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Arsineh Annalya Amirkhanian, Yliana Cetina, Michelle M Hammond, Bennett McAllister, Pinakin Gunvant Davey; Evaluation of Evans Letter Contrast Test and Pelli-Robson chart in assessing threshold contrast sensitivity. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1089.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast sensitivity can be an asset and “true” representation functional vision when compared to visual acuity measured using the high contrast Snellen or ETDRS acuity charts. The Pelli-Robson chart is utilized clinically worldwide and is a printed chart that requires external illumination. It has optotype of 20/700 when viewed at one meter, whereas, the Evans Letter Contrast Test (ELCT) is backlit chart and presents the ETDRS standard 20/630 at 1-meter. Given these differences we sought to evaluate and compare the threshold contrast as determined by the Evans Letter Contrast Test and Pelli-Robson chart in an ocular healthy population.
One hundred and forty eyes of 140 individuals (mean age 25.3 SD 3.02 years, range 21-44 years, 64 Males and 76 Females) were evaluated for the study purposes. All participants were free from any known ocular pathology and had best corrected visual acuity of 20/20 on a high contrast Snellen equivalent chart. All participants underwent testing using the Evans Letter Contrast Test and the Pelli-Robson chart by one of three trained observers (AAA, YC or MMH). The sequence of testing was randomized. The luminance of both these charts were set at 85 cd/m2. Both charts have three letters in each contrast sensitivity level and subjects had to read at least 2/3 letters correctly to be qualified for that contrast threshold. If they did not meet that criteria, the level above was recorded as the threshold.
The mean contrast threshold for Evans Letter Contrast Test and the Pelli-Robson chart were 2.025 and 1.932 (SD 0.17 and 0.07 respectively) which was significantly different (paired t-test t=7.58, p= 4.53 E-12). The mean values of Evans Letter Contrast Test and the Pelli-Robson chart was not different in males versus females (p=1.0 and 0.94 respectively). The Altman and Bland analysis shows that the Pelli-Robson chart on average has lower contrast threshold when compared to Evans Letter Contrast Test (bias= -0.093) and upper limit of agreement was + 0.192 and lower limit of agreement was -0.379.
The measured mean contrast threshold is significantly different when measuring with the between the Evans and Pelli-Robson charts and should not be used interchangeably.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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