8. Visual, auditory and vestibular analyzers. Anatomy and physiology. Diseases.

Optic never - anatomy, physiology, examination, syndromes

Anatomy: The optic nerve (CN II) is a sensory cranial nerve responsible for vision.

Visual Pathway

Important Rule: Nasal retinal fibers cross at the chiasm.. Temporal retinal fibers remain uncrossed.

Physiology

Functions: Vision. Visual acuity. Visual fields. Color vision. Afferent limb of the pupillary light reflex

Pupillary Light Reflex

Light → Retina → Optic nerve (CN II) → Midbrain → Oculomotor nerve (CN III) → Pupillary constriction

Examination of the Optic Nerve

1. Visual Acuity: Assessed using a Snellen chart (or near-vision chart).

• Tests: Each eye separately. With corrective lenses if used

2. Visual Fields: Assessed by confrontation testing.

• Examines: Peripheral vision. Detection of visual field defects.

3. Color Vision: Usually tested with Ishihara plates.

• Useful in: Optic neuritis. Optic neuropathies

4. Pupillary Light Reflex

• Evaluate: Direct response (illuminated eye constricts). Consensual response (opposite eye constricts). Tests integrity of CN II and CN III.

5. Fundoscopy (Ophthalmoscopy)

• Examination of: Optic disc. Retina. Retinal vessels
• Normal optic disc: Pink. Sharp margins

Optic Nerve Syndromes

1. Optic Neuritis: Inflammation of the optic nerve.

• Features: Sudden visual loss. Pain on eye movement. Reduced color vision. Relative afferent pupillary defect (RAPD)
• Common Cause: Multiple sclerosis

2. Optic Atrophy: Degeneration of optic nerve fibers.

• Features: Progressive visual loss. Pale optic disc. Reduced visual acuity

3. Papilledema: Optic disc swelling due to increased intracranial pressure.

• Features: Blurred vision. Headache. Nausea/vomiting. Bilateral swollen optic discs

1. 4.Visual Field Defects

• Monocular Blindness: Lesion in the Optic nerve
• Finding: Complete loss of vision in one eye.
• Bitemporal Hemianopia: Lesion at the Optic chiasm
• Cause: Pituitary tumor (classic)
• Finding: Loss of temporal visual fields in both eyes.
• Homonymous Hemianopia: Lesion can be seen in ptic tract, optic radiation, or occipital cortex
• Finding: Loss of the same visual field in both eyes.
• Example: Right-sided lesion → Left homonymous hemianopia
• Quadrantanopia: Temporal Lobe Lesion
• Superior quadrantanopia ("Pie in the sky"): Parietal Lobe Lesion. Inferior quadrantanopia ("Pie on the floor")

Scotoma Definition: Localized area of decreased or absent vision surrounded by normal field. Types: Central scotoma. Paracentral scotoma. Arcuate scotoma( bow shaped)