Corneal and External Diseases

Corneal and external diseases involve the cornea, anterior chamber of the eye, iris, lens, conjunctiva and eyelids, including cataracts; corneal allergies, infections and irregularities; refractive errors (nearsightedness, farsightedness and astigmatism); conjunctivitis (pink eye); dry eye; tear disorders; keratoconus; pterygium; endophthalmitis; Fuch's Dystrophy and many others.

What is the cornea?

The cornea is the transparent, dome-shaped, outermost layer that covers the iris and pupil in the front of the eye. Corneal tissue consists of five basic layers: epithelium, Bowman's layer, stroma, Descemet's membrane and endothelium. Although the cornea is clear, it contains a highly organized group of cells and proteins. Unlike most tissues in the body, the cornea contains no blood vessels to nourish or protect it against infection. Instead, the cornea receives its nourishment from the tears and aqueous humor that fill the chamber behind it.

The cornea, one of the protective layers of the eye, serves two functions:

• First, along with the eyelid, eye socket, and sclera (white part of the eye), and the tear film, the cornea shields the eye from dust, germs, and other harmful matter.
  
  
• Second, as the eye's outermost lens, it is the entry point for light into the eye. When light strikes the cornea, it bends, or refracts, the incoming light onto the lens. The lens further refocuses the light onto the retina, a layer of light-sensing cells lining the back of the eye.

To see clearly, the cornea and lens must focus the light rays precisely on the retina. This refractive process is similar to the way a camera takes a picture. The cornea and lens in the eye act as would a camera's lens. The retina approximates the film. If the cornea is unable to focus the light properly, then the retina receives a blurry image.

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What injuries, and irregularities affect the cornea?

Some trauma, including projectile foreign bodies, lacerations and blunt trauma can cause scarring that clouds the cornea. Hereditary conditions including degenerations and dystrophies may also cloud the cornea. The most common hereditary condition seen in young people is keratoconus, a condition in which the cornea assumes a cone shape. This is common in children with Down's syndrome and in people with allergic conjunctivitis. These patients may be able to use contact lenses or glasses for a period of time, but may eventually develop scarring and high astigmatism that cannot be corrected without corneal transplantation.

Occasionally, it may become necessary to perform a corneal transplant following cataract surgery, if bullous keratopathy occurs. Bullous keratopathy is a condition where the endothelial cells on the back of the cornea decrease in number after cataract surgery. However, this is less common today because of new techniques and improved lens design.

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How can the cornea be damaged?

The eye surface can be severely damaged by a number of problems, including:

• Chemical and thermal injuries
• Pathological diseases such as Stevens-Johnson syndrome and pemphigoid
• Chronic infections or inflammations
• New tissue growths such as pterygium (thought to be related to sun damage) and tumors
• Neurotrophic conditions (due to damage to the eye's sensory nerves)
• Rare hereditary conditions such as aniridia (congenital absence of the iris)

These problems can result in extensive damage on the eye surface, leading to new blood vessel formation and scarring --- damage which results in loss of vision.

Bascom Palmer researchers are evaluating the potential of normal tears for modulating and promoting the healing of these conditions. A full understanding of the exact role of tears in the healing process should lead to strategies that would speed visual recovery and increase the percentage of patients fully satisfied after surgery.

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What is a corneal transplant?

Corneal transplants are one of medicine's most successful transplant operations. In the past 35 years, more than 250,000 corneal transplants have been performed in the United States. At Bascom Palmer, more than 250 procedures are performed annually. The procedure involves removing the cornea from the donor eye with a special instrument resembling a small cookie cutter. The same method is used to remove the damaged cornea from the patient's eye. The surgeon then stitches the new cornea into place.

For many individuals, a corneal transplant may be the only hope for restored vision, and may be necessary when the cornea is cloudy or damaged due to disease, injury, accident, or hereditary conditions. In these situations, the cornea must be removed and replaced with healthy donor tissue. The procedure is successful in 90 percent of cases, restoring sight and, in some cases, even providing sight for the first time.

Members of Bascom Palmer's corneal transplant team teach patients the acronym RSVP to alert them to potential problems. This RSVP alert is:

R: increased Redness

S: increased Sensitivity to light

V: decreased Vision

P: increased Pain

Today, regrafts are one of the most common reasons for corneal transplants. Regrafts occur when a patient needs a second corneal transplant because the first one was unsuccessful. Some additional reasons include:

• Corneal ulcers, a type of infection that often leads to scarring
• Trauma
• Fuch's Dystrophy
• Damage to the epithelial layer of the cornea, through improper cleaning and use of contact lenses. Sleeping in contact lenses leads to a greater risk of corneal ulcers; the symptoms include eye pain, decreased vision, and redness.

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What advances has Bascom Palmer Eye Institute made in corneal transplantation?

The physicians in the Corneal and External Disease Service have developed techniques and instrumentation to make corneal transplants safer for patients. They have developed instruments known as "trephines," which are used to cut donor and recipient tissues. In addition, Bascom Palmer physicians and scientists have created special diamond knives to be used in surgery and have developed storage solutions to prolong the viability of donor corneas prior to transplantation.

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What are refractive errors?

The cornea and lens bend or refract light rays so they can be focused on the retina, the nerve layer that lines the back of the eye. The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve. A refractive error means that the shape of the eye does not allow the light to be properly refracted making images blurry. Refractive errors include:

• myopia (nearsightedness)
• hyperopia (farsightedness)
• astigmatism
• presbyopia
• monovision

What is myopia (nearsightedness)?

Myopia (nearsightedness) occurs when light rays are focused in front of the retina instead of directly on the retina. Myopia is a vision problem experienced by approximately one-third of the population. When the eyeball is too long from front to back, the image of a distant object focuses in front of the retina, instead of directly on it. As a result, the distant object appears blurred. The more myopic the eye, the closer an object must be before it is in sharp focus. Nearsighted people have difficulty seeing objects at a distance, such as highway signs, but usually can see up-close for tasks such as reading or sewing.

Some people with myopia can use their natural nearsightedness to read without glasses at an age when other people must wear reading glasses. However, if they have refractive surgery to correct myopia, they may be able to see distant objects without glasses, but will probably need to wear glasses to read sometime after age 40, due to presbyopia.

What are signs of myopia?

Nearsighted people may experience headaches or eyestrain and might squint or feel fatigued when driving or playing sports. Patients who experience these symptoms while wearing glasses or contact lenses may need a comprehensive eye examination, as well as a new prescription.

What causes myopia?

Nearsightedness runs in families and usually appears in childhood. This vision problem may stabilize at a certain point, although sometimes it worsens with age. This is known as "myopic creep."

What is the treatment for myopia?

Non- surgical treatment options for myopia include glasses and contact lenses. Surgical treatment options include ALK, clear lens extraction, LASEK, LASIK, LASEK, phakic IOL and RK. While there are numerous surgical options available, not all individuals are good candidates for specific procedures. Patients should review these options in depth with their physicians prior to making any final decisions.

What is hyperopia (farsightedness)?

Hyperopia or farsightedness occurs when light rays are not bent enough to focus on the retina. Hyperopia is a common vision problem, affecting about one-fourth of the population. If the eye is too short from front to back, light rays reach the retina before they converge (focus). People with hyperopia can sometimes see distant objects very well, but may have difficulty seeing objects that are close.

Young eyes can sometimes compensate for this refractive error --- depending on age and the degree of hyperopia present. But with aging, the human lens loses this ability and a hyperopic person eventually may have difficulty seeing objects at a distance, as well as those that are nearby. In fact by age 40, even those with little or no refractive error will begin to experience difficulty focusing on close objects.

What are signs of hyperopia?

Farsighted people sometimes have headaches or eyestrain, and may squint or feel fatigued when performing work at close range. Patients who experience these symptoms while wearing glasses or contact lenses may need an eye exam and a new prescription.

What causes hyperopia?

Most children are born with hyperopia, but most of them "outgrow" it as the eyeball lengthens with normal growth. Sometimes people confuse hyperopia with astigmatism; both cause difficulty in seeing close objects, but have different causes.

What is the treatment for hyperopia?

Non-surgical treatment options include glasses and contact lenses. Surgical treatment options include clear lens extraction, CK, LASIK, LTK, phakic IOL, and PRK. While there are numerous surgical options available, not all individuals are good candidates for specific procedures. Patients should review these options in depth with their physicians prior to making any final decisions.

What is astigmatism?

Regular astigmatism occurs when light rays are focused at more than one point on the retina. Astigmatism is the most common vision problem. It occurs when the cornea surface is not ideally rounded, but is curved more along one axis than the other --- that is, when the eye is shaped more like the side of a football than a basketball. Light entering the eye does not focus symmetrically on the retina. The result is astigmatism, which blurs both near and distance vision. This refractive error may occur in patients who are either myopic (nearsighted) or hyperopic (farsighted). There are various types of astigmatism included regular, mixed and irregular astigmatism.

What are the signs of astigmatism?

Patients with only a small amount of astigmatism may not notice it or may have slightly blurred vision. Sometimes uncorrected astigmatism can cause headaches or eyestrain and distort or blur vision.

Eyeglasses or contact lens prescriptions with three parts indicate some amount of astigmatism. A prescription with three parts looks like this: -2.75 -1.25 x 180. The first part indicates the main spherical correction, while parts two and three show the extent and location of your astigmatism.

What is the treatment for astigmatism?

Currently, excimer lasers in the US are approved for treatment of regular and mixed astigmatism. Recent advances in technology now allow for the therapeutic treatment of induced irregular astigmatism. In the future, this application may be expanded to include all types of irregular astigmatism. Patients who believe they have astigmatism should discuss this subject in further detail with their physician to gain a better understanding of the mechanisms in their case.

What is presbyopia (age-related difficulty with near vision)?

With increasing age, the lens inside of the eyes loses the ability to focus on nearby objects. The problem usually manifests itself around age 40 and can be corrected with bifocals or reading glasses. This is a normal aging process, called presbyopia and all people develop.

Some people with myopia can use their natural nearsightedness to read without glasses at an age when other people must wear reading glasses. However, if they have refractive surgery to correct myopia, they will be able to see distant objects without glasses, but probably will need to wear glasses to read sometime after age 40 due to presbyopia.

What is monovision?

Monovision is a method of distance vision correction to account for presbyopia. In monovision, refractive surgery is used to adjust one eye for "near" vision and the other eye for "distance" vision. Contact lenses or glasses may be required for best distance or night vision activities, including driving. This option is not suitable for everyone and a trial period of monovision using contact lenses may help decide if it is right for the patient.

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What is conjunctivitis (pink eye)?

This term describes a group of diseases that cause swelling, itching, burning, and redness of the conjunctiva, the protective membrane that lines the eyelids and covers exposed areas of the sclera, or white of the eye. It is caused by a virus which is very contagious and spreads easily. The virus may affect one or both eyes. At its onset, conjunctivitis is usually painless and does not adversely affect vision but can be uncomfortable. The body's defenses will clear viral conjunctivitis in one to three weeks, and medication is not always necessary. Cold compresses several times a day on the eyes may offer relief as may artificial tears and dark sunglasses.

But for some forms of conjunctivitis, treatment will be needed. If treatment is delayed, the infection may worsen and cause corneal inflammation and a loss of vision.

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What is a pterygium?

A pterygium is a triangular-shaped tissue growth, yellow-white to pinkish in color, on the nasal side of the cornea. It may become red, inflamed or advance toward the center of the eye. Some pterygia grow slowly throughout a person's life, while others stop growing after a certain point. A pterygium rarely grows so large that it begins to cover the pupil of the eye.

Pterygia are more common in sunny climates and in the 20-40 age group. Scientists do not know what causes pterygia to develop. However, since people who have pterygia usually have spent a significant time outdoors, many doctors believe ultraviolet (UV) light from the sun may be a factor. In areas where sunlight and wind is strong or dust is prevalent, wearing protective eyeglasses, sunglasses, and/or hats with brims are suggested.

It is a benign condition and will not spread to damage the internal part of the eye. Because a pterygium is visible, many people want to have it removed for cosmetic reasons. Lubricants can reduce the redness and provide relief from the chronic irritation.

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What are cataracts?

"Cataract" is the name used to describe a condition wherein the lens of the eye becomes opacified or cloudy blocking some light from reaching the retina and interfering with vision. Cataracts are multi-faceted. We don't know all the causes, but we do know that time, aging, and hereditary factors all play a role in cataract development. Cataract formation can be accelerated by trauma, diabetes, sunlight, and certain medications. Typically, cataracts occur in adults ("adult onset"), but may occur as a congenital disorder. More than half of all Americans age 65 and older have a cataract.

What are the symptoms of cataracts?

Early signs of cataracts include blurred or cloudy vision; frequent changes in eyeglass or contact lens prescriptions; night glare and hazy vision; and colors that seem to fade. An ophthalmologist must determine if these symptoms are really caused by a cataract or by some other eye problem that may need treatment.

For an adult, a cataract should be removed only when it interferes with lifestyle and makes it difficult to continue normally enjoyable activities. Generally, there is no such thing as a cataract being "ripe" or "not ripe" for removal. What matters is whether or not the problem interferes with vision. In rare instances, a "hyper-mature" cataract may cause elevated eye pressure or inflammation of the eye. In this case, it must be removed immediately. Otherwise, removal of a cataract is at the patient's discretion.

What are the different types of cataracts?

• Age-related cataract: Most cataracts are related to aging.
• Congenital cataract: Some babies are born with cataracts or develop them in childhood, often in both eyes. These cataracts may not affect vision. If they do, they may need to be removed.
• Secondary cataract: Cataracts are more likely to develop in people who have certain other health problems, such as diabetes. Also, cataracts are sometimes linked to steroid use.
• Traumatic cataract: Cataracts can develop soon after an eye injury, or years later.

What can one expect during cataract surgery?

Cataract surgery is the most frequently performed surgery in the United States - and the most successful. Over 95 percent of those who have cataract surgery regain vision levels between 20/40 and 20/20.

Cataract surgery usually lasts less than one hour and is almost painless. Many people choose to stay awake during surgery and have an anesthetic to numb the nerves in and around the eye.

A lens implant (intraocular lens) inserted during cataract surgery gives the surgeon an opportunity to correct nearsightedness or farsightedness. Current research on intraocular lens implants also may provide high quality correction for astigmatism and for both bifocal and multi-focal vision. Bifocal implants are currently used, but physicians have yet to achieve consistently satisfactory outcomes.

The time required for recuperation after cataract removal depends on the type of procedure performed and the patient's individual rate of healing. The decision as to which procedure is best for an individual's eye is made by the patient's ophthalmologist.

One technique ophthalmologists use is phacoemulsification. This procedure involves making a tiny incision, about 2.5 to 3.5 millimeters in length. A pencil-like instrument, inserted through the opening, is used to emulsify (breakdown in to tiny pieces) and aspirate the clouded lens material. Then the intraocular lens is inserted into place.

Other techniques include:

• Phacofracture cataract surgery - the lens is removed through a small incision by "fracturing" it into several small segments
  
  
• Extracapsular cataract surgery - the lens is removed in one piece through a larger incision
  
  
• Intracapsular surgery - the lens and capsule are completely removed, a rarely used procedure

In some cases after cataract surgery, a haziness develops in the membrane or capsule supporting the intraocular lens implant. When this happens, a laser is sometimes used to create a small opening in the membrane (a capsulotomy) through which the patient can see clearly. Lasers are used because they are able to make a small, very precise opening.

Are lasers used during cataract surgery?

During the past three decades, the techniques and results of cataract surgery in the U.S. have changed dramatically:

• Ophthalmologists have moved from intracapsular cataract extraction as the preferred method to almost exclusive use of extracapsular techniques.
• Smaller incisions have become the standard: Ultrasonic (U/S) phacoemulsification is now the method of choice for most surgeons.
• Improved surgical techniques for removing the anterior lens capsule have decreased the incidence of both intraoperative (during surgery) and postoperative capsular complications.
• Along with these advances have come improved intraocular lens materials and designs, which are especially well suited for use with smaller incisions.
• Improved wound construction allows many wounds to be left unsutured.
• Smaller wounds require shorter recovery time and allow greater intraoperative control and safety.

Despite these advances, however, U/S phacoemulsification techniques are not without potential sight-threatening complications.

Complications related to U/S phacoemulsification include the possibility of corneal or scleral burn, iris trauma, rupture of the posterior capsule, loss of vitreous fluid, cystoid macular edema, and induced astigmatism. These complications may lead to compromised vision prompting investigations into newer techniques of using laser energy to remove cataracts.

The advantages of using a laser to remove cataracts include the ability to use fiber optics with a smaller diameter than typical ultrasonic probes; and direct energy precisely on target tissue by means of a smooth, blunt, stationary probe.

Theoretically, the use of a laser, compared with U/S phacoemulsification:

• reduces heat and vibration in the wound and in the eye
• decreases the chance of capsular rupture
• requires smaller incisions
• allows faster recovery

Currently, Bascom Palmer Eye Institute is one of several sites involved in a clinical study to see if laser energy can safely break the cataract into pieces. This study also will determine if the laser method of cataract removal, called laser photofragmentation or phacolysis, is as good as or better than ultrasound phacoemulsification.

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What is dry eye?

Among the many different reasons for eye discomfort, by far the most common is "dry eye." This condition, characterized by unstable tear film, is distinct from other mechanical dysfunctions (i.e., blepharitis and blocked tear ducts) which have comparable symptoms but are less serious.

Prior to the development of explicit tests, a dry eye diagnosis often masked additional underlying dysfunctions which resulted in ineffective treatments. Now, with our ability to diagnose all abnormalities, there is new and valuable insight into the actual cause and effects of the disease. For example, it was previously assumed that the irritation suffered by dry eye patients was due to a lack of tears. Given new information, Bascom Palmer specialists have disproved this theory. They've shown that eye comfort depends not on "tears," but on the lubricating "mucous layer" of tears produced by cells on the conjunctiva of the eye. Patients with a significant loss of these cells suffer what is described as Keratoconjunctivitis sicca.

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Who are the cornea and external disease and refractive surgery specialists at Bascom Palmer Eye Institute?

Eduardo C. Alfonso, M.D.
William W. Culbertson, M.D.
Kendall E. Donaldson, M.D., M.S.
Richard K. Forster, M.D.
Anat Galor, M.D.
David A. Goldman, M.D.
Carol L. Karp, M.D.
Yunhee Lee, M.D., M.P.H.
Terrence P. O'Brien, M.D.
Victor L. Perez, M.D.
Jill Rodila, M.D.
Lana Srur, M.D.
Leejee Suh, M.D.
Sonia Yoo, M.D.

Other Cornea and External Disease and Refractive Error Resources

American Academy of Ophthalmology
Cornea Research Foundation of American
Eye Bank Association of America
Eye Resources on the Internet
Fuch's Dystrophy
The LASIK Institute
National Eye Institute
National Keratoconus Foundation
Research to Prevent Blindness

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