Development of Pocket Vision Screener and its effectiveness at screening visual acuity deficits

The aim was to construct a visual acuity chart and find its effectiveness at screening visual acuity deficits.

Two phases were involved in this study.Construction of the screener: Ten Sloan letters (C, D, H, K, N, O, R, S, V, and Z) were selected and the letters were constructed and reduced to 0.2 logMAR acuity size (6.92 mm) for viewing at 3 m. The screener contains three lines with seven letters in each. Few combinations of the seven letter sequences were chosen based on the row legibility scores. Three seven letter combinations close to the median of all combinations were selected, such that maximum difficulty score difference between the lines are <1%. Finding the effectiveness of the screener: 100 literate subjects with unaided visual acuity better than or equal to 6/60 were recruited for the study. Unaided visual acuity was tested using both the newly constructed Pocket Vision Screener and a logMAR visual acuity chart and the time taken to measure the visual acuity using both the charts was noted.

The mean age of the subjects was 43 ± 17 years. Subjects were classified as normal or deficient based on the logMAR visual acuity measurement. The screener was found to have 81% sensitivity, 94% specificity. The positive and negative predictive values were found to be 91% and 87%, respectively. A significant difference (P < 0.001) was found in the time taken to record visual acuity using both the charts.

The Pocket Vision Screener can be used as a quick and accurate tool to screen subjects for visual acuity deficits, being highly sensitive, specific, and cost-effective.