Unilateral retinitis pigmentosa and cone-rod dystrophy

Abstract

Purpose: The purpose of this paper is to report 14 new cases of unilateral retinitis pigmentosa and three new cases of cone-rod dystrophy and to compare the similarities and dissimilarities to those found in the bilateral forms of these disorders.

Methods: A total of 272 cases of retinitis pigmentosa and 167 cases of cone-rod dystrophy were studied by corneal full field electroretinograms and electrooculograms. The student t-test was used to compare categories.

Results: The percentage of familial and nonfamilial cases was the same for the bilateral and unilateral forms of the disease. In our series, unilateral retinitis pigmentosa makes up approximately 5% of the total population of retinitis pigmentosa, while unilateral cone-rod dystrophy makes up only about 2% of the total. In the familial forms of unilateral retinitis pigmentosa the most common inheritance pattern was autosomal dominant and all affected relatives had bilateral disease.

Conclusion: Unilateral retinitis pigmentosa and cone-rod dystrophy appear to be directly related to the more common bilateral forms of these disorders. The genetic mechanisms which account for asymmetric disorders are not currently understood. It may be a different unidentified mutation at a single loci or it is possible that nonlinked mutations in multiple loci account for this unusual disorder.

Keywords: age of onset; correlations; nonlinked mutations; unilateral cone-rod dystrophy; unilateral retinitis pigmentosa.

Figure 1

Retinal photograph OS showing widespread pigmentary clumping (boney spicule changes) in the peripheral fields and attenuation of the vessels. OD was perfectly normal.

Figure 2

Electroretinogram shows normal responses OD and an absent response OS to blue flash. White flash in both the dark-adapted and light-adapted states have marked reduced a- and b-waves with prolonged implicit times. This pattern is consistent with moderately advanced retinitis pigmentosa with the rod responses being more affected than the cones. The electrooculogram shows a normal light response OD and no response to light OS. These results confirm severe damage to the retinal pigment epithelial layer.

Figure 3

Electroretinogram and electrooculogram in a more advanced case of unilateral retinitis pigmentosa. In this example the affected eye is OD, where no responses to any stimuli elicited. OS has normal responses in both the dark-adapted and light-adapted states. The electrooculogram demonstrates no response to light OD while OS has a normal response to light.

Figure 4

Electroretinogram and electrooculogram in one of the individuals with unilateral cone-rod dystrophy. OS is the affected eye and shows residual rod function to white flash in the dark-adapted state. The a- and b-waves are reduced in amplitude and the implicit times prolonged. The b-wave is poorly formed, reduced in amplitude and has a prolonged implicit time to 30 Hz white flicker. White flash in the light-adapted state shows abnormally small a- and b-waves with prolonged implicit times. The electrooculogram demonstrates no response to light OS and a normal response OD.