Skip to content
Download PDF

Disorders of the Eye

Chapter 34 | Part 2: Cardinal Manifestations and Presentation of Diseases · Part 2 – Cardinal Manifestations & Presentation · Chapter 34

Key Clinical Points

  1. Pinhole testing improves acuity in refractive errors but not in optic nerve disease.
  2. PERRLA is redundant if light response is good; check near response if light is poor (e.g., Argyll Robertson, Parinaud's, or Adie's).
  3. Anisocoria increasing in dim light indicates sympathetic paresis (Horner's syndrome).
  4. Roth's spots are seen in subacute bacterial endocarditis, leukemia, and diabetes.
  5. Cherry-red fovea with a milky retina is characteristic of central retinal artery occlusion.
  6. Amaurosis fugax is a transient ischemic attack of the retina requiring urgent stroke evaluation.
  7. Herpes zoster ophthalmicus requires antiviral therapy and cycloplegics to prevent scarring.
  8. Acute angle-closure glaucoma is treated with acetazolamide, beta blockers, and pilocarpine.
  9. Legal blindness is defined as best corrected acuity of 6/60 (20/200) or less in the better eye.
  10. Temporal pallor of the optic disc is a more reliable sign of optic atrophy than pallor of the nasal rim.

DEFINITION & CLASSIFICATION

• Legal Blindness:

Definition (Harrison's 22e): best corrected acuity of 6/60 (20/200) or less in the better eye or a binocular visual field subtending 20° or less. • Optic Atrophy: Definition (Harrison's 22e): not a specific diagnosis but refers to the combination of optic disc pallor, arteriolar narrowing, and nerve fiber layer destruction produced by a host of eye diseases, especially optic neuropathies.

ETIOLOGY & PATHOPHYSIOLOGY

Anatomy of the Visual System

• Retina: - Function: Transducer converting light energy into neuronal signals. - Photoreceptors: ◦ Rods: 100 million; function in dim (scotopic) illumination. ◦ Cones: 5 million; function in daylight (photopic); specialized for color and high spatial resolution. - Macula: Contains the majority of cones; serves the central 10° of vision. - Fovea: Located in the center of the macula; packed exclusively with cones; provides best visual acuity. • Neural Pathways: - Ganglion Cells: 1 million per retina; translate images into action potentials. - Optic Nerve: Contains 1 million fibers; carries signals to the brain. - Primary Pathway: Retinogeniculocortical (Retina → Lateral Geniculate Nucleus → Primary Visual Cortex). • Specialized Ganglion Cells: - Melanopsin-containing cells: Govern pupillary constriction and circadian rhythms via pretectal olivary nuclei and the suprachiasmatic nucleus. • Motor System (Efferent): - Purpose: Foveation (moving targets onto the fovea). - Muscles: 6 extraocular muscles per eye. - Innervation: Cranial nerves III, IV, and VI; coordinated by pontine and midbrain centers.

Refractive States

• Myopia: Globe too long → focus in front of retina → distant objects blurry. - Correction: Diverging lens. • Hyperopia: Globe too short → requires converging lens. • Astigmatism: Non-spherical cornea → requires cylindrical corrective lens. • Presbyopia: Age-related loss of accommodation due to lens changes; requires reading glasses or bifocals. • Tonic Pupil: - Cause: Seen in multiple system atrophy, segmental hypohidrosis, diabetes, and amyloidosis. - Diagnosis: 0.125% pilocarpine → produces constriction in tonic pupils but no response in normal pupils. • Gardener's Pupil: Mydriasis induced by tropane alkaloids (e.g., nightshade, jimsonweed).

CLINICAL FEATURES

Pupillary Examination

• PERRLA: - Note: 'Near' response is only necessary if light response is poor. - Light-near dissociation: Seen in neurosyphilis (Argyll Robertson), Parinaud's syndrome, or Adie's tonic pupil. • Anisocoria: - Stable size → essential/physiologic. - Increases in dim light → sympathetic paresis (Horner's syndrome: miosis, ptosis, anhidrosis). - Increases in bright light → parasympathetic palsy (e.g., CN III palsy). • Marcus Gunn Pupil: - Mechanism: Relative afferent pupillary defect (RAPD) during swinging flashlight test. - Significance: Useful for retrobulbar optic neuritis and other optic nerve diseases.

Eye Movements & Alignment

• Saccades: Rapid, accurate jumps between targets. - Assessment: Patient looks back and forth between two stationary points. • Alignment: - Test: Cover test (detects heterotropia as small as 1°). - Measurement: Prism power used to determine magnitude of deviation. • Stereacuity: - Normal: 40 s of arc. - Screening: Random dot stereograms.

Color Vision

• Cones: Three types (Red, Green, Blue) with peaks at 560nm, 530nm, and 430nm. - Genetics: Red/Green on X chromosome; Blue on Chromosome 7. - Congenital Color Blindness: Affects 8% of males (anomalous trichromats or dichromats). • Acquired Defects: - Cause: Macular disease, optic nerve damage, or bilateral strokes (cerebral achromatopsia). - Clinical Signs: Color desaturation, prosopagnosia (difficulty recognizing faces), or color anomia.

DIAGNOSTIC APPROACH

Visual Acuity Testing

  1. Initial Assessment: Determine if refractive error is present.
  2. Pinhole Test:
  3. Improvement → Refractive error → Proceed to refraction.
  4. No improvement → Potential optic nerve/retinal disease.
  5. Standard Testing:
  6. Snellen Chart: Used at 6 m (20 ft).
  7. Rosenbaum Card: Used at 36 cm (14 in) for near vision.
  8. Thresholds: If < 6/240 (20/800), record as counting fingers, hand motions, light perception, or no light perception.

Pupillary Examination

  1. Basic Exam: Test individually in dim light.
  2. If light response is poor → test near response (to rule out Argyll Robertson, Parinaud's, or Adie's).
  3. RAPD Check:
  4. Swing flashlight test → identify Marcus Gunn pupil (indicates optic nerve disease).
  5. Anisocoria Evaluation:
  6. Test with 0.125% pilocarpine → identifies tonic pupil.
  7. Test with 1% apraclonidine → dilates miotic pupil in Horner's syndrome.

Visual Field Mapping

  1. Localization Strategy: Determine if lesion is pre-chiasmal, at the chiasm, or post-chiasmal.
  2. Pre-chiasmal (Monocular):
  3. Central scotoma → Macula/Papillomacular fibers.
  4. Arcuate scotoma → Optic nerve (Glaucoma, optic neuritis).
  5. Altitudinal field cut → Ischemic optic neuropathy.
  6. Chiasmal:
  7. Bitemporal hemianopia → Symmetric compression of chiasm (e.g., Pituitary adenoma).
  8. Junctional scotoma → Asymmetric compression (e.g., Tuberculum sella).
  9. Post-chiasmal (Binocular):
  10. Homonymous hemianopia → Optic tract or radiations.
  11. Superior quadrantanopia → Meyer's loop (temporal lobe).
  12. Inferior quadrantanopia → Parietal lobe.

MANAGEMENT & TREATMENT

Acute Angle-Closure Glaucoma

  1. Initial Treatment:
  2. Acetazolamide.
  3. Beta blockers.

  4. Pilopicrine.

  5. Medical Therapy:

  6. Antiviral therapy.
  7. Cycloplegics (to prevent scarring).

KEY PEARLS & HIGH-YIELD POINTS

• Pinhole Test: Improvement → Refractive error; No improvement → Optic nerve disease. • PERRLA: Redundant if light response is good; check near response if light is poor. • Horner's Syndrome: Triad of miosis, ptosis, and anhidrosis (anhidrosis is inconsistent). • Roth's Spots: Pathognomonic for subacute bacterial endocarditis; also seen in leukemia/diabetes. • Cherry-red Fovea: Indicates central retinal artery occlusion (CRAO). • Amaurosis Fugax: Transient ischemic attack of the retina → urgent stroke evaluation. • Legal Blindness: 6/60 (20/200) or less in better eye OR binocular field ≤ 20°. • Optic Atrophy: Not a specific diagnosis; reflects damage from various neuropathies. • Temporal vs. Nasal Pallor: Temporal pallor is a more certain sign of optic atrophy than nasal rim pallor.