Evaluation of clinical validity of the Rabin cone contrast test in normal phakic or pseudophakic eyes and severely dichromatic eyes

PURPOSE To evaluate the clinical validity of the Rabin cone contrast test (RCCT; Innova Systems, Inc.) in patients with normal phakic/pseudophakic eyes and severe dichromatic colour vision deficiency (CVD). METHODS We evaluated age-related changes in the RCCT scores in 166 phakic eyes and 34 pseudophakic eyes and the RCCT sensitivity and specificity in 28 men with severe dichromatic CVD (10 with protanopia, 18 with deutanopia) and nine age-matched controls. All participants had 20/20 or better Snellen best-corrected visual acuity (BCVA). The RCCT was used to measure the L, M and S-CCT scores (range, 0-100). RESULTS In normal phakic eyes, the mean L, M and S-CCT scores decreased gradually with ageing, with normal levels in patients in the second to seventh decades of life and some below normal in the eighth and ninth decades of life. In normal pseudophakic eyes, the mean L, M and S-CCT scores were normal in patients in the seventh to ninth decades of life. In eyes with severe CVD, the mean L, M and S-CCT scores were, respectively, 31.5 ± 18.3, 86.0 ± 12.6 and 98.0 ± 6.3 in patients with protanopia; 92.8 ± 10.5, 50.8 ± 19.6 and 97.8 ± 5.2 in patients with deutanopia; and 99.4 ± 1.7, 98.3 ± 5.0 and 99.4 ± 1.7 in controls. The RCCT sensitivity and specificity were 100% for diagnosing the CVD type. CONCLUSION The RCCT can be used in non-visually impaired patients up to the seventh decade of life and after cataract surgery in elderly patients. The RCCT is available for CVD screening and typing and the score has a wide distribution range even in patients with severe CVD.