학술논문
Object frequency characteristics of visual acuity.
Document Type
Academic Journal
Author
McAnany JJ; Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois 60612, USA. jmcana1@uic.edu; Alexander KR; Lim JI; Shahidi M
Source
Publisher: Association For Research In Vision And Ophthalmology (Arvo) Country of Publication: United States NLM ID: 7703701 Publication Model: Electronic Cited Medium: Internet ISSN: 1552-5783 (Electronic) Linking ISSN: 01460404 NLM ISO Abbreviation: Invest Ophthalmol Vis Sci Subsets: MEDLINE
Subject
Language
English
Abstract
Purpose: To examine the extent to which visual acuity (VA) for broadband optotypes is scale invariant by determining whether the same object frequencies mediate VA for individuals with different levels of VA.
Methods: LogMAR (minimum angle of resolution) VA for briefly presented tumbling E's was measured in 10 visually normal individuals and in five patients with VA loss. The E's were either unblurred or blurred with Gaussian low-pass filters that had cutoff frequencies spanning a 1.2-log unit range. The data were fit with a standard equivalent intrinsic blur model to estimate each subject's unblurred VA (MAR(0) in minutes of arc) and equivalent intrinsic blur (σ(int) in minutes of arc). From these estimates, the high-frequency cutoff of the band of retinal frequencies (cpd(crit) in cycles per degree) and object frequencies (cpl(crit) in cycles per letter) mediating VA were derived.
Results: LogMAR(0) was related linearly to log σ(int) with a slope of 1.47, which is steeper than that predicted by scale invariance. Log cpd(crit) was related linearly to logMAR(0) by a slope of -0.64, which is shallower than that predicted by scale invariance. This lack of scale invariance is due to a linear relationship between log cpl(crit) and logMAR(0) that had a slope of 0.36.
Conclusions: The overall pattern of results is not consistent with the expectation of scale invariance underlying the MAR scale. Optotypes that conform to the expectations of scale invariance are needed to improve vision assessment and to provide equivalency of VA defined in terms of MAR and cpd.
Methods: LogMAR (minimum angle of resolution) VA for briefly presented tumbling E's was measured in 10 visually normal individuals and in five patients with VA loss. The E's were either unblurred or blurred with Gaussian low-pass filters that had cutoff frequencies spanning a 1.2-log unit range. The data were fit with a standard equivalent intrinsic blur model to estimate each subject's unblurred VA (MAR(0) in minutes of arc) and equivalent intrinsic blur (σ(int) in minutes of arc). From these estimates, the high-frequency cutoff of the band of retinal frequencies (cpd(crit) in cycles per degree) and object frequencies (cpl(crit) in cycles per letter) mediating VA were derived.
Results: LogMAR(0) was related linearly to log σ(int) with a slope of 1.47, which is steeper than that predicted by scale invariance. Log cpd(crit) was related linearly to logMAR(0) by a slope of -0.64, which is shallower than that predicted by scale invariance. This lack of scale invariance is due to a linear relationship between log cpl(crit) and logMAR(0) that had a slope of 0.36.
Conclusions: The overall pattern of results is not consistent with the expectation of scale invariance underlying the MAR scale. Optotypes that conform to the expectations of scale invariance are needed to improve vision assessment and to provide equivalency of VA defined in terms of MAR and cpd.