Blind Spot
Small area in the visual field corresponding to the retina’s optic disc or optic nerve head (where the optic nerve emerges), where no photoreceptors are present and where there is no sensitivity to light; not noticed with both eyes open because the part of the visual field containing the blind spot of one eye is overlapped by a light-sensitive area in the other eye

Conjunctiva
The thin, moist tissue that lines the inner surfaces of the eyelids and the outer surface of the sclera.

Cornea
The transparent, anterior, dome-shaped portion of the eyeball that covers the iris and pupil, acting like a window which admits light into the eye

Crystalline Lens
The highly transparent biconvex, lens-shaped or nearly spherical body in the eye, situated immediately behind the pupil, which focuses light rays entering the eye typically onto the retina

Eyelid
Either of the movable lids of skin and muscle that can be closed over the eyeball, providing eye protection and distribution of tears over the cornea while blinking

Gland, Lacrimal
Tear gland; a gland, about the size and shape of an almond, that is the major producer of a watery secretion which forms the middle (lacrimal), thickest layer of the tear film

Glands, Tear
Glands located near the eye and in the eyelids which produce the lipid, lacrimal, and mucoid layers of the tear film coating the surface of the cornea; consist of the lacrimal gland, Meibomian glands, Zeis glands, Krause glands, Wolfring glands

Iris
Contains pigment that determines the color of the eye and helps regulate the amount of light that enters the eye.

Limbus
Junction between the cornea and the sclera

Optic disc (or disk)

Optic nerve head in the eye, in which no photoreceptors are present, thus resulting in a blind spot in the visual field

Optic nerve
The sensory nerve which carries electrical impulses from visual stimuli in the retina out of the eye to the visual cortex of the brain for interpretation

Optic neuritis
Inflammation of the optic nerve within the eyeball or behind the eyeball

Optic neuropathy
An abnormal and usually degenerative state of the optic nerve

Orbit
Eye socket; the bony cavity of the skull that contains the eye

Photoreceptors
Light-sensitive cells (cones and rods) in the retina; contain chemicals which react to specific wavelengths of light and trigger nerve impulses

Posterior chamber
A narrow space inside the eye, located behind the peripheral part of the iris and in front of the suspensory ligament of the lens and the ciliary processes; contains aqueous humor

Posterior compartment

The large space inside the eye, located posteriorly to the crystalline lens; contains the vitreous humor

Pupil
The contractile, usually round aperture in the iris of the eye which allows light to pass into the crystalline lens.

Punctum

The opening of either the upper or the lower tear duct at the inner corner of the eye

Retina
Layer of nervous tissue, covering the back two-thirds of the eyeball, in which stimulation by light initiates an electrochemical reaction in which electrical impulses are transmitted to the brain, producing the sensation of vision; actually an extension of the brain, formed embryonically from brain tissue and connected to the brain proper by the optic nerve

Sclera
The tough, white, outer layer of the eyeball; with the cornea, it protects the entire eyeball.

Vitreous Humor

A clear, jelly-like substance that fills the middle of the eye.