POSTRECEPTORAL CONTRIBUTION TO MACULAR DYSFUNCTION IN RETINITIS-PIGMENTOSA

Purpose. To understand the sites of macular dysfunction in retinitis p igmentosa by evaluating focal electroretinogram (FERG) fundamental and second harmonic components, which are dominated by the activity of th e outer and inner retina, respectively. Methods. FERGs were recorded i n response to a uniform field (9 degrees X 9 degrees) flickered sinuso idally at either 8 Hz or 32 Hz. The fundamental components of the resp onses to bath the 8-Hz and 32-Hz stimuli and the second harmonic of th e response to the 8-Hz stimulus were measured in their amplitudes and phases. Normal subjects (n = 17), as well as patients with typical ret initis pigmentosa (n = 22), cone dystrophy (CD, n = 7) and X-linked co ngenital retinoschisis (XLR, n = 5) served as subjects. The fundamenta l (32 Hz)-second harmonic (8 Hz) amplitude ratio was taken as an index of the relative function of outer-inner lavers of the macula. Results . Compared to controls, patients with retinitis pigmentosa showed loss es of both FERG fundamental and second harmonic and an increase of the fundamental-second harmonic ratio. Patients with CD also showed losse s of both fundamental and second harmonic, but the fundamental-second harmonic ratio was normal. Patients with XLR had a selective loss of t he second harmonic, resulting in an increased fundamental-second harmo nic ratio. On average, the fundamental-second harmonic ratio of patien ts with retinitis pigmentosa tended to increase with age. Conclusions. The results suggest that in retinitis pigmentosa, both receptoral and postreceptoral sites contribute to macular dysfunction. This differs from CD and XLR, where losses appear more selective for the outer and the inner retina. Postreceptoral losses in retinitis pigmentosa may be come larger with increasing age.