Electro-oculography in albinos

Function of the Retinal Pigment Epithelium in Patients With Neurofibromatosis Type 1

Purpose

Retinal and choroidal abnormalities in neurofibromatosis type 1 (NF1) remain poorly studied. It has been reported, however, that the function of the retinal pigment epithelium (RPE) in NF1 was abnormal, with a supra-normal Arden ratio of the electro-oculogram (EOG). This study aims to evaluate the function of the RPE, using EOG, first in patients with NF1 compared to controls and second in patients with NF1 with choroidal abnormalities compared to patients with NF1 without choroidal abnormalities.

Methods

This prospective case-control study included 20 patients with NF1 (10 patients with choroidal abnormalities and 10 patients without) and 10 healthy patients, matched for age. A complete ophthalmologic assessment with multimodal imaging, an EOG, and a full-field electroretinogram were performed for each included patient. The main outcome measured was the EOG light peak (LP)/dark trough (DT) ratio.

Results

The LP/DT ratio was 3.02 ± 0.52 in patients with NF1 and 2.63 ± 0.31 in controls (P = 0.02). DT values were significantly lower in patients with NF1 than in controls (240 vs. 325 µV, P = 0.02), while light peak values were not significantly different (P = 0.26). No difference was found for peak latencies. No significant correlation between the surface and number of choroidal abnormalities and EOG parameters was demonstrated.

Conclusions

This study confirms the dysfunction of the RPE in patients with NF1, involving a lower DT and a corresponding higher LP/DT ratio. We hypothesize that this pattern may be due to a dysregulation of the melanocytogenesis, inducing a disruption in Ca2+ ion flux and an abnormal polarization of the RPE.

Clinical electro-oculography

Electro-oculography (EOG), a retinal function test, indirectly records slow, light-induced changes in the potential difference between the anterior and posterior poles of the eye. EOG is a valuable clinical tool in diagnosis of tapetoretinal degenerations, vitelliform foveal dystrophy including the carriers of this disease, retinal intoxications and in differential diagnosis of choroidal malignant melanomas. EOG is not an alternative to electroretinography but yields additional information on the function of the retinal pigment epithelium. The main drawback of the present technique is the high inter- and intraindividual variability of the results.

Retinal function in X-linked ocular albinism (OA1)

PURPOSE

To characterize retinal function in human recessive X-linked ocular albinism (OA1) across the normal lifespan.

METHODS

Retinal function was evaluated in 14 OA1 patients (ages 11 to 71 years) and five obligate carriers (ages 41 to 50 years) and compared to normal controls using full-field and multi-focal electroretinograms (ERG and mERG, respectively) and electro-oculography (EOG).

RESULTS

No consistent differences in ERG response parameters were observed when OA1 patients were compared as a group to normal controls. A trend in the direction of better correlations of response parameters with age was, however, observed in OA1. EOG Arden ratios were normal or hypernormal for all patients, but were uncorrelated with age. Central retinal function measured with the mERG suggested a flat response topography with depressed macular function compared to normal controls.

CONCLUSIONS

Panretinal function in OA1 is within normal limits at all ages, consistent with previous reports in generalized albinism. The stronger correlations with age in OA1 may suggest a different rate of age-related change in OA1 compared to normal populations, but the precise nature of this change must await an appropriate prospective study. The topography of mERG amplitudes in OA1 is relatively flat across the central retina with a reduction in amplitude in the macular region consistent with anatomical studies demonstrating an underdeveloped macular region in albinism.

Copper metabolism in retinitis pigmentosa

Clinically and electrophysiologically confirmed cases of primary retinitis pigmentosa have been investigated regarding their copper metabolic state. It is observed that these patients show a normal or near normal serum copper concentration, very low plasma caeruloplasmin concentration, and a very high copper urinary excretion. A similarity between this condition and hepatolenticular degeneration is drawn and it is suggested that retinitis pigmentosa may also be a condition caused by an inborn error of copper metabolism.

Normal values in clinical electrooculography. II. Analysis of potential and time parameters and their relation to other variables

The following EOG potential and time parameters from 72 normal subjects were analysed: base value B, dark trough D, light peak L, light induced potential rise L-D, interval between beginning of dark adaptation and occurrence of dark through d and interval between dark trough and light peak l. Their relations to sex, age pupillary diameter, degree of iris pigmentation, refractive error, axial length, corneal curvature and diameter, ocular protrusion and interpupillary distance were assessed. Right eye and left eye samples of the EOG parameters were congruent, although individual differences were sometimes appreciable. The levels of B and D were higher in the female half of the sample. A positive correlation existed between age and D level. L-D was negatively correlated to the degree of refractive error and positively correlated to the ocular protrusion. A positive correlation was found between d and the four potential parameters, and there was a positive correlation between age and l. Practical consequences of the statistical analysis relating to the interpretation of such EOG data are discussed.