Anatomy and Examination of the Eye - High-Yield Notes

1. Basic Anatomy of the Eye

A. Orbit and adnexa

• Orbit: Bony cavity containing the globe, extraocular muscles, optic nerve, vessels, nerves, and orbital fat.
• Eyelids: Protect the eye and spread tear film.
  • Levator palpebrae superioris elevates upper lid, supplied by CN III.
  • Superior tarsal muscle assists lid elevation, supplied by sympathetics.
  • Orbicularis oculi closes eyelids, supplied by CN VII.
• Conjunctiva: Thin mucous membrane lining the inner eyelids (palpebral conjunctiva) and covering anterior sclera (bulbar conjunctiva).

B. Coats of the globe

C. Important structures

• Cornea: Transparent anterior surface. Major refractive surface of the eye.
• Sclera: Tough white outer coat.
• Iris: Coloured diaphragm controlling pupil size.
  • Parasympathetic: constriction, miosis
  • Sympathetic: dilation, mydriasis
• Pupil: Central aperture in iris.
• Ciliary body:
  • Produces aqueous humour.
  • Ciliary muscle changes lens shape during accommodation.
• Lens: Biconvex, transparent structure that fine-focuses light on retina.
• Choroid: Vascular pigmented layer supplying outer retina.
• Retina:
  • Macula: Area for central detailed vision.
  • Fovea: Centre of macula, highest visual acuity.
  • Optic disc: Exit point of optic nerve, physiologic blind spot.
• Optic nerve (CN II): Carries visual information from retina to brain.

D. Chambers and fluids

• Anterior chamber: Between cornea and iris.
• Posterior chamber: Between iris and lens.
• Both contain aqueous humour.
• Vitreous chamber: Behind lens, filled with vitreous gel.

E. Extraocular muscles and nerve supply

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2. Method of Examination of the Eye

General principles

• Examine each eye separately, then both eyes together.
• Compare both sides.
• Use the sequence:
  Visual acuity → visual fields → external exam → ocular movements → pupils → anterior segment → intraocular pressure → fundus.
• Ask about pain, redness, discharge, trauma, photophobia, floaters, flashes, diplopia, loss of vision, spectacles/contact lenses, and systemic disease.

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A. Visual acuity

Method

• Test with a Snellen chart at 6 m or 20 ft.
• Test right eye, left eye, then both eyes, with the other eye completely covered.
• Test using the patient’s usual corrective lenses.
• If acuity is reduced, use a pinhole.

Interpretation

• 6/6 or 20/20: Normal acuity.
• Pinhole improvement suggests a refractive error.
• If the patient cannot read the chart, record:
  • CF: Counts fingers
  • HM: Hand movements
  • PL: Perception of light
  • NPL: No perception of light

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B. Visual fields

Confrontation test

1. Sit opposite the patient at eye level.
2. Patient covers one eye and examiner covers the opposite eye.
3. Bring fingers from the periphery toward the centre in all four quadrants.
4. Compare the patient's field with your own.

Defects

• Monocular visual-field loss: Eye, retina, or optic nerve lesion.
• Bitemporal hemianopia: Optic chiasm lesion.
• Homonymous hemianopia: Retrochiasmal lesion.
• Central scotoma: Macular disease or optic neuritis.

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C. External examination

• Eyelid position: ptosis, lid lag, entropion, ectropion.
• Eyelid swelling, masses, crusting.
• Conjunctival injection, chemosis, haemorrhage, discharge.
• Corneal clarity, opacity, ulcer, foreign body.
• Globe position:
  • Proptosis/exophthalmos: Forward displacement.
  • Enophthalmos: Posterior displacement.
• Facial sensation around the orbit, especially after trauma.

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D. Eye movements and alignment

Inspection

• Strabismus or squint
• Nystagmus
• Head tilt
• Diplopia
• Limitation of movement

H-test

Key movements

• Abduction: Lateral rectus, CN VI
• Adduction: Medial rectus, CN III
• Elevation in adduction: Inferior oblique, CN III
• Depression in adduction: Superior oblique, CN IV
• Elevation in abduction: Superior rectus, CN III
• Depression in abduction: Inferior rectus, CN III

Cover tests

• Cover-uncover test: Detects manifest squint, or tropia.
• Alternate cover test: Detects latent squint, or phoria.

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E. Pupillary examination

1. Size
2. Shape
3. Equality
4. Direct light reflex
5. Consensual light reflex
6. Near response
7. Relative afferent pupillary defect, RAPD

Pupillary reflex pathway

• Afferent limb: Retina → optic nerve, CN II
• Efferent limb: Oculomotor nerve, CN III → sphincter pupillae

Swinging flashlight test

• Normally, both pupils constrict equally when either eye is illuminated.
• In an RAPD / Marcus Gunn pupil, both pupils dilate relatively when the light is moved to the affected eye.
• This suggests significant unilateral or asymmetric optic nerve disease or severe retinal disease.

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F. Examination of the anterior segment

Torchlight examination

• Lids and lashes
• Conjunctiva
• Cornea
• Anterior chamber depth
• Iris
• Pupil
• Lens, if visible

Slit-lamp examination

• Eyelids and conjunctiva
• Corneal epithelium and stroma
• Anterior chamber cells/flare
• Iris
• Lens
• Anterior vitreous

Fluorescein staining

• Corneal abrasion
• Corneal ulcer
• Foreign body-related epithelial defect
• Dendritic ulcer in herpes simplex keratitis
• Seidel sign, indicating aqueous leak from corneal perforation

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G. Intraocular pressure

Tonometry

• Applanation tonometry: most accurate standard method.
• Non-contact tonometry.
• Tono-Pen.

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H. Fundus examination

Direct ophthalmoscopy

1. Red reflex
2. Optic disc
3. Retinal vessels
4. Macula
5. Peripheral retina, as far as visible

Normal findings

• Red reflex: Uniform orange-red glow.
• Optic disc: Pink, well-defined margins.
• Cup-disc ratio: Usually less than 0.5 and similar in both eyes.
• Macula: Darker area temporal to disc, with foveal light reflex in young people.
• Vessels: Arteries narrower and brighter than veins.

Important abnormal findings

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3. Rapid Examination Checklist

• Visual acuity
• Visual fields
• External examination and extraocular movements
• Pupils
• Slit lamp and staining
• Fundus examination

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4. High-Yield Clinical Correlations

• Painful red eye + reduced vision + halos + nausea/vomiting: Think acute angle-closure glaucoma.
• Painful red eye + photophobia + corneal fluorescein uptake: Consider keratitis/corneal ulcer.
• Painless sudden visual loss + RAPD: Consider optic nerve or retinal pathology.
• Flashes, floaters, curtain-like loss of vision: Suspect retinal detachment.
• Ptosis + dilated pupil + ophthalmoplegia: CN III palsy, potentially compressive and urgent.
• Diplopia worse on looking laterally: CN VI palsy.
• Diplopia worse on looking down and in: CN IV palsy.
• Papilloedema: Raised intracranial pressure until proven otherwise.

Anatomy and Examination of the Eye

1. Anatomy of the Eye

Coats of the eyeball

1. Fibrous coat
   • Cornea: Transparent anterior part, main refracting surface.
   • Sclera: Tough white outer coat.
2. Vascular coat / Uvea
   • Iris: Controls pupil size.
   • Ciliary body: Produces aqueous humour and helps accommodation.
   • Choroid: Vascular layer supplying the outer retina.
3. Neural coat
   • Retina: Converts light into nerve impulses.
   • Macula/fovea: Area of maximum visual acuity.
   • Optic disc: Site where optic nerve leaves the eye, blind spot.

Chambers

• Anterior chamber: Cornea to iris.
• Posterior chamber: Iris to lens.
• Both contain aqueous humour.
• Vitreous chamber: Behind lens, contains vitreous gel.

Extraocular muscles

• Lateral rectus: abducts eye, CN VI
• Superior oblique: depresses eye in adduction, CN IV
• Remaining muscles: CN III

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2. Examination of the Eye

Sequence

A. Visual acuity

• Test each eye separately with Snellen chart.
• Use spectacles if normally worn.
• If reduced, test with pinhole.
• Record severe reduction as:
  • CF: counting fingers
  • HM: hand movements
  • PL: perception of light
  • NPL: no perception of light

B. Visual fields

• Test by confrontation in all four quadrants.
• Detects major peripheral field defects.

C. External examination

• Ptosis, lid swelling, discharge
• Redness, conjunctival haemorrhage
• Corneal opacity/foreign body
• Proptosis or enophthalmos
• Compare both eyes.

D. Eye movements

• Test with the H-test.
• Look for diplopia, nystagmus, squint, or restricted movement.

E. Pupils

• Size, shape, equality
• Direct and consensual light reflexes
• Near response
• RAPD with swinging flashlight test

F. Slit lamp and fluorescein

• Slit lamp examines cornea, anterior chamber, iris, lens, and anterior vitreous.
• Fluorescein detects corneal abrasion, ulcer, and aqueous leak.

G. Intraocular pressure

• Measure by tonometry.
• Normal IOP: 10-21 mmHg.
• Do not measure if open-globe injury is suspected.

H. Fundus examination

• Red reflex
• Optic disc
• Retinal vessels
• Macula
• Retina

High-yield findings

• Blurred disc margins: Papilloedema
• Large cup-disc ratio: Glaucoma
• Pale disc: Optic atrophy
• Retinal haemorrhages/exudates: Diabetic or hypertensive retinopathy
• Absent red reflex: Cataract or vitreous haemorrhage

Quick mnemonic

• Visual acuity
• Visual fields
• External exam and eye movements
• Pupils
• Slit lamp
• IOP
• Fundus

Anatomy and Methods of Examination of the Eye

1. Anatomy of the Eye

A. Orbit

• The eye lies in the bony orbit.
• The orbit has 4 walls: roof, floor, medial wall, and lateral wall.
• Most orbital walls are related to paranasal sinuses, so sinus infection can spread to the orbit.

Important openings

• Optic canal: optic nerve (CN II) and ophthalmic artery.
• Superior orbital fissure: CN III, IV, VI, ophthalmic division of CN V, and superior ophthalmic vein.
• Inferior orbital fissure: maxillary division of CN V, infraorbital vessels, and inferior ophthalmic vein.

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B. Eyeball

C. Internal structures

• Anterior chamber: between cornea and iris.
• Posterior chamber: between iris and lens.
• Lens: focuses light on retina.
• Zonules: suspensory ligaments holding the lens.
• Vitreous body: gel filling the posterior cavity.

Simple diagram

                Cornea
                  ↓
      ┌─────────────────────────┐
      │ Anterior chamber        │
      │      Iris → Pupil       │
      │ Posterior chamber       │
      │          Lens           │
      │                         │
      │     Vitreous body       │
      │                         │
      │ Retina → Optic nerve    │
      └─────────────────────────┘
        Sclera = outer coat
        Choroid = vascular coat
        Retina = inner neural coat

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2. Accessory Organs

Eyelids

• Protect the eye and distribute tears.
• Orbicularis oculi closes the eyelids.
• Levator palpebrae superioris elevates the upper eyelid.

Conjunctiva

• Thin transparent mucous membrane.
• Covers the inner surface of eyelids and anterior sclera.

Lacrimal apparatus

• Produces and drains tears.
• Tears lubricate and protect the ocular surface.

Extraocular muscles

• Lateral rectus: CN VI
• Superior oblique: CN IV
• All remaining extraocular muscles: CN III

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3. Methods of Examination of the Eye

1. History

• Reduced vision
• Pain, redness, discharge
• Photophobia
• Floaters or flashes
• Trauma
• Diplopia
• Previous eye disease, surgery, spectacles, and systemic illness

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2. External examination

• Eyelids and lashes
• Conjunctiva and sclera
• Corneal clarity
• Eye position and symmetry
• Swelling, redness, discharge, trauma, or proptosis

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3. Side focal illumination

• Eye is examined under a focused beam of light.
• Helps assess lids, conjunctiva, cornea, anterior chamber, iris, and lens.

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4. Transmitted-light examination

• Light is directed through the pupil.
• Normally produces a pink-red fundus reflex.
• A normal red reflex indicates transparent ocular media.
• Reduced/absent reflex may occur with corneal opacity, cataract, vitreous haemorrhage, or retinal disease.

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5. Visometry

• Test each eye separately.
• Use a Snellen chart where possible.
• Record vision with correction if spectacles are usually worn.
• If vision is poor: document counting fingers, hand movements, light perception, or no light perception.

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6. Biomicroscopy

• Examination of the eye using a slit lamp microscope.
• Allows detailed examination of:
  • Cornea
  • Anterior chamber
  • Iris
  • Lens
  • Anterior vitreous

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7. Intraocular pressure measurement

• Measures pressure inside the eye using tonometry.
• Important for detecting and monitoring glaucoma.
• Normal intraocular pressure is approximately 10-21 mmHg.

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8. Ophthalmoscopy

• Optic disc
• Retinal vessels
• Macula
• Retina

Types

• Direct ophthalmoscopy: through the pupil; upright, magnified view.
• Indirect ophthalmoscopy: wider view of retina.
• Binocular ophthalmoscopy: stereoscopic retinal view.
• Biomicroscopic ophthalmoscopy: slit lamp with lens.
• Fundus photography: documents retinal findings.

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9. Imaging investigations

Ultrasound

• Ocular biometry: measures dimensions of the eye.
• Ophthalmo-echography: evaluates intraocular and orbital structures, especially when fundus cannot be seen.

Optical coherence tomography, OCT

• High-resolution cross-sectional imaging.
• Used for:
  • Retina and macula
  • Optic disc
  • Anterior segment

Fluorescein angiography

• Dye-based imaging of retinal circulation.
• Detects retinal vascular leakage, ischemia, and neovascularisation.

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Quick Revision Box

EYE EXAMINATION

History
   ↓
Visual acuity
   ↓
External examination
   ↓
Focal illumination / slit lamp
   ↓
Red reflex
   ↓
Intraocular pressure
   ↓
Fundus examination
   ↓
OCT / ultrasound / fluorescein angiography if needed

1. Simple Diagram of Eyeball

                      OPTIC NERVE
                           │
                           ▼
       ______________________________________
      /                                      \
     /                                        \
    |              VITREOUS BODY               |
    |                                           |
    |   Retina  ───────────────────────────►    |
    |   Choroid ───────────────────────────►    |
    |   Sclera  ───────────────────────────►    |
    |                                           |
    |                      LENS                 |
    |                     (  )                  |
    |                      │                    |
    |                   IRIS                    |
    |                    │                      |
    |                  PUPIL                    |
     \        ANTERIOR CHAMBER                 /
      \____________ CORNEA ___________________/

      Outer to inner: Sclera → Choroid → Retina

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2. Chambers of the Eye

CORNEA  →  Anterior chamber  →  IRIS  →  Posterior chamber  →  LENS
                 │                              │
                 └────── Aqueous humour ────────┘

LENS  →  Vitreous chamber  →  Retina
             │
             └── Vitreous body

Aqueous humour flow

Ciliary body
     ↓
Posterior chamber
     ↓ through pupil
Anterior chamber
     ↓
Trabecular meshwork
     ↓
Canal of Schlemm

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3. Extraocular Muscles

                 Superior rectus
                       ↑
                       │
  Medial rectus  ←   EYE   →  Lateral rectus
                       │
                       ↓
                 Inferior rectus

Superior oblique: depresses adducted eye
Inferior oblique: elevates adducted eye

LR6 SO4, all others 3
Lateral rectus = CN VI
Superior oblique = CN IV
All others = CN III

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4. Examination Flow Diagram

HISTORY
   ↓
VISUAL ACUITY
   ↓
EXTERNAL EXAMINATION
   ↓
PUPILS + EYE MOVEMENTS
   ↓
SLIT-LAMP EXAMINATION
   ↓
INTRAOCULAR PRESSURE
   ↓
OPHTHALMOSCOPY / FUNDUS EXAMINATION
   ↓
OCT / ULTRASOUND / FAG if required

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5. Fundus Diagram

             Retina
        __________________
       /                  \
      |    Optic disc      |──── Optic nerve
      |        ●           |
      |       / \          |
      |      /   \         |  Retinal vessels
      |                    |
      |             ●      |
      |          Macula    |
      |          /Fovea    |
       \__________________/

• Optic disc = blind spot
• Macula/fovea = maximum visual acuity
• Retina = light-sensitive neural layer