Lecture 13 - Visual Diseases and Disorders

Why are visual symptoms clinically important?

They may be the first sign of serious neurological disease including multiple sclerosis, pituitary adenoma, stroke, brain tumors, increased intracranial pressure, or traumatic brain injury.

What structures make up the visual pathway?

Retina, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus (LGN), optic radiations, and primary visual cortex (V1).

What determines the visual field defect in visual pathway disorders?

The location of the lesion.

What visual defects are produced by pre-chiasmal lesions?

Monocular visual loss.

What visual defect is produced by chiasmal lesions?

Bitemporal hemianopia.

What visual defects are produced by post-chiasmal lesions?

Contralateral homonymous visual field defects.

What structures are involved in pre-chiasmal lesions?

Retina and optic nerve.

What structures are involved in post-chiasmal lesions?

Optic tract, LGN, optic radiations, and visual cortex.

What is monocular blindness?

Complete or partial loss of vision in one eye due to a lesion anterior to the optic chiasm.

What are the causes of monocular blindness?

Optic neuritis, ischemic optic neuropathy, retinal artery occlusion, retinal detachment, severe glaucoma, and trauma.

What is optic neuritis?

Inflammation and demyelination of the optic nerve.

What is the most common cause of optic neuritis?

Multiple sclerosis.

What are the clinical features of optic neuritis?

Sudden unilateral vision loss, pain with eye movement, reduced color vision, and relative afferent pupillary defect (RAPD).

Why does optic neuritis cause pain with eye movement?

Pulling on the inflamed optic nerve.

Why is color vision reduced in optic neuritis?

Damage to optic nerve fibers carrying signals from cone photoreceptors.

What is a relative afferent pupillary defect (RAPD)?

An abnormal pupillary light reflex caused by reduced sensory input through one optic nerve.

What is another name for RAPD?

Marcus Gunn pupil.

What test is used to detect RAPD?

The swinging flashlight test.

What happens during the swinging flashlight test in RAPD?

When light is moved from the normal eye to the affected eye, both pupils dilate slightly because the damaged optic nerve transmits a weaker signal.

What disorders commonly cause RAPD?

Optic neuritis, ischemic optic neuropathy, optic nerve compression, severe retinal disease, and CRAO.

What is ischemic optic neuropathy?

Infarction of the optic nerve caused by reduced blood supply.

What are the clinical features of ischemic optic neuropathy?

Sudden painless vision loss, optic disc swelling, and RAPD.

What are the risk factors for ischemic optic neuropathy?

Hypertension, diabetes mellitus, and giant cell arteritis.

What is the pupillary light reflex?

Automatic constriction of both pupils in response to light.

What is the purpose of the pupillary light reflex?

To regulate the amount of light entering the eye and protect the retina.

What structures make up the pupillary light reflex pathway?

CN II (afferent), pretectal nucleus, CN III (efferent), and sphincter pupillae muscle.

What are the two pupillary responses produced by the light reflex?

Direct and consensual constriction.

What is papilledema?

Bilateral optic disc swelling caused by increased intracranial pressure.

What are the symptoms of papilledema?

Headache, transient visual obscurations, nausea, vomiting, enlarged blind spot, and late blurred vision.

What causes papilledema?

Brain tumors, hydrocephalus, intracranial hemorrhage, and idiopathic intracranial hypertension.

What are optic chiasm lesions?

Damage to the optic chiasm affecting crossing nasal retinal fibers.

What visual field defect is produced by optic chiasm lesions?

Bitemporal hemianopia.

What are the causes of optic chiasm lesions?

Pituitary adenoma, craniopharyngioma, meningioma, and aneurysm.

What is bitemporal hemianopia?

Loss of the temporal visual fields in both eyes.

What is the mechanism of bitemporal hemianopia?

Compression of crossing nasal retinal fibers.

What is the most common cause of bitemporal hemianopia?

Pituitary adenoma.

What is a pituitary adenoma?

A benign pituitary tumor that commonly compresses the optic chiasm.

What are the clinical features of pituitary adenoma?

Progressive peripheral vision loss, bitemporal hemianopia, headache, hormonal abnormalities, and possible decreased visual acuity.

How is pituitary adenoma evaluated?

MRI of the brain and visual field testing.

What is an optic tract lesion?

Damage to one optic tract after the optic chiasm.

What visual field defect is caused by an optic tract lesion?

Contralateral homonymous hemianopia.

What are the causes of optic tract lesions?

Stroke, tumors, trauma, and demyelinating disease.

What is homonymous hemianopia?

Loss of the same half of the visual field in both eyes.

What is the lateral geniculate nucleus (LGN)?

The primary visual relay nucleus of the thalamus.

What visual field defects result from LGN lesions?

Contralateral homonymous hemianopia and sector-shaped visual field defects.

What causes LGN lesions?

Thalamic infarction, hemorrhage, and tumors.

What is Meyer's loop?

The inferior optic radiations in the temporal lobe.

What visual field defect is caused by a Meyer's loop lesion?

Contralateral superior quadrantanopia.

What mnemonic is associated with Meyer's loop lesions?

Pie in the Sky.

What causes Meyer's loop lesions?

Temporal lobe stroke, tumors, temporal lobectomy, and trauma.

What are the parietal optic radiations?

Superior optic radiations within the parietal lobe.

What visual field defect is caused by parietal optic radiation lesions?

Contralateral inferior quadrantanopia.

What mnemonic is associated with parietal optic radiation lesions?

Pie on the Floor.

What causes parietal optic radiation lesions?

Parietal lobe stroke, tumors, and trauma.

What is an occipital cortex lesion?

Damage to the primary visual cortex (V1) in the occipital lobe.

What visual field defect is characteristic of occipital cortex lesions?

Contralateral homonymous hemianopia with macular sparing.

What are the causes of occipital cortex lesions?

Posterior cerebral artery stroke, occipital lobe tumors, and trauma.

What is macular sparing?

Preservation of central vision despite loss of peripheral visual fields.

In which lesion is macular sparing commonly seen?

Occipital cortex lesions.

Why does macular sparing occur?

The macula has dual blood supply from the posterior cerebral artery and middle cerebral artery.

What is the clinical significance of macular sparing?

Patients retain central reading vision despite significant visual field loss.

What is thalamic pain syndrome?

Chronic burning pain on the side of the body opposite a thalamic lesion.

What is another name for thalamic pain syndrome?

Dejerine-Roussy syndrome.

Which thalamic nucleus is damaged in thalamic pain syndrome?

The ventral posterolateral (VPL) nucleus.

What is the most common cause of thalamic pain syndrome?

Stroke.

Why does thalamic pain syndrome occur?

Damage to the VPL disrupts normal sensory processing.

What is allodynia?

Pain in response to normally nonpainful stimuli.

What is Anton syndrome?

Cortical blindness with denial of blindness.

What causes Anton syndrome?

Bilateral occipital lobe damage, most commonly from posterior cerebral artery stroke.

What are the key features of Anton syndrome?

Cortical blindness, anosognosia, confabulation, and normal pupillary reflexes.

What is anosognosia?

Lack of awareness of a neurological deficit.

What is confabulation?

Fabrication of experiences or explanations despite lack of supporting perception.

What is retinal detachment?

Separation of the neurosensory retina from the retinal pigment epithelium.

What are the risk factors for retinal detachment?

High myopia, trauma, and previous eye surgery.

What are the clinical features of retinal detachment?

Sudden floaters, photopsia, progressive visual field loss, curtain-like vision loss, and painless vision loss.

What is photopsia?

Perception of flashes of light.

What is central retinal artery occlusion (CRAO)?

Acute occlusion of the central retinal artery causing sudden painless monocular vision loss.

What are the causes of CRAO?

Thromboembolism, giant cell arteritis, and carotid artery disease.

What are the clinical features of CRAO?

Sudden painless monocular vision loss, pale edematous retina, cherry-red spot, and RAPD.

Why does a cherry-red spot occur in CRAO?

The ischemic retina becomes pale while the fovea remains red due to choroidal blood supply.

What is central retinal vein occlusion (CRVO)?

Obstruction of the central retinal vein causing sudden painless monocular vision loss.

What are the risk factors for CRVO?

Hypertension, diabetes mellitus, glaucoma, and hyperviscosity states.

What are the clinical features of CRVO?

Sudden painless vision loss, flame-shaped retinal hemorrhages, optic disc swelling, and dilated tortuous veins.

Which retinal vascular occlusion produces a cherry-red spot?

CRAO.

Which retinal vascular occlusion produces flame-shaped hemorrhages?

CRVO.

Which retinal vascular occlusion produces a pale edematous retina?

CRAO.

Which retinal vascular occlusion produces dilated tortuous veins?

CRVO.

What is glaucoma?

Progressive optic neuropathy associated with retinal ganglion cell loss, usually due to elevated intraocular pressure.

What are the two major types of glaucoma?

Open-angle glaucoma and closed-angle glaucoma.

What are the characteristic findings of glaucoma?

Gradual peripheral visual field loss, increased cup-to-disc ratio, and elevated intraocular pressure.

What are arcuate scotomas?

Curved visual field defects that follow retinal nerve fiber bundles.

Why do arcuate scotomas occur in glaucoma?

Damage to retinal nerve fiber bundles.

What happens to the optic cup in glaucoma?

It enlarges, increasing the cup-to-disc ratio.

Why does the cup-to-disc ratio increase in glaucoma?

Retinal ganglion cell loss causes optic nerve fiber loss and enlargement of the optic cup.

What is the major risk factor for glaucoma?

Elevated intraocular pressure.

Can glaucoma occur with normal intraocular pressure?

Yes.

What is normal-tension glaucoma?

Glaucoma that occurs despite normal intraocular pressure.

What is open-angle glaucoma?

Chronic glaucoma in which the drainage angle remains open but aqueous outflow through the trabecular meshwork is reduced.

What are the characteristics of open-angle glaucoma?

Open drainage angle, inefficient trabecular meshwork, gradual pressure rise, painless course, and slowly progressive vision loss.

What is the classic analogy for open-angle glaucoma?

The drain is open but clogged.