Assessment of Cone Functions in Congenital Retinoschisis by Multifocal ERGs and Flicker Perimetry

Abstract

Abstract: : Purpose: To evaluate cone functions in the macula and periphery in patients with X–linked recessive retinoschisis (XLRS). Methods: We studied multifocal electroretinograms (mfERGs) from 16 eyes (16 patients) and critical flicker frequency (CFF) from 34 eyes (34 patients). The central 40°–diameter stimulus array of mfERGs consisted of 61 scaled hexagons. CFF was recorded at the center of the field and toward the periphery up to 60° on four meridians. The eyes were grouped into two, based on the fundus appearance; Type 1: macular abnormality without peripheral retinoschisis; Type 2: macular abnormality and typical ballooning peripheral retinoschisis. In type 1, 5 eyes and 13 eyes, in type 2, 11 eyes and 21 eyes were tested for mfERG and CFF, respectively. Results: The amplitudes and implicit times of the summed first–order kernels for 61 local responses in type 1, type 2 and normal control, were 10.8±2.8, 8.0±3.1 and 18.6±6.3 µV; 38.5±2.5, 41.4±3.7 and 31.3±1.3 milliseconds, respectively. The responses of type 1 and type 2 were significantly reduced in amplitude and delayed when compared to normal control, but there were no significant differences between the two types. However, the response densities at three eccentric half rings in the upper and lower field and the nasal and temporal field showed a difference between the two types. Type 1 were significantly reduced in amplitude in upper and temporal field, while type 2 showed a significant decrease in all fields. The mean normalized values of CFF were decreased at all visual fields in both types, especially more in the center of retina (71±13 % in type 1 and 53±16 % in type 2). Type 2 showed significant decrease in the CFF at the center of the retina and 20° upper, 40° lower, 20° nasal and 40° nasal from center when compared to type 1. Conclusions: These results represent a direct proof that the functional defect is diffuse and widespread even in the eyes whose visible fundus abnormalities were limited to the macula in this disease. The mfERGs and CFF are useful in understanding the location and degrees of abnormality in congenital retinoschisis.

Keywords: electroretinography: clinical • perimetry • macula/fovea