| 1. |
- Baskaran, Karthikeyan, et al.
(author)
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Effects of Optical Defocus on Resolution Acuity in Preferred Retinal Locus
- 2011
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In: <em>Invest Ophthalmol Vis Sci</em> 2011;52: E-Abstract 1900..
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Conference paper (peer-reviewed)abstract
- PurposeResolution acuity in the peripheral visual field is primarily limited by retinal sampling. In healthy eyes, the correction of peripheral refractive errors does not produce significant visual benefits other than improved detection and low contrast acuity. However, studies (Lundstrom L et al, Optom Vis Sci, 2007;84:1046-52) have shown that peripheral refractive corrections improve resolution acuity in subjects with central visual field loss (CFL) who have an established preferred retinal locus (PRL). The aim of this study was to evaluate the effect of optical defocus on high contrast resolution acuity in the PRL. MethodsResolution acuity was evaluated under spherical defocus in the PRL of three low vision subjects (mean age 75 years) with long standing CFL (due to age-related macular degeneration). Off-axis refractive error at the PRL was measured by an open-field COAS-HD VR aberrometer and was corrected accordingly. The PRL for subject 1 was located at 10{degrees} in the temporal visual field (left eye), subject 2 at 20{degrees} in the nasal visual field (right eye) and subject 3 at 15{degrees} in the inferior visual field (left eye). Stimuli consisting of high-contrast Gabor patches with a visible diameter of 3{o} were presented on a CRT monitor situated 1.0 meter from the subject. Resolution thresholds for static visual acuity (SVA) and dynamic visual acuity (DVA) were obtained using an adaptive Bayesian algorithm. Fixation was aided using illuminated concentric rings covering {+/-}25{degrees} in the visual field. Defocus was altered in 1D steps up to {+/-}4D. When measuring DVA, the sine-wave gratings drifted within the Gaussian envelope at an angular velocity of 1{degrees}/sec. ResultsResolution thresholds for both SVA and DVA in the PRL varied significantly with the amount of optical defocus. The results show a 2 - 3 line decrease (logMAR) in SVA and DVA with 4 D positive and negative defocus. There was no significant difference between SVA and DVA with increasing defocus. In the absence of defocus, SVA was significantly better than DVA in the PRL. ConclusionsDefocus as low as one dioptre has an impact on both static and dynamic high contrast resolution acuity for CFL subjects using a PRL. The results of this study suggest that, for CFL subjects using a PRL, resolution acuity is not only sampling limited but also influenced by the optics of the eye.
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| 2. |
- Kristiansson, Håkan, et al.
(author)
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Effect of Optical Defocus on Peripheral Resolution Acuity in Old Healthy Emmetropes
- 2011
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Conference paper (peer-reviewed)abstract
- Background: A recent study by Rosén et al found peripheral low contrast resolution acuity, but not high contrast acuity, to be affected by defocus in young healthy eyes. Since aging causes considerable degradation in peripheral optics even in healthy subjects we wanted to see if, older subjects were also sensitive to defocus in low contrast acuity. Purpose: The aim of this study was to evaluate the effect of optical defocus on high and low contrast resolution acuity in the peripheral visual field of healthy older emmetropes. Subjects: High- and low-contrast resolution acuity was evaluated under spherical defocus in the 20° nasal visual field of four healthy older emmetropic subjects. The off-axis refractive error at the 20° nasal visual field was measured by a COAS-HD VR aberrometer and was corrected accordingly for each subject. Methods: Resolution thresholds for visual acuity (VA) were obtained using stimuli consisting of high- (100%) and low- (10%) contrast gratings that were presented on a CRT monitor situated 1.0 meter from the subject. Stimuli, 3° in diameter were presented for 300 ms using a 2AFC paradigm. Two repeated measurements, for both high and low contrast, were obtained for each point of defocus in 1.0 D steps up to ±4 D at 45mm vertex distance. The results are corrected to effective defocus at the corneal plane. Results: Defocus had no visible effect on high contrast VA, although there was a slight decrease in VA with higher amounts of positive defocus. However, defocus was found to have a significant effect on low contrast VA. Moreover, low contrast resolution was more sensitive to positive defocus than the negative defocus. Conclusions: Defocus has an impact on low contrast resolution whereas no such effect was found for high contrast resolution. These results are similar to those obtained by Rosén et al1 in young eyes. These results suggest that low contrast optotypes could possibly be used for determining subjective refraction in low vision subjects.
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| 3. |
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| 4. |
- Lewis, Peter, 1971-, et al.
(author)
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Dynamic Visual Acuity in the Peripheral Visual Field Using Gabor Patches
- 2010
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Conference paper (peer-reviewed)abstract
- Purpose:To evaluate dynamic visual acuity (DVA) in the peripheral visual field. This ability is important within the areas of sports, traffic safety, as well as for people with low vision; specifically those with central visual field loss. In this study we investigated both static- and dynamic visual acuity in the periphery of normally sighted observers using Gabor patches. Methods:DVA and static visual acuity (SVA) was measured on the right eye of normally sighted emmetropes. Stimuli consisted of high-contrast Gabor patches; sine wave gratings multiplied by a Gaussian hull with a diameter of 2º, with the sine gratings drifting at 1, 2, and 4 degrees per second. Stimuli were presented, using MATLAB and Psychophysics Toolbox, on one of seven CRT monitors at the following retinal eccentricities: 10, 20 and 30 degrees, nasally and temporally as well as in the fovea. Subjects were informed to maintain fixation on a central fixation object during measurements at eccentric locations. An Adaptive Bayesian algorithm was employed to determine resolution thresholds at each eccentricity. Results:The results show a trend towards both better static- and dynamic visual acuities for the temporal visual field at retinal eccentricities 20° and 30° compared to nasally. There appears to be a more rapid decrease in both static- and dynamic visual acuity with increasing eccentricity for the nasal visual field. In addition, we did not find any difference in DVA and SVA in the peripheral visual field for the velocities used in this study. Conclusions:Results of these first preliminary measurements suggest that dynamic visual acuity measured with drifting Gabor patches is greater in the temporal visual field for eccentricities 20 degrees or larger. To confirm these results more measurements need to be performed on a lager sample of subjects.
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| 5. |
- Lewis, Peter, 1971-
(author)
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Improving Peripheral Vision Through Optical Correction and Stimulus Motion
- 2016
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Doctoral thesis (other academic/artistic)abstract
- The loss of central vision subsequent to macular disease is often extremely debilitating. People with central field loss (CFL) must use other peripheral areas of the retina in order to see; areas with inferior resolution capacity, which are also affected by off-axis optical errors. The overall aim of the work encompassed by this thesis was to identify and evaluate methods of improving vision for people with CFL; with focus on the effects of off-axis optical correction and stimulus motion on resolution acuity and contrast sensitivity.Off-axis optical errors were measured using a commercially-available COAS-HD VR open-view aberrometer. We used adaptive psychophysical methods to evaluate grating resolution acuity and contrast sensitivity in the peripheral visual field; drifting gratings were employed to measure the effect of motion on these two measures of visual performance. The effect of sphero-cylindrical correction and stimulus motion on visual performance in healthy eyes and in subjects with CFL was also studied; in addition, the effect of adaptive optics aberration correction was examined in one subject with CFL.The COAS-HD aberrometer provided rapid and reliable measurements of off-axis refractive errors. Correction of these errors gave improvements in low-contrast resolution acuity in subjects with higher amounts of oblique astigmatism. Optical correction also improved high-contrast resolution acuity in most subjects with CFL, but not for healthy subjects. Adaptive optics correction improved both high and low contrast resolution acuity in the preferred retinal locus of a subject with CFL. The effect of stimulus motion depended on spatial frequency; motion of 7.5 Hz improved contrast sensitivity for stimuli of low spatial frequency in healthy and CFL subjects. Motion of 15 Hz had little effect on contrast sensitivity for low spatial frequency but resulted in reduced contrast sensitivity for higher spatial frequencies in healthy subjects. Finally, high-contrast resolution acuity was relatively insensitive to stimulus motion in the periphery.This thesis has served to broaden the knowledge regarding peripheral optical errors, stimulus motion and their effects on visual function, both in healthy subjects and in people with CFL. Overall it has shown that correction of off-axis refractive errors is important for optimizing peripheral vision in subjects with CFL; the use of an open-view aberrometer simplifies the determination of these errors. In addition, moderate stimulus motion can have a beneficial effect on contrast sensitivity for objects of predominantly low spatial frequency.
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| 6. |
- Lewis, Peter, 1971-, et al.
(author)
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Naso-temporal Asymmetry of Peripheral Static and Dynamic Visual Acuity
- 2011
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Conference paper (peer-reviewed)abstract
- SummaryStatic and dynamic visual acuity was evaluated in the peripheral visual field on normally sighted emmetropes. The results show a significant asymmetry for both static and dynamic visual acuity between the nasal and temporal visual fields. IntroductionIt is well known that visual performance thresholds decrease rapidly with increasing retinal eccentricity1. This reduction in performance can be attributed to both optical factors and reduced neural sampling2-3; the latter being the predominant limiting factor in the peripheral retina3. Previous studies have shown that slowly moving stimuli are more easily resolved than stationary stimuli in the peripheral retina4. There is little evidence published regarding resolution thresholds for moving stimuli in more than a few limited directions in the visual field. In this study, static visual acuity (SVA) and dynamic visual acuity (DVA) thresholds were measured at 10° intervals both nasally and temporally on healthy, young emmetropes. DVA was measured at angular velocities of 1 °/s and 2 °/s using drifting Gabor patches. DiscussionStatic and dynamic visual acuity was measured on the right eye of emmetropic subjects. Results for SVA showed significantly better resolution in the temporal visual field compared with the nasal visual field at eccentricities 20° and beyond. The mean difference in acuity at 20° was approximately 0.2 LogMAR and at 30°, 0.3 LogMAR. The difference between the thresholds for DVA showed a similar naso-temporal asymmetry; the reduction in DVA paralleling the decrease in SVA for eccentricities 10° and beyond. No significant differences were observed between averaged results of SVA and DVA for the eccentricities tested in this study. ConclusionsThe results of this study confirm previous research conducted by Frisén (1987) showing better resolution for static stimuli presented in the temporal visual field compared to the nasal visual field. We have found that this is also true for DVA.
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| 7. |
- Lewis, Peter, et al.
(author)
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Objectively Determined Refraction Improves Peripheral Vision
- 2014
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In: Optometry and Vision Science. - 1040-5488 .- 1538-9235. ; 91:7, s. 740-746
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Journal article (peer-reviewed)abstract
- Purpose. The purpose of this study was twofold: to verify a fast, clinically applicable method for determining off-axis refraction and to assess the impact of objectively obtained off-axis refractive correction on peripheral low-contrast visual acuity. Methods. We measured peripheral low-contrast resolution acuity with Gabor patches both with and without off-axis correction at 20 degrees in the nasal visual field of 10 emmetropic subjects; the correction was obtained using a commercial open-field Hartmann-Shack wavefront sensor, the COAS-HD VR aberrometer. Off-axis refractive errors were calculated for a 5-mm circular pupil inscribed within the elliptical wavefront by COAS using the instruments' inbuilt "Seidel sphere" method. Results. Most of the subjects had simple myopic astigmatism, at 20 degrees in the nasal visual field ranging from -1.00 to -2.00 DC, with axis orientations generally near 90 degrees. The mean uncorrected and corrected low-contrast resolution acuities for all subjects were 0.92 and 0.86 logMAR, respectively (an improvement of 0.06 logMAR). For subjects with a scalar power refractive error of 1.00 diopters or more, the average improvement was 0.1 logMAR. The observed changes in low-contrast resolution acuity were strongly correlated with off-axis astigmatism (Pearson r = 0.95; p < 0.0001), the J(180) cross-cylinder component (Pearson r = 0.82; p = 0.0034), and power scalar (Pearson r = -0.75; p = 0.0126). Conclusions. The results suggest that there are definite benefits in correcting even moderate amounts of off-axis refractive errors; in this study, as little as -1.50 DC of off-axis astigmatism gave improvements of up to a line in visual acuity. It may be even more pertinent for people who rely on optimal peripheral visual function, specifically those with central visual field loss; the use of open-field aberrometers could be clinically useful in rapidly determining off-axis refractive errors specifically for this patient group who are generally more challenging to refract.
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| 8. |
- Lewis, Peter, 1971-, et al.
(author)
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Resolution of static and dynamic stimuli in the peripheral visual field
- 2011
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In: Vision Research. - : Elsevier BV. - 0042-6989 .- 1878-5646. ; 51:16, s. 1829-1834
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Journal article (peer-reviewed)abstract
- In a clinical setting, emphasis is given to foveal visual function, and tests generally only utilize static stimuli. In this study, we measured static (SVA) and dynamic visual acuity (DVA) in the central and peripheral visual field on healthy, young emmetropic subjects using stationary and drifting Gabor patches. There were no differences between SVA and DVA in the peripheral visual field; however, SVA was superior to DVA in the fovea for both velocities tested. In addition, there was a clear naso-temporal asymmetry for both SVA and DVA for isoeccentric locations in the visual field beyond 10 degrees eccentricity. The lack of difference in visual acuity between static and dynamic stimuli found in this study may reflect the use of drift-motion as opposed to displacement motion used in previous studies.
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| 9. |
- Lewis, Peter, 1971-, et al.
(author)
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The Effect of Refractive-Correction on Peripheral Low-Contrast Resolution Acuity
- 2012
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Conference paper (other academic/artistic)abstract
- Purpose: High-contrast resolution acuity in the peripheral retina has been shown to be sampling-limited, however, a recent study indicates that peripheral low-contrast resolution acuity (PLCRA) is degraded by imposition of optical defocus. On the other hand, it has not been investigated whether refractive errors present in the peripheral field of normal, emmetropic eyes are sufficient to degrade PLCRA. The aim of this study was to evaluate the effect of peripheral refractive-correction on PLCRA in young emmetropes.Methods: Low-contrast (10 %) resolution acuity was measured off-axis (20° nasal visual field) on the right eyes of 10 emmetropic subjects (age 22 ± 2 years), both with and without peripheral refractive correction. Central and peripheral refractive errors were acquired using an open-field COAS-HD VR aberrometer. Stimuli, consisting of low-contrast Gabor patches with a visible diameter of 2°, were presented on a CRT monitor situated 3.0 meters from the subjects. Resolution thresholds were determined using a 2-alternative forced-choice Bayesian algorithm.Results: All the subjects had off-axis astigmatism (against-the-rule) at 20° in the nasal visual field ranging from -1.00 DC to -2.00 DC; of which four had -1.00 DC, three had -1.25 DC, one had -1.50 DC and the remaining two had -2.00 DC. Two of the subjects with -1.25 DC had -0.50 DS to -0.75 DS spherical errors; the rest had purely cylindrical errors. The mean uncorrected and corrected low-contrast resolution acuities for all subjects were 0.92 logMAR and 0.86 logMAR respectively. This shows an improvement in resolution acuity of 0.06 logMAR (p = 0.028) after correction of off-axis refractive errors. However when grouped according to the amount of astigmatism, the -1.00 DC group showed no difference in acuity with correction, the -1.25 DC, -1.50 DC and -2.00 DC groups improved on average by 0.05, 0.14 and 0.16 logMAR respectively.Conclusions: Correction of off-axis refractive errors had a positive effect on low-contrast resolution thresholds in the peripheral visual field on the emmetropic subjects in this study. Moreover, the effects become appreciable only for those subjects having larger degrees of astigmatism. This suggests that optical factors influence peripheral visual tasks involving low-contrast. There may be benefits in correcting even moderate amounts of off-axis refractive errors, especially for people who rely on optimal peripheral visual function.
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