Criteria for Progression of Primary Open-Angle Glaucoma Based on the Study of Neurophysiological Mechanisms of Glaucoma Development

Abstract

Primary glaucoma is a disease causing the greatest number of vision-related problems. The latest clinical research methods such as scanning laser polarimetry and optical coherence tomography measure structural changes at different functional levels of the retina and the optic nerve. The studies of the optic nerve head, the peripapillary retinal nerve fiber layer and the macula area are considered as informative ones. According to literature data, structural changes in progressive glaucomatous optic neuropathy occur prior to apparent functional and clinical manifestations of the disease, however, this statement is true until the peripapillary retinal nerve fiber layer thickness is less than 72 mcm. Retinal ganglion cells are known to reduce in number with age (by 5,000 a year). In optical coherence tomography of glaucomatous eyes a scan of the macula is recommended to be performed using the Fast Macular Thickness Map protocol; it allows detecting the additional information on the pathological process. Neurophysiological methods - visual evoked potentials and electroretinography – allow us to study the processes in the visual cortex of the brain and at different morphofunctional levels of the retina as well as to clarify the localization and nature of pathological changes in the above-mentioned structures of primary damage at various stages of the glaucomatous process.

The objective of the research was to determine diagnostically significant criteria for the progression of primary open-angle glaucoma based on the study of neurophysiological mechanisms of glaucoma development.

Materials and methods. Complex clinical and neurophysiological study of eyes of 144 patients (274 eyes) with primary open-angle glaucoma was performed at the Filatov Institute of Eye Diseases and Tissue Therapy of National Academy of Medical Sciences of Ukraine. The main group included 59 (51.75%) females and 55 (48.08%) males with different stages of the glaucomatous process. The average age of patients was 58.41±3.96 years. Neurophysiological methods - visual evoked potentials (both flash and checkerboard type) and electroretinography using a RETI-scan multifocal ERG system (Roland Consult, Wiesbaden, Germany) - were used to diagnose the pathological condition.

Results. There were established criteria for the progression of primary open-angle glaucoma considering neurophysiological indicators: the reduction in the bioelectrical activity of retinal ganglion cells according to the amplitude of the N75-P100 peaks and the elongation of the P-100 latency when using visual evoked potentials elicited by checkerboard stimuli; the reduction in the bioelectrical activity and the elongation of latency according to the characteristics of the a- and b-waves in photoreceptor cells and second-order neurons of the retina when using electroretinography. Pathological changes in the external, internal and deep retinal layers were found to occur simultaneously at all the stages of the glaucomatous process since the initial one. They are progressive and significantly expressed in the cell body of the third-order neuron of ganglion cells.