Equivalent intrinsic blur in amblyopia

Levi, Dennis M.; Klein, Stanley A.

doi:10.1016/0042-6989(90)90017-f

Cited by 43 publications

(13 citation statements)

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“…As in Figure 2, the corresponding Snellen equivalents are shown on the right y-axis for reference. Log MAR 0 (estimated VA for the unblurred stimulus) increased systematically with log σ int (equivalent intrinsic blur), as has been reported previously for two-line resolution,3,4 and there was a statistically significant correlation between the two parameters ( r = 0.95, p < 0.01). The data were fit with a line with unit slope, which corresponds to the slope of the linear function used previously to describe the relationship between two-line resolution and equivalent intrinsic blur 3,4…”

Section: Resultssupporting

confidence: 86%

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Contributions of Optical and Non-Optical Blur to Variation in Visual Acuity

McAnany

Shahidi

Applegate

et al. 2011

Optometry and Vision Science

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Purpose To determine the relative contributions of optical and non-optical sources of intrinsic blur to variations in visual acuity (VA) among normally sighted subjects. Methods Best-corrected VA of sixteen normally sighted subjects was measured using briefly presented (59 ms) tumbling E optotypes that were either unblurred or blurred through convolution with Gaussian functions of different widths. A standard model of intrinsic blur was used to estimate each subject’s equivalent intrinsic blur (σint) and VA for the unblurred tumbling E (MAR0). For 14 subjects, a radially averaged optical point spread function due to higher-order aberrations was derived by Shack-Hartmann aberrometry and fit with a Gaussian function. The standard deviation of the best-fit Gaussian function defined optical blur (σopt). An index of non-optical blur (η) was defined as: 1-σopt/σint. A control experiment was conducted on 5 subjects to evaluate the effect of stimulus duration on MAR0 and σint. Results Log MAR0 for the briefly presented E was correlated significantly with log σint (r = 0.95, p < 0.01), consistent with previous work. However, log MAR0 was not correlated significantly with log σopt (r = 0.46, p = 0.11). For subjects with log MAR0 equivalent to approximately 20/20 or better, log MAR0 was independent of log η, whereas for subjects with larger log MAR0 values, log MAR0 was proportional to log η. The control experiment showed a statistically significant effect of stimulus duration on log MAR0 (p < 0.01) but a non-significant effect on σint (p = 0.13). Conclusions The relative contributions of optical and non-optical blur to VA varied among the subjects, and were related to the subject’s VA. Evaluating optical and non-optical blur may be useful for predicting changes in VA following procedures that improve the optics of the eye in patients with both optical and non-optical sources of VA loss.

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Section: Resultssupporting

confidence: 86%

“…However, when σ stim greatly exceeds σ int , VA is proportional to stimulus blur. Using the equivalent intrinsic blur paradigm, it has been shown previously that normal variation in Vernier acuity,2 two-line resolution thresholds,3,4 and Landolt C acuity6 is related to equivalent intrinsic blur.…”

mentioning

confidence: 98%

Contributions of Optical and Non-Optical Blur to Variation in Visual Acuity

McAnany

Shahidi

Applegate

et al. 2011

Optometry and Vision Science

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“…This function is actually a form of the more familiar function that has been frequently used to quantify equivalent intrinsic noise (Barlow, 1962; Pelli, 1990), i.e., the amount of noise that must be added to a stimulus to elevate thresholds by √2. Levi & Klein (1990) used this parameterization, to quantify the amount of intrinsic blur in amblyopia, i.e., the amount of blur that had to be added to the stimulus to elevate thresholds by √2. This is effectively a measure of the amount of blur (or noise) one can tolerate before performance is degraded.…”

Section: Discussionmentioning

confidence: 99%

Visual deficits in anisometropia

2011

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Amblyopia is usually associated with the presence of anisometropia, strabismus or both early in life. We set out to explore quantitative relationships between the degree of anisometropia and the loss of visual function, and to examine how the presence of strabismus affects visual function in observers with anisometropia. We measured optotype acuity, Pelli-Robson contrast sensitivity and stereoacuity in 84 persons with anisometropia and compared their results with those of 27 persons with high bilateral refractive error (isoametropia) and 101 persons with both strabismus and anisometropia. All subjects participated in a large scale study of amblyopia (McKee, Levi & Movshon, 2003). We found no consistent visual abnormalities in the strong eye, and therefore report only on vision in the weaker, defined as the eye with lower acuity. LogMAR acuity falls off markedly with increasing anisometropia in non-strabismic anisometropes, while contrast sensitivity is much less affected. Acuity degrades rapidly with increases in both hyperopic and myopic anisometropia, but the risk of amblyopia is about twice as great in hyperopic than myopic anisometropes of comparable refractive imbalance. For a given degree of refractive imbalance, strabismic anisometropes perform considerably worse than anisometropes without strabismus – visual acuity for strabismics was on average 2.5 times worse than for non-strabismics with similar anisometropia. For observers with equal refractive error in the two eyes there is very little change in acuity or sensitivity with increasing (bilateral) refractive error except for one extreme individual (bilaterally refractive error of -15 D). Most pure anisometropes with interocular differences less than 4 D retain some stereopsis, and the degree is correlated with the acuity of the weak eye. We conclude that even modest interocular differences in refractive error can influence visual function.

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“…Jarak ini ditentukan melalui plot keluk Gaussian pada data ketepatan respons. Nisbah jarak kesesakan mendatar-menegak ditunjukkan dalam ruang paling kanan Keputusan kajian ini mencadangkan bahawa kemerosotan penglihatan fovea subjek ambliopia anisometropik berlaku akibat peningkatan kabur intrinsik (Levi & Klein 1990) berbanding subjek normal. Oleh itu, penggunaan kabur ke atas subjek normal, sama ada dengan menggunakan kabur optik atau kabur penuras digital Gaussian, boleh digunakan sebagai model penglihatan fovea ambliopia anisometropik.…”

Section: Uji Kaji 2: Akuiti Periferi Subjek Normal Yang Dikaburkan Peunclassified

“…Pesakit ambliopia anisometropik dilaporkan memiliki kabur intrinsik yang lebih besar daripada individu normal (Levi & Klein 1990). Kabur intrinsik adalah jumlah kabur yang apabila digabungkan dengan kabur rangsangan akan menghasilkan kabur efektif rangsangan tersebut.…”

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