Anatomy & Physiology: The Eye – Structures, Dissection, and Muscles

The Eye: Structures, Dissection, and Muscles

Overview

This study guide covers the anatomical structures of the human and cow eye, including external and internal features, as well as the extrinsic muscles responsible for eye movement. Understanding these components is essential for practical lab identification and for comprehending the functional anatomy of the visual system.

Human Eye Structures

Looking at Your Own Eye in a Mirror

• Pupil: The central opening in the iris that regulates the amount of light entering the eye.

• Iris: The colored part of the eye (can be blue, brown, green) that controls the size of the pupil.

• Sclera: The white, opaque outer layer of the eyeball, often visible around the iris; covered by the conjunctiva.

• Lacrimal caruncle: The small, pink, globular nodule at the inner corner (medial canthus) of the eye, containing sebaceous and sweat glands.

Viewing a Lab Partner’s Eye from the Side

• Cornea: The transparent, dome-shaped surface that covers the front of the eye and allows light to enter.

Cow Eye Dissection

External Structures

• Optic nerve: The nerve that transmits visual information from the retina to the brain.

• Sclera: The tough, white outer layer of the eyeball.

• Conjunctiva: The thin, transparent membrane covering the sclera and lining the inside of the eyelids.

• Cornea: The clear, curved front surface of the eye, continuous with the sclera.

Internal Structures

• Vitreous (body) humor: The clear, gel-like substance filling the space between the lens and the retina, helping maintain the eye’s shape.

• Retina: The innermost layer of the eye containing photoreceptor cells (rods and cones) that detect light and convert it into neural signals.

• Optic disc (blind spot): The point on the retina where the optic nerve exits the eye; lacks photoreceptors, creating a natural blind spot.

• Choroid: The vascular layer between the retina and sclera, providing oxygen and nutrients to the eye.

• Ciliary body: The structure containing the ciliary muscle and ciliary processes; controls lens shape and produces aqueous humor.

• Ora serrata: The serrated junction between the retina and the ciliary body.

• Suspensory ligaments: Fibers that connect the ciliary body to the lens, holding it in place and enabling focus adjustment.

• Lens: The transparent, biconvex structure that focuses light onto the retina.

• Pupil: The opening in the center of the iris through which light enters the eye.

• Anterior chamber: The fluid-filled space between the cornea and the iris, containing aqueous humor.

• Posterior chamber: The small space between the iris and the lens, also filled with aqueous humor.

Human Eye Model and Diagrams

• Be able to locate and identify the same structures listed above in both external and internal views of the cow eye dissection.

• Familiarize yourself with the Snellen Eye Chart, which is used to measure visual acuity.

Six Extrinsic Muscles of the Eye

The extrinsic (extraocular) muscles control the movement of the eyeball within the orbit. Each muscle has a specific function in directing the gaze.

• Superior rectus: Elevates the eye (moves it upward) and turns it medially.

• Inferior rectus: Depresses the eye (moves it downward) and turns it medially.

• Medial rectus: Moves the eye medially (toward the nose).

• Lateral rectus: Moves the eye laterally (away from the nose).

• Superior oblique: Depresses the eye and turns it laterally.

• Inferior oblique: Elevates the eye and turns it laterally.

Summary Table: Extrinsic Eye Muscles and Their Actions

Muscle	Primary Action
Superior rectus	Elevation, medial rotation
Inferior rectus	Depression, medial rotation
Medial rectus	Medial movement (adduction)
Lateral rectus	Lateral movement (abduction)
Superior oblique	Depression, lateral rotation
Inferior oblique	Elevation, lateral rotation

Example: Application in Clinical Practice

• Testing the function of each extrinsic muscle is part of a standard cranial nerve examination. For example, the lateral rectus is innervated by the abducens nerve (CN VI), and its dysfunction can result in an inability to move the eye laterally.

Additional info: The structures and muscles listed are essential for understanding both normal vision and common clinical conditions such as strabismus (misalignment of the eyes), cataracts (clouding of the lens), and glaucoma (increased intraocular pressure affecting the optic nerve).