Multifocal ERG Reveals Several Patterns of Cone Degeneration in Retinitis Pigmentosa with Concentric Narrowing of the Visual Field Ma´rta Jana´ky, 1 Andrea Pa´lffy, 1 Andrea Dea´k, 1 Mo´nika Szila´gyi, 1 and Gyo¨rgy Benedek 2 PURPOSE. To analyze multifocal ERGs (mfERGs) in patients with retinitis pigmentosa (RP), with constricted visual fields and visual acuity satisfactory for steady fixation. METHODS. The mfERGs of 86 eyes of 43 patients with various forms of inheritance and durations of RP were analyzed. A retinal scanning system with a 20-in. monitor was used to map central cone function. Electrical signals of the retina were detected by using DTL fiber electrodes. RESULTS. The site of the best response density of the mfERGs in the patients with RP was found in a central or eccentric position of the trace array. Depending on the position of the best response density in the two eyes, the patients were cate- gorized into three groups. In the first group, the best response density was recorded from the central hexagon in both eyes, producing a central peak surrounded by very low responses in the three-dimensional presentation. In the second group of patients, the best responses were found to correspond to the central hexagon on only one side. In the fellow eye, however, the best response density appeared to be in an eccentric position. The patients in the third group did not present a central peak in the mfERG on either side. In scattered parts of the trace arrays, several acceptable responses were observed in all three groups that might represent patches of functioning retinal cone receptors. CONCLUSIONS. The results suggest highly variable central re- sponses and groups of cones with preserved function in areas previously considered nonresponsive. The high variability of the central responses could be a result of variable foveal cone density, with differences in inheritance- and duration-related cone degeneration at the time of the examination. The authors stress the value of step-by-step analysis of the trace array of the mfERGs, which can reveal the still-functioning groups of cones. (Invest Ophthalmol Vis Sci. 2007;48:383–389) DOI: 10.1167/iovs.06-0661 R etinitis pigmentosa (RP) is a hereditary, progressive retinal photoreceptor dystrophy in which the final consequences of cone degeneration on the central vision are rather variable. Some patients maintain good visual acuity throughout life al- though their full-field electroretinograms (ERGs) are not mea- surable, and the visual field is constricted to 5° to 10°. Others, however, lose central vision, even at a young age, and are therefore much more disabled. 1 These observations are in line with the widely held notion that RP is not a homogenous disease; instead, it can reveal differing manifestations. Several morphologic, 2–4 psychophysical, 5–7 and electrophysiologi- cal 8,9 studies have been performed to reveal the course and nature of the photoreceptor loss in RP. The relationship be- tween visual abilities and electrophysiological indicators seems to be an important practical problem in the follow-up of pa- tients with RP. It is well known that the full-field ERG (i.e., the gross electrical response of the retina) can be extinguished in the early stage of the disease, when the central visual acuity is still entirely preserved. 10,11 Because the traditional ERG does not seem to be sensitive enough to indicate the condition of the central retina, other methods have been sought. First, several attempts were made to use focal electroretinography for esti- mation of the residual function of the central retina in RP. 9,12 These techniques, however, require special procedures to min- imize the effect of stray light, and in addition it is rather time-consuming to obtain responses from more than one re- gion. The multifocal (mf)ERG technique, which allows a high- resolution mapping of the macular area of the retina, 13 initially seemed to be a more promising method for detection of the remaining foveal cone function in some patients with RP. The first experiences obtained with this method, however, showed that there were no detectable mfERG responses in a substantial proportion of patients with RP, even if they had good visual acuity. 14 –17 Most of the later investigators introduced rather strict inclusion criteria for participation in their mfERG studies. Nonetheless, mfERG alterations reflecting a progressive con- striction of the visual field and generally regarded as typical of RP were found in only a proportion of the recordings. For example, only 27 (71%) of the selected 38 patients produced a recordable, “typical” mfERG in the study performed by Seeliger et al. 14 This result raises the question of the sensitivity of the method. It is rather difficult to regard an alteration as typical if it is found in only a proportion of patients with RP. Difficulty in maintaining fixation during recording is unlikely to have been the cause of the abnormal responses, because these patients were young and had good visual acuity. Alternatively, the insufficient sensitivity of the method could be responsible for its ineffectiveness in detecting residual function in this hereditary retinal degeneration. Finally, the solution of this problem could lie in the peculiar characteristics of the degen- erating cone receptors. In a search for the answers to these questions, we analyzed the mfERG recordings of all our pa- tients with RP who had sufficient visual acuity to maintain fixation. To cover the whole patient population, we analyzed the responses irrespective of whether they were of good or poor quality. Another difference relative to the earlier studies is that we repeated the stimulation monocularly in the cases in which the best responses were not in the central position (31st hexagon). From the Departments of 1 Ophthalmology and 2 Physiology, Fac- ulty of Medicine, University of Szeged, Szeged, Hungary. Supported by Grant OTKA/Hungary T042610. Submitted for publication June 15, 2006; revised August 23, 2006; accepted October 16, 2006. Disclosure: M. Jana´ky, None; A. Pa´lffy, None; A. Dea´k, None; M. Szila´gyi, None; G. Benedek, None The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked “advertise- ment” in accordance with 18 U.S.C. §1734 solely to indicate this fact. Corresponding author: Ma ´rta Jana ´ky, Department of Ophthalmol- ogy, H-6720 Szeged, Kora ´nyi rkpt. 10-11, Pf: 427, Hungary; janaky@opht.szote.u-szeged.hu. Investigative Ophthalmology & Visual Science, January 2007, Vol. 48, No. 1 Copyright © Association for Research in Vision and Ophthalmology 383 Downloaded from iovs.arvojournals.org on 06/07/2020