Degeneration of axons of ganglion cells of the retina in glaucoma leads to an increase in the size of excavation and loss of the tissue of the neuroretinal girdle. Its average area is usually reduced in glaucomatous liscals compared to normal discs - this is a better indicator than the excavation / disc ratio when differentiating the early stages of glaucoma from a variant of the norm. The loss of the neuroretinal girdle can be focal or concentric.
The focal loss of the neuroretinal girdle often begins with a small localized defect in the contour of the inner edge of the excision, leading to a narrowing of the neuroretinal girdle.
This condition is called focal cavity or pit changes.
This defect may increase and lead to the development of breakthrough excavation. When narrowing to the edge of the optic nerve disk and the absence of the tissue of the neuroretinal girdle, marginal excavation appears. Vessels crossing the thinned ring sharply bend. This phenomenon is called forced bending, it is important in estimating the width of the girdle.
Concentric glaucomatous atrophy with increasing excavation in the form of concentric circles is sometimes more difficult to distinguish from physiological excavation. In this situation, you should remember the ISNT rule and the fact that normally the excavation is in the form of a horizontal, rather than a vertically oriented oval.
Symptom of lattice points
On the surface of the nipple of the optic nerve, the axons are strongly curved, leave the eye through the fenestrated connective tissue sheets or the trellis plate.
Deeper excavation of the optic nerve disk in glaucoma can lead to the transmission of holes in the trellis plate - a sign of latticed points. It is not clear whether the excavation depth in itself has any clinical significance.
Splintery or flame-like hemorrhages at the border of the optic nerve disk - Drans haemorrhage. These hemorrhages are considered an unfavorable prognostic sign for the development of glaucomatous optic neuropathy. Dranz haemorrhages are often observed in glaucoma with low intraocular pressure. They are associated with defects in the layer of nerve fibers, notches in the psyre retinal band and annular scotoma of the field of vision.
Defects of the layer of nerve fibers
Normally, the stratification of the retinal layer of nerve fibers during ophthalmoscopy is visible as light reflections from bundles of nerve fibers. Loss of axons retinal retinal ganglion cells in glaucoma leads to a loss of tissue neyoretinalnoy belt and defects of the visible layer of nerve fibers (SNV). The places of depletion of the retinal layer of nerve fibers are visible in ophthalmoscopy as dark wedge-shaped defects directed toward the edge of the optic nerve disk or affecting its boundaries. Defects of the layer of nerve fibers are best seen in green light or without red light. Their detection is used for early diagnosis of glaucomatous lesions. Nevertheless, this is not a pathognomonic sign of glaucomatous damage, since defects also appear in the eyes with optic neuropathy of a different origin.
Parapapillary chorioretinal atrophy
Parapapillary atrophy, especially in the beta zone, is often larger in the eyes with glaucomatous lesions. It correlates with the loss of the neuroretinal girdle. In the sector of its greatest loss, the maximum area of atrophy. Since parapapil-lar atrophy is less common in eyes with non-glaucomatous lesion of the optic nerve disc, its detection helps to distinguish gla-comatose optic neuropathy from non-glaucomatous.
Type of vessels
The type of vessels on the optic disc can help in assessing glaucomatous nerve damage. In addition to forced bending, some researchers consider the phenomenon of trestle as a sign of glaucomatous lesion. The sign of the flyover is enclosed in the overturning of vessels in the form of a bridge over a deeper excavation. With a progressive loss of the underlying tissue, the vessels lose support and look hanging over the empty excavation space.
Many other changes are nonspecific. Focal narrowing of retinal arterioles and diffuse constriction of its vessels, more pronounced in the region of the greatest loss of the neuroretinal girdle, can be observed with optic nerve neuropathies of various genesis.
Non-glaucomatous optic nerve neuropathy
It is difficult to distinguish glaucomatous from non-glaucomatous optical non-iropathy. Pallor, disproportionate to excavation or pallor in the intact neuroretinal girdle - signs of non-glaucomatous optical non-iropathy. Examples of non-glaucomatous optical neuropathy can be giant cell arteritis and compression injuries of the optic nerve. Non-glaucomatous damage to the optic disc is not always associated with loss of the neuroretinal girdle. So its shape is little changed. In contrast, with glaucomatous non-proliferation of the optic nerve, the tissue of the neuroretinal ring is lost with increasing pallor due to an increase in the size of the excavation.
Over time, color stereophotos can be used to assess changes in the optic nerve. Stereo photographs can be obtained by sequentially taking two photographs, the camera can be moved either manually or with a sliding adapter (Allen separator). Another method of obtaining stereophotographs is to take two photos synchronously with two cameras, using the principle of indirect ophthalmoscopy (Donaldson's stereoscopic fundus camera) or a two-prismatic separator. In general, simultaneous disk images are more reproducible.
Other methods that allow to obtain images and measure the optic nerve disk for comparison in time include HRT, GDx laser polarimetry and optical coherence tomography (OCT).