Primary open-angle glaucoma, the cause of which is not fully understood, may be related to genetics and other factors. It is characterized by elevated intraocular pressure and a consistently open atrial angle, meaning that atrial outflow is obstructed by the trabecular meshwork Schlemm’s canal system.
The pathological changes found on histological examination include degeneration of collagen and elastic fibers of the trabecular meshwork, detachment or proliferation of endothelial cells, thickening of the trabecular meshwork, narrowing or occlusion of the meshwork, deposition of patchy material in the proximal tubular connective tissue beneath the inner wall of Schlemm’s canal, and reduction of vacuoles in the endothelial cells of the Schlemm’s canal wall.
Clinical manifestations
(A) Symptoms
The onset of the disease is insidious, except for a few patients who develop foggy vision and eye distention when the intraocular pressure is elevated, most patients may not have any conscious symptoms, often until the late stage, when the visual function suffers serious damage.
(II) IOP
Early manifestations are unstable and can sometimes be in the normal range. Measurement of 24-hour IOP makes it easier to detect IOP peaks and large fluctuations. The overall IOP level is mostly higher than normal. As the disease progresses, IOP gradually increases.
(C) Anterior segment
The anterior chamber is normal or deep, with a flat iris and an open atrial angle. Relative afferent pupillary disorders may be found when the degree of optic nerve damage is not uniform in both eyes. In addition, the anterior segment of the eye is mostly free of significant abnormalities.
(iv) Fundus
Glaucomatous optic disc changes are mainly manifested as.
1. Progressive enlargement and deepening of the disc depression.
2. Narrowing of the upper and lower confined disc rims, and an increase in the C/D value (cup-to-disc ratio, i.e., the ratio of the cup diameter to the optic disc diameter), or the formation of a tangent.
3, Eye optic disc depression asymmetry, C/D difference > 0.2.
4, Superficial linear hemorrhage on or around the disc.
5, Retinal nerve fiber layer defect.
Early glaucoma acquired optic disc changes and normal physiological large depressions are sometimes not easily distinguished. In recent years, a variety of fundus image analysis systems, such as confocal laser fundus scanning system and optic nerve analyzer, are used to evaluate early glaucomatous optic disc changes and to quantitatively detect and track relevant optic disc parameters such as disc rim area and cup volume, which help to detect fundus changes in glaucoma at an early stage.
Fundus image analysis systems can provide quantitative measurements of the optic disc, but the sensitivity and specificity in morphological identification have yet to be improved. A more valuable method for evaluating the optic disc in glaucoma is still high-quality simultaneous stereoscopic fundus photography.
(E) Visual function
Visual function changes, especially visual field defects, are important indicators for glaucoma diagnosis and disease assessment. A typical early visual field defect presents as an isolated paracentral dark spot and a nasal step. The paracentral dark spot is most often seen in the 5- to 5-degree range, above and below the physiologic blind spot. As the disease progresses, the paracentral dark spot gradually enlarges and deepens, and multiple dark spots fuse with each other and expand nasally, forming a bow-shaped dark spot around the center of gaze, while the peripheral visual field also narrows centripetally and merges with the paracentral defect to form a quadrant or hemianopsia-type defect.
In advanced stages, only the tubular visual field and the temporal visual island remain. Quantitative examination of light thresholds using a computerized automated visual field meter can reveal earlier glaucomatous visual field changes, such as diffuse or restricted light threshold increase and increased threshold fluctuation.
According to clinical observation, the morphological changes of the optic disc in most glaucoma patients appear before the visual field defects. One of the reasons for this inconsistency between morphological changes and functional changes may be that the existing visual field examination methods are not yet sensitive enough. In recent years, many scholars have devoted themselves to studying more sensitive visual field detection methods, such as blue-yellow visual field examination and graphic-resolution visual field examination, in order to detect visual field defects at a much earlier stage.
In the past, it was thought that glaucoma had little effect on central visual acuity because some patients with advanced, or even only tubular, visual fields could still retain a central visual acuity of about 1.0. In recent years, however, it has been found that in addition to visual field changes, glaucoma also impairs macular function, as evidenced by acquired color vision impairment, decreased visual contrast sensitivity, and certain electrophysiological indicators. However, abnormalities in these indicators are not as specific as visual field changes.
Primary open-angle glaucoma is usually bilateral, but usually manifests as bilateral IOP, optic disc, and visual field changes, as well as asymmetry of the pupil’s reflex to light, due to the different onset times in both eyes.