reading in amblyopic children is due to binocular inhibition; that is, the amblyopic eye is interfering during binocular reading. METHODS In a cross-sectional study, 38 children with amblyopia and 36 age-similar control children who completed grades 1 to 6 were enrolled. Children silently read grade-appropriate paragraphs during binocular reading and fellow eye reading while wearing ReadAlyzer eye-tracking goggles (Compevo AB, Stockholm, Sweden). Reading rate, number of forward saccades, number of regressive saccades, and fixation duration were analyzed between groups and between viewing conditions. We also examined whether sensory factors (amblyopia severity, stereoacuity, suppression) were related to slow reading. RESULTS For amblyopic children, binocular reading versus fellow eye reading did not differ for reading rate (176 ± 60 vs. 173 ± 53 words per minute, P = .69), number of forward saccades (104 ± 35 vs. 97 ± 33 saccades/100 words, P = .18), number of regressive saccades (21 ± 15 vs. 22 ± 13 saccades/100 words, P = .75), or fixation duration (0.31 ± 0.06 vs. 0.32 ± 0.07 seconds, P = .44). As expected, amblyopic children had a slower reading rate and more forward saccades than control children during binocular reading and fellow eye reading. Slow reading was not related to any sensory factors. CONCLUSIONS Binocular reading did not differ from fellow eye reading in amblyopic children. Thus, binocular inhibition is unlikely to play a role in slow binocular reading and is instead a fellow eye deficit that emerges from a disruption in binocular visual experience during development.
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Affiliation(s)
| | - Reed M Jost
- Retina Foundation of the Southwest, Dallas, Texas
| | | | - David R Stager
- Pediatric Ophthalmology and Adult Strabismus, PA, Plano, Texas
| | | | | | - Lori M Dao
- ABC Eyes Pediatric Ophthalmology, PA, Dallas, Texas
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Birch EE, Kelly KR. Amblyopia and the whole child. Prog Retin Eye Res 2023; 93:101168. [PMID: 36736071 PMCID: PMC9998377 DOI: 10.1016/j.preteyeres.2023.101168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 01/04/2023] [Accepted: 01/05/2023] [Indexed: 02/04/2023]
Abstract
Amblyopia is a disorder of neurodevelopment that occurs when there is discordant binocular visual experience during the first years of life. While treatments are effective in improving visual acuity, there are significant individual differences in response to treatment that cannot be attributed solely to difference in adherence. In this considerable variability in response to treatment, we argue that treatment outcomes might be optimized by utilizing deep phenotyping of amblyopic deficits to guide alternative treatment choices. In addition, an understanding of the broader knock-on effects of amblyopia on developing visually-guided skills, self-perception, and quality of life will facilitate a whole person healthcare approach to amblyopia.
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Affiliation(s)
- Eileen E Birch
- Pediatric Vision Laboratory, Retina Foundation of the Southwest, 9600 North Central Expressway #200, Dallas, TX, 75225, USA; Department of Ophthalmology, University of Texas Southwestern Medical Center, 5303 Harry Hines Boulevard, Dallas, TX, 75390, USA.
| | - Krista R Kelly
- Department of Ophthalmology, University of Texas Southwestern Medical Center, 5303 Harry Hines Boulevard, Dallas, TX, 75390, USA; Vision and Neurodevelopment Laboratory, Retina Foundation of the Southwest, 9600 North Central Expressway #200, Dallas, TX, 75225, USA.
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Hao X, Liu Q, Chan J, Li N, Shi X, Gu Y. Dark exposure can partly restore the disrupted cortical reliability Binocular visual experience drives the maturation of response variability and reliability in the visual cortex. iScience 2022; 25:104984. [PMID: 36105593 PMCID: PMC9465340 DOI: 10.1016/j.isci.2022.104984] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2022] [Revised: 06/23/2022] [Accepted: 08/16/2022] [Indexed: 10/25/2022] Open
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Levi DM. Amblyopia. HANDBOOK OF CLINICAL NEUROLOGY 2021; 178:13-30. [PMID: 33832673 DOI: 10.1016/b978-0-12-821377-3.00002-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Amblyopia is a neurodevelopmental abnormality that results in physiological alterations in the visual pathways and impaired vision in one eye, less commonly in both. It reflects a broad range of neural, perceptual, oculomotor, and clinical abnormalities that can occur when normal visual development is disrupted early in life. Aside from refractive error, amblyopia is the most common cause of vision loss in infants and young children. It causes a constellation of perceptual deficits in the vision of the amblyopic eye, including a loss of visual acuity, position acuity, and contrast sensitivity, particularly at high spatial frequencies, as well as increased internal noise and prolonged manual and saccadic reaction times. There are also perceptual deficits in the strong eye, such as certain types of motion perception, reflecting altered neural responses and functional connectivity in visual cortex (Ho et al., 2005). Treatment in young children consists of correction of any refractive error and patching of the strong eye. Compliance with patching is challenging and a substantial proportion of amblyopic children fail to achieve normal acuity or stereopsis even after extended periods of treatment. There are a number of promising experimental treatments that may improve compliance and outcomes, such as the playing of action video games with the strong eye patched. Although there may be a sensitive period for optimal effects of treatment, there is evidence that amblyopic adults may still show some benefit of treatment. However, there is as yet no consensus on the treatment of adults with amblyopia.
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Affiliation(s)
- Dennis M Levi
- School of Optometry & Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, United States.
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Abstract
Recent work has transformed our ideas about the neural mechanisms, behavioral consequences and effective therapies for amblyopia. Since the 1700's, the clinical treatment for amblyopia has consisted of patching or penalizing the strong eye, to force the "lazy" amblyopic eye, to work. This treatment has generally been limited to infants and young children during a sensitive period of development. Over the last 20 years we have learned much about the nature and neural mechanisms underlying the loss of spatial and binocular vision in amblyopia, and that a degree of neural plasticity persists well beyond the sensitive period. Importantly, the last decade has seen a resurgence of research into new approaches to the treatment of amblyopia both in children and adults, which emphasize that monocular therapies may not be the most effective for the fundamentally binocular disorder that is amblyopia. These approaches include perceptual learning, video game play and binocular methods aimed at reducing inhibition of the amblyopic eye by the strong fellow eye, and enhancing binocular fusion and stereopsis. This review focuses on the what we've learned over the past 20 years or so, and will highlight both the successes of these new treatment approaches in labs around the world, and their failures in clinical trials. Reconciling these results raises important new questions that may help to focus future directions.
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Affiliation(s)
- Dennis M Levi
- University of California, Berkeley, School of Optometry & Helen Wills Neuroscience Institute, Berkeley, CA, USA.
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Wu Y, Reynaud A, Tao C, Mao Y, He Z, Zhou J, Hess RF. Two Patterns of Interocular Delay Revealed by Spontaneous Motion-in-Depth Pulfrich Phenomenon in Amblyopes with Stereopsis. Invest Ophthalmol Vis Sci 2020; 61:22. [PMID: 32181800 PMCID: PMC7401735 DOI: 10.1167/iovs.61.3.22] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Purpose To assess interocular delays in amblyopes with stereopsis and to evaluate the relationship between interocular delays and the clinical characteristics. Methods Twenty amblyopes with stereopsis (median, 400 arcseconds) and 20 controls with normal or corrected to normal visual acuity (≤0 logMAR) and normal stereopsis (≤60 arcseconds) participated. Using a rotating cylinder defined by horizontally moving Gabor patches, we produced a spontaneous Pulfrich phenomenon in order to determine the interocular delays, that is, the interocular phase difference at which ambiguous motion in plane was perceived. Two spatial frequencies—a low (0.95 cycles/degree [c/d]) and a medium (2.85 c/d) spatial frequency—were tested. Results The absolute interocular delays of the amblyopic group was significantly longer than that of the controls at both low or medium spatial frequencies (P < 0.01). However, the interocular delays was not always in favor of the fellow eye: 35% of the amblyopes (7/20) showed a faster processing of the amblyopic eye than that of the fellow eye at 0.95 c/d and 29.5% (5/17) at 2.85 c/d. No significant correlation was found between interocular delays and the clinical characteristics (e.g., age, treatment history, stereoacuity, and magnitude of anisometropia) in this amblyopic cohort. Conclusions The interocular delays in amblyopes with stereopsis might result from either a faster or slower processing of the amblyopic eye relative to the fellow eye. This work provides important additional information for binocular processing of dynamic visual stimuli in amblyopia. However, the special role between this form of interocular delays and patients’ clinical characteristics remains unknown.
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10
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Abstract
Amblyopia is a cortical visual disorder caused by unequal visual input to the brain from the two eyes during development. Amblyopes show reduced visual acuity and contrast sensitivity and abnormal binocularity, as well as more “global” perceptual losses, such as figure-ground segregation and global form integration. Currently, there is no consensus on the neural basis for these higher-order perceptual losses. One contributing factor could be that amblyopes have deficiencies in attention, such that the attentional processes that control the selection of information favor the better eye. Previous studies in amblyopic adults are conflicting as to whether attentional deficits exist. However, studies where intact attentional ability has been shown to exist were conducted in adults; it is possible that it was acquired through experience. To test this hypothesis, we studied attentional processing in amblyopic children. We examined covert endogenous attention using a classical spatial cueing paradigm in amblyopic and visually typical 5- to 10-year old children. We found that all children, like adults, independently of visual condition, benefited from attentional cueing: They performed significantly better on trials with an informative (valid) cue than with the uninformative (neutral) cue. Response latencies were also significantly shorter for the valid cue condition. No statistically significant difference was found between the performance of the amblyopic and the visually typical children or between dominant and nondominant eyes of all children. The results showed that covert spatial attention is intact in amblyopic and visually typical children and is therefore not likely to account for higher-order perceptual losses in amblyopic children.
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11
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Wu H, Li X, Tang Y, Xu Q, Zhang X, Zhou L, Lan W, Zhang B, Yang Z. Optimal Stereoacuity Reveals More Than Critical Time in Patients With Intermittent Exotropia. Front Neurosci 2020; 14:133. [PMID: 32132901 PMCID: PMC7040177 DOI: 10.3389/fnins.2020.00133] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Accepted: 02/03/2020] [Indexed: 01/06/2023] Open
Abstract
Synopsis Both optimal stereoacuity and integration time to achieve that are impaired in patients with intermittent exotropia. The deterioration of stereoacuity is more revealing since it correlates well with exotropia control score. Background Despite the periodic misalignment of two eyes, some intermittent exotropia (IXT) patients exhibit normal stereoacuity, particularly when evaluated with static tests. It is not clear if the temporal integration process of stereopsis is altered in IXT patients, thus warranting further research. Methods IXT patients (n = 29) and age-matched normal controls (n = 36) were recruited. Static stereopsis was measured with the Titmus stereoacuity test. In computer-generated random dots tests, stereoacuity was measured with a stimuli presentation duration varying from 100 to 1,200 ms. And the relationship between stereoacuity and stimuli duration was fitted into a quadratic model. Optimal stereoacuity was achieved when fitted curve flattened and the critical integration time was the duration needed to achieve optimal stereoacuity. Results IXT patients were not found to differ significantly from control subjects under the Titmus test, while the Random Dots stereotest showed significantly worse optimal stereoacuity and significantly longer critical integration time. Multiple regression analysis showed that age (R = −4.83; P = 0.04) had statistically significant negative correlation on the critical integration time, age (R = −6.45; P = 0.047) and exotropia control scores (R = 60.71; P = 0.007) had statistically significant effects on optimal stereoacuity. Conclusion The temporal integration for stereopsis is impaired in IXT patients, requiring longer critical integration time to achieve elevated optimal stereoacuity.
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Affiliation(s)
- Haoran Wu
- Aier School of Ophthalmology, Central South University, Changsha, China.,Aier Institute of Optometry and Vision Science, Changsha, China
| | - Xiaoning Li
- Aier Institute of Optometry and Vision Science, Changsha, China.,Aier School of Optometry and Vision Science, Hubei University of Science and Technology, Xianning, China
| | - Yao Tang
- Aier Institute of Optometry and Vision Science, Changsha, China
| | - Qinglin Xu
- Aier Institute of Optometry and Vision Science, Changsha, China
| | - Xuhong Zhang
- College of Medicine, Zhejiang University, Hangzhou, China
| | - Lu Zhou
- Department of Ophthalmology, Children's Hospital of Nanjing Medical University, Nanjing, China
| | - Weizhong Lan
- Aier School of Ophthalmology, Central South University, Changsha, China.,Aier School of Optometry and Vision Science, Hubei University of Science and Technology, Xianning, China
| | - Bin Zhang
- College of Optometry, Nova Southeastern University, Davie, FL, United States
| | - Zhikuan Yang
- Aier School of Ophthalmology, Central South University, Changsha, China.,Aier School of Optometry and Vision Science, Hubei University of Science and Technology, Xianning, China
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12
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Understanding the development of amblyopia using macaque monkey models. Proc Natl Acad Sci U S A 2019; 116:26217-26223. [PMID: 31871163 DOI: 10.1073/pnas.1902285116] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Amblyopia is a sensory developmental disorder affecting as many as 4% of children around the world. While clinically identified as a reduction in visual acuity and disrupted binocular function, amblyopia affects many low- and high-level perceptual abilities. Research with nonhuman primate models has provided much needed insight into the natural history of amblyopia, its origins and sensitive periods, and the brain mechanisms that underly this disorder. Amblyopia results from abnormal binocular visual experience and impacts the structure and function of the visual pathways beginning at the level of the primary visual cortex (V1). However, there are multiple instances of abnormalities in areas beyond V1 that are not simply inherited from earlier stages of processing. The full constellation of deficits must be taken into consideration in order to understand the broad impact of amblyopia on visual and visual-motor function. The data generated from studies of animal models of the most common forms of amblyopia have provided indispensable insight into the disorder, which has significantly impacted clinical practice. It is expected that this translational impact will continue as ongoing research into the neural correlates of amblyopia provides guidance for novel therapeutic approaches.
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Acar K, Kiorpes L, Movshon JA, Smith MA. Altered functional interactions between neurons in primary visual cortex of macaque monkeys with experimental amblyopia. J Neurophysiol 2019; 122:2243-2258. [PMID: 31553685 PMCID: PMC6966320 DOI: 10.1152/jn.00232.2019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 09/24/2019] [Accepted: 09/24/2019] [Indexed: 11/22/2022] Open
Abstract
Amblyopia, a disorder in which vision through one of the eyes is degraded, arises because of defective processing of information by the visual system. Amblyopia often develops in humans after early misalignment of the eyes (strabismus) and can be simulated in macaque monkeys by artificially inducing strabismus. In such amblyopic animals, single-unit responses in primary visual cortex (V1) are appreciably reduced when evoked by the amblyopic eye compared with the other (fellow) eye. However, this degradation in single V1 neuron responsivity is not commensurate with the marked losses in visual sensitivity and resolution measured behaviorally. Here we explored the idea that changes in patterns of coordinated activity across populations of V1 neurons may contribute to degraded visual representations in amblyopia, potentially making it more difficult to read out evoked activity to support perceptual decisions. We studied the visually evoked activity of V1 neuronal populations in three macaques (Macaca nemestrina) with strabismic amblyopia and in one control animal. Activity driven through the amblyopic eye was diminished, and these responses also showed more interneuronal correlation at all stimulus contrasts than responses driven through the fellow eye or responses in the control animal. A decoding analysis showed that responses driven through the amblyopic eye carried less visual information than other responses. Our results suggest that part of the reduced visual capacity of amblyopes may be due to changes in the patterns of functional interaction among neurons in V1.NEW & NOTEWORTHY Previous work on the neurophysiological basis of amblyopia has largely focused on relating behavioral deficits to changes in visual processing by single neurons in visual cortex. In this study, we recorded simultaneously from populations of primary visual cortical (V1) neurons in macaques with amblyopia. We found changes in the strength and pattern of shared response variability between neurons. These changes in neuronal interactions could impair the visual representations of V1 populations driven by the amblyopic eye.
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Affiliation(s)
- Katerina Acar
- Center for the Neural Basis of Cognition, Pittsburgh, Pennsylvania
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Lynne Kiorpes
- Center for Neural Science, New York University, New York, New York
| | | | - Matthew A Smith
- Center for the Neural Basis of Cognition, Pittsburgh, Pennsylvania
- Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
- Department of Biomedical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania
- Carnegie Mellon Neuroscience Institute, Pittsburgh, Pennsylvania
- Department of Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania
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Candy TR. The Importance of the Interaction Between Ocular Motor Function and Vision During Human Infancy. Annu Rev Vis Sci 2019; 5:201-221. [PMID: 31525140 DOI: 10.1146/annurev-vision-091718-014741] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Numerous studies have demonstrated the impact of imposed abnormal visual experience on the postnatal development of the visual system. These studies have provided fundamental insights into the mechanisms underlying neuroplasticity and its role in clinical care. However, the ocular motor responses of postnatal human infants largely define their visual experience in dynamic three-dimensional environments. Thus, the immature visual system needs to control its own visual experience. This review explores the interaction between the developing motor and sensory/perceptual visual systems, together with its importance in both typical development and the development of forms of strabismus and amblyopia.
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Affiliation(s)
- T Rowan Candy
- Optometry & Vision Science, School of Optometry; Psychological & Brain Sciences; and Neuroscience and Cognitive Science, Indiana University, Bloomington, Indiana 47401, USA;
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15
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Birch EE, Jost RM, Wang YZ, Kelly KR, Giaschi DE. Impaired Fellow Eye Motion Perception and Abnormal Binocular Function. Invest Ophthalmol Vis Sci 2019; 60:3374-3380. [PMID: 31387113 PMCID: PMC6685447 DOI: 10.1167/iovs.19-26885] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 07/02/2019] [Indexed: 11/24/2022] Open
Abstract
Purpose Binocular discordance due to strabismus, anisometropia, or both may result in not only monocular visual acuity deficits, but also in motion perception deficits. We determined the prevalence of fellow-eye deficits in motion-defined form (MDF) perception, the ability to identify a two-dimensional (2D) shape defined by motion rather than luminance contrast. We also examined the following: the causative role of reduced visual acuity and binocularity, associations with clinical and sensory factors, and effectiveness of binocular amblyopia treatment in alleviating deficits. Methods Participants included 91 children with residual amblyopia (strabismic, anisometropic, or both; age, 9.0 ± 1.7 years), 79 nonamblyopic children with treated strabismus or anisometropia (age, 8.5 ± 2.1 years), and 20 controls (age, 8.6 ± 1.5 years). MDF coherence thresholds, visual acuity, stereoacuity, and interocular suppression were measured. Results MDF deficits, relative to controls, were present in the fellow eye of 23% of children with residual amblyopia and 20% of nonamblyopic children. Stereoacuity and age first patched were correlated with MDF threshold (r = 0.29, 95% CI: 0.09-0.47; r = -0.33, 95% CI: -0.13 to -0.50, respectively). MDF deficits were more common in children treated with patching alone than in those receiving contrast-rebalanced binocular treatment with games or movies (t89 = 3.46; P = 0.0008). The latter was associated with a reduction in mean fellow eye MDF threshold (t26 = 6.32, P < 0.0001). Conclusions Fellow eye MDF deficits are common and likely reflect abnormalities in binocular cortical mechanisms that result from early discordant visual experience. Binocular amblyopia treatment, which is effective in improving amblyopic eye visual acuity, appears to provide a benefit for the fellow eye.
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Affiliation(s)
- Eileen E. Birch
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation of the Southwest, Dallas, Texas, United States
- Department of Ophthalmology, UT Southwestern Medical Center, Dallas, Texas, United States
| | - Reed M. Jost
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation of the Southwest, Dallas, Texas, United States
| | - Yi-Zhong Wang
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation of the Southwest, Dallas, Texas, United States
| | - Krista R. Kelly
- Crystal Charity Ball Pediatric Vision Laboratory, Retina Foundation of the Southwest, Dallas, Texas, United States
| | - Deborah E. Giaschi
- Department of Ophthalmology and Visual Sciences, University of British Columbia, Vancouver, British Columbia, Canada
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16
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Spiking Noise and Information Density of Neurons in Visual Area V2 of Infant Monkeys. J Neurosci 2019; 39:5673-5684. [PMID: 31147523 DOI: 10.1523/jneurosci.2023-18.2019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 05/20/2019] [Accepted: 05/22/2019] [Indexed: 11/21/2022] Open
Abstract
Encoding of visual information requires precisely timed spiking activity in the network of cortical neurons; irregular spiking can interfere with information processing especially for low-contrast images. The vision of newborn infants is impoverished. An infant's contrast sensitivity is low and the ability to discriminate complex stimuli is poor. The neural mechanisms that limit the visual capacities of infants are a matter of debate. Here we asked whether noisy spiking and/or crude information processing in visual cortex limit infant vision. Since neurons beyond the primary visual cortex (V1) have rarely been studied in neonates or infants, we focused on the firing pattern of neurons in visual area V2, the earliest extrastriate visual area of both male and female macaque monkeys (Maccaca mulatta). For eight stimulus contrasts ranging from 0% to 80%, we analyzed spiking irregularity by calculating the square of the coefficient of variation (CV2) in interspike intervals, the trial-to-trial fluctuation in spiking (Fano factor), and the amount of information on contrast conveyed by each spiking (information density). While the contrast sensitivity of infant neurons was reduced as expected, spiking noise, both the magnitude of spiking irregularity and the trial-to-trial fluctuations, was much lower in the spike trains of infant V2 neurons compared with those of adults. However, information density for V2 neurons was significantly lower in infants. Our results suggest that poor contrast sensitivity combined with lower information density of extrastriate neurons, despite their lower spiking noise, may limit behaviorally determined contrast sensitivity soon after birth.SIGNIFICANCE STATEMENT Despite >50 years of investigations on the postnatal development of the primary visual cortex (V1), cortical mechanisms that may limit infant vision are still unclear. We investigated the quality and strength of neuronal firing in primate visual area V2 by analyzing contrast sensitivity, spiking variability, and the amount of information on contrast conveyed by each action potential (information density). Here we demonstrate that the firing rate, contrast sensitivity, and dynamic range of V2 neurons were depressed in infants compared with adults. Although spiking noise was less, information density was lower in infant V2. Impoverished neuronal drive and lower information density in extrastriate visual areas, despite lower spiking noise, largely explain the impoverished visual sensitivity of primates near birth.
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17
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Amblyopia Affects the ON Visual Pathway More than the OFF. J Neurosci 2019; 39:6276-6290. [PMID: 31189574 PMCID: PMC6687897 DOI: 10.1523/jneurosci.3215-18.2019] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 06/03/2019] [Accepted: 06/05/2019] [Indexed: 02/03/2023] Open
Abstract
Visual information reaches the cerebral cortex through parallel ON and OFF pathways that signal the presence of light and dark stimuli in visual scenes. We have previously demonstrated that optical blur reduces visual salience more for light than dark stimuli because it removes the high spatial frequencies from the stimulus, and low spatial frequencies drive weaker ON than OFF cortical responses. Therefore, we hypothesized that sustained optical blur during brain development should weaken ON cortical pathways more than OFF, increasing the dominance of darks in visual perception. Here we provide support for this hypothesis in humans with anisometropic amblyopia who suffered sustained optical blur early after birth in one of the eyes. In addition, we show that the dark dominance in visual perception also increases in strabismic amblyopes that have their vision to high spatial frequencies reduced by mechanisms not associated with optical blur. Together, we show that amblyopia increases visual dark dominance by 3-10 times and that the increase in dark dominance is strongly correlated with amblyopia severity. These results can be replicated with a computational model that uses greater luminance/response saturation in ON than OFF pathways and, as a consequence, reduces more ON than OFF cortical responses to stimuli with low spatial frequencies. We conclude that amblyopia affects the ON cortical pathway more than the OFF, a finding that could have implications for future amblyopia treatments.SIGNIFICANCE STATEMENT Amblyopia is a loss of vision that affects 2-5% of children across the world and originates from a deficit in visual cortical circuitry. Current models assume that amblyopia affects similarly ON and OFF visual pathways, which signal light and dark features in visual scenes. Against this current belief, here we demonstrate that amblyopia affects the ON visual pathway more than the OFF, a finding that could have implications for new amblyopia treatments targeted at strengthening a weak ON visual pathway.
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18
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Thompson B, Maehara G, Goddard E, Farivar R, Mansouri B, Hess RF. Long-Range Interocular Suppression in Adults with Strabismic Amblyopia: A Pilot fMRI Study. Vision (Basel) 2019; 3:vision3010002. [PMID: 31735803 PMCID: PMC6802762 DOI: 10.3390/vision3010002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Revised: 12/15/2018] [Accepted: 12/31/2018] [Indexed: 11/24/2022] Open
Abstract
Interocular suppression plays an important role in the visual deficits experienced by individuals with amblyopia. Most neurophysiological and functional MRI studies of suppression in amblyopia have used dichoptic stimuli that overlap within the visual field. However, suppression of the amblyopic eye also occurs when the dichoptic stimuli do not overlap, a phenomenon we refer to as long-range suppression. We used functional MRI to test the hypothesis that long-range suppression reduces neural activity in V1, V2 and V3 in adults with amblyopia, indicative of an early, active inhibition mechanism. Five adults with amblyopia and five controls viewed monocular and dichoptic quadrant stimuli during fMRI. Three of five participants with amblyopia experienced complete perceptual suppression of the quadrants presented to their amblyopic eye under dichoptic viewing. The blood oxygen level dependant (BOLD) responses within retinotopic regions corresponding to amblyopic and fellow eye stimuli were analyzed for response magnitude, time to peak, effective connectivity and stimulus classification. Dichoptic viewing slightly reduced the BOLD response magnitude in amblyopic eye retinotopic regions in V1 and reduced the time to peak response; however, the same effects were also present in the non-dominant eye of controls. Effective connectivity was unaffected by suppression, and the results of a classification analysis did not differ significantly between the control and amblyopia groups. Overall, we did not observe a neural signature of long-range amblyopic eye suppression in V1, V2 or V3 using functional MRI in this initial study. This type of suppression may involve higher level processing areas within the brain.
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Affiliation(s)
- Benjamin Thompson
- School of Optometry and Vision Science, University of Waterloo, Waterloo, ON N2L 3G1, Canada
- McGill Vision Research, Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC H4A 3S5, Canada
- School of Optometry and Vision Science, University of Auckland, Auckland 1142, New Zealand
- Correspondence: ; Tel.: +1-519-888-4567 (39398)
| | - Goro Maehara
- Department of Human Sciences, Kanagawa University, Yokohama 221-8686, Japan
| | - Erin Goddard
- McGill Vision Research, Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC H4A 3S5, Canada
| | - Reza Farivar
- McGill Vision Research, Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC H4A 3S5, Canada
| | - Behzad Mansouri
- Department of Ophthalmology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
| | - Robert F. Hess
- McGill Vision Research, Department of Ophthalmology and Visual Sciences, McGill University, Montreal, QC H4A 3S5, Canada
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19
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Takahata T, Patel NB, Balaram P, Chino YM, Kaas JH. Long-term histological changes in the macaque primary visual cortex and the lateral geniculate nucleus after monocular deprivation produced by early restricted retinal lesions and diffuser induced form deprivation. J Comp Neurol 2018; 526:2955-2972. [PMID: 30004587 DOI: 10.1002/cne.24494] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 06/02/2018] [Accepted: 06/15/2018] [Indexed: 12/12/2022]
Abstract
Ocular dominance (OD) plasticity has been extensively studied in various mammalian species. While robust OD shifts are typically observed after monocular eyelid suture, relatively poor OD plasticity is observed for early eye removal or after tetrodotoxin (TTX) injections in mice. Hence, abnormal binocular signal interactions in the visual cortex may play a critical role in eliciting OD plasticity. Here, we examined the histochemical changes in the lateral geniculate nucleus (LGN) and the striate cortex (V1) in macaque monkeys that experienced two different monocular sensory deprivations in the same eye beginning at 3 weeks of age: restricted laser lesions in macular or peripheral retina and form deprivation induced by wearing a diffuser lens during the critical period. The monkeys were subsequently reared for 5 years under a normal visual environment. In the LGN, atrophy of neurons and a dramatic increase of GFAP expression were observed in the lesion projection zones (LPZs). In V1, although no obvious shift of the LPZ border was found, the ocular dominance columns (ODCs) for the lesioned eye shrunk and those for the intact eye expanded over the entirety of V1. This ODC size change was larger in the area outside the LPZ and in the region inside the LPZ near the border compared to that in the LPZ center. These developmental changes may reflect abnormal binocular interactions in V1 during early infancy. Our observations provide insights into the nature of degenerative and plastic changes in the LGN and V1 following early chronic monocular sensory deprivations.
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Affiliation(s)
- Toru Takahata
- Interdisciplinary Institute of Neuroscience and Technology, Qiushi Academy for Advanced Studies, Zhejiang University, Hangzhou, Zhejiang, People's Republic of China.,Department of Psychology, Vanderbilt University, Nashville, Tennessee
| | - Nimesh B Patel
- Department of Vision Sciences, College of Optometry, University of Houston, Houston, Texas
| | - Pooja Balaram
- Department of Psychology, Vanderbilt University, Nashville, Tennessee.,Department of Otolaryngology, Harvard Medical School, Boston, Massachusetts
| | - Yuzo M Chino
- Department of Vision Sciences, College of Optometry, University of Houston, Houston, Texas
| | - Jon H Kaas
- Department of Psychology, Vanderbilt University, Nashville, Tennessee
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20
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Abstract
Amblyopia, a developmental disorder of vision, affects many aspects of spatial vision as well as motion perception and some cognitive skills. Current models of amblyopic vision based on known neurophysiological deficiencies have yet to provide an understanding of the wide range of amblyopic perceptual losses. Visual spatial attention is known to enhance performance in a variety of detection and discrimination tasks in visually typical humans and nonhuman primates. We investigated whether and how voluntary spatial attention affected psychophysical performance in amblyopic macaques. Full-contrast response functions for motion direction discrimination were measured for each eye of six monkeys: five amblyopic and one control. We assessed whether the effect of a valid spatial cue on performance corresponded to a change in contrast gain, a leftward shift of the function, or response gain, an upward scaling of the function. Our results showed that macaque amblyopes benefit from a valid spatial cue. Performance with amblyopic eyes viewing showed enhancement of both contrast and response gain whereas fellow and control eyes' performance showed only contrast gain. Reaction time analysis showed no speed accuracy trade-off in any case. The valid spatial cue improved contrast sensitivity for the amblyopic eye, effectively eliminating the amblyopic contrast sensitivity deficit. These results suggest that engaging endogenous spatial attention may confer substantial benefit to amblyopic vision.
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Affiliation(s)
- Amelie Pham
- Center for Neural Science and Department of Psychology, New York University, New York, NY, USA
| | - Marisa Carrasco
- Center for Neural Science and Department of Psychology, New York University, New York, NY, USA
| | - Lynne Kiorpes
- Center for Neural Science and Department of Psychology, New York University, New York, NY, USA
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21
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Smith EL, Hung LF, Arumugam B, Wensveen JM, Chino YM, Harwerth RS. Observations on the relationship between anisometropia, amblyopia and strabismus. Vision Res 2017; 134:26-42. [PMID: 28404522 DOI: 10.1016/j.visres.2017.03.004] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2017] [Revised: 03/15/2017] [Accepted: 03/19/2017] [Indexed: 11/26/2022]
Abstract
We investigated the potential causal relationships between anisometropia, amblyopia and strabismus, specifically to determine whether either amblyopia or strabismus interfered with emmetropization. We analyzed data from non-human primates that were relevant to the co-existence of anisometropia, amblyopia and strabismus in children. We relied on interocular comparisons of spatial vision and refractive development in animals reared with 1) monocular form deprivation; 2) anisometropia optically imposed by either contact lenses or spectacle lenses; 3) organic amblyopia produced by laser ablation of the fovea; and 4) strabismus that was either optically imposed with prisms or produced by either surgical or pharmacological manipulation of the extraocular muscles. Hyperopic anisometropia imposed early in life produced amblyopia in a dose-dependent manner. However, when potential methodological confounds were taken into account, there was no support for the hypothesis that the presence of amblyopia interferes with emmetropization or promotes hyperopia or that the degree of image degradation determines the direction of eye growth. To the contrary, there was strong evidence that amblyopic eyes were able to detect the presence of a refractive error and alter ocular growth to eliminate the ametropia. On the other hand, early onset strabismus, both optically and surgically imposed, disrupted the emmetropization process producing anisometropia. In surgical strabismus, the deviating eyes were typically more hyperopic than their fellow fixating eyes. The results show that early hyperopic anisometropia is a significant risk factor for amblyopia. Early esotropia can trigger the onset of both anisometropia and amblyopia. However, amblyopia, in isolation, does not pose a significant risk for the development of hyperopia or anisometropia.
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Affiliation(s)
- Earl L Smith
- College of Optometry, University of Houston, TX 77204, USA; Brien Holden Vision Institute, Sydney, Australia.
| | - Li-Fang Hung
- College of Optometry, University of Houston, TX 77204, USA; Brien Holden Vision Institute, Sydney, Australia
| | - Baskar Arumugam
- College of Optometry, University of Houston, TX 77204, USA; Brien Holden Vision Institute, Sydney, Australia
| | | | - Yuzo M Chino
- College of Optometry, University of Houston, TX 77204, USA
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