Abstract
Abstract: :
Purpose: We tested the hypothesis that multifocal ERG (mfERG) amplitude losses in patients with progressive cone dystrophy (CD) are due to a selective ON–system deficit (1). In previous research (2), we found a non–selective loss of both ON– and OFF–responses using the VERIS system (EDI); however, this technique used a CRT stimulus which did not produce continuous on stimulation (3). In the current study, long–duration LED stimuli (RETIscan, Roland Instruments) were used to examine local ON– and OFF–responses. Methods: Nine patients with CD participated in this study (mean age of 34.4 and visual acuity > 20/200). The control group consisted of ten age–similar observers. Humphrey threshold fields were obtained for 61 positions (corresponding to the mfERG array). Following pupil dilation, mfERGs to long duration stimuli were recorded using the RETIscan stimulator (Roland Instruments). The display contained 61 scaled hexagons and was 45 degrees in diameter. The LEDs were on for 100 msec (180 cd/m2) and off for 100 msec. The mfERGs were obtained using an m–sequence and two eight–minute recordings were averaged. In addition, standard full–field photopic and flicker ERGs were recorded using Ganzfeld stimulation. Results: For all patients, visual field sensitivity was reduced at all retinal locations; the amount of threshold elevation averaged 0.7 log units. For the LED mfERGs, the control subjects had a single ON–response peaking at 36 ms and two OFF–responses, peaking at 122 ms and 151 ms. For the patients, the ON–response amplitude was reduced by an average of 0.97 log units, the first OFF–response was reduced by an average of 0.61 log units, and the second OFF–response was reduced by an average of 0.12 log units. The full–field single flash ERG was reduced in amplitude by 0.6 log–units and the 30 Hz flicker was reduced by 0.56 log–units. Conclusions: We found amplitude losses in ON– and OFF–responses in patients with CD; these losses were greater for the ON–system responses than for either of the OFF–responses. This latter finding differs from that obtained using a CRT stimulus. (1). Shinoda, et al. (2002) Acta Opthalmol Scan 80, 219 (2). Holopigian, et al. (2003) ARVO (3). Keating, et al. (2001) Doc Ophthalmol 102, 95.
Keywords: electroretinography: clinical • retinal degenerations: hereditary • visual fields