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He Y, Feng L, Zhou Y, Zhuang Y, Xu Z, Yao Y, Chen X, Jiang R, Yuan J, Ye Q, Wen Y, Jia Y, Liu J, Li J. Characteristics and predictive factors of visual function improvements after monocular perceptual learning in amblyopia. Heliyon 2023; 9:e17281. [PMID: 37416659 PMCID: PMC10320034 DOI: 10.1016/j.heliyon.2023.e17281] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2022] [Revised: 06/02/2023] [Accepted: 06/13/2023] [Indexed: 07/08/2023] Open
Abstract
Monocular perceptual learning has shown promising performance in restoring visual function in amblyopes beyond the critical period in the laboratory. However, the treatment outcome is variable and indeterminate in actual clinical and neuroscientific practice. We aimed to explore the efficacy of monocular perceptual learning in the clinical setting. By combining continuous monitoring of perceptual learning and clinical measurements, we evaluated the efficacy and characteristics of visual acuity and contrast sensitivity function improvement and further explored the individualized effect after perceptual learning. Amblyopes (average age:17 ± 7 years old) were trained in a monocular two-alternative forced choice identification task at the 50% contrast threshold of the amblyopic eye for 10-15 days. We found that monocular perceptual learning improves both visual acuity and contrast sensitivity function in amblyopia. The broader activation of spatial contrast sensitivity, with a significant improvement in lower spatial frequencies, contributed to improving visual acuity. Visual acuity changes in the early stage can predict the endpoint treatment outcomes. Our results confirm the efficacy of monocular perceptual learning and suggest potential predictors of training outcomes to assist in the future management of clinical intervention and vision neuroscience research in amblyopia beyond the critical period of visual plasticity.
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Fernández J, Rodríguez-Vallejo M, Martínez J, Burguera N, Piñero DP. Agreement between subjective and predicted high and low contrast visual acuities with a double-pass system. Graefes Arch Clin Exp Ophthalmol 2020; 259:1651-1657. [PMID: 33128671 DOI: 10.1007/s00417-020-04987-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Revised: 09/23/2020] [Accepted: 10/20/2020] [Indexed: 10/23/2022] Open
Abstract
PURPOSE To evaluate the agreement between subjective high and low contrast visual acuity (VA) and predicted values from double-pass system measurements in healthy candidates to laser refractive surgery. METHODS Ninety-two eyes measured during the preoperative screening to laser refractive surgery were included in this retrospective analysis. High contrast subjective visual acuity (HCVA) and low contrasts at 20% (LCVA20) and 9% (LCVA9) were compared with the predicted VA obtained with a commercial double-pass system (OQAS) at the same levels of contrast, 100% (OV100), 20% (OV20), and 9% (OV9). The agreement was evaluated with Bland-Altman analysis computing the limits of agreement (LoAs) and the correlations with the spearman rho. RESULTS An underestimation of VA was obtained with the double-pass system for the highest contrast. Differences between predictive and subjective measurements were statistically significant for 100% contrast (- 0.08 logMAR, p < 0.0005), but not for 20% (- 0.03 logMAR, p = 0.07) and 9% (- 0.02 logMAR, p = 0.9) of contrasts. The LoAs increased with the decrease of contrast from 0.29 with 100% to 0.39 logMAR with 9% of contrast. A weak correlation was obtained between subjective and predicted VA (rho ≤ 0.33) that was only significant for 100% (p = 0.001) and 20% (p = 0.004) contrasts. CONCLUSION Mean differences between methods were reasonably small so mean results obtained for predicted VA in OQAS studies can be considered as reliable, at least in healthy subjects and for low contrast. However, limits of agreement were considerably poor which means that OQAS cannot replace individual subjective measurements of VA in clinical practice.
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Affiliation(s)
- Joaquín Fernández
- Department of Ophthalmology (Qvision), Vithas Virgen del Mar Hospital, 04120, Almería, Spain
| | | | - Javier Martínez
- Department of Ophthalmology (Qvision), Vithas Virgen del Mar Hospital, 04120, Almería, Spain
| | - Noemi Burguera
- Department of Ophthalmology (Qvision), Vithas Virgen del Mar Hospital, 04120, Almería, Spain
| | - David P Piñero
- Department of Optics, Pharmacology and Anatomy, University of Alicante, Alicante, Spain.,Department of Ophthalmology (IMQO-Oftalmar), Vithas Medimar International Hospital, Alicante, Spain
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Abstract
Optical blur from defocus is quite frequently considered as equivalent to low-pass filtering. Yet that belief, although not entirely wrong, is inaccurate. Here, we wish to disentangle the concepts of dioptric blur, caused by myopia or mis-accommodation, from blur due to low-pass filtering when convolving with a Gaussian kernel. Perhaps surprisingly-if well known in optometry-the representation of a blur kernel (or point-spread function) for dioptric blur is, to a good approximation and disregarding diffraction, simply a cylinder. Its projection onto the retina is classically referred to as a blur circle, the diameter of which can easily be deduced from a light-ray model. We further give the derivation of the relationship between the blur-disk's diameter and the extent of blur in diopters, as well as the diameter's relation to the near or far point, and finally its relationship to visual acuity.
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Affiliation(s)
- Hans Strasburger
- Institute of Medical Psychology, Ludwig-Maximilians-Universität, München, Germany; Department of Medical Psychology and Medical Sociology, Georg-August University, Göttingen, Germany
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Almaguer C, Acosta E, Arines J. Pupil size stability of the cubic phase mask solution for presbyopia. JOURNAL OF BIOMEDICAL OPTICS 2018; 23:1-8. [PMID: 29297211 DOI: 10.1117/1.jbo.23.1.015002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2017] [Accepted: 12/04/2017] [Indexed: 06/07/2023]
Abstract
Presbyopia correction involves different types of studies such as lens design, clinical study, and the development of objective metrics, such as the visual Strehl ratio. Different contact lens designs have been proposed for presbyopia correction, but performance depends on pupil diameter. We will analyze the potential use of a nonsymmetrical element, a cubic phase mask (CPM) solution, to develop a contact or intraocular lens whose performance is nearly insensitive to changes in pupil diameter. We will show the through focus optical transfer function of the proposed element for different pupil diameters ranging from 3 to 7 mm. Additionally, we will show the images obtained through computation and experiment for a group of eye charts with different visual acuities. Our results show that a CPM shaped as 7.07 μm*(Z33-Z3-3)-0.9 μmZ20 is a good solution for a range of clear vision with a visual acuity of at least 0.1 logMar from 0.4 to 6 m for pupil diameters in the 3- to 7-mm range. Our results appear to be a good starting point for further development and study of this kind of CPM solution for presbyopia.
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Affiliation(s)
- Citlalli Almaguer
- Universidade de Santiago de Compostela, Facultade de Óptica e Optometría, Dept. Física Aplicada, San, Spain
| | - Eva Acosta
- Universidade de Santiago de Compostela, Facultade de Óptica e Optometría, Dept. Física Aplicada, San, Spain
| | - Justo Arines
- Universidade de Santiago de Compostela, Facultade de Óptica e Optometría, Dept. Física Aplicada, San, Spain
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Thompson WB, Legge GE, Kersten DJ, Shakespeare RA, Lei Q. Simulating visibility under reduced acuity and contrast sensitivity. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2017; 34:583-593. [PMID: 28375328 PMCID: PMC5558613 DOI: 10.1364/josaa.34.000583] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Architects and lighting designers have difficulty designing spaces that are accessible to those with low vision, since the complex nature of most architectural spaces requires a site-specific analysis of the visibility of mobility hazards and key landmarks needed for navigation. We describe a method that can be utilized in the architectural design process for simulating the effects of reduced acuity and contrast on visibility. The key contribution is the development of a way to parameterize the simulation using standard clinical measures of acuity and contrast sensitivity. While these measures are known to be imperfect predictors of visual function, they provide a way of characterizing general levels of visual performance that is familiar to both those working in low vision and our target end-users in the architectural and lighting-design communities. We validate the simulation using a letter-recognition task.
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Affiliation(s)
- William B. Thompson
- School of Computing, University of Utah, 50 So. Central Campus Dr., Room MEB-3190, Salt Lake City, UT 84112-9205
| | - Gordon E. Legge
- Department of Psychology, University of Minnesota, N218 Elliott Hall, 75 E River Rd, Minneapolis, MN 55455
| | - Daniel J. Kersten
- Department of Psychology, University of Minnesota, N218 Elliott Hall, 75 E River Rd, Minneapolis, MN 55455
| | - Robert A. Shakespeare
- Department of Theatre, Drama, and Contemporary Dance, Indiana University, 275 North Jordan, Bloomington, IN 47405-1101
| | - Quan Lei
- Department of Psychology, University of Minnesota, N218 Elliott Hall, 75 E River Rd, Minneapolis, MN 55455
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Arines J, Almaguer C, Acosta E. Potential use of cubic phase masks for extending the range of clear vision in presbyopes: initial calculation and simulation studies. Ophthalmic Physiol Opt 2017; 37:141-150. [DOI: 10.1111/opo.12348] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 11/22/2016] [Indexed: 11/27/2022]
Affiliation(s)
- Justo Arines
- Departamento de Física Aplicada (área de Optometría); Facultade de Óptica e Optometría; Universidade de Santiago de Compostela; Santiago de Compostela Spain
| | - Citlalli Almaguer
- Departamento de Física Aplicada (área de Optometría); Facultade de Óptica e Optometría; Universidade de Santiago de Compostela; Santiago de Compostela Spain
| | - Eva Acosta
- Departamento de Física Aplicada (área de Óptica); Facultade de Física; Universidade de Santiago de Compostela; Santiago de Compostela Spain
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Abstract
PURPOSE To compare differences in contrast threshold among individual Sloan letters presented in additive white luminance noise and in the absence of noise. METHODS Contrast threshold for letter identification was measured for three visually normal subjects (aged 22, 25, and 34 years) using letters from the Sloan set (C, D, H, K, N, O, R, S, V, and Z). The letter size was equivalent to 1.5 logMAR (logarithm of the minimum angle of resolution), and the letters were either unfiltered or band-pass filtered to limit the object frequency content (cycles per letter) to a one-octave wide band centered at 1.25, 2.5, 5, and 10 cycles per letter. Letters were presented for an unlimited duration against a uniform adapting field or in the presence of additive white luminance noise. Contrast threshold for each letter was determined using a 10-alternative forced-choice interleaved staircase procedure. RESULTS For standard unfiltered Sloan letters presented against a uniform field, contrast threshold for individual letters differed by as much as a factor of 1.5, consistent with a previous report. When measured in luminance noise, the individual letters differed by as much as a factor of 1.8. Band-pass filtering the letters to include only low object frequencies increased the differences in contrast threshold among the individual letters (about a factor of 3) compared with unfiltered letters and letters filtered into high object frequency bands. CONCLUSIONS The addition of white luminance noise had relatively small effects on interletter contrast threshold differences, whereas band-pass filtering had large effects on interletter threshold differences, greatly increasing variation among the letters that contained only low object frequencies. Letters that contain only high object frequencies may be useful in the design of letter charts because the interletter threshold differences are relatively small for these optotypes and the object frequency information mediating identification is known.
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Kord Valeshabad A, Wanek J, McAnany JJ, Shahidi M. Effects of optical blur reduction on equivalent intrinsic blur. Optom Vis Sci 2015; 92:494-9. [PMID: 25785538 DOI: 10.1097/opx.0000000000000563] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
PURPOSE To determine the effect of optical blur reduction on equivalent intrinsic blur, an estimate of the blur within the visual system, by comparing optical and equivalent intrinsic blur before and after adaptive optics (AO) correction of wavefront error. METHODS Twelve visually normal subjects (mean [±SD] age, 31 [±12] years) participated in this study. Equivalent intrinsic blur (σint) was derived using a previously described model. Optical blur (σopt) caused by high-order aberrations was quantified by Shack-Hartmann aberrometry and minimized using AO correction of wavefront error. RESULTS σopt and σint were significantly reduced and visual acuity was significantly improved after AO correction (p ≤ 0.004). Reductions in σopt and σint were linearly dependent on the values before AO correction (r ≥ 0.94, p ≤ 0.002). The reduction in σint was greater than the reduction in σopt, although it was marginally significant (p = 0.05). σint after AO correlated significantly with σint before AO (r = 0.92, p < 0.001), and the two parameters were related linearly with a slope of 0.46. CONCLUSIONS Reduction in equivalent intrinsic blur was greater than the reduction in optical blur after AO correction of wavefront error. This finding implies that visual acuity in subjects with high equivalent intrinsic blur can be improved beyond that expected from the reduction in optical blur alone.
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Affiliation(s)
- Ali Kord Valeshabad
- *MD, MPH †MS ‡PhD Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois (all authors)
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McAnany JJ. The effect of exposure duration on visual acuity for letter optotypes and gratings. Vision Res 2014; 105:86-91. [PMID: 25281413 DOI: 10.1016/j.visres.2014.08.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 08/26/2014] [Accepted: 08/29/2014] [Indexed: 10/24/2022]
Abstract
This study compared the effects of exposure duration on letter and grating targets in a visual acuity (VA) task and determined if the broadband nature of letters accounts for their temporal summation characteristics. Log MAR (minimum angle of resolution) VA of five individuals (ages 25-36) was measured with a set of tumbling E optotypes for durations of 24 ms to 1s. The Es were either unfiltered or low-pass filtered to determine the object frequencies (cycles per letter; cplE) mediating VA. The retinal frequencies mediating VA for the unfiltered E (cycles per degree; cpdE) were derived from the ratio of cplE to MAR. Values of cpdE were compared to threshold retinal frequency obtained with band-limited Es and gratings to further evaluate the effects of stimulus bandwidth. Both log MAR and log cplE for the unfiltered E decreased as duration increased up to approximately 260 ms, and were constant thereafter. VA also improved for gratings and band-pass filtered Es, but over a shorter time course (approximately 150 ms). The effect of duration on VA for the broadband E, Gabor, and band-pass filtered E was similar when the object frequencies mediating VA were included in the definition of VA by converting to cpdE. The results indicate that the pattern of temporal integration for the tumbling E is related to its broadband nature. Band-pass filtered letters can simplify the interpretation of VA because the object frequency information mediating VA is known exactly and is independent of duration and letter size.
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Affiliation(s)
- J Jason McAnany
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, 1855 W. Taylor St., Chicago, IL 60612, USA; Department of Psychology, University of Illinois at Chicago, 1007 W. Harrison St., Chicago, IL 60612, USA; Department of Bioengineering, University of Illinois at Chicago, 851 South Morgan St., Chicago, IL 60607, USA.
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Hall C, Wang S, Bhagat R, McAnany JJ. Effect of luminance noise on the object frequencies mediating letter identification. Front Psychol 2014; 5:663. [PMID: 25071637 PMCID: PMC4080385 DOI: 10.3389/fpsyg.2014.00663] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2013] [Accepted: 06/09/2014] [Indexed: 12/03/2022] Open
Abstract
Purpose: To determine if the same object frequency information mediates letter contrast threshold in the presence and absence of additive luminance noise (i.e., “noise-invariant processing”) for letters of different size. Methods: Contrast thresholds for Sloan letters ranging in size from 0.9 to 1.8 log MAR were obtained from three visually normal observers under three paradigms: (1) high- and low-pass Gaussian filtered letters were presented against a uniform adapting field; (2) high- and low-pass Gaussian filtered letters were presented in additive white luminance noise; and (3) unfiltered letters were presented in high- and low-pass Gaussian filtered luminance noise. A range of high- and low-pass filter cutoffs were used to limit selectively the object frequency content of the letters (paradigms 1 and 2) or noise (paradigm 3). The object frequencies mediating letter identification under each paradigm were derived from plots of log contrast threshold vs. log filter cutoff frequency. Results: The object frequency band mediating letter identification systematically shifted to higher frequencies with increasing log MAR letter size under all three paradigms. However, the relationship between object frequency and letter size depended on the paradigm under which the measurements were obtained. The largest difference in object frequency among the paradigms was observed at 1.8 log MAR, where the addition of white noise nearly doubled the center frequency of the band of object frequencies mediating letter identification, compared to measurements made in the absence of noise. Conclusion: Noise can affect the object frequency band mediating letter contrast threshold, particularly for large letters, an effect that is likely due to strong masking of the low frequency letter components by low frequency noise checks. This finding indicates that noise-invariant processing cannot necessarily be assumed for large letters presented in white noise.
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Affiliation(s)
- Cierra Hall
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago Chicago, IL, USA ; Department of Bioengineering, University of Illinois at Chicago, Chicago IL, USA
| | - Shu Wang
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago Chicago, IL, USA ; Department of Electrical and Computer Engineering, University of Illinois at Chicago Chicago, IL, USA
| | - Reema Bhagat
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago Chicago, IL, USA
| | - J Jason McAnany
- Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago Chicago, IL, USA ; Department of Bioengineering, University of Illinois at Chicago, Chicago IL, USA ; Department of Psychology, University of Illinois at Chicago Chicago, IL, USA
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Abstract
PURPOSE Visual acuity (VA) in normally sighted individuals is highly correlated with equivalent intrinsic blur, a measure of the amount of blur within the visual system that is generated by optical and neural sources. This study assessed the extent to which VA, equivalent intrinsic blur, optical blur, and neural blur are abnormal in subjects with proliferative diabetic retinopathy (PDR) and characterized the relationships among these parameters. METHODS Best-corrected VA of 10 subjects with PDR (ages 25 to 68) and 10 normally sighted individuals (ages 46 to 63) was measured for tumbling E optotypes. The Es were either unblurred or blurred through convolution with Gaussian functions of different widths. Values of equivalent intrinsic blur (σ(int)) and unblurred VA (MAR0) were derived using a standard model. Optical blur (σ(opt)), a measure of blur generated by higher-order aberrations, was quantified using Shack-Hartmann aberrometry. An index of neural blur (η) was defined as 1--σ(opt)/σ(int), which represents the remaining blur once the contributions of σ(opt) to σ(int) have been accounted for. RESULTS Log MAR0 and log σ(int) were correlated significantly (r = 0.98, p < 0.05) for the PDR subjects and the values of these parameters ranged from normal to more than a factor of 2 above the upper limit of normal. In comparison, log MAR measured for the most blurred E was elevated by a relatively small amount for all PDR subjects and was not correlated significantly with log σ(int) (r = 0.40, p = 0.25). MAR0, σ(int), and η differed significantly between the PDR subjects and the controls (all p < 0.05) but σ(opt) did not (p = 0.50). CONCLUSIONS Subjects with PDR and VA loss had higher than normal equivalent intrinsic blur that resulted primarily from neural blur elevations, suggesting that neural blur is an important factor that limits VA in these patients.
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Abstract
PURPOSE To develop a predictive optical modeling process that utilizes individual computer eye models along with a novel through-focus image quality metric. METHODS Individual eye models were implemented in optical design software (Zemax, Bellevue, WA) based on evaluation of ocular aberrations, pupil diameter, visual acuity, and accommodative response of 90 subjects (180 eyes; 24-63 years of age). Monocular high-contrast minimum angle of resolution (logMAR) acuity was assessed at 6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, 33 cm, 28 cm, and 25 cm. While the subject fixated on the lowest readable line of acuity, total ocular aberrations and pupil diameter were measured three times each using the Complete Ophthalmic Analysis System (COAS HD VR) at each distance. A subset of 64 mature presbyopic eyes was used to predict the clinical logMAR acuity performance of five novel multifocal contact lens designs. To validate predictability of the design process, designs were manufactured and tested clinically on a population of 24 mature presbyopes (having at least +1.50 D spectacle add at 40 cm). Seven object distances were used in the validation study (6 m, 2 m, 1 m, 67 cm, 50 cm, 40 cm, and 25 cm) to measure monocular high-contrast logMAR acuity. RESULTS Baseline clinical through-focus logMAR was shown to correlate highly (R² = 0.85) with predicted logMAR from individual eye models. At all object distances, each of the five multifocal lenses showed less than one line difference, on average, between predicted and clinical normalized logMAR acuity. Correlation showed R² between 0.90 and 0.97 for all multifocal designs. CONCLUSIONS Computer-based models that account for patient's aberrations, pupil diameter changes, and accommodative amplitude can be used to predict the performance of contact lens designs. With this high correlation (R² ≥ 0.90) and high level of predictability, more design options can be explored in the computer to optimize performance before a lens is manufactured and tested clinically.
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Poulere E, Moschandreas J, Kontadakis GA, Pallikaris IG, Plainis S. Effect of blur and subsequent adaptation on visual acuity using letter and Landolt C charts: differences between emmetropes and myopes. Ophthalmic Physiol Opt 2013; 33:130-7. [PMID: 23297779 DOI: 10.1111/opo.12020] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2012] [Accepted: 11/26/2012] [Indexed: 11/26/2022]
Abstract
PURPOSE To compare the effects of defocus induced blur and blur adaptation on visual acuity and to evaluate any differences between emmetropes and myopes using letter and Landolt C logMAR charts. METHODS The sample consisted of 26 volunteers, with a mean age of 27 ± 3 years, comprising 13 emmetropes (spherical equivalent range: -0.63 to +0.50 D) and 13 myopes (spherical equivalent range: -0.75 to -5.00 D). Monocular visual acuity (VA) was measured in each eye using letter and Landolt C logMAR charts under the following conditions: (1) with the distance refractive correction, (2) immediately after exposure to +2.00 D defocus and (3) following 60 min of binocular adaptation to +2.00 D blur. Objective refraction at the beginning and at the end of the experimental procedure was evaluated. Averaged VA data between the two eyes were used for analysis. RESULTS Deterioration in VA with +2.00 D defocus was greater in the emmetropes compared to myopes for both charts. The mean difference between the two refractive groups was more pronounced for the Landolt-C (0.17 logMAR) compared to the letter chart (0.10 logMAR). The reduction in VA with blur was related to the amount of the refractive error. Following 60 min of adaptation, a significant improvement in VA was observed in both groups that did not differ between the two charts. The improvement in VA following adaptation using the letter chart was linearly correlated with spherical equivalent refractive correction. CONCLUSIONS Myopes show higher tolerance to retinal defocus compared to emmetropes, which could be attributed to previous blur experience. The effect of blur on VA is more pronounced using Landolt C optotypes than with letters. Prolonged exposure to blur results in equally improved performance for both refractive groups.
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Affiliation(s)
- Eleni Poulere
- Institute of Vision and Optics (IVO), School of Health Sciences, University of Crete, Heraklion, Greece
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