Anatomy of eye

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I now have rich textbook content and multiple high-quality diagrams. Here is a complete, well-illustrated guide to the anatomy of the eye.

Anatomy of the Eye

Overview

The eyeball is a roughly spherical structure sitting in a bony socket (orbit) in the skull. It is ~24 mm in diameter and is composed of three concentric coats (tunics) surrounding fluid-filled chambers.

Cross-section of the eye showing all major labeled structures

Fig. 1 - Complete cross-sectional anatomy of the eye (Ganong's Review of Medical Physiology, 26th Ed.)

1. The Three Tunics (Coats) of the Eyeball

A. Outer Fibrous Tunic

Structure	Description
Sclera	The tough, white, opaque outer coat covering the posterior 5/6 of the eyeball. It is protective and maintains the shape of the globe. No light passes through it.
Cornea	The transparent, avascular anterior modification of the sclera covering the front 1/6. Light enters through it. It is nourished by the aqueous humor (not blood vessels). It is continuous with the conjunctiva at its lateral margin (limbus).

B. Middle Vascular Tunic (Uvea)

The uvea comprises three interconnected structures: the choroid, ciliary body, and iris.

Structure	Description
Choroid	A highly vascular layer lining the posterior 2/3 of the sclera. Provides oxygen and nutrients to the outer retina.
Ciliary body	Contains circular and longitudinal smooth muscle fibers. Attached near the corneoscleral junction. Controls lens shape for accommodation. Also produces aqueous humor.
Iris	The pigmented, opaque, colored disc in front of the lens. Contains two muscles: sphincter pupillae (miosis - parasympathetic) and dilator pupillae (mydriasis - sympathetic). Variations in pupil diameter produce up to a 16-fold change in light reaching the retina.

C. Inner Neural Tunic

Structure	Description
Retina	Neural tissue lining the posterior 2/3 of the choroid. Contains the photoreceptors (rods and cones). The point of greatest visual acuity is the fovea centralis, located within the macula lutea.

2. Lens and Supporting Structures

Gross anatomy showing pupil, iris, cornea, extraocular muscles and optic nerve

Fig. 2 - Gross anatomy of the eye showing external structures and the eyeball in its orbit (Neuroscience: Exploring the Brain, 5th Ed.)

Structure	Description
Crystalline Lens	A transparent, biconvex structure behind the iris. Its shape is changed by the ciliary muscle to focus near or far objects (accommodation).
Zonule (Suspensory Ligament)	Zonule fibers (of Zinn) attach the lens to the ciliary body and hold it in place. Relaxation of the ciliary muscle tenses the zonule and flattens the lens; contraction relaxes the zonule and allows the lens to become more convex.

3. Internal Chambers and Fluids

Cross-section showing light path, lens, ciliary muscle, vitreous humor, fovea, and optic nerve

Fig. 3 - Internal cross-section showing the path of light and lens support system (Neuroscience: Exploring the Brain, 5th Ed.)

Chamber	Location	Contents
Anterior Chamber	Between cornea and iris	Aqueous humor
Posterior Chamber	Narrow space between iris, zonule, and lens	Aqueous humor
Vitreous Chamber (Posterior Cavity)	Between lens and retina	Vitreous humor (clear, gelatinous)

Aqueous Humor:

Produced by the ciliary body via diffusion and active transport from plasma
Clear, protein-free liquid that nourishes the cornea and lens
Flows: ciliary body → posterior chamber → through pupil → anterior chamber → drained via trabecular meshwork into the Canal of Schlemm (at the filtration angle/iridocorneal angle)
Obstruction of drainage raises intraocular pressure (IOP) → risk factor for glaucoma

Vitreous Humor:

More viscous and jellylike than aqueous humor
Lies between lens and retina
Keeps the eyeball spherical

4. The Retina in Detail

Ophthalmoscopic view of the retina showing optic disk, macula, fovea, blood vessels

Fig. 4 - Retina as viewed through an ophthalmoscope showing the optic disk (blind spot), macula, fovea, and retinal blood vessels (Neuroscience: Exploring the Brain, 5th Ed.)

Feature	Detail
Optic Disk	Where the optic nerve exits; blood vessels originate here; contains NO photoreceptors = physiological blind spot
Macula Lutea	Central region of the retina; responsible for high-acuity color vision
Fovea Centralis	The pit at the center of the macula; highest density of cones; point of sharpest vision
Nasal vs Temporal Retina	The retina is divided by a vertical line through the fovea into nasal (medial) and temporal (lateral) halves
Central Artery/Vein	Travel with the optic nerve; the central retinal artery and vein branch across the retinal surface

5. Extraocular Structures

Structure	Function
Conjunctiva	Clear mucous membrane folding from the inner eyelids onto the anterior sclera. Keeps the surface moist.
Lacrimal Apparatus	Lacrimal gland (superolateral orbit) produces tears, which drain via lacrimal duct into the nose. Blinking spreads tears across the cornea.
Extraocular Muscles	3 pairs (6 muscles total) inserted into the sclera move the eyeball in the orbit: superior/inferior rectus, medial/lateral rectus, superior/inferior oblique.
Orbit	Bony eye socket in the skull that protects the globe.

6. Pupil Control - Autonomic Summary

Action	Muscle	Nerve
Miosis (constriction)	Sphincter pupillae	Parasympathetic (CN III)
Mydriasis (dilation)	Dilator pupillae	Sympathetic (cervical chain)

7. Light Path Through the Eye

Light enters in this sequence: Cornea → Aqueous Humor → Pupil → Lens → Vitreous Humor → Retina (Fovea)

Refraction occurs primarily at the cornea (greatest bending) and the lens (fine-tuned by accommodation). The image is focused inverted and reversed on the retina.

Sources:

Ganong's Review of Medical Physiology, 26th Ed., Chapter 10 (Eye Anatomy)
Neuroscience: Exploring the Brain, 5th Ed., Chapter 9 (Gross & Cross-Sectional Anatomy of the Eye)
Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Ed., Chapter 17 (Anatomy of the Eye for Ophthalmologic Anesthesia)

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