Eye movement abnormalities in carriers of blue-cone monochromatism.

PURPOSE Although impaired color vision and ERG changes have been detected in carriers of blue-cone monochromatism (BCM), no eye movement abnormalities have been identified. Quantitative eye movements of three obligate carriers of BCM were analyzed. METHODS Horizontal and vertical eye movements of three obligate carriers of two families with BCM with visual acuity of 20/20 or better were recorded using the magnetic search coil technique. Subjects were examined fixing in primary and eccentric gaze and during horizontal and vertical smooth pursuit at 20 degrees, 40 degrees, and 80 degrees per second. RESULTS All carriers displayed fixation instability. In two subjects, fine-amplitude upbeat, jerk-type nystagmus was detected. Reduced pursuit gain was found in the carriers. The third subject had small downbeat nystagmus. CONCLUSION Abnormal eye movements are described for the first time in carriers of BCM. The nystagmus is clearly distinct from congenital or latent nystagmus and is similar to the nystagmus reported in BCM. Because all carriers had excellent visual acuity, in BCM, nystagmus is intrinsic to the disease and can appear independently of the visual defect.