Evaluation of contrast sensitivity in visually impaired individuals using K-CS test. A novel smartphone-based contrast sensitivity test-Design and validation

Background To describe the development and investigate the accuracy of a novel smartphone-based Contrast Sensitivity (CS) application, the K-CS test. Methods A total of 67 visually impaired and 50 normal participants were examined monocularly using the novel digital K-CS test and the Pelli-Robson (PR) chart. The K-CS test examines letter contrast sensitivity in logarithmic units, using eight levels of contrast from logCS = similar to 0,1 to logCS = similar to 2,1 at two spatial frequencies of 1.5 and 3 cycles per degree (cpd). The K-CS test was compared to the gold standard, PR test and intra-session test repeatability was also examined. Results The K-CS test in normally sighted was found to agree well with the PR, providing comparable mean scores in logCS (+/- SD) (K-CS = 1.908 +/- 0.06 versus PR = 1.93 +/- 0.05) at 1.5 cpd and mean (+/- SD) logCS at 3 cpd (K-CS = 1.83 +/- 0.13 versus PR = 1.86 +/- 0.07). The mean best corrected visual acuity of visually impaired participants was 0.67 LogMAR (SD = 0.21) and the K-CS was also found to agree well with the Pelli-Robson in this group, with an equivalent mean (+/- SD) logCS at 1.5 cpd: (K-CS = 1.19 +/- 0.27, PR = 1.15 +/- 0.31), 3 cpd: K-CS = 1.01 +/- 0.33, PR = 0.94 +/- 0.34. Regarding the intra-session test repeatability, both the K-CS test and the PR test showed good repeatability in terms of the 95% limits of agreement (LoA): K-CS = +/- 0.112 at 1.5 cpd and +/- 0.133 at 3 cpd, PR = +/- 0.143 at 1.5 cpd and +/- 0.183 in 3 cpd in visually impaired individuals. Conclusion The K-CS test provides a quick assessment of the CS both in normally sighted and visually impaired individuals. The K-CS could serve as an alternative tool to assess contrast sensitivity function using a smartphone and provides results that agree well with the commonly used PR test.