PIII and derived PII analysis in a patient with retinal dysfunction with supernormal scotopic ERG Subtitle: Retinal dysfunction with supernormal scotopic ERG

Purpose: To present electroretinographic (ERG) findings in a patient with retinal dysfunction with supernormal scotopic ERG, and to analyze rod and cone PIII components and rod inner nuclear layer (derived PII) responses. Patient: A Japanese 11-year-old girl complained of poor visual acuity. There was no parental consanguinity in her family. The corrected visual acuity was 0.7 in both eyes. No abnormal finding was observed in both fundi. Methods: The patient underwent full-field ERGs. Rod and cone a-waves were analyzed using photoreceptor models. The derived PII responses were analyzed using a technique described by Hood and Birch. Results: In the photopic ERG, responses to single flash and 30-Hz flicker were attenuated. In the scotopic ERG, b-wave was supernormal in amplitude in response to intense flashes, but smaller than normal and markedly delayed over a lower range of flash intensities. By the PIII analysis, phototransductions (values of S) of both rod and cone were remarkably decreased. The derived PII responses for this patient were larger than the responses for normal subjects, and the onset of the PII responses in this patient are significantly delayed compared to those in normal Page3, Tanimoto et al. subjects. Conclusions: The ophthalmological findings in this patient are consistent with previous publications of this disease. Although it has been reported that the sites of disease action were beyond the outer segment (values of S were within the normal range), our results suggest that photoreceptors could be involved in sites of disease action in at least some patients with this disease. Abbreviations: ERGelectroretinogram; cGMPcyclic guanosine monophosphate; Page4, Tanimoto et al. Introduction Cone dystrophy with unusual rod electroretinographic (ERG) findings was first reported in two siblings by Gouras et al [1]. The scotopic flash ERG b-wave was supernormal in amplitude in response to intense flashes, but smaller than normal and markedly delayed over a lower range of flash intensities. The rectangular shapes of the scotopic standard combined ERG a-wave were also peculiar in the patients. Since the first report, similar patients have been reported by several authors [2-8]. Hood et al [8] suggested that this disease could be called “supernormal and delayed rod ERG syndrome”. The pathophysiological mechanism of this disease still remains unknown. Because similar ERG changes to this disease had been reported from rod receptors in which intracellular level of cyclic guanosine monophosphate (cGMP) had been elevated [9-11], Gouras et al [1] suggested that the basis for the abnormalities in the rod ERG lie in the rod photoreceptors. On the contrary, Hood et al [8] suggested that the sites of disease action were beyond the outer segment, since there was no evidence for a delayed activation and deactivation of transduction of the outer segment. Here we report one patient with this disease, who showed different rod and cone functions from those by Hood et al [8]. Page5, Tanimoto et al. Patient A Japanese 11-year-old girl complained of a poor visual acuity. There was no family history of inherited eye disease, amblyopia, or nystagmus. There was no parental consanguinity in her family. Ophthalmological examinations: The corrected visual acuity was 0.7 in each eye, with optical correction (-0.5 axis 30, right eye; -0.75 axis 35, left eye). No nystagmus was observed. The cornea, lens, and vitreous were clear. No abnormal finding was observed in both fundi by an ophthalmoscope and by fluorescein angiography. Kinetic visual fields measured with a Goldmann perimeter showed mild constriction to V and I targets at intensity 4e. Color vision was abnormal with no specific axis (Farnsworth D-15). Electro-oculogram complied with the International Society for Clinical Electrophysiology of Vision (ISCEV) protocol [12] showed normal light rise (the ratio of light peak and dark baseline was 2.5 in the right eye and 2.6 in the left). The dark adaptation curve, examined with the Goldmann-Weekers adaptometer (HAAG-STREIT AG, Koelnz/Bern, Switzerland), showed normal timing of cone-rod break, although the cone threshold was slightly elevated by about 0.1 log unit and the final rod threshold was elevated by about 1 log unit (Figure 1). She has been aware of hemeralopia, although she denied nyctalopia. Physical examinations: The patient did not show any abnormalities on Page6, Tanimoto et al. general physical and neurological examinations. The serum cGMP level of this patient was within the normal range (2.4 pMOL/ml; normal range 1.8-4.8 pMOL/ml). Brain magnetic resonance imaging showed no abnormality. ---Figure 1 near here -----