Impaired Vision
Ocular Lesions
Causes: refractive error, opacity of ocular media, or retinal abnormality (e.g., retinal detachment, inflammation, hemorrhage, vascular occlusion). Sometimes with pain or soft-tissue swelling.
Optic Nerve Lesions
Hallmarks: blurring, dimming, darkening of vision; decreased pupillary reaction to light; usually monocular.
Relative afferent pupillary defect: sign of optic nerve lesion; due to decreased transmission of visual signals through affected optic nerve. Elicited by shining light in one eye and then alternating to other eye (swinging flashlight test): affected pupil constricts with light on normal eye, dilates with light on affected eye, which constricts less rapidly, less completely and less persistently than normal eye.
Scotoma (limited area of absent vision, a “pathological” blind spot) may be present; usually central (surrounded by areas of normal vision), centrocecal (elongated shape of deficit covering fovea, extends to normal blind spot), or altitudinal (covers upper or lower half of visual field). May be symptomatic (recognized by patient) or found on visual field examination.
Bilateral optic nerve lesion: suggests hereditary, toxic, nutritional, demyelinating disorder.
Unilateral optic nerve lesion: ischemia, inflammation, compression.
Optic Nerve Infarct (Anterior Ischemic Optic Neuropathy)
Patient usually older than 50.
Visual defect usually altitudinal, occasionally centrocecal, sudden onset, stable.
Etiology
Idiopathic (most common), temporal arteritis, carotid occlusive disease (rare).
Optic Neuritis
Usually young adult.
Central or centrocecal scotoma; subacute progression, followed by gradual (partial or complete) resolution. Disc swollen (optic neuritis) or normal (retrobulbar neuritis). Local tenderness or pain on eye movement.
Compressive Optic Neuropathy
Steady progression of visual loss. Disc may appear normal until optic atrophy ensues.
Lesions of Optic Chiasm
Characteristic visual defect: bitemporal hemianopia (due to compression of crossing fibers). Variants: (a) bitemporal superior quadrantanopia; (b) blind in one eye, superior temporal quadrantanopia in other eye.
Etiology
Compression of chiasm by pituitary tumor, craniopharyngioma, meningioma, aneurysm.
Retrochiasmal Lesions
Homonymous hemianopia: loss of vision in right or left half of visual field in both eyes. Patient often not aware of defect; trouble reading may be only symptom. Visual acuity usually intact.
Lesion anterior to lateral geniculate nucleus: optic atrophy.
Retrogeniculate lesions: opticokinetic nystagmus abnormal, especially with movement of test strip toward the lesion. Damage to optic radiation: homonymous quadrantanopia (superior for temporal radiations, inferior for parietal).
Transient Visual Events
Formed visual hallucinations: temporal lobe lesions.
Unformed visual hallucinations: occipital; includes scintillating homonymous scotoma of migraine.
Phosphenes (light flashes): optic nerve lesions, eye movement.
Amaurosis fugax: transient visual obscuration, usually in one eye; ophthalmic-carotid hypoperfusion or embolization, cardiogenic emboli, vasospasm of migraine.
Impaired Ocular Motility
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