Designing a new “turtle” optotype for use with Aboriginal and Torres Strait Islander children

PURPOSE: To evaluate whether luminance-matching of non-target elements (Study 1) and incorporating artwork (Study 2) within the newly designed turtle optotype would impact visual acuity (VA) measures. METHODS: Study 1 evaluated the redesigned four alternative forced choice (4-AFC) turtle optotype to confirm whether luminance-matching of the non-target and target elements was required, through comparing VA with different turtle optotype luminance designs to the Landolt C. Study 2 evaluated whether including artwork in the turtle optotype impacted on VA as compared with the Landolt C chart. RESULTS: In Study 1 (n = 12, mean age = 34.9 ± 5.7 years), there was a significant effect of chart type (p < 0.001), where VA was significantly better in the non-luminance-matched design (M = -0.31 logMAR) compared to either of the luminance-matched designs (M = -0.09 logMAR) and the Landolt C (M = -0.13 logMAR) which were not significantly different from one another (p > 0.4). In Study 2 (n = 14, mean age = 29.1 ± 8.8 years), including the new artwork did not affect VA (p = 0.5); mean VA of the new 4-AFC turtle optotype (M = -0.10 logMAR) was not significantly different to the Landolt C (M = -0.13 logMAR). CONCLUSIONS: Findings confirmed that the optotype target needed to be luminance-matched with non-target elements and that new co-designed artwork could be incorporated without a significant effect on VA. Further work will validate the chart in children.