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Titolo:
The slope of the psychometric function for Bailey-Lovie letter charts: Defocus effects and implications for modeling letter-by-letter scores
Autore:
Carkeet, A; Lee, L; Kerr, JR; Keung, MM;
Indirizzi:
Singapore Eye Res Inst, Singapore 168751, Singapore Singapore Eye Res Inst Singapore Singapore 168751 pore 168751, Singapore Paterson Burn Optometrists, Hamilton, New Zealand Paterson Burn Optometrists Hamilton New Zealand , Hamilton, New Zealand
Titolo Testata:
OPTOMETRY AND VISION SCIENCE
fascicolo: 2, volume: 78, anno: 2001,
pagine: 113 - 121
SICI:
1040-5488(200102)78:2<113:TSOTPF>2.0.ZU;2-#
Fonte:
ISI
Lingua:
ENG
Soggetto:
VISUAL-ACUITY MEASUREMENT; VISION; REPEATABILITY;
Keywords:
visual acuity; logarithm of the minimum angle of resolution; probit analysis; psychometric function slope; termination rules;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Clinical Medicine
Citazioni:
21
Recensione:
Indirizzi per estratti:
Indirizzo: Carkeet, A Singapore Eye Res Inst, 11 3rd Hosp Ave, Singapore 168751, Singapore Singapore Eye Res Inst 11 3rd Hosp Ave Singapore Singapore 168751
Citazione:
A. Carkeet et al., "The slope of the psychometric function for Bailey-Lovie letter charts: Defocus effects and implications for modeling letter-by-letter scores", OPT VIS SCI, 78(2), 2001, pp. 113-121

Abstract

Background. Visual acuity measurement often results in an imprecise endpoint because subjects correctly identify some but not all of the letters on one or more size levels on a letter chart. The extent of this transition zone from seeing to nonseeing can be described by probit size, which is calculated by performing Probit Analysis on letter chart data. There has been no previous research into the effects of optical defocus on letter chart probit size. Methods. We tested 18 young visually normal subjects monocularly during three different defocus conditions: best spectacle correction (zero defocus) and +1.00 D and +2.00 D additions. Stimuli were Bailey-Lovie-style logarithm of the minimum angle of resolution (log MAR) letter charts constructed with a 0.05 logMAR size progression between size levels. Frequency of seeing data from these charts were used to calculate probit size. Results. There were statistically significant effects of optical defocus on mean probit size. After Monte Carlo correction for bias, we believe that true mean values for probit size are about 0.07 logMAR for well-corrected subjects and up to 0.12 logMAR with optical defocus. Conclusion. The smaller probit size for well-corrected subjects should correspond to a sharper logMAR visualacuity endpoint and less intrasubject variability in logMAR acuity than for subjects with a larger probit size (optical defocus). Our modeling shows that these different probit sizes can also significantly affect letter-by-letter visual acuity scoring.

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Documento generato il 04/04/20 alle ore 08:15:30