PUPIL EXAMINATION

1. BASIC ANATOMY & PHYSIOLOGY 

 Muscles of Iris

  • Sphincter pupillae (parasympathetic) → constriction (miosis)
  • Dilator pupillae (sympathetic) → dilation (mydriasis)


 Parasympathetic Pathway (Constriction)

EdingerWestphal nucleus→Oculomotor nerve→Ciliary ganglion→Short ciliary nerves→Sphincter pupillae

  • Afferent: Retina → optic nerve
  • Efferent: CN III → ciliary ganglion → sphincter
  • Function: Light reflex + accommodation


 Sympathetic Pathway (Dilation)

Hypothalamus→Ciliospinal center (C8T2)→Superior cervical ganglion→Long ciliary nerves→Dilator pupillae

  • Long 3-neuron pathway
  • Function: Mydriasis, lid elevation (Müller muscle), sweating

2. COMPONENTS OF PUPIL EXAMINATION

 A. Size 

6

Pupil Size

Clinical Significance

Pinpoint (<2 mm)

Opioids, pontine lesion

Mid-position (4–6 mm, fixed)

Brain death, severe hypoxia

Dilated (>6 mm)

CN III palsy, herniation, atropine

Anisocoria

Physiological vs pathological

Sudden unilateral dilated pupil = uncal herniation until proven otherwise


 B. Shape

Shape

Causes

Round

Normal

Irregular

Trauma, surgery

Oval pupil

Early herniation

Keyhole pupil

Post-surgical

 C. Symmetry (Anisocoria)

  • Physiological anisocoria (<1 mm) → normal (20% population)
  • Pathological if:
    • Sudden onset
    • Associated with neuro deficit

 3. PUPILLARY REFLEXES 

A. Light Reflex

  • Afferent: Retina → CN II
  • Efferent: CN III

 Types

  • Direct reflex → same eye constricts
  • Consensual reflex → opposite eye constricts

 Lesion Localization 

Condition

Direct

Consensual

Optic nerve lesion (afferent)

 absent

 absent

Oculomotor lesion (efferent)

 absent

 present in opposite eye

 B. Swinging Flashlight Test (RAPD)

  • Detects Relative Afferent Pupillary Defect (Marcus Gunn pupil)

 Interpretation

  • Light moved from normal → affected eye
     Both pupils paradoxically dilate

 Seen in:

  • Optic neuritis
  • Severe retinal disease

 C. Accommodation Reflex

 Near Response Triad:

  1. Miosis
  2. Convergence
  3. Lens thickening

4. IMPORTANT PUPILLARY ABNORMALITIES 

Pathology

Pupil Size

Combined Features 

Horner Syndrome

Miosis (small pupil)

Light reflex present (sluggish), near reflex present; Ptosis + anhidrosis + dilation lag in dark; Lesion in sympathetic pathway (brainstem stroke, Pancoast tumor, carotid dissection)

Oculomotor (CN III) Palsy

Mydriasis (large pupil)

Light reflex absent, near reflex absent; “Down & out eye”, ptosis, diplopia; Aneurysm (especially Posterior communicating artery aneurysm), diabetes (pupil-sparing), trauma

Argyll Robertson Pupil

Small, irregular

Light reflex absent, near reflex present (light-near dissociation); “Prostitute pupil” – accommodates but does not react; Cause: Neurosyphilis

Adie (Tonic) Pupil

Dilated

Light reflex poor/absent, near reflex slow tonic constriction; Segmental sphincter palsy, vermiform movements; Idiopathic, viral, autonomic neuropathy

Relative Afferent Pupillary Defect (RAPD)

Usually normal

Light reflex defective in affected eye, near reflex present; Swinging flashlight test positive; Optic nerve disease (optic neuritis, ischemic optic neuropathy)

Amaurotic Pupil

Dilated

Direct light reflex absent, consensual present, near reflex absent; Blind eye; Severe retinal/optic nerve damage

Wernicke Hemianopic Pupil

Normal

Light reflex absent when light in blind hemifield, near reflex present; Seen in optic tract lesions; Stroke, tumor

Holmes-Adie Syndrome

Dilated

Light reflex poor, near reflex slow; Absent deep tendon reflexes; Peripheral neuropathy

Pharmacologic Mydriasis

Dilated

Light reflex absent, near reflex absent; No response to pilocarpine; Atropine, tropicamide

Pharmacologic Miosis

Constricted

Light reflex present/variable, near reflex present; Pinpoint pupils; Opioids, organophosphates

Hutchinson Pupil

Initially constricted → dilated

Progressive loss of light reflex and near reflex; Ipsilateral CN III compression; Raised ICP, uncal herniation

Marcus Gunn Pupil (RAPD)

Normal

Paradoxical dilation on light (swinging flashlight sign), near reflex present; Optic neuritis, MS

Midbrain (Central) Pupil

Mid-position

Light reflex absent, near reflex absent; Neither constricts nor dilates; Midbrain lesion

Pinpoint Pupil

Very small

Light reflex present, near reflex present; Reactive but small; Causes include Pontine hemorrhage, opioids

Fixed Dilated Pupil

Dilated

Light reflex absent, near reflex absent; Emergency sign; Brain herniation, severe hypoxia

Irregular Pupil (Corectopia)

Variable

Light reflex variable, near reflex variable; Structural iris damage; Trauma, surgery

 5. Pharmacological Pupils

Drug

Effect

Opioids

Pinpoint

Atropine

Dilated

Organophosphate

Constricted

Cocaine

Dilated

5. PUPILS IN COMA 

Finding

Localization

Small reactive

Metabolic encephalopathy

Pinpoint

Pontine lesion / opioids

Mid-position fixed

Brainstem damage

Unilateral dilated

CN III compression (herniation)

Bilateral dilated fixed

Severe hypoxia / brain death

6. PUPIL EXAMINATION IN BRAIN DEATH

Criteria (Guidelines-based)

  • Fixed, dilated pupils (>6 mm)
  • No response to light
  • Confirms midbrain dysfunction

7. STEPWISE CLINICAL EXAMINATION (OSCE STYLE)

  1. Inspect:
    • Size
    • Shape
    • Symmetry
  1. Check light reflex:
    • Direct
    • Consensual
  1. Perform swinging flashlight test
  2. Check accommodation
  3. Look for associated signs:
    • Ptosis
    • Eye deviation
    • Sweating