Changing the shape of the eye’s lens to focus on near and far objects.

The capacity to discriminate fine details of objects.

Type of glaucoma in which the aqueous is trapped by the iris bending too close to the cornea. If this occurs suddenly, it may be a medical emergency.

Chemical coatings applied to lenses to reduce glare inside and outside eyeglasses. Reduced glare improves both day and night vision and reaction time, thereby enhancing safety. Coatings also make eyeglasses more attractive to look at by reducing their “shop window” appearance.

The diameter (mm) of the opening of an optical system which determines the size of the shaft of light that travels through the instrument; the diameter of an objective lens of a telescope or microscope.

A watery liquid between the lens and cornea which bathes and feeds the cornea, lens and iris.

A lens with a front surface that is not curved like a sphere and that has a relatively flatter outside edge. Useful for correction of high refractive errors.

A common vision defect caused by the irregular shape of the cornea which blurs and distorts eyesight.

The first stage of diabetic retinopathy. Although vision is rarely affected at this stage, there is bloodvessel damage.

Eyeglasses with two visioncorrection zones one for seeing near objects and one for distance vision. Bifocal lenses are really two lenses, with an obvious line separating the two viewing zones.

The brain’s ability to combine the images received in both eyes to form a single, sharp image. Convergence and divergence of both eyes are necessary to achieve binocular vision at all distances.

The connection point of the optic nerve from the retina to the brain. There are no rods or cones around this area of the retina. Therefore, this is the one part of the eye which does not sense light, or “see.”

Cloudiness of the eye’s crystalline lens, which may prevent a clear image from forming on the retina.

The central area of the field of view in which vision is strongest and sharpest in humans.

A harmless bump caused by a blocked oilgland duct in the upper or lower eyelid.

The middle membrane of the eye, the choroid is part of the uveal tunic, between the retina and outer coating. It supplies blood to the eye. See uvea.

The form of angleclosure glaucoma in which the pressure build up of liquid in the front part of the eye acts over time and not suddenly.

Also called the ciliary body. A tiny muscle that changes the thickness of the lens to achieve close and distant vision.

Secretes the liquid from behind the iris which feeds and bathes the middle and front eye structures.

A vision defect in which colors are not seen normally. A term covering a broad range of conditions in which colorsensing cone cells of the eye are either absent or do not function properly.

Defined by the American Academy of Optometry as “the complex of eye and vision problems related to near work which are experienced during or related to computer use.”

Coneshaped photoreceptors located in the retina that sense color and detail in bright lighting conditions. Three pigments of cones sense the three colors of light (red, green and blue) to provide color vision.

The ability of both eyes to converge, or move closer together, in order to focus on near objects.

A relief map that reveals corneal contours and shows any variations in corneal curvature.

An operation that removes a defective cornea and replaces it with healthy corneal tissue from a donor. When used for keratoconus, it has a 90% success rate.

The eye’s outer window. Sensitive, protective and transparent, the cornea’s unchanging, curved surface provides 75% of the eye’s focusing ability, or refractive index.

With this type of cataract, wedgeshaped spokes extend from the outer rim of the lens to the central core (nucleus). The spokes block light, causing glare and loss of contrast.

The common name for strabismus. Crossedeyes, or (more accurately) eye misalignment, is a common vision defect in which either one or both eyes are turned inward, outward, upward or downward. One or both eyes may show irregular movement. Many factors can cause this defect, including the development and shape of the eye and its component parts, muscles within and around the eye, eyebrain functioning and the presence of disease or brain disorders.

Microscopic pockets, located in the loose sections of conjunctiva around the eyeball, that secrete mucin into tears.

A retinal bloodvessel disease that affects people with diabetes.

Sensitivity to two colors rather than the three needed to perceive all the colors in the spectrum by combining primary colors.

The ability of both eyes to diverge, or move further apart, in order to focus on distant objects.

Dryness of the eye’s surface caused by too little tear production, too much tear drainage, changes in tear quality and a host of other problems. Symptoms include red, burning eyes and foreign body sensations.

In this operation, an eye surgeon grafts a layer of corneal epithelial cells (“skin” cells from the cornea’s upper layers) around the central cone of someone with keratoconus. The grafted cells flatten the cornea, improving nearsightedness and blurred vision. This operation has a success rate to similar corneal transplantation.

The size of a shaft of light transmitted to the eye through a telescope or pair of binocular lenses; an important indicator of lowlight performance; usually measured in millimeters (diameter).

The surgical removal of a cloudy lens that opens the front but leaves the back of its surrounding capsule intact.

The distance between the eye and an eyepiece of a telescope, set of binoculars or microscope.

The liquid form of any active medication (in various strengths) that is applied by letting a drop glide under the lower eyelid. Some conditions require taking colorcoded types of eye drops at specific moments in a day.

The organ of sight. The key parts of the eye are as follows the sclera, the choroid, the cornea, the aqueous humour, the iris, the pupil, the lens, the vitreous humor, the retina, the macula, the fovea and the optic nerve.

A common name for hyperopia, a widespread vision defect in which distant objects are seen clearly and close objects are seen less clearly. Farsightedness occurs when the eye is too short and/or the cornea too flat.

The width, measured in degrees, feet or millimeters, of the viewing area visible through a pair of binoculars, a telescope or a microscope at a specified distance.

Stimulation of the retina and/or optic nerve that creates the illusion that we are seeing “stars” or streaks of light. Continuous flashes persisting for more than 20 minutes are potentially dangerous and require immediate medical attention.

A test to detect leaky and abnormal blood vessels in the eye. In hospital, an eye specialist injects a yellow or red dye into an arm vein. Exposed to ultraviolet rays, the dye glows yellow-green. The eye specialist photographs the fluorescent dye, as it travels through blood vessels in the eye.

A small depression in the centre of the macula which contains only cones. The fovea is the area of sharpest vision, or acuity, in the eye.

A layer of the retina, which transmits signals to the optic nerve.

Microscopic glands within the bulbar conjunctiva, arranged in a ring around the cornea, near the scleral junction. Secrete mucin, a proteinous substance that makes up the inner layer of tears.

Oil producing glands that surround the eyelashes. The oil forms the outer layer of tears.

A harsh, uncomfortably bright light or reflection.

Original material used for eyeglasses. Made mainly of sand (silicon dioxide) plus various elements according to special needs (titanium dioxide for thinness). Glass lenses are long lasting and naturally scratch-resistant. But like a regular drinking glass, they may break if you drop them.

Condition with moderate to severe vision loss due to areas of failing optic nerves. Excess pressure exerted by the liquid in the front part of the eye (the aqueous), damages the nerves.

Large glands in the conjunctiva that secrete mucin, which forms the inner layer of tear film. The mucin layer enables tears to glide across the eye’s surface. Missing or damaged in people with dry eye.

Advanced plastic lenses that are thinner and flatter than conventional plastic or glass lenses.

The third wave of plastic materials for those with moderate to severe correction needs. Effectively hides the level of correction.

See farsightedness.

The surgical removal of a cloudy lens and its surrounding capsule.

A measure of how much the liquid contained in front of and behind the iris pushes in all directions (particularly affecting the retina in the back of the eye).

See intraocular pressure.

The colored or pigmented eye tissue behind the cornea. The iris acts like a muscular diaphragm, regulating the amount of light that enters the eye through the pupil.

A mechanical means of measuring the curvature of the cornea. A series of concentric circles is projected on a 3mm wide spot in the central cornea by a keratometer. If wavy lines appear in the circles, the person is nearsighted. By using these lines as a guide, the eye doctor can measure the amount of astigmatism (blurred vision). Can also be used to detect and monitor keratoconus.

Accessory tear glands located under the eyelids where the upper and lower conjunctiva meet.

An almond-shaped gland that produces tears. It is located above the eyeball, under a bone near the eyebrow.

Surgical procedure to reshape the cornea using an excimer laser. Approved for correcting myopia. Also known as PRK.

A common name for amblyopia, the loss or lack of development of vision, usually in one eye during childhood.

A transparent lentil-shaped body behind the iris controlled by the ciliary muscle. The lens provides 25% of the eye’s focusing power. To focus on closeup objects, the ciliary muscle squeezes the lens to make it thicker. For faraway objects, it flattens the lens to make it thinner.

A Latin word, meaning spot, that is used to describe the yellow central area of the retina, where vision is sharpest.

Deterioration of the macula (central spot) of the retina that eventually causes the permanent loss of central vision. There are two types dry and wet. The most common cause of vision loss in people over 60 years of age.

Swelling of the central spot (macula) in the retina, often caused by blood vessel leakage in certain eye diseases, e.g. diabetic retinopathy.

Oil producing glands located within the eyelid. The oil, which forms the outer layer of tears, drains through ducts that open on the eyelid margins.

A new generation of plastic materials that reduces lens thickness while providing the same optical performance as earlier plastics. Recommended for light to moderate correction.

Vision therapy in which a contact lens with closeup correction is worn in one eye, and (if necessary) a contact for distance correction in the other eye.

The perceived motion of near and far objects when either the object or the observer moves.

See nearsightedness.

A common name for myopia, a widespread vision defect in which close objects are seen clearly and distant objects are seen less clearly. Nearsightedness generally occurs because the eyeball is too long or the cornea too curved. Correctable with single-vision lenses.

This type of cataract clouds the central part (nucleus) of the eye’s lens.

A lens or system of lenses that creates an image of an object.

The most common type of glaucoma. Caused by high intracular pressure resulting from clogging of the filter mechanism that returns liquid to the bloodstream from the front chambers of the eye.

A medical doctor specializing in the eye. Has completed medical school. Licensed to examine eyes, treat eye diseases and perform eye surgery.

Also called the optic disk. The area where the optic nerve is attached to the retina and the location of the blind spot.

The bundle of nerve fibers which transmits lightgenerated electrical impulses from the retina to the brain.

Doctors of optometry are independent primary healthcare providers who examine, diagnose, treat and manage diseases and disorders of the visual system, the eye and associated structures as well as diagnose related systemic conditions.

Vision therapy that can strengthen, coordinate and improve the functions of both eyes, especially in the early years of life.

A technique for removing a cloudy lens during cataract surgery. Sound waves are used to shatter the cataract. The broken pieces are vacuumed from the lens capsule using a long, narrow tube.

Lenses that darken in bright sunlight and clear in dim light.

Cells at the back of the retina containing light-sensitive pigments. When light hits these pigments, they triggers nerve impulses, resulting in vision (see cones; rods).

A manufacturing process that adds certain materials to optical lenses which separate light into beams that vibrate in one plane only instead of all planes (like normal light); cuts glare.

Plastic lenses designed for impact resistance and UV protection. Increasingly popular for sport/sunglasses and prescription lenses.

The degree to which an object is enlarged. Also called magnification.

A common vision defect associated with the aging eye’s diminishing ability to focus on close objects. Correctable with bifocals or progressive addition lenses.

Surgical procedure to reshape the cornea with excimer laser; approved for use in correcting myopia; also known as laser vision correction.

Lenses that have progressively more reading power from top to bottom; for correcting presbyopia.

Severe retinal blood vessel disease that occurs in people with diabetes. Fragile, new blood vessels and fibrous tissue grows on the retina and extends into the vitreous. These blood vessels may leak, leading to macular edema, retinal detachment and vision loss.

One entrance to the eye’s drain pipe. The eye has two drains or puncta in the upper and lower corners of the eyelid margins near the nose. Pulling back the eyelid will reveal these tiny holes.

The space in the center of the iris where light enters the inner eye. The widening, or dilation, of the pupil is controlled by the iris.

The bending of light rays as they pass through a substance. In the eyes, light is refracted by the cornea and lens, and focused on each retina.

A measure of how much light rays are bent when they pass from one medium to another. Water, air, glass and plastic each have a specific refraction index.

Separation of the light sensitive retina from the back of the eye, which may cause vision loss. Laser surgery is required as soon as possible after detachment is detected to secure the retina to the inner eye.

The inner layer at the back of the eye, where light sensitive rods and cones are located. Chemical changes in the retina transmit electrical signals through the optic nerve to the brain to produce sight.

A group of rare, inherited degenerative diseases affecting the retina which can lead to various degrees of vision loss or blindness.

The ability to judge depth accurately or see in three dimensions. The brain achieves stereoscopic vision by merging the images it receives from the slightly different angles provided by each eye.

A hard synthetic resin that is light and impact resistant, but thick and damage prone (scratches) unless coated with protective varnish.

Pieces of embryonic blood vessels, specks of pigment on the muscle fibers attached to the iris, particles caught in the tear layer in front of the eye, or clumps of collagen in the vitreous humor. Usually harmless, these tiny objects drift freely in the eye and cast shadows across our line of vision.

A lens with a smooth, sphere-shaped or rounded surface that bends light rays equally in all directions.

A biomicroscope that helps eye doctors examine the various parts of the eye under high magnification. This special microscope has a chin and headrest. Colored filters can enhance the doctor’s view.

An immune disorder that causes mild to extreme dryness in the eyes and mouth. It dries mucous membranes and affects the lacrimal glands, which make tears. About 3 million Americans suffer from this disorder, which may be related to arthritis.

Eyeglass lenses that correct a single refractive need, e.g., myopia, hyperopia.

Hardened coatings to protect plastic lenses from scratching.

The tough white part of the eye, or outermost shell, that contains the eyeball.

The cylindrical, rod-shaped photoreceptors that do not sense color but enhance peripheral vision and vision in dim light.

Identifiable characteristics or life history for which there is an observable link to a problem, disease or predisposition toward a health condition.

Hard plastic contact lenses that allow oxygen and carbon dioxide to pass.

Also called visual purple, a lightsensitive pigment in the rods. It bleaches in light and regenerates in the dark using vitamin A compounds.

Infections of the glands around the eyelashes and under the upper and lower eyelids that may be associated with stress or other eye conditions.

See crossedeyes.

This type of cataract affects the back of the eye’s lens, causing blurriness and glare.

Thick paste of any active medication (in various strengths) that is applied by placing it along the lower eyelid and gently applying it around the tear duct.

A lens with a cylindrical as well as rounded shape; used to correct astigmatism.

Tissue that filters the liquid aqueous after it has circulated toward the outer front edge of the iris. The trabecular meshwork drains back into the bloodstream.

The distance between two similar points of a given wave. UV light has a shorter wavelength than the light the eye can see.

The clear, jellylike substance that fills the bulk of the eyeball.

A thick, transparent, gel-like substance which fills the eye, located between the lens and retina.

The replacement of clouded vitreous humor (the gel-like substance that fills the eye) with clear saline solution.

What you see, particularly the area surrounding the center of vision. Each eye has a visual field.

The part of the cerebral cortex of the brain primarily responsible for interpreting signals from the eye.

Invisible radiation from sunlight, sunlamps and video terminals. Potentially harmful to the eyes. Strongly linked to the development of cataracts.

Eyeglasses with three different viewing areas to provide clear near, midrange, distance vision. Have two well-defined visible lines separating the viewing zones.