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Yesa Yang, Caterina Ripamonti, Neruban Kumaran, Angelos Kalitzeos, Navjit Singh, James Tee, James W B Bainbridge, Michel Michaelides; Quantification of color vision impairment in RPGR-associated Retinitis Pigmentosa. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2805.
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Disease-causing variants in RPGR (retinitis pigmentosa GTPase regulator) account for 70-90% of cases of X-linked Retinitis Pigmentosa (RP) and is currently the subject of multiple ongoing clinical trials. We sought to determine the extent of cone function impairment by assessing color discrimination.
Twenty four subjects (23 adults, 1 child; aged 14 – 35) with RPGR-associated RP were assessed using the Trivector component of the low vision version of the Cambridge Colour Test (lvvCCT). Contrast sensitivity (CS) using the Pelli-Robson chart and best corrected visual acuity (BCVA) were also evaluated. A subset of 15 subjects additionally undertook testing with the Ellipse component of the lvvCCT and the American Optical Hardy Rand Rittler (AO-HRR) plates. Tests were performed monocularly in both eyes and repeated three times.
Testing with lvvCCT demonstrated a wide range of color discrimination abilities in the study group, from near normal to severe impairment. The median saturation threshold along the protan, deutan and tritan axes, as assessed by the Trivector assessment were: 19.8, 21.4 and 55.7 respectively. The median ellipse area was 2212.7. (For comparison, a normal trichromatic subject has a saturation threshold of less than 10 in all three axes and ellipse area smaller than 340.)Color discrimination along the tritan axis was the most severely affected, indicated by both lvvCCT components used.Out of the three axes, saturation threshold along the tritan axis correlated most strongly with both BCVA [Pearson correlation coefficient (PCC) =-0.69, p<0.001] and CS (PCC= -0.74, p<0.001). PCC for ellipse area with BCVA and with CS was -0.57 (p=0.026) and -0.66 (p = 0.007) respectively.Both Trivector and Ellipse assessments also correlated with performance using AO-HRR plates, indicating consistency across methods [PCC of minimum -0.77 across three axes (p<0.001) and -0.81 (p<0.001)] respectively.
Both the Ellipse and Trivector components of the lvvCCT are able to identify mild to severe color vision impairment in a group of genetically confirmed RPGR-associated RP subjects. The preponderance of tritan axis impairment suggests early loss of S-cone function in the disease. The monitoring of color vision with such methods provides information about cone function and disease progression, which may prove useful when assessing the efficacy of novel therapies.
This is a 2021 ARVO Annual Meeting abstract.
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