Use of Neurophysiological Methods in Early Diagnosis of Primary Open-Angle Glaucoma
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Keywords

early diagnosis
visual evoked potentials
ganglion cells
primary open-angle glaucoma

Abstract

Glaucoma is a leading cause of irreversible vision loss. The study of structural and neurophysiological processes of the upper divisions of the visual analyzer in patients with primary glaucoma helps in detecting primary structural lesions in this pathology. The investigation of brain evoked potentials provides the most important information about the processes in the visual cortex of the brain, and the study of visual evoked potentials (VEP) provides us with the most valuable information. When performing a comparative evaluation of VEP responses for each eye good correlation between the obtained VEP parameters and the results of Humphrey perimetry is observed. It is well known that in clinical practice there are no specific neurophysiological tests for diagnosing glaucoma. However, neurophysiological examinations detect the changes which are asymptomatic for a remarkably long period of time until the occurrence of clinical manifestations quite often being especially important for early diagnosis of any glaucomatous process.The objective of the research was to study the appropriateness of using neurophysiological methods for early detection of primary open-angle glaucoma.Materials and methods. Complex clinical and neurophysiological study of both eyes of 186 patients (358 eyes) with primary open-angle glaucoma (POAG) and those whose diagnosis was still not clarified was performed at the Filatov Institute of Eye Diseases and Tissue Therapy of National Academy of Medical Sciences of Ukraine. The main group included 81 (51.92%) females and 75 (48.08%) males with different stages of the glaucomatous process. The average age of patients was 56.8±4.26 years. Neurophysiological methods - VEPs (both flash and checkerboard type) - were used to diagnose the pathological condition. The study of VEPs was performed using a RETI-scan multifocal ERG system (Roland Consult, Wiesbaden, Germany). Results. In patients with suspected glaucoma latency values of the N75 and P100 remained within the normal range in 96.1% (р<0.05) and 86.2% (р<0.05) of cases, respectively. When examining the N75-P100 and P100-N135 peaks an increase in the amplitude above the normal range (according to the standards of the equipment and the laboratory where the research was conducted) was observed in 78.6% (р<0.05) and 65.5% (р<0.05) of cases, respectively. The threshold for electrically induced phosphenes was within normal limits (65.61±7.32 Hz); the lability of the visual analyzer (phosphene electrical stimulation) increased by 13.63%, р<0.05 compared to the control group. In patient with mild glaucoma latency values of the N75 and P100 remained within the normal range in 86.4% (р<0.05) і 81.2% (р<0.05) of cases, respectively. When examining the N75-P100 and P100-N135 peaks an increase in the amplitude above the normal range was observed in 65.15% (р<0.05) and 58.14% (р<0.05) of cases, respectively. The threshold for electrically induced phosphenes was within normal limits (71.69±9.08 Hz); the lability of the visual analyzer (phosphene electrical stimulation) reduced by 9.63%, р<0.05 compared to the control group. In 78.4% of patients with suspected glaucoma the diagnosis of primary open-angle glaucoma was confirmed by clinical investigations 6 months and 1 year after the examination. Additional neurophysiological methods revealed more pronounced changes in the glaucomatous process in 34.80% of patients with mild glaucoma. They were included to the group of patients with advanced glaucoma. Optimal treatment tactics was applied. 
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