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Zeri F, Di Vizio A, Lucia S, Berchicci M, Bianco V, Pitzalis S, Tavazzi S, Naroo SA, Di Russo F. Cortical dynamics in visual areas induced by the first use of multifocal contact lenses in presbyopes. Cont Lens Anterior Eye 2024; 47:102137. [PMID: 38485618 DOI: 10.1016/j.clae.2024.102137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Revised: 01/19/2024] [Accepted: 03/06/2024] [Indexed: 05/20/2024]
Abstract
A common non-spectacle strategy to correct presbyopia is to provide simultaneous images with multifocal optical designs. Understanding the neuroadaptation mechanisms behind multifocal devices usage would have important clinical implications, such as predicting whether patients will be able to tolerate multifocal optics. The aim of this study was to evaluate the brain correlates during the initial wear of multifocal contact lenses (CLs) using high-density visual evoked potential (VEP) measures. Fifteen presbyopes (mean age 51.8 ± 2.6 years) who had previously not used multifocal CLs were enrolled. VEP measures were achieved while participants looked at arrays of 0.5 logMAR Sloan letters in three different optical conditions arranged with CLs: monofocal condition with the optical power appropriate for the distance viewing; multifocal correction with medium addition; and multifocal correction with low addition. An ANOVA for repeated measures showed that the amplitude of the C1 and N1 components significantly dropped with both multifocal low and medium addition CL conditions compared to monofocal CLs. The P1 and P2 components showed opposite behavior with an increase in amplitudes for multifocal compared to monofocal conditions. VEP data indicated that multifocal presbyopia corrections produce a loss of feedforward activity in the primary visual cortex that is compensated by extra feedback activity in extrastriate areas only, in both early and late visual processing.
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Affiliation(s)
- Fabrizio Zeri
- Department of Materials Science. University of Milano-Bicocca, Milan, Italy; COMiB Research Centre in Optics and Optometry. University of Milano-Bicocca, Milan, Italy; College of Health and Life Sciences. Aston University, Birmingham, UK.
| | - Assunta Di Vizio
- COMiB Research Centre in Optics and Optometry. University of Milano-Bicocca, Milan, Italy; Department of Science, Roma Tre University, Rome, Italy
| | - Stefania Lucia
- Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy
| | - Marika Berchicci
- Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy; Department of Psychological, Humanistic and Territorial Sciences, University "G. d'Annunzio", Chieti-Pescara, Italy
| | - Valentina Bianco
- Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy; Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy
| | - Sabrina Pitzalis
- Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy; IRCCS Santa Lucia Foundation Rome, Italy
| | - Silvia Tavazzi
- Department of Materials Science. University of Milano-Bicocca, Milan, Italy; COMiB Research Centre in Optics and Optometry. University of Milano-Bicocca, Milan, Italy
| | - Shehzad A Naroo
- College of Health and Life Sciences. Aston University, Birmingham, UK
| | - Francesco Di Russo
- Department of Movement, Human and Health Sciences, University of Rome "Foro Italico", Rome, Italy; IRCCS Santa Lucia Foundation Rome, Italy
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2
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Effects of visual blur and contrast on spatial and temporal precision in manual interception. Exp Brain Res 2021; 239:3343-3358. [PMID: 34480594 PMCID: PMC8542000 DOI: 10.1007/s00221-021-06184-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2021] [Accepted: 07/22/2021] [Indexed: 12/04/2022]
Abstract
The visual system is said to be especially sensitive towards spatial but lesser so towards temporal information. To test this, in two experiments, we systematically reduced the acuity and contrast of a visual stimulus and examined the impact on spatial and temporal precision (and accuracy) in a manual interception task. In Experiment 1, we blurred a virtual, to-be-intercepted moving circle (ball). Participants were asked to indicate (i.e., finger tap) on a touchscreen where and when the virtual ball crossed a ground line. As a measure of spatial and temporal accuracy and precision, we analyzed the constant and variable errors, respectively. With increasing blur, the spatial and temporal variable error, as well as the spatial constant error increased, while the temporal constant error decreased. Because in the first experiment, blur was potentially confounded with contrast, in Experiment 2, we re-ran the experiment with one difference: instead of blur, we included five levels of contrast matched to the blur levels. We found no systematic effects of contrast. Our findings confirm that blurring vision decreases spatial precision and accuracy and that the effects were not mediated by concomitant changes in contrast. However, blurring vision also affected temporal precision and accuracy, thereby questioning the generalizability of the theoretical predictions to the applied interception task.
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Abstract
Myopes exhibit a larger capability of adaptation to defocus. Adaptation produces a boost in visual performance that can be characterized through different metrics. The ability of myopes to adapt to other sources of blur, such as diffusion, has not been studied so far. In this work, a group of 20 myopes with normal vision underwent high-contrast visual acuity (VA) measurements under different viewing conditions, wearing their refractive correction with or without a diffuser (Bangerter filter, BF). VA decreased immediately after wearing the BF of density 0.6, showing a significant relationship with the ocular refraction. After 40 minutes of binocular vision through the BF, a statistically significant increase (p = 0.02) in VA from 0.54 to 0.62 in decimal scale (from 0.3 to 0.2 logMAR) was obtained. No correlation with the refraction was observed. After removing the diffuser, VA returned to baseline. A control group (17 subjects) underwent the same experimental protocol but without diffuser filters. No significant changes in VA were found in this group. We describe a new type of contrast adaptation to blur in myopes caused by scattering, rather than by defocus. The effects of low scattering levels in vision might be relevant in the analysis of early stage of cataract, amblyopia treatments, and myopia understanding.
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Logan NS, Radhakrishnan H, Cruickshank FE, Allen PM, Bandela PK, Davies LN, Hasebe S, Khanal S, Schmid KL, Vera-Diaz FA, Wolffsohn JS. IMI Accommodation and Binocular Vision in Myopia Development and Progression. Invest Ophthalmol Vis Sci 2021; 62:4. [PMID: 33909034 PMCID: PMC8083074 DOI: 10.1167/iovs.62.5.4] [Citation(s) in RCA: 51] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The role of accommodation in myopia development and progression has been debated for decades. More recently, the understanding of the mechanisms involved in accommodation and the consequent alterations in ocular parameters has expanded. This International Myopia Institute white paper reviews the variations in ocular parameters that occur with accommodation and the mechanisms involved in accommodation and myopia development and progression. Convergence is synergistically linked with accommodation and the impact of this on myopia has also been critiqued. Specific topics reviewed included accommodation and myopia, role of spatial frequency, and contrast of the task of objects in the near environment, color cues to accommodation, lag of accommodation, accommodative-convergence ratio, and near phoria status. Aspects of retinal blur from the lag of accommodation, the impact of spatial frequency at near and a short working distance may all be implicated in myopia development and progression. The response of the ciliary body and its links with changes in the choroid remain to be explored. Further research is critical to understanding the factors underlying accommodative and binocular mechanisms for myopia development and its progression and to guide recommendations for targeted interventions to slow myopia progression.
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Affiliation(s)
- Nicola S Logan
- School of Optometry, Aston University, Birmingham, United Kingdom
| | - Hema Radhakrishnan
- Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Fiona E Cruickshank
- Division of Pharmacy and Optometry, School of Health Sciences, Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, United Kingdom
| | - Peter M Allen
- Vision and Hearing Sciences Research Centre, School of Psychology and Sports Sciences, Anglia Ruskin University, Cambridge, United Kingdom
| | - Praveen K Bandela
- Brien Holden Vision Institute, Sydney, New South Wales, Australia.,School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia
| | - Leon N Davies
- School of Optometry, Aston University, Birmingham, United Kingdom
| | - Satoshi Hasebe
- Department of Ophthalmology, Kawasaki Medical School, Kurashiki, Okayama, Japan
| | - Safal Khanal
- School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Katrina L Schmid
- School of Optometry and Vision Science, Queensland University of Technology, Brisbane, Australia
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5
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Bulson RC, Ciuffreda KJ, Hayes J, Ludlam DP. Effect of retinal defocus on basketball free throw shooting performance. Clin Exp Optom 2021; 98:330-4. [DOI: 10.1111/cxo.12267] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2014] [Revised: 10/20/2014] [Accepted: 11/18/2014] [Indexed: 11/30/2022] Open
Affiliation(s)
- Ryan C Bulson
- Pacific University College of Optometry, Forest Grove, Oregon, USA
| | | | - John Hayes
- Pacific University College of Optometry, Forest Grove, Oregon, USA
| | - Diana P Ludlam
- State University of New York College of Optometry, New York, New York, USA
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Xu J, Tao C, Mao X, Lu X, Bao J, Drobe B, Chen H. Blur Detection Sensitivity Increases in Children Using Orthokeratology. Front Neurosci 2021; 15:630844. [PMID: 33790734 PMCID: PMC8006440 DOI: 10.3389/fnins.2021.630844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2020] [Accepted: 02/24/2021] [Indexed: 11/29/2022] Open
Abstract
Purpose To investigate changes in blur detection sensitivity in children using orthokeratology (Ortho-K) and explore the relationships between blur detection thresholds (BDTs) and aberrations and accommodative function. Methods Thirty-two children aged 8–14 years old who underwent Ortho-K treatment participated in and completed this study. Their BDTs, aberrations, and accommodative responses (ARs) were measured before and after a month of Ortho-K treatment. A two forced-choice double-staircase procedure with varying extents of blur in three images (Tumbling Es, Lena, and Street View) was used to measure the BDTs. The participants were required to judge whether the images looked blurry. The BDT of each of the images (BDT_Es, BDT_Lena, and BDT_Street) was the average value of the last three reversals. The accommodative lag was quantified by the difference between the AR and the accommodative demand (AD). Changes in the BDTs, aberrations, and accommodative lags and their relationships were analyzed. Results After a month of wearing Ortho-K lenses, the children’s BDT_Es and BDT_Lena values decreased, the aberrations increased significantly (for all, P ≤0.050), and the accommodative lag decreased to a certain extent [T(31) = 2.029, P = 0.051]. Before Ortho-K treatment, higher-order aberrations (HOAs) were related to BDT_Lena (r = 0.463, P = 0.008) and the accommodative lag was related to BDT_Es (r = −0.356, P = −0.046). After one month, no significant correlations were found between the BDTs and aberrations or accommodative lags, as well as between the variations of them (for all, P ≥ 0.069). Conclusion Ortho-K treatment increased the children’s level of blur detection sensitivity, which may have contributed to their good visual acuity.
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Affiliation(s)
- Jingjing Xu
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China.,WEIRC, Wenzhou Medical University-Essilor International Research Center, Wenzhou, China
| | - Chunwen Tao
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China
| | - Xinjie Mao
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China.,WEIRC, Wenzhou Medical University-Essilor International Research Center, Wenzhou, China
| | - Xin Lu
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China
| | - Jinhua Bao
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China.,WEIRC, Wenzhou Medical University-Essilor International Research Center, Wenzhou, China
| | - Björn Drobe
- WEIRC, Wenzhou Medical University-Essilor International Research Center, Wenzhou, China.,R&D AMERA, Essilor International, Singapore, Singapore
| | - Hao Chen
- School of Ophthalmology and Optometry, Affiliated Eye Hospital, State Key Laboratory of Ophthalmology, Optometry and Vision Science, Wenzhou Medical University, Wenzhou, China.,WEIRC, Wenzhou Medical University-Essilor International Research Center, Wenzhou, China
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7
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Sudhir RR, Farhath Pattan H, Rathore M, Kuppuswamy Parthasarathy M, Padmanabhan P, Lakshminarayanan V. The effect of refractive surgery on blur thresholds. Indian J Ophthalmol 2020; 68:2998-3001. [PMID: 33229685 PMCID: PMC7856997 DOI: 10.4103/ijo.ijo_1512_20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Purpose: The aim of this study was to measure blur thresholds before and after refractive surgery. Methods: In this prospective cohort study conducted in a tertiary eye hospital in South India. Blur thresholds were measured for 30 young adult myopic patients 1 month prior to and after refractive surgery. Patients were asked to report three stages of blur, namely Detectable Blur (DB), Bothersome Blur (BB), and Non-resolvable Blur (NB). Blur was created by adding plus lenses (in steps of 0.12D) over their optimal subjective refraction. The blur judgments were made both monocularly and binocularly when looking through a 3 mm artificial pupil at one line above the best-corrected visual acuity. Results: A total of 30 participants were included in this study (mean age = 25.5 ± 3.8 (20–36) years; 77% female). The mean binocular preoperative blur of this group was: DB = 0.39 ± 0.26D, BB = 0.74 ± 0.28D and NB = 1.04 ± 0.42D. The corresponding mean binocular blur one-month post-operatively was DB = 0.46 ± 0.28D, BB = 0.83 ± 0.35D, and NB = 1.21 ± 0.44D. Although there was a marginal increase in the blur thresholds postoperatively, the difference was not statistically significant (DB: P = 0.320; BB: P = 0.229; NB: P = 0.054). Conclusion: All three blur thresholds showed an insignificant minimal increase at 1 month post-operatively suggesting that patients adapt to the induced blur following refractive surgery. A longer follow up would reveal how the adaptation to blur would change with time.
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Affiliation(s)
- Rachapalle Reddi Sudhir
- Department of Cornea & Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
| | - Hadiya Farhath Pattan
- Department of Cornea & Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
| | - Mehal Rathore
- Elite School of Optometry, Unit of Medical Research Foundation, Chennai, Affiliated to SASTRA University, Thanjavur, Tamil Nadu, India
| | | | - Prema Padmanabhan
- Department of Cornea & Refractive Surgery, Medical Research Foundation, Sankara Nethralaya, Chennai, Tamil Nadu, India
| | - Vasudevan Lakshminarayanan
- School of Optometry and Vision Science, Departments of Physics, ECE and Systems Design Engineering, University of Waterloo, Canada
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8
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The time course of the onset and recovery of axial length changes in response to imposed defocus. Sci Rep 2020; 10:8322. [PMID: 32433541 PMCID: PMC7239843 DOI: 10.1038/s41598-020-65151-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Accepted: 04/20/2020] [Indexed: 12/18/2022] Open
Abstract
The human eye is capable of responding to the presence of blur by changing its axial length, so that the retina moves towards the defocused image plane. We measured how quickly the eye length changed in response to both myopic and hyperopic defocus and how quickly the eye length changed when the defocus was removed. Axial length was measured at baseline and every 10 minutes during 1 hour of exposure to monocular defocus (right eye) with the left eye optimally corrected for two defocus conditions (+3 D and −3 D) and a control condition. Recovery was measured for 20 minutes after blur removal. A rapid increase in axial length was observed after exposure (~2 minutes) to hyperopic defocus (+7 ± 5 μm, p < 0.001) while the reduction in axial length with myopic defocus was slower and only statistically significant after 40 minutes (−8 ± 9 μm, p = 0.017). The eye length also recovered toward baseline levels during clear vision more rapidly following hyperopic than myopic defocus (p < 0.0001). These findings provide evidence that the human eye is able to detect and respond to the presence and sign of blur within minutes.
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9
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Cufflin MP, Mallen EA. Blur adaptation: clinical and refractive considerations. Clin Exp Optom 2019; 103:104-111. [PMID: 31801179 DOI: 10.1111/cxo.13033] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 11/08/2019] [Accepted: 11/13/2019] [Indexed: 01/28/2023] Open
Abstract
The human visual system is amenable to a number of adaptive processes; one such process, or collection of processes, is the adaptation to blur. Blur adaptation can be observed as an improvement in vision under degraded conditions, and these changes occur relatively rapidly following exposure to blur. The potential important future directions of this research area and the clinical implications of blur adaptation are discussed.
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Affiliation(s)
- Matthew P Cufflin
- School of Optometry and Vision Science, University of Bradford, Bradford, West Yorkshire, UK
| | - Edward Ah Mallen
- School of Optometry and Vision Science, University of Bradford, Bradford, West Yorkshire, UK
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10
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Factors Influencing Pseudo-Accommodation-The Difference between Subjectively Reported Range of Clear Focus and Objectively Measured Accommodation Range. Vision (Basel) 2019; 3:vision3030034. [PMID: 31735835 PMCID: PMC6802792 DOI: 10.3390/vision3030034] [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: 03/28/2019] [Revised: 06/06/2019] [Accepted: 06/20/2019] [Indexed: 02/07/2023] Open
Abstract
The key determinants of the range of clear focus in pre-presbyopes and their relative contributions to the difference between subjective range of focus and objective accommodation assessments have not been previously quantified. Fifty participants (aged 33.0 ± 6.4 years) underwent simultaneous monocular subjective (visual acuity measured with an electronic test-chart) and objective (dynamic accommodation measured with an Aston open-field aberrometer) defocus curve testing for lenses between +2.00 to −10.00 DS in +0.50 DS steps in a randomized order. Pupil diameter and ocular aberrations (converted to visual metrics normalized for pupil size) at each level of blur were measured. The difference between objective range over which the power of the crystalline lens changes and the subjective range of clear focus was quantified and the results modelled using pupil size, refractive error, tolerance to blur, and ocular aberrations. The subjective range of clear focus was principally accounted for by age (46.4%) and pupil size (19.3%). The objectively assessed accommodative range was also principally accounted for by age (27.6%) and pupil size (15.4%). Over one-quarter (26.0%) of the difference between objective accommodation and subjective range of clear focus was accounted for by age (14.0%) and spherical aberration at maximum accommodation (12.0%). There was no significant change in the objective accommodative response (F = 1.426, p = 0.229) or pupil size (F = 0.799, p = 0.554) of participants for levels of defocus above their amplitude of accommodation. Pre-presbyopes benefit from an increased subjective range of clear vision beyond their objective accommodation due in part to neural factors, resulting in a measured depth-of-focus of, on average, 1.0 D.
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Labhishetty V, Chakraborty A, Bobier WR. Is blur sensitivity altered in children with progressive myopia? Vision Res 2018; 154:142-153. [PMID: 30472331 DOI: 10.1016/j.visres.2018.11.002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2018] [Revised: 11/07/2018] [Accepted: 11/13/2018] [Indexed: 12/25/2022]
Abstract
School aged children with progressive myopia show large accommodative lags to blur only cue which is suggestive of a large depth of focus (DOF). While DOF measures are lacking in this age group, their blur detection and discrimination capacities appear to be similar to their non-myopic peers. Accordingly, the current study quantified DOF and blur detection ability in progressive myopic children showing large accommodative lags compared to their non-myopic peers and adults. Blur sensitivity measures were taken from 12 children (8-13 years, 6 myopes and 6 emmetropes) and 6 adults (20-35 years). DOF was quantified using step changes in the lens induced defocus while the subjects viewed a high contrast target through a Badal lens at either 2 or 4D demand. Blur detection thresholds (BDT) were tested using a similar high contrast target in a 2-alternate forced-choice paradigm (2AFC) at both the demands. In addition to the large accommodative lags, micro fluctuations and DOF were significantly larger in myopic children compared to the other groups. However, BDTs were similar across the three groups. When limited to blur cues, the findings of a large DOF coupled with large response lags suggests that myopes are less sensitive to retinal defocus. However, in agreement to a previous study, refractive error had no influence on their BDTs suggesting that the reduced sensitivity to the defocus in a myopic eye appears to be compensated by some form of an adjustment in the higher visual processes to preserve the subjective percept even with a poor retinal image quality.
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Affiliation(s)
- Vivek Labhishetty
- School of Optometry and Vision Science, University of Waterloo, Waterloo, ON N2L3G1, Canada.
| | - Arijit Chakraborty
- School of Optometry and Vision Science, University of Waterloo, Waterloo, ON N2L3G1, Canada
| | - William R Bobier
- School of Optometry and Vision Science, University of Waterloo, Waterloo, ON N2L3G1, Canada
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12
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Neural adaptation to peripheral blur in myopes and emmetropes. Vision Res 2016; 132:69-77. [PMID: 27919674 DOI: 10.1016/j.visres.2016.09.017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/30/2016] [Accepted: 09/23/2016] [Indexed: 11/20/2022]
Abstract
In the presence of optical blur at the fovea, blur adaptation can improve visual acuity (VA) and perceived image quality over time. However, little is known regarding blur adaptation in the peripheral retina. Here, we examined neural adaptation to myopic defocus at the fovea and parafovea (10° temporal retina) in both emmetropes and myopes. During a 60-min adaptation period, subjects (3 emmetropes and 3 myopes) watched movies with +2 diopters of defocus blur through a 6-mm artificial pupil in two separate, counter-balanced sessions for each retinal location. VA was measured at 10-min intervals under full aberration-corrected viewing using an adaptive optics (AO) vision simulator. By correcting subjects' native optical aberrations with AO, we bypassed the influence of the individual subjects' optical aberrations on visual performance. Overall, exhibited a small but significant improvement after the 60-min of adaptation at both the fovea (mean±SE VA improvement: -0.06±0.04 logMAR) and parafovea (mean±SE VA improvement: -0.07±0.04 logMAR). Myopic subjects exhibited significantly greater improvement in parafoveal VA (mean±SE VA improvement: 0.10±0.02 logMAR), than that of emmetropic subjects (mean±SE VA improvement: 0.04±0.03 logMAR). In contrast, there was no significant difference in foveal VA between the two refractive-error groups. In conclusion, our results reveal differences in peripheral blur adaptation between refractive-error groups, with myopes displaying a greater degree of adaptation.
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13
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Khan KA, Cufflin MP, Mallen EAH. The effect of interrupted defocus on blur adaptation. Ophthalmic Physiol Opt 2016; 36:649-656. [PMID: 27790776 DOI: 10.1111/opo.12323] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 08/25/2016] [Indexed: 01/22/2023]
Abstract
PURPOSE Blur adaptation occurs when an observer is exposed to continuous defocus. However, it is unclear whether adaptation requires constant defocus, or whether the effect can still be achieved when the adaptation period is interrupted by short periods of clear vision. METHODS The study included 12 emmetropes and 12 myopes. All observers wore full refractive correction throughout the experiment. 1D and 3D of myopic defocus was introduced using spherical convex lenses. An automated system was used to place the blurring lens before the RE for varying periods of blurred and clear vision during adaptation. Participants watched a DVD at 3 m during each 15 min trial. Visual acuity was measured using Test Chart 2000 before and after adaptation. RESULTS Blur adaptation occurs to varying degrees depending on the periods of incremental blur exposure. Significant improvements in defocused visual acuity occur with continuous blur, equal blur and clear periods, as well as for longer blur periods. However, longer clear periods showed reduced adaptation and this trial is significantly different to the other three trials for both defocus levels (p < 0.001). No refractive group differences were observed for neither 1D nor 3D defocus (p = 0.58 and p = 0.19 respectively). CONCLUSIONS Intervening periods of clear vision cause minimal disruption to improvements in defocused visual acuity after adaptation, indicating that blur adaptation is a robust phenomenon. However, when the exposure to clear vision exceeds the defocused periods, adaptation is inhibited. This gives insight into the effects of real-world tasks on adaptation to blur.
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Affiliation(s)
- Kiren A Khan
- School of Optometry and Vision Science, University of Bradford, Bradford, UK
| | - Matthew P Cufflin
- School of Optometry and Vision Science, University of Bradford, Bradford, UK
| | - Edward A H Mallen
- School of Optometry and Vision Science, University of Bradford, Bradford, UK.
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14
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Myopes experience greater contrast adaptation during reading. Vision Res 2016; 121:1-9. [PMID: 26804636 DOI: 10.1016/j.visres.2016.01.001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 01/13/2016] [Accepted: 01/14/2016] [Indexed: 11/20/2022]
Abstract
In this study, we investigated whether reading influences contrast adaptation differently in young adult emmetropic and myopic participants at the spatial frequencies created by text rows and character strokes. Pre-adaptation contrast sensitivity was measured for test gratings with spatial frequencies of 1cdeg(-1) and 4cdeg(-1), presented horizontally and vertically. Participants then adapted to reading text corresponding to the horizontal "row frequency" of text (1cdeg(-1)), and vertical "stroke frequency" of the characters (4cdeg(-1)) for 180s. Following this, post-adaptation contrast sensitivity was measured. Twenty young adults (10 myopes, 10 emmetropes) optimally corrected for the viewing distance participated. There was a significant reduction in logCS post-text adaptation (relative to pre-adaptation logCS) at the row frequency (1cdeg(-1) horizontal) but not at the stroke frequency (4cdeg(-1) vertical). logCS changes due to adaptation at 1cdeg(-1) horizontal were significant in both emmetropes and myopes. Comparing the two refractive groups, myopic participants showed significantly greater adaptation compared to emmetropic participants. Reading text on a screen induces contrast adaptation in young adult observers. Myopic participants were found to exhibit greater contrast adaptation than emmetropes at the spatial frequency corresponding to the text row frequency. No contrast adaptation was observed at the text stroke frequency in either participant group. The greater contrast adaptation experienced by myopes after reading warrants further investigation to better understand the relationship between near work and myopia development.
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15
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Charman WN. Developments in the correction of presbyopia II: surgical approaches. Ophthalmic Physiol Opt 2014; 34:397-426. [PMID: 24716827 DOI: 10.1111/opo.12129] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Accepted: 03/05/2014] [Indexed: 11/28/2022]
Abstract
PURPOSE To discuss the various static and dynamic surgical approaches which attempt to give presbyopes good vision at far, intermediate and near viewing distances. CONTENT Static methods broadly adopt the same optical techniques as those used in presbyopic contact lens correction and aim to satisfy the needs of the presbyope by increasing binocular depth-of-focus, often using monovision as well as simultaneous-imagery. Dynamic methods generally attempt to make use of at least some of the still-active elements of the accommodation system. They include procedures which are supposed to modify the relative geometry of the ciliary muscle and lens, or which reduce the stiffness of the presbyopic lens either by replacing it with other natural or man-made material or by subjecting it to femtosecond laser treatment. Alternatively the natural lens may be replaced by some form of intraocular lens which changes power as a result of forces derived from the still-active ciliary muscle, zonule and capsule, or other sources. CONCLUSIONS At present, multifocal intraocular lenses appear to offer the most consistent and reliable surgical approach to surgical presbyopic correction. They have obvious advantages in convenience and stability over optically-similar, simultaneous-image presbyopic contact lenses but this must be balanced against their relative inflexibility in cases of patient dissatisfaction. Dynamic methods remain largely experimental. Although some approaches show promise, as yet no method has demonstrated a reliable, long-term ability to correct distance refractive error and to appropriately change ocular power in response to changes in viewing distance over the normal range of interest.
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Affiliation(s)
- W Neil Charman
- Faculty of Life Sciences, University of Manchester, Manchester, UK
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Abstract
PURPOSE Astigmatic subjects are adapted to their astigmatism and perceptually recalibrate upon its correction. However, the extent to which prior adaptation to astigmatism affects visual performance, whether this effect is axis dependent, and the time scale of potential changes in visual performance after astigmatism correction are not known. Moreover, the effect of possible positive interactions of aberrations (astigmatism and coma) might be altered after recalibration to correction of astigmatism. METHODS Visual acuity (VA) was measured in 25 subjects (astigmats and non-astigmats, corrected and uncorrected) under induction of astigmatism and combinations of astigmatism and coma while controlling subject aberrations. Astigmatism (1.00 diopter) was induced at three different orientations, the natural axis, the perpendicular orientation, and 45 degrees for astigmats and at 0, 90, and 45 degrees for non-astigmats. Experiments were also performed, adding coma (0.41 μm at a relative angle of 45 degrees) to the same mentioned astigmatism. Fourteen different conditions were measured using an 8-Alternative Forced Choice procedure with Tumbling E letters and a QUEST algorithm. Longitudinal measurements were performed up to 6 months. Uncorrected astigmats were provided with proper astigmatic correction after the first session. RESULTS In non-astigmats, inducing astigmatism at 90 degrees, produced a statistically lower reduction in VA than at 0 or 45 degrees, whereas in astigmats, the lower decrease in VA occurred for astigmatism induced at the natural axis. Six months of astigmatic correction did not reduce the insensitivity to astigmatic induction along the natural axis. Differences after orientation of astigmatism were also found when adding coma to astigmatism. CONCLUSIONS The impact of astigmatism on VA is greatly dependent on the orientation of the induced astigmatism, even in non-astigmats. Previous experience to astigmatism plays a significant role on VA, with a strong bias toward the natural axis. In contrast to perceived isotropy, the correction of astigmatism does not shift the bias in VA from the natural axis of astigmatism.
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Khan KA, Dawson K, Mankowska A, Cufflin MP, Mallen EAH. The time course of blur adaptation in emmetropes and myopes. Ophthalmic Physiol Opt 2013; 33:305-10. [PMID: 23662962 DOI: 10.1111/opo.12031] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2012] [Accepted: 01/10/2013] [Indexed: 11/28/2022]
Abstract
PURPOSE/BACKGROUND This study examined the effect of myopic defocus on visual acuity (VA) over time, with attention being paid to the first point at which blur adaptation had a significant and measurable effect on defocused VA. Visual acuity was sampled at a higher rate than previous studies in order to assess the time course of blur adaptation processes in myopic and emmetropic observers. METHODS Participants were 24 normally-sighted observers (12 emmetropes and 12 myopes, median age: 22.5 years). All ametropic participants wore their full refractive correction throughout the experiment. 1 D and 3 D of myopic defocus were introduced in two separate, randomised sessions. Visual acuity was measured using Test Chart 2000 at 2 min intervals over a 30 min session whilst looking through defocus lenses. Recovery clear VA was also measured every 2 min for a further 20 min. RESULTS Defocused VA was found to improve significantly within 4 min after the introduction of defocus for both 1 D (P < 0.0001) and 3 D conditions (P < 0.0001). The improvements reached a plateau shortly after, with no significant further improvements in defocused VA after 6 min. There were no significant differences found in the temporal blur adaptation profiles between emmetropes and myopes (P = 0.267). Data were fitted with an exponential decay function; the lowest R(2) value for this fit was 0.95. CONCLUSIONS Blur adaptation has a clinically significant and measurable effect on VA within 4 min of exposure to defocus. This finding indicates that the visual system instigates the neural compensatory mechanisms shortly after the appearance of defocus. Our results relate particularly to real-life vision of uncorrected myopes or myopes who remove their correction for part of the day.
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Affiliation(s)
- Kiren A Khan
- Bradford School of Optometry and Vision Science, University of Bradford, Bradford, UK
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Vera-Diaz FA, Woods RL, Peli E. Shape and individual variability of the blur adaptation curve. Vision Res 2010; 50:1452-61. [PMID: 20417657 PMCID: PMC2902630 DOI: 10.1016/j.visres.2010.04.013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Revised: 04/01/2010] [Accepted: 04/09/2010] [Indexed: 10/19/2022]
Abstract
We are interested in clinical implications of adaptation to blurred and sharpened images. Therefore, we investigated repeatability, individual variability and characteristics of the adaptation curves of 39 normally-sighted individuals. The point of subjective neutrality (PSN - the slope of the spatial spectrum of the image that appears normal) following adaptation was measured for each adaptation level and was used to derive individual adaptation curves for each subject. Adaptation curves were fitted with a modified Tukey biweight function as the curves were found to be tumbled-S shaped and asymmetrical for blur and sharp in some subjects. The adaptation curve was found to be an individual characteristic as inter-subject variability exceeds test/re-test variability. The existence of individual variability may have implications for the prescription and clinical success of optical devices as well as image enhancement rehabilitation options.
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Affiliation(s)
- Fuensanta A Vera-Diaz
- Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston, MA 02114, United States.
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19
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Ohlendorf A, Schaeffel F. Contrast adaptation induced by defocus – A possible error signal for emmetropization? Vision Res 2009; 49:249-56. [DOI: 10.1016/j.visres.2008.10.016] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 10/20/2008] [Accepted: 10/20/2008] [Indexed: 11/25/2022]
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20
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Abstract
PURPOSE Adaptation to defocus is known to influence the subjective sensitivity to blur in both emmetropes and myopes. Blur is a major contributing factor in the closed-loop dynamic accommodation response. Previous investigations have examined the magnitude of the accommodation response following blur adaptation. We have investigated whether a period of blur adaptation influences the dynamic accommodation response to step and sinusoidal changes in target vergence. METHOD Eighteen subjects (six emmetropes, six early onset myopes, and six late onset myopes) underwent 30 min of adaptation to 0.00 D (control), +1.00 D or +3.00 D myopic defocus. Following this adaptation period, accommodation responses to a 2.00 D step change and 2.00 D sinusoidal change (0.2 Hz) in target vergence were recorded continuously using an autorefractor. RESULTS Adaptation to defocus failed to influence accommodation latency times, but did influence response times to a step change in target vergence. Adaptation to both +1.00 and +3.00 D induced significant increases in response times (p = 0.002 and p = 0.012, respectively) and adaptation to +3.00 D increased the change in accommodation response magnitude (p = 0.014) for a 2.00 D step change in demand. Blur adaptation also significantly increased the peak-to-peak phase lag for accommodation responses to a sinusoidally oscillating target, although failed to influence the accommodation gain. These changes in accommodative response were equivalent across all refractive groups. CONCLUSION Adaptation to a degraded stimulus causes an increased level of accommodation for dynamic targets moving towards an observer and increases response times and phase lags. It is suggested that the contrast constancy theory may explain these changes in dynamic behavior.
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Bulson RC, Ciuffreda KJ, Hung GK. The effect of retinal defocus on golf putting. Ophthalmic Physiol Opt 2008; 28:334-44. [DOI: 10.1111/j.1475-1313.2008.00575.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Cufflin MP, Hazel CA, Mallen EAH. Static accommodative responses following adaptation to differential levels of blur. Ophthalmic Physiol Opt 2007; 27:353-60. [PMID: 17584286 DOI: 10.1111/j.1475-1313.2007.00491.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
PURPOSE To investigate the effects of two levels of blur adaptation on visual resolution and steady-state accommodation responses in emmetropes and myopes. METHODS Eleven emmetropes (mean refractive error +0.01 +/- 0.31 DS) and 11 early-onset myopes (EOM, mean refractive error -4.44 +/- 1.64 DS) fixated monocularly at 4 m in three trials of 45 min duration with either: optimal refractive correction, +1 DS defocus, or +3 DS defocus. Monocular logMAR visual acuity (VA) was measured at 10 min intervals during each trial, and immediately following completion of the trial. Accommodative stimulus-response function (ASRF), refractive error and pupil size were measured before and after each trial. RESULTS Blur adaptation was found to have no effect on pupil size or baseline refraction, irrespective of the power of the blurring lens. Adaptation to +1 DS of defocus yielded an improvement in VA of -0.16 +/- 0.07 logMAR and -0.17 +/- 0.11 logMAR in the emmetropes and myopes respectively. An improvement in VA of -0.20 +/- 0.18 logMAR in the emmetropes and -0.26 +/- 0.17 logMAR in the myopes was observed following adaptation to +3 DS of defocus. The changes in acuity became significant following 30 min of exposure to defocus. Blur adaptation was found to have no effect on the ASRF gradient or individual steady-state accommodative responses. CONCLUSIONS Following blur adaptation, visual resolution was found to increase in both emmetropes and myopes. The magnitude of the blur level did not produce significantly different increases in resolution. Blur adaptation failed to affect either the steady-state responses to an accommodative stimulus or ASRF gradient.
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Affiliation(s)
- Matthew P Cufflin
- Department of Optometry, University of Bradford, Richmond Road, Bradford, West Yorkshire BD7 1DP, UK
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Ciuffreda KJ, Wang B, Vasudevan B. Conceptual model of human blur perception. Vision Res 2007; 47:1245-52. [PMID: 17223154 DOI: 10.1016/j.visres.2006.12.001] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2006] [Revised: 12/04/2006] [Accepted: 12/06/2006] [Indexed: 11/25/2022]
Abstract
An empirically based, conceptual model of human blur perception is presented. It incorporates the concepts of blur detection and blur discrimination in depth, and across the central and peripheral retina, in two- and three-dimensional visual space. Key aspects of the model are its dynamic nature, predictability regarding the blur-based depth-ordering of objects, patterns of retinal defocus with far and near viewing, and interactions related to retinal defocus between the central and peripheral retina. Furthermore, a two-dimensional schematic representation of the blur-free region during near viewing is depicted in dioptric space. This model has implications with respect to accommodative control, depth perception, and refractive error development and progression.
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Affiliation(s)
- Kenneth J Ciuffreda
- SUNY/State College of Optometry, Department of Vision Sciences, 33 West, 42nd Street, New York, NY 10036, USA.
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Wang B, Ciuffreda KJ, Irish T. Equiblur zones at the fovea and near retinal periphery. Vision Res 2006; 46:3690-8. [PMID: 16750552 DOI: 10.1016/j.visres.2006.04.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2006] [Revised: 04/10/2006] [Accepted: 04/13/2006] [Indexed: 11/23/2022]
Abstract
Knowledge regarding successive blur discrimination thresholds (i.e., equiblur zones) in depth and across the near retinal periphery, and their relation to blur detection (i.e., depth-of-focus), remains unknown. The blur detection threshold and four successive blur discrimination thresholds were measured psychophysically at the fovea, as well as at retinal eccentricities of 0.25 degrees , 2 degrees , 4 degrees , and 8 degrees . A Badal optometer system was used to assess blur sensitivity monocularly in five visually normal young adults with cycloplegia. The foveal test stimulus consisted of a small irregularly shaped black form, and the peripheral test stimulus consisted of high contrast circular apertures of different radii. Both the group mean blur detection and successive blur discrimination thresholds progressively increased with retinal eccentricity. At retinal eccentricities of 0 degrees , 0.25 degrees , 2 degrees , 4 degrees , and 8 degrees , the group mean blur detection thresholds were 0.53+/-0.06 D, 0.59+/-0.10 D, 0.93+/-0.11 D, 0.98+/-0.16D, and 1.25+/-0.25 D, while the average values of the group mean blur discrimination thresholds across the steps were 0.29+/-0.01 D, 0.37+/-0.01 D, 0.48+/-0.00 D, 0.51+/-0.01 D, and 0.72+/-0.02 D, respectively. At each retinal eccentricity, the blur discrimination thresholds were similar to each other, and they were approximately 60% of the blur detection threshold magnitude. These findings provide a conceptual representation of blur perception throughout the central visual field. Possible mechanisms are proposed for the decreased blur sensitivity in the near retinal periphery, as well as for the difference between the blur detection and blur discrimination thresholds.
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Affiliation(s)
- Bin Wang
- SUNY State College of Optometry, New York, NY 10036, USA.
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