Practice Effects and the Lanthony D15

Recent studies have shown that subjects with congenital colour vision deficiency (CVD) can pass the saturated Farnsworth D15 (FD15) through practice. The Lanthony D15 (LD15) uses desaturated colours and is a difficult test even for patients with mild CVD. This study investigated if subjects could improve their performance on the LD15 with intentional practice.

Twenty-one male subjects (mean/SD age = 30.2/8.9 years) with congenital CVD were enrolled in the two-visit study. Their CVD status was evaluated with colour vision book screening, anomaloscope, and FD15 tests. The recruited subjects completed four trials of the LD15 at the baseline visit. Once all data collection was completed at the first visit, it was revealed to the subjects that the correct cap order could be determined by viewing the undersides of the caps. The subjects were given an LD15 test kit to practice at home to improve their performance before returning for a second visit. At the second visit, subjects performed another four trials of the LD15. The colour confusion indices for each trial were recorded for both visits, and the average values were used in paired t-tests to determine if significant improvement occurred.

A significant decrease in colour confusion index (CCI) of 0.51 (visit 1 mean/SE = 3.75/0.20; visit 2 mean/SE = 3.23/0.24) between the two visits was observed (p = 0.01). Further, subjects with deutan deficiency showed a significant (p = 0.003) decrease, whereas subjects with protan deficiency did not (p = 0.88).

Despite an already challenging test, this study showed that subjects with congenital red-green CVD can improve their performance on the Lanthony D15 test. However, this is unlikely to change pass-fail rates when the baseline CCI is high, and further study on this issue is warranted.