Anatomy, Physiology, and Pathology of the Hearing, Vision, and Speech Organs - Shvetsov A.G. 2006

Anatomy, Physiology, and Pathology of the Visual Analyzer
Pathology of the Visual Analyzer
Pathology of the Conducting Pathway of the Visual Analyzer

Optic nerve anomalies are typically detected during ophthalmoscopy and can be either congenital or acquired. Complete, irreversible blindness is associated with congenital optic nerve atrophy, whereas congenital hypoplasia (underdevelopment) and pigmentation of the optic disc may occur with preserved Vision.

Among acquired anomalies, papilledema (choked disc) is the most frequently observed. This is a non-inflammatory Swelling of the optic disc, typically caused by increased intracranial pressure. Papilledema is usually the result of the retention of interstitial fluid, which normally drains along the optic nerve into the cranial cavity. This condition can be caused by various space-occupying lesions in the Brain, such as abscesses, Hydrocephalus, parasitic cysts (cerebral echinococcosis), tuberculomas, Skull and orbital trauma, tumors, and other factors. With papilledema, visual acuity rapidly declines, the visual field narrows significantly, and complete blindness occurs in advanced cases. The rate of papilledema development depends on how fast the intracranial pressure rises. If the pressure increase is mild, Cytology/cytology/16.html">Early stages of papilledema can persist for years.

Atrophic processes in the optic nerve can occur As a result of inflammatory or congestive Changes in the blind spot (optic disc), intoxication from poisoning with methyl alcohol, quinine, and other substances, or due to botulism.

The decrease in visual acuity in optic nerve atrophy is determined by the localization and severity of the atrophic process. If the atrophic process extends to the macula, a significant decline in visual acuity is observed. However, if the peripheral fibers of the optic nerve are affected, visual acuity may be only slightly impaired, while peripheral vision deterioration is more pronounced due to the constriction of its boundaries.

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1 — lesion of the outer (uncrossed) fibers of the optic nerve before the chiasm — unilateral temporal hemianopsia (loss of the temporal half of the visual field); 2 — lesion of the inner (crossed) fibers of the optic nerve before the chiasm — unilateral nasal hemianopsia (loss of the nasal half of the visual field); 3 — lesion of the optic chiasm — bilateral nasal hemianopsia (loss of the nasal halves of the visual fields); 4—5 — lesion of the optic tract and the central neuron of the visual pathway (optic radiation) — homonymous hemianopsia (loss of the same-side visual fields in each eye); 6 — lesion of the occipital lobe cortex — loss of various areas of the visual fields

Fig. 6. Levels of visual pathway lesions causing visual impairment (the left side of the visual pathway is shown in black)

The Clinical presentation of optic disc atrophy is almost always characterized by dilated pupils with a near-total absence of pupillary light reflex, as well as the absence of tracking and gaze fixation ("wandering gaze").

The Nature of visual changes when other PARTS OF THE visual pathways are affected depends on the localization of the pathological process, which is typically a tumor, vascular aneurysm, or lesion of the cerebral ventricles (Fig. 6).

Complete lesion of the optic nerve before the chiasm (decussation) leads to blindness in the corresponding eye, while preserving the consensual pupillary light reflex. In visual pathway lesions, visual field defects for green and red colors develop first, followed by white.