The ability of the eye to readjust its focus from remote to close to objects; procedure achieved by the lens an altering its shape. The lens in the eye is an elastic framework that alters shape in bespeak to emphasis things close to or much onto the retina. Optically, the greater the curvature that the lens, the higher its refractive power. To lug close objects into focus on the retina the lens must have a greater refractive power than in its relaxing state. This is accomplished via contraction of the ciliary muscles that host the lens in place. When these muscle yarn contract, the lens, via that elasticity, springs right into a much more convex shape permitting a focused image of close to objects. This is an energy requiring process since muscular initiative is necessary, and also therefore deserve to be tiring.

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Anterior Chamber

This front room of the three uncovered in the eyeball is found between the cornea and also the iris.

Aqueous Humor, Aqueous liquid (A-kwe-us)

Clear, watery liquid that operation between and also nourishes the lens and the cornea; secreted by the ciliary processes. This fluid fills the anterior and also posterior chambers. It is do by cells of the ciliary body and circulates native the posterior chamber, over the lens come the anterior chamber and exits via the Canal the Schlemm. That is comparable to plasma yet contains very tiny protein.

Astigmatism (uh-STIG-muh-tizm)

A condition in which the surface ar of the cornea is not spherical; reasons a blurred picture to be received at the retina.

Binocular Vision

The mix of the separate photos seen by every eye into a single image; enables images to it is in seen with depth.

Blind Spot

(1) A little area the the retina where the optic nerve enters the eye; occurs normally in every eyes. (2) any gap in the intuitive field corresponding to an area that the retina whereby no visual cells room present; connected with eye disease.

Central Retinal Artery

Blood vessel that carries blood into eye; offers nutrition to the retina.

Central Retinal Vein

Blood vessel that carries blood native the retina.

Choroid (KOR-oyd)

This is the vascular great of the eye. A class filled through blood vessels that nourishes the retina; component of the uvea.

Ciliary Body

This is an growth of the choroid in ~ the former of the eye at the level of the lens. The lens is attached to the ciliary body, which has actually smooth muscle in ~ it. Contraction of this smooth muscle transforms the shape of the lens and enables the eye to focus on objects. Part of the ciliary human body is dedicated to do aqueous humor.

Ciliary Muscles

The muscles that relax the zonules to enable the lens to change shape in order come focus.

Ciliary Processes

The extensions or projections the the ciliary body the secrete aqueous humor.

Cones, Cone Cells

One kind of dedicated light-sensitive cells (photoreceptors) in the retina that administer sharp main vision and color vision. Also see RODS.

Conjunctiva (KAHN-junk-TY-vuh)

The thin, moist organization (membrane) the lines the inner surface of the eyelids and the external surface the the sclera.

Contrast Sensitivity

The capacity to perceive differences between an object and its background.

Cornea (KOR-nee-uh)

Transparent, colorless anterior making up one 6th of the extending of the eyeball. The cornea is composed of 5 layers; the external layer consisting of epithelium created of 5-6 layers of cells that turnover every 7 work or so. This layer and the internal endothelium room responsible for keeping the cornea transparent. They do this by maintaining the middle layers relatively dehydrated, i m sorry keeps the parallel collagen fibers current there from gift opaque. The cornea contains no blood vessels and also gets its nutrients from those in the anterior chamber fluid and also surrounding vessels.


A procedure by which the pupil is in the interim enlarged through special eye drops (mydriatic); allows the eye treatment specialist to much better view the inside of the eye.


Tiny yellow or white deposits in the retina or optic nerve head.

Fluorescein Angiography (FLOR-uh-seen an-jee-AHG-ruh-fee)

A test to research blood ship in the retina, choroids and also iris. A one-of-a-kind dye is injected right into a vein in the arm and pictures are taken together the dye passes through blood ship in the eye.

Fovea (FOH-vee-uh)

This committed area of the retina is for the most acute vision. As soon as a human being is proactively focusing or attending to an object the eye are moved so the the photo is concentrated on the fovea. The is thinner, containing just the cones vital for detection of sharp images. The cones in this area are long and also thin, resembling rods, so the they have the right to be closely packed. Blood vessels are lacking as well. Every foveal cone is directly associated to a neuron in the optic nerve.


The internal lining that the eyeball, consisting of the retina, optic disc, and also macula; section of the inside eye that deserve to be seen during an eye check by looking with the pupil.

Hyperopia (hy-pur-OH-pee-uh)

Farsightedness; capacity to see far-off objects more clearly than nearby objects; might be corrected through glasses or contact lenses.

Intraocular press (IOP)

Pressure that the fluid inside the eye; typical IOP varies amongst individuals.


Another development of the choroid that partly covers the lens formed by colors cells, fibroblasts, blood vessels and contractile colors cells. The pigment found in the iris prevents light native entering the eye except through the pupil. The melanocytes (pigmented cells) space responsible because that the shade of the eyes. If over there is little pigment in the cells the light reflected from the choroid at the earlier of the eye will make the iris show up blue. Together the amount of pigment increases the iris shows up greenish-blue, gray or brown.

Lacrimal Gland (LAK-rih-mul)

The small almond-shaped framework that to produce tears; situated just over the outer corner of the eye.

Legal Blindness

In the U.S., (1) visual acuity that 20/200 or worse in the much better eye v corrective lenses (20/200 method that a human must be at 20 feet from an eye graph to check out what a human being with typical vision deserve to see in ~ 200 feet) or (2) intuitive field limited to 20 levels diameter or much less (tunnel vision) in the better eye. NOTE: this criteria are provided to identify eligibility because that government handicap benefits and do no necessarily indicate a person"s capacity to function.


This biconvex framework is very elastic, at least in the young. With age the lens loser its elasticity and also therefore the ability to emphasis on near objects decreases. The facility of the lens is developed by elongated cells (fibers) that have lost all organelles and are filled with special proteins referred to as crystallins. These fibers are changed throughout life however the renewal slows down with age. Mature cataracts occur when these fibers accumulate pigment granules so the they are much less transparent.

Low Vision

Visual loss that cannot it is in corrected through eyeglasses or contact lenses and also interferes with everyday living activities.

Macula (MAK-yoo-luh)

The small, perceptible area that the main retina; offers vision for fine work and reading.

Myopia (my-OH-pee-uh)

Nearsightedness; capability to view close objects more clearly than distant objects; might be corrected with glasses or contact lenses.


After the eyes space dilated, this tool gives the eye treatment professional with a broader view the the retina.

Optic Cup

The white, cup-like area in the center of the optic disc.

Optic Disc/Optic Nerve Head

The one area (disc) wherein the optic nerve connects to the retina.

Optic Nerve

The bundle of end one million nerve yarn that carry visual messages from the retina to the brain.


The frontal, maxilla, zygomatic, sphenoid, ethmoid, lacrimal and palatine bones form this cone-shaped cavity in the skull. This bones are thin and also are frequently subject come fractures. The eye occupies the front portion on the cavity with the remainder being filled v fat, nerves, blood vessels, muscle and the lacrimal (tear) gland.

Posterior Chamber

This room occupies room between the iris and the lens.

Peripheral Vision (per-IF-ur-al)

Side vision; ability to watch objects and movement outside of the straight line that vision.


Tool that measures the prescription because that corrective lenses.

Posterior Chamber

The an are between the earlier of the iris and the front challenge of the vitreous; filled with aqueous fluid.

Presbyopia (prez-bee-OH-pee-uh)

The steady loss of the eye"s capacity to change focus (accommodation) for seeing close to objects brought about by the lens ending up being less elastic; connected with aging; occurs in practically all human being over period 45.


Round opening in the iris that allows light to pass through. Pupil size changes based upon the lot of irradiate present. Much more light reasons the pupil to contract when the pupil widens in the dark to collection as much light together possible.


A test to determine the ideal eyeglasses or call lenses to correct a refractive error (myopia, hyperopia, or astigmatism).

Retina (RET-in-nuh)

This photosensitive component of the eye lies in between the vitreous body and the choroid layer in ~ the earlier of the eyeball and is a complicated network of photosensitive cells and also various types of neurons. Light that reaches the retina must travel through several layers the transparent neurons in ~ the former of the retina prior to reaching the photosensitive rods and cones. The photosensitive component of rods and also cones is housed in expansions of the cells that look similar to their names. The rods are responsible for black and also white vision if the cap detect color. The neurons in ~ the retina action to incorporate the visual signals received by the rods and cones and transfer the info to the optic nerve.

Retinal colors Epithelium (RPE) (ep-ih-THEE-lee-um)

This great lying between the retina and also choroid, has melanocytes the make for its characteristic black color color. This pigment layer nourishes the retinal cells and enables the inside of the eye to absorb stray light ray of light prefer the black repaint inside a camera or in ~ a dark room.

Rods, stick Cells

One type of committed light-sensitive cell (photoreceptors) in the retina that administer side vision and also the capacity to see objects in dim irradiate (night vision).

Schlemm’s Canal

This canal drains liquid from the anterior chamber. Obstruction the this canal leads to an boosted intraocular pressure, i beg your pardon can damage the retina. This condition is also called glaucoma.

Slit Lamp

A cleft lamp, v its high magnification, allows the eye treatment professional to study the front of the eye.

Sclera (SKLEH-ruh)

The tough, white, external layer (coat) the the eyeball; together with the cornea, that protects the whole eyeball.


A device that measures pressure within the eye and is one of several tests crucial to finding glaucoma.


The conventional to recognize the fluid pressure inside the eye (intraocular pressure).

Trabecular Meshwork (truh-BEC-yoo-lur)

The spongy, mesh-like tissue close to the former of the eye that permits the aqueous liquid (humor) to flow to Schlemm"s canal and also then the end of the eye with ocular veins.

Uvea, Uveal tract (YOO-vee-uh)

The middle coat the the eyeball, consists of the choroid in the back of the eye and the ciliary body and also iris in the prior of the eye.

Visual Acuity

The capacity to differentiate details and shapes of objects; also called main vision.

Visual Field

The entire area that deserve to be seen once the eye is forward, consisting of peripheral vision.

Vitreous (VIT-ree-us)

The transparent, colorless massive of gelatin that lies behind lens and also in former of retina.

Vitreous Space

The chamber the occupies the space behind the lens to the retina. It is filled with a gelatinous substance dubbed the vitreous body.

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Zonules (ZAHN-yoolz)

The yarn that keep the lens rely in position and enable it to readjust shape throughout accommodation.

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