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Cataracts are the clouding of a normally clear lens. Almost all people will have cataracts to some degree during aging, and about half of all Americans between the ages of 65 and 75 will have cataracts severe enough to decrease their vision noticeably. Cataracts are not a skin or film over the eye, nor is it a growth or infection, but merely a loss of transparency of the normally clear lens. The more cloudy the lens and the more the center of the lens is involved, the worse the vision and, like a dull pane of glass, the whole thing must be replaced. (See more separately.)

Central vision is the “straight-ahead” vision in the visual field and is controlled by the macula, a tiny section of the retina. Although the macula occupies only one percent of the retina, it is responsible for distinguishing all vision detail. The retina is the light-sensitive layer between the choroid and the vitreous gel. It contains rods and cones that receive light information about an object in view. The rods react to faint light, movement, and shape, and are responsible for peripheral or side vision. The cones distinguish color and detail, but require high levels of light to function. They are responsible for central vision. The retina encodes the information from the rods and cones into electrical impulses which are sent via the optic nerve to the brain, where they are translated into an image. The cones of the retina are concentrated into a central section called the macula. Within the macula is an indentation known as the fovea, which contains the greatest concentration of cones and is the site of the sharpest vision. Light is focused by the cornea and the lens onto the macula, specifically onto the fovea. When the macula or fovea are damaged, central vision is affected.Macular disease is a common problem affecting central vision and may be caused by an injury, heredity, aging, or from other diseases such as arteriosclerosis and age-related maculopathy (ARM), which is the most common form of this disease. It is a progressive disease in which the macula deteriorates, and central vision is lost. In some cases, ARM can be treated with laser therapy. but there is no cure for the disease. Tobacco amblyopia is a condition in which the excessive use of tobacco impairs central vision but usually rights itself when tobacco use is discontinued or drastically reduced.

Chalazion is an inflammation of the eyelid gland. It is not an infection but is a swelling caused by a blockage of one of the small oil glands that help lubricate the eye (the meibomian gland, a sebaceous follicle of the eyelid). Unlike a sty, it develops a little farther up and within the eyelid. A chalazion appears as a bump or swelling on either the top or bottom eyelid. It is relatively painless and may develop slowly over many weeks, becoming unsightly and annoying. It usually goes away without treatment but may take a week or two to do so. Treatment may include warm compresses (chamomile tea is the best) and sulfonamide eye drops. Gently, and carefully, massaging the area to break up the lump may also help. If it becomes large enough to affect vision, an eye doctor should be consulted. As soon as the chalazion has grown large enough to press on the eyeball, it may cause damage to vision by producing an astigmatism. In such cases, surgery to remove the chalazion may be required. Chalazions may become chronic. If they do reoccur, it could be an indication of a more serious condition and should be checked. Sometimes a biopsy is performed to see if the tissues are cancerous. Prevention is achieved through strict hygiene and the application of warm compresses at the first sign of inflammation. The delicate tissues surrounding the eyes and eyelids, as well as the actual eye itself, need vitamin A and vitamin C in order to maintain optimal health. Thus, using a multivitamin and mineral supplementation will often prevent the reoccurrence of such eyelid problems.

Chlamydia is a type of sexually transmitted disease that can cause conjunctivitis, both in adults and babies who are affected at birth. Caused by a bacterium, chlamydia is the leading sexually transmitted disease in the US and responsible for over four million new cases each year. Newborns affected while in the birth canal may develop conjunctivitis or pneumonia. Typically, symptoms of eye problems will occur within the first ten days of life and the eye infection will usually be treated with antibiotics.

Chorioretinitis is ometimes called posterior uveitis. It is a secondary condition caused by choroiditis, a swelling of the choroid. Because of the close proximity of the choroid and the retina, the inflammation of choroiditis often spreads to the underlying retina, resulting in chorioretinitis. When this occurs, the vision becomes acutely blurred. If the inflammation involves the macular region of the retina, permanent central vision loss could occur.

Choroid is the dark, pigmented, middle tissue layer between the retina and the sclera. It is the back (posterior) portion of the uveal tract, a vascularized tissue layer that supplies blood to the eye, which includes the iris and ciliary body in the anterior section. Blood circulates through the choroid layer to nourish and support the eye. The uvea, or uveal tract, contains the pigmented portions of the eye and consists of the iris, the ciliary body, and the choroid. When uveitis (inflammation of the uvea) occurs, the choroid may also be involved. Inflammation of the choroid is called choroiditis, or posterior uveitis. Symptoms include pain, redness of the eye, and light sensitivity. However, it may also be without symptoms; and, since it may be present only in the peripheral field, it may persist unnoticed. The inflammation may spread to the retina and the vitreous, in which case, the vision becomes blurred.

Choroiditis is the inflammation of the choroid. It is a type of uveitis, sometimes referred to as “arthritis of the eye.” The uveal tract is composed of the iris, the ciliary body, and the choroid. Uveitis is categorized as either anterior or posterior. When the iris and the ciliary body are involved, the condition is termed anterior uveitis. When the choroid is involved, it is termed posterior uveitis, or choroiditis. Symptoms of choroiditis include redness of the eye, light sensitivity, and lost or blurred vision; but symptoms may not be noticeable if they are located in the areas of peripheral vision. Choroiditis may occur spontaneously and may be linked to viruses, injuries, toxoplasmosis, arthritis, tuberculosis, venereal disease, parasites, and sarcoidosis. It is usually treated with systemic or locally applied corticosteroids.

Ciliary body is the group of ciliary muscles that are attached to the zonule, a group of fibers that hold the lens in place. The ciliary muscles change the shape of the lens when focusing and they open and shut the pupil. The ciliary muscles contract to bulge the lens forward and focus on a near object and expand to flatten the lens and focus on a distant object. The ciliary body also produces the aqueous fluid of the eye which flows through the anterior chamber where it nourishes the lens and cornea and carries away waste. Changes in the ciliary body may affect the production and flow of the aqueous fluid, which can result in an increase in intraocular pressure and glaucoma. Iritis, an inflammation of the iris, can cause inflammation of the ciliary body, called cyclitis. This results in pain, redness, light sensitivity, and constricted pupil. Iritis and cyclitis are usually treated with steroid pills, eyedrops, or ointments.

Coloboma is a cleft or notch in the iris, retina, and/or choroid due to incomplete formation or closure of the optic during gestation. The cleft produces a section of missing iris, retina, and/or choroid that may extend from the optic disc to the periphery of the fundus. Coloboma most often appears as a keyhole-shaped pupil. The condition may be bilateral, but usually one eye is more acutely affected than the other. If the iris is minimally affected, vision interference may be insignifant. However, if the retina (particularly the macular area) and the choroid are involved, vision loss could be serious. Coloboma is a birth defect inherited in a dominant pattern. It is sometimes accompanied by other developmental flaws. There is currently no treatment to correct the condition.

Color vision is routinely screened during the regular eye examinations to detect any gross color deficiencies. For such occupations requiring an excellent “color sense” as a printer, art director, stage-scenery designer, cloth dyer, and others, or for the detection of an early stage of a disease, more extensive color tests are administered. One such test requires arranging a series of round, colored discs in the correct sequence of hues. The most sophisticated color test, the anomaloscope, used mostly in research, challenges the person to mix primary green and red light sources together to match a standard yellow light.

Conjunctiva is the transparent mucous membrane that covers the inside of the eyelid and the sclera. The little bumps at the inner corners of the eyes are special folds of the conjunctiva that help direct the flow of tears into the ducts located at the inner margins of the eyelids. Conditions that are commonly associated with the conjunctiva include conjunctivitis, hemorrhage, pinguecula, and pterygium. A hemorrhage in the conjunctiva (subconjunctival hemorrhage) may occur as a result of an injury, excessive rubbing, or coughing and sneezing. A hemorrhage shows itself as a bright red mark on the sclera (white part of the eye). It may look frightening but rarely has any long-term effect and generally goes away without treatment. A pinguecula is a small, benign, yellowish spot on the bulbar conjunctiva. It is more often seen in the elderly. A pterygium is a winglike structure or an abnormal triangular fold of membrane in a fissure that extends from the conjunctiva to the cornea.

Contrast enhancement is a non-optical, or environmental, aid that maximizes residual vision. Contrast is enhanced by using dissimilar colors or brightness levels to make an object more visible. Highly contrasting colors near one another enhance contrast. Black and white are the most common colors of contrast. Complementary colors that can be used together to create improved contrast include reds with greens, blues with oranges, and yellows with violet hues. Light objects on a dark background, or the reverse, improve contrast. Light plates on a dark tablecloth improve visibility. Black letters on a white or yellow page are more readable than blue letters. Dark stairs are more easily seen when next to a light wall or when lined with a fluorescent strip. Other aids can be used to improve contrast. A sheet of yellow or amber acetate can be placed over pale or bluish print to increase visibility. A typoscope, or slit reader, isolates one line of print to reduce the page glare and adds contrast.Convergence is the coordinated movement of the eyes to focus together on a near object. Convergence is tested in an eye examination by slowly bringing a light or object close to the bridge of the nose. The patient is instructed to keep the object in focus as long as possible. As the object moves closer to the nose, the eyes turn inward to a cross-eyed position. Divergence occurs when the object can no longer be seen as one image and the eyes then move from the convergent position. The near point of convergence is the last point at which the object can be seen as one image. This point is measured in millimeters as the distance from the bridge of the nose to the object. A normal near point of convergence is approximately 50 millimeters.

Cortical Blindness is a rare condition that occurs as a result of lesions on the occipital lobes of the brain where the visual cortex is located. The lobes control the visual field of each eye. A lesion on one occipital lobe may result in hemianopsia, which is the loss of half the field of vision, but does not affect the central vision acuity. Lesions on both lobes cause bilateral loss of vision with normally reactive pupils. This is known as cortical blindness. Cortical blindness can be a congenital problem, but is most commonly seen in ageing eyes affected by vascular disease. There may be a history of cerebrovascular incidents and loss of cerebral function. Cortical blindness may be a temporary condition that follows a cerebrovascular embolism or circulatory occlusion caused by a stroke, myocardial infarction, or heart surgery.

Cortisone is a steroid hormone used in drugs to treat eye disorders. It may be an ingredient in prescribed eye drops, ointments, or pills. Cortisone is most often used to combat inflammation and prevent scarring, as in corneal disease. It must be used with caution since it increases the eye’s susceptibility to infection. Antiviral or antibacterial drugs are often taken at the same time to augment the eye’s natural defenses. Cortisone should be used in the eyes for the prescribed period of time only as long-term use may cause glaucoma or cataract.

Cortisporin ophthalmic antibiotic is a drug used to treat bacterial eye infections. It may be prescribed in drop or ointment form. Equivalent forms include triple antibiotics. Side effects from the use of this drug may include burning or stinging of the eyes, redness, blurred or reduced vision, and headache. Eye pain, changes in vision, and headaches indicate a serious problem that should be checked immediately. The drug should not be prescribed for fungal or viral eye infections or those that involve the back sections of the eye. Those with an allergy to hydrocortisone or any other ingredient, as well as those with tuberculosis, should not use this drug. Those with inner-ear problems, myasthenia gravis, or kidney disease should use the drug with caution. The eye infection should be monitored during the time the drug is taken, even if the drug is used for a short period of time. If the drug is used long-term, the eye should be examined regularly for any developments of cataract or secondary infections.

Cryosurgery is a procedure that uses very low temperatures to induce adhering scars in tissue. It is used to repair retinal detachments. Cryosurgery employs a cryoprobe, a pencil-like probe with a tip that is cooled to a temperture between thirty and seventy degrees below freezing.A retinal detachment occurs whenever the retina is disconnected to the back layers of the eye. Normally, the retina adheres closely to the pigment epithelium and is supported by the vitreous gel. When the retina detaches or separates from the epithelium layer, vision is threatened and surgery is needed to reattach it. In order to do this, the choroid, which lies just below the epithelial layer and the retina, must be irritated to form adhering scar tissue.The surgeon may use surgical diathermy, a procedure in which a needle transmitting high-frequency electrical current is touched to the sclera. The heat of the electricity is transmitted to the choroid, which is stimulatd to form scar tissue. An alternative method uses cryosurgery. The cryoprobe is touched to points on the sclera, which is unaffected by the procedure. A hypodermic needle is then inserted to drain any fluid that has accumulated under the retina. The surgeon may then make an indentation in the back of the eye and place a silicone buckle or band around the eye to indent it slightly inward. This pushes the epithelium into contact with the retina. Adhering scar tissue forms in the frozen area and ensures that the retina will remain in position. The band remains permanently in the eye, but it is neither seen nor felt.

Crystalline lens, or natural lens is the transparent, elastic lens of the eye located behind the posterior chamber. The lens changes shape to focus light that enters the eye through the pupil. The lens is held in place by fibers called zonules. The zonules are attached to ciliary muscles, which contract or expand to change the shape of the lens. The lens bulges forward to focus on a near object and flattens to focus on a distant object.The crystalline lens is subject to common eye disorders. It may become subluxated or develop cataracts. A subluxated lens is one that has shifted out of place due to a birth defect or an injury. The placement of the lens, usually downward from its normal position, determines the degree of affected vision. Cataracts are a clouding or opaque spot on the surface of the lens that may develop over long periods of time and may be removed surgically. In some procedures, a portion of the crystalline lens is removed, and an artificial, plastic lens is placed in the eye. This intraocular lens (IOL) replaces and serves as a permanent substitute for the removed section of the natural lens.

Cyclitis is an inflammation of the ciliary body of the eye. The ciliary body lies behind the iris and is attached to zonules, which hold the lens in place. The ciliary body produces aqueous fluid, which flows into the anterior chamber to nourish the cornea and lens and carry away waste matter. It also moves the lens, allowing it to focus properly.Cyclitis is associated with uveitis, an inflammation of the uveal tract that is sometimes referred to as “arthritis of the eye.” The ciliary body, the iris, and the choroid make up the uveal tract. When the choroid becomes inflamed (choroiditis), it is termed posterior uveitis. When the iris or ciliary body becomes involved, it is termed anterior uveitis. Since the ciliary body is linked so closely to the iris, the inflammation soon spreads from one to the other. Because of this, cyclitis is often seen in cases of iritis, an inflammation of the iris.Symptoms of cyclitis include extreme pain, contracted pupil, blurred vision, light sensitivity, and redness of the eye. It may develop quickly and spontaneously within a twenty-four-hour period. Cyclitis has been linked to such other conditions as arthritis, tuberculosis, venereal disease, sarcoidosis, sinus disorders, viruses, and injuries. An ophthalmologic examination plus X-rays of the sinuses, skull, and chest, as well as blood tests, may be necessary in order to determine the cause of the condition. Treatment involves steroid eye drops and cycloplegic eye drops to dilate the pupil. Untreated cyclitis may spread to the choroid, retina, and vitreous, or may result in secondary glaucoma.

Cycloplegic, or mydriatic drops dilate the pupil. Cycloplegics are most often used during the ophthalmologic examination to observe the back of the eye. Most drops reach a maximum effect after fifteen minutes and last approximately three hours. Stronger cycloplegics may last for twenty-four hours and are frequently used in young children or for lengthy examinations. In diseases where the lens and the iris have developed adhesions, as iritis, cycloplegics may be used to suspend accommodation, or movement, of the pupil. Atropine, a drug commonly administered in such cases, may last up to seven days.Occasionally, the instillation of cycloplegic drops induces glaucoma. This occurs when the dilated pupil further constricts the space in an unusually narrow anterior chamber. This impedes the flow of aqueous fluid from the eye, and intraocular pressure rises. Pilocarpine and other meiotics, drugs that constrict the pupil, can reverse the problem. In rare instances, the patient may have an allergy to an ingredient in the cycloplegic eye drops. This may result in irritation, redness of the eye, or dermatitis that should dissipate as the effectiveness of the drug wears off.

Cycloplegic refraction uses special dilating drops – of which, there are two basic kinds. One kind is that which merely make the pupil larger. The other temporarily paralyzes the muscles of accommodation. These muscles cause the natural lenses inside the eyes to change shape so that reading up close without difficulty can take place. As age forty nears, many people begin to lose this ability to accommodate. It is this loss that causes the need for bifocals or makes stubborn individuals hold the paper at arms’ length. In children, these muscles can work overtime, making it difficult to determine what glasses prescription is needed, but eye doctors have learned to outsmart the muscles by paralyzing them temporarily with eye drops. The effects of these dilating drops last anywhere from four to twenty-four hours, causing temporary blurring of the near vision. A cycloplegic refraction is the most accurate means of prescribing glasses for children.