Anatomy of the Eyeball
• Complex, spherical organ for vision.
• Situated in the orbit of skull, protected by eyelids, eyelashes, and bony structures.
• Understanding anatomy is important for vision and ocular disease management.
External Features of Eyball
• Average diameter: 24 mm
• Only cornea & part of sclera visible; rest inside orbital cavity.
Dimensions of Eyball
• Anteroposterior diameter (axial length): 24 mm (adult)
• Horizontal diameter: 23.5 mm
• Vertical diameter: 23 mm
• Circumference: 75 mm
• Volume: 6.5 ml
• Weight: 7.5 g
• Newborn eyeball: 16–18 mm axial length (grows to 24 mm in adulthood).
Layers of Eyeball
1. Fibrous Layer (Outer)
• Sclera: White, tough, opaque; maintains shape; muscle attachment; covers posterior 5/6.
• Cornea: Transparent, dome-shaped; major refractive surface; anterior 1/6.
• Limbus: Cornea–sclera junction.
2. Vascular Layer (Middle / Uvea)
• Choroid: Pigmented, vascular; nourishes retina & absorbs scattered light.
• Ciliary Body: Has ciliary muscle & processes; controls lens shape; produces aqueous humor.
• Iris: Colored part; regulates pupil size → controls light entry.
3. Nervous Layer (Inner)
• Retina: Contains rods & cones; converts light → electrical signals → optic nerve → brain.
Internal Structures
• Lens: Transparent, biconvex; focuses light onto retina (accommodation).
Chambers
• Anterior Chamber: Between cornea & iris; depth ~2.5 mm; contains ~0.25 ml aqueous humor.
• Posterior Chamber: Between iris & lens; triangular; contains ~0.06 ml aqueous humor.
• Vitreous Chamber: Largest, behind lens; filled with vitreous humor (gel) to maintain shape.
Humors
• Aqueous Humor: Clear fluid; nourishes cornea & lens; maintains intraocular pressure.
• Vitreous Humor: Jelly-like; fills vitreous chamber; supports retina.
Optic Nerve
• Exits posteriorly; transmits retinal signals to brain.
Blood Supply
• Mainly from ophthalmic artery (branch of internal carotid).
• Central retinal artery → inner retina.
• Posterior ciliary arteries → choroid.
Nerve Supply
• Vision: Optic nerve (CN II).
• Sensation: Ophthalmic branch of trigeminal nerve (CN V).
• Extraocular muscles: Oculomotor (III), Trochlear (IV), Abducens (VI).
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