| Abstract |
Purpose: Detachment of the retina is an urgent situation for the patient, where it requires immediate treatment. In difficult detachments, vitrectomy with silicone oil is often performed as a dressing material. Previous studies, have seen reduced electrophysiological responses of retinal cells as long as there is silicone oil in the eye, which may be due to an insulating effect that generates this material. The purpose of this paper is to investigate the hypothesis that silicone oil causes isolation effects on photoreceptors and other retinal cells, by reducing their responses without affecting their full function and vision. For this reason, simultaneous recording of electrophysiological responses by retinal cells and ganglion cells which transferring visual information to the optic cortex will be performed.
Methodology: In the present study, responses were recorded using two electrodetecting techniques, ERG (electroreflectivity) and VEP (optical evoked potentials) in a flash stimulus. Flash ERG and flash VEP were recorded in 9 patients, with an average age of 63.56 ± 11.65 years before (1-2 days) and after (about 2-3 weeks) the removal of silicone oil in the study eye and in the another eye that was normal for most patients, except in cases where there was a cataract, as a control eye. The record of the flash ERG measurements, took place in photopic and scotopic conditions, while the flash VEP in photopic conditions. The recording of responses was done using common technology equipment, with some variations in the parameters of each technique (TOMEYBASE PRIMUS). Silicone oil removal surgery in all patients who participated in this study, was performed in the Ophthalmology Clinic of the University Heraklion General Hospital (PGNNH). The statistical analysis of the results and the correlations of the various parameters were made with the SPSS 23 for Windows data analysis package.
Results: From the comparison of the amplitude of the ERG responses in four conditions, - two photopic (flash, flicker flash) and 2 dark flash (flash flash) - statistically significant differences were found before and after removal of the silicone oil under all conditions. In the study eye, statistically significant differences (p <0.05) were observed for the responses with strong flash ERG in photopic and scoptic conditions, while in comparison of the change of the ERG flash response ratio between the two eyes, statistically significant differences in all circumstances. In photopic conditions, the mean ERG response of ratio for the eye control was 1.06 ± 0.44 while for the study 2.81 ± 1.41 with p = 0.003, under the same conditions the ratio of the ERG alternating flash responses was 0.93 ± 0.29 and 2.91 ± 2.49 respectively, with p = 0.03. In sciatic conditions, the back ratios for the reduced flash ERG responses before were 1.13 ± 0.58 for the control eye and for the study eye 1.82 ± 0.71 with p = 0.038, while in shadow conditions with strong flash, the corresponding values were 1.23 ± 0.63 and 5.68 ± 4.09, with p = 0.005. Subsequently, compared the amplitude and time of flash VEP response before and after silicone removal and statistically significant differences were observed for both of them, for control and study eyes. The same effect was obtained by comparing the variation in amplitude and the difference in the response time between two eyes, with a ratio of 1.02 ± 0.25 for the control eye and 1.18 ± 0.65 for the study eye, where p = 0.965, and difference 3.11 ± 4.14sec and 3.89 ± 3.86sec respectively, where p = 0.985.Conclusions: The present study demonstrates that materials such as silicone oil cause a reduction in responses from retinal cells while not affecting the responses recorded by the flash VEP technique. This confirms that, the reduced flash ERG response before silicone removal is not due to the silicone toxicity and poor functioning of the photoreceptors but to the insulation effect that creates this material as it exists in the eye.
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