A comparison of two methods of logMAR visual acuity data scoring for statistical analysis

Abstract

The purpose of this study was to compare two methods of logMAR visual acuity (VA) scoring. The two methods are referred to as letter scoring (method 1) and line scoring (method 2). The two methods were applied to VA data obtained from one hundred and forty (N=140) children with oculocutaneous albinism. Descriptive, correlation andregression statistics were then used to analyze the data. Also, where applicable, the Bland and Altman analysis was used to compare sets of data from the two methods. The right and left eyes data were included in the study, but because the findings were similar in both eyes, only the results for the right eyes are presented in this paper. For method 1, the mean unaided VA (mean UAOD1) = 0.39 ±0.15 logMAR. The mean aided (mean ADOD1) VA = 0.50 ± 0.16 logMAR. For method 2, the mean unaided (mean UAOD2) VA = 0.71 ± 0.15 logMAR, while the mean aided VA (mean ADOD2) = 0.60 ± 0.16 logMAR. The range and mean values of the improvement in VA for both methods were the same. The unaided VAs (UAOD1, UAOD2) and aided (ADOD1, ADOD2) for methods 1 and 2 correlated negatively (Unaided, r = –1, p<0.05), (Aided, r = –1, p<0.05). The improvement in VA (differences between the unaided and aided VA values) (DOD1 and DOD2) were positively correlated (r = +1, p <0.05). The Bland and Altman analyses showed that the VA improvement (unaided – aided VA values) (DOD1 and DOD2) were similar for the two methods. Findings indicated that only the improvement in VA could be compared when different scoring methods are used. Therefore the scoring method used in any VA research project should be stated in the publication so that appropriate comparisons could be made by other researchers.

Keywords

• logMAR acuity
• Snellen acuity
• visual acuity scoring methods
• statistical analysis