A

Age Related Macular Degeneration (MD)

A disease with it onset usually after age 60 that progressively destroys the macula, the central portion of the retina, impairing central vision. Age-related macular degeneration (AME) rarely causes blindness because only the center of vision is affected. However, injury to the macula in the center of the retina can impair the ability to see straight ahead clearly and sometimes make it difficult to read, drive, or perform other daily activities that require fine central vision. The macula is in the center of the retina at the back of the eye. As we read, light is focused onto the macula where millions of cells change the light into nerve signals that travel to the brain and tell it what we are seeing. This is our central vision. With normal central vision, we are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision. There are two types of AMD -- the dry type and the far more frequent wet type. Neither type causes pain. An early symptom of wet AMD is that straight lines appear wavy. This happens because the newly formed blood vessels leak fluid under the macula. The fluid raises the macula from its normal place at the back of the eye and distorts vision. Another sign that a person may have wet AMD is rapid loss of central vision. This is different from dry AMD in which loss of central vision occurs slowly. In both dry and wet AMD, the person may also notice a blind spot..

Partial or complete loss of vision in one eye caused by conditions that affect normal visual development. These conditions can include an imbalance in the positioning of the eyes, such as strabismus, in which the eyes are crossed inward (esotropia) or turned outward (exotropia). Amblyopia can also result from a major difference in refractive error between the two eyes, such as nearsightedness, farsightedness, or astigmatism. Less common causes of amblyopia include ptosis (drooping) of one eyelid, disease of the cornea (preventing light from entering the eye), congenital cataract, and injury to the eye of a young child.

In amblyopia, the brain favors one eye over the other. The other eye is ignored. It is not adequately stimulated and the visual brain cells do not mature normally. Anisometropia occurs when the eyes have an unequal refractive power. Because the brain cannot reconcile this difference, it develops a preference for the image coming from one eye only.

Amblyopia is the most common cause of monocular blindness, impaired vision in one eye. Amblyopia affects 2 to 3 of every 100 children in the US. The most frequent cause is strabismus. Treatment of strabismus may involve surgical correction of the eye muscle imbalance and wearing an eye patch over the stronger eye for 2 hours a day.

Astigmatism

A common form of visual impairment in which part of an image is blurred, due to an irregularity in the curvature of the front surface of the eye, the cornea. The curve of the cornea is shaped more like an American football or a rugby ball rather than a normal spherical basketball. Light rays entering the eye there are not uniformly focused on the retina. Rays entering through the more-curved surface are focused before the rays coming through the less-curved surface. The light is focused clearly along one plane but is blurred along the other. The result is blurred vision at all distances. Only part of what you are looking at is in clear focus at any one time.

Astigmatism may be so slight that it causes no problems. Almost everyone has some degree of astigmatism. Significant astigmatism can cause headaches and eye strain and seriously blur vision. Astigmatism may contribute to poor school performance but is often not detected during routine eye screening in schools. It is a refractive error, an error of focusing, that may coexist with other refractive errors like near- sightedness or far-sightedness.

B

Blepharitis

Inflammation of the eyelids. Blepharitis occurs in two forms, anterior and posterior: Anterior blepharitis affects the outside front of the eyelid, where the eyelashes are attached. The two most common causes of anterior blepharitis are bacteria (Staphylococcus) and scalp dandruff. Posterior blepharitis affects the inner eyelid (the moist part that makes contact with the eye) and is caused by problems with the oil (meibomian) glands in this part of the eyelid. Two skin disorders can cause this form of blepharitis: rosacea and seborrheic dermatitis of the scalp (scalp dandruff). Both types of blepharitis can cause a foreign body or burning sensation, excessive tearing, itching, sensitivity to light (photophobia), red and swollen eyelids, redness of the eye, blurred vision, frothy tears, dry eye, or crusting of the eyelashes on awakening. Complications from blepharitis include: Stye: A red tender bump on the eyelid that is caused by an acute infection of the oil glands of the eyelid. Chalazion: This condition can follow the development of a stye. It is a usually painless firm lump caused by inflammation of the oil glands of the eyelid. Chalazion can be painful and red if there is also an infection. Problems with the tear film: Abnormal or decreased oil secretions that are part of the tear film can result in excess tearing or dry eye. Because tears are necessary to keep the cornea healthy, tear film problems can make people more at risk for corneal infections. Treatment for both forms of blepharitis involves keeping the lids clean and free of crusts. Warm compresses should be applied to the lid to loosen the crusts, followed by a light scrubbing of the eyelid with a cotton swab and a mixture of water and baby shampoo. Because blepharitis rarely goes away completely, most patients must maintain an eyelid hygiene routine for life. If the blepharitis is severe, an eye care professional may also prescribe antibiotics or steroid eyedrops.

C

Cataract

A clouding of the lens of the eye. The normally clear aspirin-sized lens of the eye starts to become cloudy. The result is much like smearing grease over the lens of a camera. It impairs normal vision.

There are many causes of cataracts including cortisone medication, trauma, diabetes, many other diseases and simply aging. Cataracts will affect almost all people if they are fortunate enough to live long enough. The symptoms of cataracts include double or blurred vision and unusual sensitivity to light and glare. Cataracts can be diagnosed when the doctor examines the eyes with a viewing instrument. The ideal treatment for cataracts is surgical implantation of a new lens. Wearing sunglasses can help prevent cataracts.

Conjunctivitis

Inflammation of the conjunctiva, the membrane on the inner part of the eyelids and the membrane covering the white of the eye. The conjunctival membranes react to a wide range of bacteria, viruses, allergy-provoking agents, irritants and toxic agents. Viral and bacterial forms of conjunctivitis are common in childhood. Conjunctivitis is also called pinkeye and red eye.

The leading cause of a red eye is virus infection. Viral pink eye is usually associated with more of a watery discharge, not green or yellow in color, and is frequently associated with viral cold-like symptoms. The eyelids may be swollen. Sometimes looking at bright lights is painful. While viral pink eye, may not require an antibiotic, the doctor should see the child, as occasionally this form of pink eye can be associated with infection of the cornea, (the clear portion of the front of the eyeball). This infection must be correctly detected and treated. Viral pink eye is highly contagious.

The bacteria that most commonly cause pink eye are staphylococcus, pneumococcus, and streptococcus. Symptoms include eye pain, swelling, redness, and a moderate to large amount of discharge, usually yellow or greenish in color. The discharge commonly accumulates after sleep. The eyelids may be stuck together requiring a warm wash cloth applied to the eyes to remove the discharge. This bacterial pink eye responds to repeated warm wash cloths applied to the eyes and antibiotic eye drops or ointment.

Cornea

The clear front window of the eye that transmits and focuses light into the eye. The corneal tissue is arranged in five basic layers, each having an important function. These five layers are:

1. Epithelium: The cornea's outermost region, comprising about 10 percent of the tissue's thickness. The epithelium functions primarily to: (1) Block the passage of foreign material, such as dust, water, and bacteria, into the eye and other layers of the cornea; and (2) Provide a smooth surface that absorbs oxygen and cell nutrients from tears, then distributes these nutrients to the rest of the cornea. The epithelium is filled with thousands of tiny nerve endings that make the cornea extremely sensitive to pain when rubbed or scratched. The part of the epithelium that serves as the foundation on which the epithelial cells anchor and organize themselves is called the basement membrane.
2. Bowman's Layer: A transparent sheet of tissue composed of strong layered protein fibers called collagen. Once injured, Bowman's layer can form a scar as it heals. If these scars are large and centrally located, some vision loss can occur.
3. Stroma: A layer accounting for 90% of the cornea's thickness, consisting primarily of water (78 percent) and collagen (16 percent), and does not contain any blood vessels. Collagen gives the cornea its strength, elasticity, and form. The collagen's unique shape, arrangement, and spacing are essential in producing the cornea's light-conducting transparency.
4. Descemet's Membrane: A thin but strong sheet of tissue that serves as a protective barrier against infection and injuries. Descemet's membrane is composed of collagen fibers (different from those of the stroma) and is made by the endothelial cells that lie below it. Descemet's membrane is regenerated readily after injury.
5. Endothelium: The extremely thin, innermost layer of the cornea. Endothelial cells are essential in keeping the cornea clear. Normally, fluid leaks slowly from inside the eye into the middle corneal layer (stroma). The endothelium's primary task is to pump this excess fluid out of the stroma. Without this pumping action, the stroma would swell with water, become hazy, and ultimately opaque. In a healthy eye, a perfect balance is maintained between the fluid moving into the cornea and fluid being pumped out of the cornea. Once endothelium cells are destroyed by disease or trauma, they are lost forever. If too many endothelial cells are destroyed, corneal edema and blindness ensue, with corneal transplantation the only available therapy.

D

Diabetic Retinopathy

A common complication of diabetes affecting the blood vessels in the retina (the thin light-sensitive membrane that covers the back of the eye). If untreated, it may lead to blindness. If diagnosed and treated promptly, blindness is usually preventable. Diabetic retinopathy begins without any noticeable change in vision. But even then there often are extensive changes in the retina visible to an ophthalmologist (eye doctor). It is therefore important for a diabetic to have an eye examination at least once (ideally twice) a year. There are two stages of diabetic retinopathy -- nonproliferative and proliferative retinopathy: Nonproliferative retinopathy is the earlier stage. In this stage there may be hemorrhages (bleeding) in the retina with leakage of blood causing a "wet retina" or protein deposits (exudates) in the retina. As a consequence, the retina does not receive enough oxygen. This early stage of diabetic retinopathy usually produces no visual symptoms but, if there is fluid in the central portion of the eye (macular edema), vision is diminished. Proliferative retinopathy is the second stage. New abnormal vessels develop in the retina and grow towards the center of the eye. These vessels frequently bleed into the vitreous (the clear jelly in the center of the eye). Such bleeding episodes cause severe visual problems. Small bleeds may clear up on their own but larger bleeds need surgery. The abnormal vessels may also produce large scars in the retina that may cause the underlying retina to detach (retinal detachment).

Dry Eye

A deficiency of tears. The main symptom is usually a scratchy or sandy feeling as if something is in the eye. Other symptoms may include stinging or burning of the eye; episodes of excess tearing that follow periods of very dry sensation; a stringy discharge from the eye; and pain and redness of the eye. Sometimes people with dry eye experience heaviness of the eyelids or blurred, changing, or decreased vision, although loss of vision is uncommon.

E

Eye

The organ of sight. The eye has a number of components. These components include but are not limited to the cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous.

G

Glaucoma

A common eye condition in which the fluid pressure inside the eyes rises because of slowed fluid drainage from the eye. If untreated, it may damage the optic nerve and other parts of the eye, causing the loss of vision or even blindness.

The elderly, African-Americans, and people with family histories of the disease are at greatest risk. There are no symptoms in the early stage of glaucoma. Glaucoma is often called "the sneak thief of sight." Often, by the time the patient notices vision loss, glaucoma can only be halted, not reversed.

There are several different types of glaucoma, including open-angle glaucoma and acute angle-closure glaucoma, Open-angle glaucoma is the common adult-onset type of glaucoma. Acute angle-closure glaucoma is a less common form of glaucoma but one that can rapidly impair vision.

H

Hyperopia (far-sightedness)

Hyperopia is a condition where light focuses behind the retina.  The eyeball is too short in this case. People with this condition may notice that there is more blur when looking up close than far away. Other common symptoms include eyestrain, headaches, double vision, general fatigue and difficulty reading or working at a computer.

Farsightedness is present when your eyes must exert unnecessary focusing effort to attempt to clear distance vision and thus a greater than normal focusing effort to maintain clear and comfortable close-range vision. This constant extra focusing effort causes symptoms of fatigue, headaches, tension and numerous other complaints of ocular discomfort.

The visual consequences of this condition are generally different for children than adults. Most farsighted children see clearly at distance thus the term "FAR"-sighted; however, they achieve clarity by exerting a constant focusing effort at distance and close-range. Farsighted adults, however, gradually see less clearly at distance because all adults naturally decrease focusing ability due to a secondary visual condition called presbyopia. Farsighted eyes require eyeglasses and/or contact lenses to maintain clear and comfortable vision at all ranges of vision.   Farsightedness decreases during our growth years, remains fairly stable during our twenties and thirties and as a normal healthy progression, typically increases in our forties and beyond.

I

Iris

The iris is the circular, colored curtain of the eye. Its opening forms the pupil. The iris helps regulate the amount of light that enters the eye.

K

Keratoconus

Keratoconus is a disease that affects the stability and structure of the cornea. Early in the disease patients may notice that vision has been changing frequently and that vision doesn't seem as clear as it could be. Eventually the ability to get clear vision with glasses is lost and contact lenses are needed for full correction. Instruments such as the corneal topographer aid us in the diagnosis and fitting of contact lenses in this situation. Specially designed lenses can be made to increase the vision.

L

LASIK

Abbreviation standing for laser-assisted in situ keratomileusis, a kind of laser eye surgery designed to change the shape of the cornea to eliminate or reduce the need for glasses and contact lenses in cases of severe myopia (nearsightedness).

LASIK is an ambulatory procedure done in an ophthalmology office or clinic. Numbing eye drops are used. The eyelids are held open so that there is no interference with the laser. The ophthalmologist creates an ultrathin flap on the front of the eye with a precise automated instrument. The flap is gently lifted and the preprogrammed laser then reshapes the inner cornea to refocus the eye. The flap is repositioned and holds itself in place, healing naturally without the need for any stitches. The laser pulses last on the average between 30 and 60 seconds. In all, LASIK takes about 20 minutes to do both eyes. The procedure is without much pain and recovery is quick.

Lens

The transparent structure inside the eye that focuses light rays onto the retina (the nerve layer that lines the back of the eye, senses light and creates impulses that go through the optic nerve to the brain). The lens was named after the lentil bean because it resembled it in shape and size.

M

Macula

A macula is a small spot. A macula on the skin is a small flat spot while the macula in the eye is a small spot where vision is keenest in the retina.

Myopia (near-sightedness)

Myopia is a condition where light focuses too soon in front of the retina. People with myopia tend to notice that their vision far away is blurry while their vision up close may be clear. Myopia is a common condition that affects an estimated 30% of the U.S. population. Glasses, contact lenses and laser vision correction may all be good options for correction of myopia.

Nearsightedness is caused by an eye that is naturally too strong in refractive power and/or an eye that is deeper or larger in size than average. Since the nearsighted eye requires less power to see clearly, the eyes' natural (power-rich) focusing ability cannot help correct this troublesome condition.  Nearsightedness can be easily corrected with prescription eyewear and/or contact lenses.

Progression of myopia is due to genetic and functional factors. Just as eye color is inherited, so may be the amount of myopia.  This genetic cause of myopia will usually progress until about eighteen years of age, remain fairly stable in our twenties and thirties and generally decrease beyond our forties.  Functional myopia, however, can develop and contribute to nearsightedness at any age as a stress response to close-range tasks such as reading, computer use, etc.

O

Ophthalmologist

A medical doctor who specializes in the eye. To become an Ophthalmologist one must first obtain a Medical Degree (M.D. in North America) and then complete further specialty training.

Optic Nerve

The optic nerve connects the eye to the brain. The optic nerve carries the impulses formed by the retina, the nerve layer that lines the back of the eye and senses light and creates impulses. These impulses are dispatched through the optic nerve to the brain, which interprets them as images. Using an ophthalmoscope, the head of the optic nerve can be easily seen. It can be viewed as the only visible part of the brain (or extension of it).

Optometrists

A health care professional who is licensed to provide primary eye care services: to examine and diagnose eye diseases such as glaucoma, cataracts, and retinal diseases and, in certain states in the U.S., to treat them; to diagnose related systemic (bodywide) conditions such as hypertension and diabetes that may affect the eyes; to examine, diagnose and treat visual conditions such as nearsightedness, farsightedness, astigmatism and presbyopia; and to prescribe glasses, contact lenses, low vision rehabilitation and medications as well as perform minor surgical procedures such as the removal of foreign bodies. An optometrist is a Doctor of Optometry, an O.D. (not to be confused with a Doctor of Medicine, an M.D.). To become an optometrist, one must complete pre-professional undergraduate college education followed by 4 years of professional education in a college of optometry. Some optometrists also do a residency.

P

Presbyopia

Presbyopia is a term used to describe the inevitable loss of plasticity of the lens within the eyes. This hardening is a benign problem which poses no health risks to you. Symptoms associated with presbyopia include difficulty focusing up close. Typically, this is first noticed when reading or working at a computer. Presbyopia is treated using special lenses which include bifocals, trifocals, no-line bifocals or contact lenses.

Pupil

The opening of the iris. The pupil may appear to open (dilate) and close (constrict) but it is really the iris that is the prime mover; the pupil is merely the absence of iris. The pupil determines how much light is let into the eye. Both pupils are usually of equal size. If they are not, that is termed anisocoria (from "a-", not + "iso", equal + "kore", pupil = not equal pupils).

R

Retina

The retina is the nerve layer that lines the back of the eye, senses light, and creates impulses that travel through the optic nerve to the brain. There is a small area, called the macula, in the retina that contains special light-sensitive cells. The macula allows us to see fine details clearly.

Retinitis Pigmentosa

Any one of a large group of inherited disorders in which abnormalities of the photoreceptors (the rods and cones) in the retina lead to progressive visual loss. People with retinitis pigmentosa (RP) first experience defective dark adaptation ("night blindness"), then constriction of the visual field ("tunnel vision") and eventually loss of central vision.

V

Vitreous

A clear, jelly-like substance that fills the middle of the eye. Also called the vitreous humor, "humor" in medicine referring to a fluid (or semifluid) substance.