Screening for CMV retinitis using chromatic discrimination thresholds and achromatic contrast sensitivity

Background: Many patients with cytomegalovirus retinitis (CMVR) are unaware of visual disturbance so screening is advocated for patients with HIV and low CD4 counts. Many tests of retinal function have been recommended but few are effective at detecting CMVR. We assess the potential of chromatic discrimination thresholds and achromatic contrast sensitivity as screening tests for patients with CMVR. 

Method: 11 HIV+ patients with CMVR, 16 age matched HIV+ patients, and 29 age matched controls were recruited. Visual acuity, chromatic discrimination thresholds, and achromatic contrast sensitivity were measured. Fundal examination was performed by slit lamp biomicroscopy for HIV+ patients. Those with CMVR were photographed and the CMVR graded from the photographs. 

Results: Loss of chromatic discrimination was found in patients with CMVR (tritan p < 0.0005, red/green p < 0.05). The same group had deterioration in achromatic contrast sensitivity at 2.2, 3.4, and 10 cpd (p < 0.05). There was correlation between the zone of CMVR with chromatic gratings (tritan r = 0.83, p < 0.005). No statistically significant difference was found between the HIV+ patients and the controls for all tests (p > 0.1). 

Conclusions: HIV+ patients with CMVR have a loss of chromatic discrimination and achromatic contrast sensitivity and this may be used to screen HIV+ patients for CMVR.