Afferent Visual System & Visual Fields

How is the visual field represented on the retina?

Upside down and reversed.

Superior visual field projects to which part of the retina?

Inferior retina.

Inferior visual field projects to which part of the retina?

Superior retina.

Temporal visual field projects to which part of the retina?

Nasal retina.

Nasal visual field projects to which part of the retina?

Temporal retina.

What is the normal temporal monocular visual field extent?

100-110°

What is the normal inferior monocular visual field extent?

70-75°

What is the normal nasal monocular visual field extent?

60°

What is the normal superior monocular visual field extent?

60°

What is the normal binocular visual field extent?

Approximately 180° with no blind spot.

What 5 parameters should always be evaluated when interpreting visual fields?

Reliability, blind spots, general depression, pattern of loss, pre- vs. post-chiasmal defects.

What is a relative visual field defect?

Depressed sensitivity.

What is an absolute visual field defect?

Complete loss of sensitivity.

What is a local visual field loss?

Only portions of the field are affected.

What is a general visual field loss?

Entire visual field affected.

What is the difference between total and partial hemianopia?

Total: entire hemifield absent. Partial: only part of hemifield affected.

What is a sectorial visual field defect?

Hemianopic or quadrantanopic.

What is a non-sectorial visual field defect?

Irregular or diffuse.

What is a scotoma?

A visual defect surrounded by seeing retina.

What is a non-scotomatous visual field defect?

Field loss extending to the edge of the visual field.

What is the difference between homonymous and heteronymous defects?

Homonymous: same side lost in both eyes. Heteronymous: opposite sides lost.

What is a congruous visual field defect?

Nearly identical in both eyes.

What is an incongruous visual field defect?

Different appearance between eyes.

What happens to congruity as lesions move more posteriorly?

They become more congruous.

What are the four territories of the visual pathway?

1) Outer retina/choroid, 2) Ganglion cell layer/NFL/optic nerve, 3) Optic chiasm, 4) Post-chiasmal pathway.

What are the characteristics of Territory 1 (retinal) visual field defects?

Monocular, don't follow nerve fiber bundles, don't respect vertical midline.

What are the characteristics of Territory 2 (NFL/optic nerve) defects?

Follow RNFL, respect horizontal raphe, above/below horizontal meridian (e.g., glaucoma).

What supplies blood to the retinal nerve fiber layer (RNFL)?

Retinal vasculature.

What supplies blood to the prelaminar and laminar optic nerve?

Short posterior ciliary arteries via the Circle of Zinn-Haller.

What is the cause of Anterior Ischemic Optic Neuropathy (AION)?

Occlusion of short posterior ciliary arteries.

What is the typical optic disc finding in AION?

Pale disc edema.

What is the typical visual field defect in AION?

Altitudinal defect (usually inferior).

What is the cause of papilledema?

Elevated intracranial pressure causing axoplasmic flow stasis.

Is papilledema typically unilateral or bilateral?

Bilateral.

Why does elevated ICP cause papilledema?

CSF surrounds the optic nerve and compresses axons.

What is the length of the orbital optic nerve?

20-30 mm.

Why is the orbital optic nerve S-shaped?

Allows eye movement without stretching the nerve.

What happens to papillo-macular fibers in the orbital optic nerve?

They migrate toward the center of the nerve.

What are the typical visual field defects in glaucoma?

Arcuate, paracentral, nasal step, and temporal wedge.

What are the typical visual field defects in optic neuritis?

Central scotoma, centrocecal scotoma, and arcuate defects.

What is the typical visual field defect in toxic/nutritional optic neuropathy?

Central or centrocecal scotoma.

What is the classic clinical phrase for retrobulbar optic neuritis?

"The patient sees nothing and the doctor sees nothing."

Which structures pass through the superior orbital fissure?

CN III, CN IV, CN VI, V1, and ophthalmic vein.

Which structures accompany CN II in the optic canal?

Ophthalmic artery and sympathetic fibers.

What is the length of the intracranial optic nerve?

About 10 mm.

What structures lie lateral to the intracranial optic nerve?

Internal carotid arteries.

What percentage of optic nerve fibers cross at the chiasm?

53%

What is the anterior knee of Von Willebrand?

Crossing nasal fibers briefly looping into the opposite optic nerve.

What is the most common cause of chiasmal lesions?

Pituitary adenoma.

What is the classic visual field defect of a chiasmal lesion?

Bitemporal hemianopia.

Which fibers are compressed first in a pituitary tumor, and what is the early defect?

Inferior crossing nasal fibers; causes superior temporal loss.

How large must a pituitary tumor be to cause visual field loss?

About 10 mm.

What is the main function of ACTH?

Cortisol release.

What is the main function of FSH?

Follicle maturation.

What is the main function of LH?

Ovulation and testosterone production.

What is the main function of GH?

Growth.

What is the main function of Prolactin?

Lactation.

What is the main function of TSH?

T3/T4 thyroid hormone release.

What disease is caused by ACTH excess?

Cushing disease.

What disease is caused by ACTH deficiency?

Addison disease.

What disease is caused by excess Growth Hormone?

Acromegaly or Gigantism.

What condition is caused by low Growth Hormone?

Dwarfism.

What are the key clinical findings in hyperprolactinemia?

Amenorrhea, galactorrhea, and hypogonadism.

What are four important differentials for bitemporal hemianopia?

Increased ICP, aneurysm, tilted disc syndrome, and craniopharyngioma.

Why is Tilted Disc Syndrome clinically important?

It mimics glaucoma and chiasmal lesions.

How can Tilted Disc Syndrome be distinguished from a chiasmal lesion?

Its visual field defects cross the vertical meridian.

Where is the lesion located in a Junctional Scotoma?

Junction of the optic nerve and chiasm.

What is the visual field defect in a Junctional Scotoma?

Ipsilateral central scotoma and contralateral superior temporal defect.

What is the most common tumor causing a Junctional Scotoma?

Meningioma.

What type of visual field defect do all post-chiasmal lesions produce?

Homonymous visual field defects.

What is the typical visual field defect in optic tract lesions?

Incongruous homonymous hemianopia.

In an optic tract lesion, which eye has the APD?

The contralateral eye.

What is the characteristic optic nerve appearance in optic tract lesions?

Bow-tie optic atrophy.

Where is Meyer's Loop located and what fibers does it carry?

Temporal lobe; carries inferior retinal fibers (superior visual field).

What is the typical visual field defect in temporal lobe lesions?

Superior homonymous quadrantanopia ("Pie in the Sky").

What is the typical visual field defect in parietal lobe lesions?

Inferior homonymous quadrantanopia ("Pie on the Floor").

What are the four clinical findings of Gerstmann Syndrome?

Finger agnosia, left-right confusion, acalculia, and agraphia.

What is the Riddoch Phenomenon?

Detecting moving targets better than stationary ones (seen with occipital lesions).

What is the most common cause of occipital lobe lesions?

Stroke.

What is the typical congruity of occipital lobe visual field defects?

Highly congruous.

What is the most common visual field finding in occipital lobe lesions?

Homonymous hemianopia with macular splitting or sparing.

Why does macular sparing occur in occipital lobe lesions?

Collateral blood supply from MCA and PCA to the occipital pole.

Is macular sparing anatomical or cortical?

Cortical.

What do bilateral occipital lesions cause?

Cortical blindness.

What is the status of pupillary reflexes in cortical blindness?

Normal.

What is Anton syndrome?

Denial of blindness in patients with cortical blindness.

What are the findings of a right inferior occipito-temporal lesion?

Prosopagnosia and geographic agnosia.

What are the findings of a left inferior occipito-temporal lesion?

Visual object agnosia and pure alexia without agraphia.