Electrophysiological testing as a method of cone-rod and cone dystrophy diagnoses and prediction of disease progression.

Abstract

To determine the characteristics of patients with cone (CD) and cone-rod dystrophies (CRD) and to evaluate the changes in flash electroretinograms in both groups. The retrospective study involved 48 patients-34 with CRD and 14 with CD. The patients underwent full ophthalmological examination, including Goldmann perimetry and full-field flash electroretinogram (FERG) within the initial examination. These examinations were then repeated seven, or more, years later. The longest follow-up period was 10years, with the mean at 8.2years. During both examinations, we assessed the amplitudes of the b wave in the scotopic ERG test 0.01 (which reflects rod response), the maximal scotopic ERG test 3.0 (which reflects cone and rod response) and the photopic 3.0 ERG test (which reflects cone response). The results were then compared against normal values. The progression over time of ERG b wave amplitudes in the scotopic ERG 0.01, maximal scotopic ERG 3.0 and photopic ERG tests was assessed. There were significant differences in rod, maximal and cone responses, between CD and CRD patients. While rod responses were markedly decreased in CRD patients during their initial examination, the decrease in the rod function in both CD and CRD patients was similar in their follow-up examination (p=0.2398). Moreover, during initial examination, maximal responses were less common amongst CRD patients, over those with CD. Following the observation period, patients suffering from CRD exhibited a significant decrease in both maximal (p=0.0125) and cone (p=0.0046) responses. The clinical course of CRD and CD may vary; however, the latter appears to have a more favourable course than former. Although, at initial examination, the cone function was more diminished in CD patients, the final examinations reveal a more significant drop for CRD patients. Consequently, a differential diagnosis is essential for treating patients and forecasting their disease progression.