Correlation of Optotypes with the Landolt Ring???A Fresh Look at the Comparability of Optotypes

Grimm, Wolfgang; Rassow, B.; Wesemann, W.; Saur, Konrad; Hilz, R.

doi:10.1097/00006324-199401000-00002

Cited by 49 publications

(37 citation statements)

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“…2,3,9,10,18 Our results also confirm the clinical impression that the E chart obtains a greater visual acuity score than does the C chart in younger children but not in older children. A study of 10 adult subjects by Grimm and colleagues 19 reported that visual acuity scores obtained by Tumbling E chart were greater than those obtained by the Landolt C chart (0.065 difference in logMAR). Another study using optical defocus in 10 adults with habitual optical corrections found that the Tumbling E chart was comparable with Landolt C chart, except in simulated 1.5 D against-the-rule astigmatism, where visual acuity measured by an E chart was minimally greater than that obtained by Landolt C chart (0.01 difference in logMAR).…”

Section: Discussionmentioning

confidence: 94%

Development of visual acuity in preschool children as measured with Landolt C and Tumbling E charts

Lai

Wang

Hsu

2011

Journal of American Association for Pediatric Ophthalmology and

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Section: Discussionmentioning

confidence: 94%

Development of visual acuity in preschool children as measured with Landolt C and Tumbling E charts

Lai

Wang

Hsu

2011

Journal of American Association for Pediatric Ophthalmology and

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“…The sizes of the letters were calculated for the test distance of 4 m and the characters (numbers and letters) were 5% smaller than the equivalent size of a Landolt C. 18 The highest spatial resolution that was tested was logMAR 0.0 (smallest separable angle 1Ј or 0.016°at 4 m). One pixel at 4 m was equivalent to 0.005°so that 1Ј was equivalent to about three pixels.…”

Section: Acuity Chartsmentioning

confidence: 99%

Visual Acuity with Simulated and Real Astigmatic Defocus

Ohlendorf¹,

Tabernero²,

Schaeffel³

2011

Optometry and Vision Science

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Purpose. To compare the effects of "simulated" and "real" spherical and astigmatic defocus on visual acuity (VA). Methods. VA was determined with letter charts that were blurred by calculated spherical or astigmatic defocus (simulated defocus) or were seen through spherical or astigmatic trial lenses (real defocus). Defocus was simulated using ZEMAX and the Liou-Brennan eye model. Nine subjects participated [mean age, 27.2 Ϯ 1.8 years; logarithm of the minimum angle of resolution (logMAR), Ϫ0.1]. Three different experiments were conducted in which VA was reduced by 20% (logMAR 0.0), 50% (logMAR 0.2), or 75% (logMAR 0.5) by either (1) imposing positive spherical defocus, (2) imposing positive and negative astigmatic defocus in three axes (0, 45, and 90°), and (3) imposing cross-cylinder defocus in the same three axes as in (2). (1): there were only minor differences in VA with simulated and real positive spherical defocus. Experiment (2): simulated astigmatic defocus reduced VA twice as much as real astigmatic defocus in all tested axes (p Ͻ 0.01 in all cases). Experiment (3): simulated cross-cylinder defocus reduced VA much more than real cross-cylinder defocus (p Ͻ 0.01 in all cases), similarly for all three tested axes. Conclusions. Results. ExperimentThe visual system appears more tolerant against "real" spherical, astigmatic, and cross-cylinder defocus than against "simulated" blur. Possible reasons could be (1) limitations in the modeling procedures to simulate defocus, (2) higher ocular aberrations, and (3) fluctuations of accommodation. However, the two optical explanations (2) and (3) cannot account for the magnitude of the effect, and (1) was carefully analyzed. It is proposed that something may be special about the visual processing of real astigmatic and cross-cylinder defocus-because they have less effect on VA than simulations predict. (Optom Vis Sci 2011;88:562-569)

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“…These include Sloan letters, the Landoldt C, the Snellen E, numbers in various fonts, pictograms, and letters in non-Roman alphabets. It would be useful to understand, from a theoretical point of view, any variations in acuity that result from the optotype selection (Dobson, Maguire, Orel-Bixler, Quinn, Ying; Vision in Preschoolers (VIP) Study Group, 2003;Grimm, Rassow, Wesemann, Saur, & Hilz, 1994;Pointer, 2008). There are, at present, no principled methods of translating between acuities measured with different optotypes.…”

Section: Introductionmentioning

confidence: 99%

Modeling acuity for optotypes varying in complexity

Watson

Ahumada

2012

Journal of Vision

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Watson and Ahumada (2008) described a template model of visual acuity based on an ideal-observer limited by optical filtering, neural filtering, and noise. They computed predictions for selected optotypes and optical aberrations. Here we compare this model's predictions to acuity data for six human observers, each viewing seven different optotype sets, consisting of one set of Sloan letters and six sets of Chinese characters, differing in complexity (Zhang, Zhang, Xue, Liu, & Yu, 2007). Since optical aberrations for the six observers were unknown, we constructed 200 model observers using aberrations collected from 200 normal human eyes (Thibos, Hong, Bradley, & Cheng, 2002). For each condition (observer, optotype set, model observer) we estimated the model noise required to match the data. Expressed as efficiency, performance for Chinese characters was 1.4 to 2.7 times lower than for Sloan letters. Efficiency was weakly and inversely related to perimetric complexity of optotype set. We also compared confusion matrices for human and model observers. Correlations for off-diagonal elements ranged from 0.5 to 0.8 for different sets, and the average correlation for the template model was superior to a geometrical moment model with a comparable number of parameters (Liu, Klein, Xue, Zhang, & Yu, 2009). The template model performed well overall. Estimated psychometric function slopes matched the data, and noise estimates agreed roughly with those obtained independently from contrast sensitivity to Gabor targets. For optotypes of low complexity, the model accurately predicted relative performance. This suggests the model may be used to compare acuities measured with different sets of simple optotypes.

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Correlation of Optotypes with the Landolt Ring???A Fresh Look at the Comparability of Optotypes

Cited by 49 publications

References 0 publications

Development of visual acuity in preschool children as measured with Landolt C and Tumbling E charts

Development of visual acuity in preschool children as measured with Landolt C and Tumbling E charts

Visual Acuity with Simulated and Real Astigmatic Defocus

Modeling acuity for optotypes varying in complexity

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