Eye Anatomy and Function Quiz

Study Notes

Eye Anatomy and Function

The eye is located in the bony orbital cavity, protected by a cushion of fat.
The palpebral fissure is the elliptical open space between the eyelids.
Tarsal plates contain meibomian glands, which secrete oil to lubricate the eyelids.
The conjunctiva is a transparent protective covering over the eye.
The cornea covers and protects the iris and pupil.
The lacrimal apparatus provides irrigation to the eye.

Extraocular Muscles

Six extraocular muscles, attached to the orbit, control eye movement.
Muscles work in pairs to allow both straight and rotary movements.
Parallel axes are important for binocular, single-image vision.
Eye movement is controlled by three cranial nerves:
- Abducens nerve (Cranial Nerve VI) innervates the lateral rectus muscle, responsible for abduction of the eye.
- Trochlear nerve (Cranial Nerve IV) innervates the superior oblique muscle.
- Oculomotor nerve (Cranial Nerve III) innervates the superior, inferior, and medial rectus muscles, as well as the inferior oblique muscle.

Internal Anatomy: Three Concentric Coats

Outer Fibrous Layer
- Sclera: tough, protective, white outer covering.
- Cornea: transparent, allows light to enter the eye and bends incoming light rays for focus.
- Corneal Reflex: contact with a wisp of cotton stimulates a blink in both eyes, involving the trigeminal nerve (afferent) and facial nerve (efferent).
Middle Vascular Layer
- Choroid: dark pigmented layer preventing light reflection, vascularized to supply blood to the retina.
- Iris: functions as a diaphragm, controlling pupil size.
  - Pupil constriction occurs in bright light and for near vision, controlled by the parasympathetic nervous system (cranial nerve III).
  - Pupil dilation occurs in dim light and for far vision, controlled by the sympathetic nervous system.
- Pupil: round and regular opening in the center of the iris.
- Lens: biconvex disc located behind the pupil, a refracting medium for focusing on the retina.
- Anterior and Posterior Chambers: contain aqueous humor, produced by the ciliary body and continuously flowing to provide nutrients and drain waste.
- Intraocular Pressure: determined by the balance between aqueous production and outflow resistance.
Inner Layer
- Retina: visual receptive layer, converting light waves into nerve impulses.
  - Can be examined using an ophthalmoscope to view the optic disc, retinal vessels, background, and macula.
- Optic Disc: area where retinal fibers converge to form the optic nerve, located nasally, with specific color, shape, and margin characteristics.
- Retinal Vessels: paired artery and vein in each quadrant.
- Macula: slightly darker pigmented area located temporally, responsible for central vision.

Visual Pathways and Visual Fields

Light rays are refracted through the transparent media of the eye (cornea, aqueous humor, lens, vitreous humor) and strike the retina.
The image projected on the retina is inverted and reversed.
Nerve impulses travel through the optic nerve, optic chiasm, optic tract, thalamus, and finally to the visual cortex in the occipital lobe of the brain.
Each optic nerve carries impulses from the same half of each retina.
This ensures that each side of the brain receives visual information from both eyes.
The right side of the brain receives impulses from the left visual field, and the left side receives impulses from the right visual field.