Purpose: To report the findings in two patients with unilateral cone-rod dysfunction with the a-wave larger than the b-wave, i.e., negative-type, full-field electroretinogram (ERG).
Methods: Standard ophthalmological examinations were performed including the medical history, measurements of the best-corrected visual acuity and intraocular pressures, slit-lamp biomicroscopy, ophthalmoscopy, spectral-domain optical coherence tomography, fundus autofluorescence, fluorescein angiography, and perimetry. ERG examinations were carried out with the ISCEV standard. Immunoblot analysis using the patient's sera was performed to determine the presence of the recoverin1 antibody.
Results: The common findings in these two patients were: unilateral, male sex, sudden onset of photophobia or a reduction in the vision at an advanced age, preserved visual acuity, no complaint of night blindness, normal fundus appearance, negative-type dark-adapted 3.0 ERGs with reduced a-wave amplitudes, absent light-adapted 3.0 ERGs, and very reduced but recordable dark-adapted 0.01 ERGs. In addition, the multifocal ERGs in all areas except that in a hexagonal area within a 2.5° radius of the fovea were very reduced. Patients with similar findings have been reported earlier, but the subnormal a-wave of the dark-adapted 3.0 ERGs and extensive morphological alterations of the retina in the posterior pole in the OCT images were different from those of the reported patients. The OCT images showed an indistinct interdigitation zone and discontinuous ellipsoid zone. Anti-recoverin antibodies were not detected.
Conclusions: Negative ERGs with severely reduced cone and rod components suggest that both the cone and rod bipolar cell visual pathways may be disturbed. Slightly decreased a-wave suggests minor abnormality of photoreceptors. It is important to determine whether these patients represent a new clinical entity or a phenotypic variation of an already described retinal disorder.
Keywords: Cone-rod dysfunction; Negative ERG; Normal fundus; Normal visual acuity; Subnormal a-wave; Unilateral.