Vision and Neuropathologic Disease Flashcards
Sudden vs. Progressive Loss of vision
Sudden: Vascular
- Migraine
- retinal emboli
- giant cell arteritis
Progressive: Inflammatory or compressive
- optic neuritis
- optic nerve tumor
Amaurosis Fugax
Transient Monocular Blindness (TMB)
- One eye
- <24 hours
- Ischemic cause (usually affecting anterior circulation)
- PRESUMED TO BE TIA
Giant Cell Arteritis
- Preceding transient visual loss in 31%
- swollen optic disc
- Elderly females
- Headaches, wt loss, jaw claudication
- Tender, palpable sup temp a.
- Histology: inflammation, thrombosis, occlusion of vessels, infarction
Visual Pathway
Let’s assume visual pathway entering right eye
- Right optic nerve: UNILATERAL
- Optic chiasm (Lateral Geniculate Body): BILATERAL & HETERONYMOUS
Decussation
- BILATERAL & HOMONYMOUS
3. Left Optic tract
4a. Left Meyer’s Loop in Temporal Lobe: gives right upper quadrantic vision
4b. Left Dorsal optic radation in parietal lobe: gives right lower quadrantic vision
OPTIC CHIASMAL LESION
- results in BITEMPORAL field deficits
Causes:
- Tumor (80%): e.g., Pituitary Adenoma (SELLAR LESION)
- Demyelinating disease
- Vascular lesions less frequent
Retrochiasmal Lesions
- Homonymous Hemianopias
- More posteriorly located = more congruous
- Occipital lobe lesions are exquisitely congruous
Temporal Lobe Lesions
Involve Meyer’s Loop: represents the inferior retina (provides contralateral upper quadrant vision)
- more common caused by tumors than vascular lesions
Parietal Lobe Lesions
Involve Dorsal optic radiation: represents the superior retina (provides contralateral lower quadrant vision)
Cortical Blindness
- Complete lesion of the visual cortex (occipital lobe)
- Complete loss of all visual sensation, including light and dark
- Retention of pupillary light reflex
- May see loss of reflex lid closure to bright light or threat
- Retina and extraocular movements are normal
CN III
- effect of damage
- Pupil constriction
- Lid elevation
- Adduction
- Elevation
- Depression
Damage results in:
- eye looking down and out
- ptosis
- pupillary dilation
- loss of accommodation
CN IV
- effect of damage
- Innervates superior olbique: eye movement down and medially
Damage results in:
- eye moves upward
- with contralateral gaze and ipsilateral head tilt
CN VI
- effect of damage
- innervates lateral rectus
Damage results in:
- medially directed eye that cannot abduct
Internuclear Ophthalmoplegia
- MLF syndrome, classically seen in Multiple Sclerosis
- CN6 (Lateral rectus muscle innervation) sends signal via MLF to CN3 of opposite eye to innervate Medial Rectus Muscle
- If damage to MLF: CN6 eye can look lateral, but opposite eye (CN3) cannot look medially
- abducting eye gets NYSTAGMUS (CN6 overfires to stimulate CN3) and DIPLOPIA
**CONVERGENCE IS NORMAL: CN3 works fine otherwise
Monocular diplopia
- Persists when one eye is covered
- Resolves when looking through a pinhole
Binocular Diplopia
- Double vision resolves when either eye is covered
Common etiologies:
- Cranial nerve palsy
- Neuromuscular disorder
- Infiltration, inflammation or entrapment of muscle
