Unique characteristics of two types of retinitis pigmentosa patients with different rod sensitivities

Purpose: To determine the psychophysical differences between two types of retinitis pigmentosa (RP) patients with different rod sensitivities. Methods: Thirty-five RP patients with a visual acuity of ≥0.7 or better were classified by cone-rod perimetry into type 1, those with undetectable rod sensitivity, and type 2, those with measurable rod sensitivity. Their symptoms, age at onset of symptoms, cone and rod sensitivity, and full-field electroretinograms (ERGs) were compared. Results: The age when the symptoms of night blindness were first noticed was 13.1 ± 3.3 years (mean ± SD) for type 1 and 34.5 ± 14.4 years for type 2 patients (P = 0.0001). One of nine type 1 patients (11%) and 10 of 26 type 2 patients (38%) did not have any symptoms of night blindness. The average rod sensitivity within the central 10° was 43.7 ± 12.0dB for type 2 patients with night blindness, and 54.8 ± 6.4dB for type 2 patients without night blindness (P = 0.014). One of nine (11%) type 1 patients and 9 of 23 (39%) type 2 patients had recordable ERGs (P = 0.13). Conclusions: These findings indicate that the two types of RP patients, distinguished by their rod sensitivity, have different psychophysical characteristics of the visual system. The course of the disease process and the long-term prognosis for these two types of patients are different.