About the Cornea, Infections,
Dystrophy & Conditions
The cornea is an important structure of the eye that functions in a number of ways to help provide clear vision. First, it acts as the clear outermost “lens” of the eye that allows light rays to pass through to the retina. Normally it is about the size and thickness of a dime and is curved in a dome like shape. It is critical for the cornea to maintain its transparency and optical clarity as well as its regular curvature and thickness in order to function properly. The cornea also serves as a filter, screening out some of the most damaging ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and the retina would be highly susceptible to injury from UV radiation. Last, the cornea serves to protect the internal structures of the eye by shielding it from easy penetration of microorganisms, dust and debris. There are a number of eye diseases, conditions or problems that can affect the functioning of the cornea and thus your ability to see clearly.
Corneal Ulcer & Keratitis
The outermost layer of the cornea is called the epithelium. If it is damaged from trauma of any type, i.e. getting a foreign body in your eye such as piece of metal, a poke in the eye from a branch or a finger or even from a dirty or damaged contact lens, it is possible for bacteria, viruses or fungi to penetrate the cornea and cause an infection. An infection of the cornea is called a Keratitis or Ulcer. Keratitis can cause a painful inflammation with a discharge, which if not treated quickly and appropriately, can lead to corneal erosion, corneal ulceration and corneal scarring. Corneal scarring results in a loss of corneal transparency and can require a corneal transplant in order to restore vision.
Herpes Zoster Keratitis (Shingles)
Herpes Zoster Keratitis is actually caused by the same virus that causes chicken pox, called Varicella-Zoster Virus. It is entirely possible that after having chicken pox as a child, the Varicella-Zoster Virus remains in the nerve cells of your body in an inactive state. For a number of possible reasons, the Varicella-Zoster Virus can reactivate later in life and travel through the nerves in your body causing a painful blistering rash. If the Varicella-Zoster Virus travels to your head or neck it can affect the eye and thus cause a corneal infection. It is critical to have a physician diagnose this quickly as the infection can penetrate deeply into the cornea and it can cause scarring. The infection can also result in a loss of corneal sensation, which can be permanent. We may prescribe both oral medications and eye drops to try and resolve the infection and prevent serious damage from occurring.
Ocular Herpes and Herpes Keratitis
Ocular Herpes, or Herpes of the eye is caused by the Herpes Simplex Virus and is the most common causes of corneal blindness in the United States today. Up to 50% of people who have a single Herpes Simplex viral infection of the eye will experience a flare up or recurrence. The virus often leads to irreversible scarring of the cornea. Ocular Herpes may start as a painful sore on the eyelid or surface of the eye. If left untreated, it may multiply and begin to destroy epithelial cells and progress deeper into the cornea. If the Ocular Herpes penetrates the deeper layers of the cornea and causes a Stromal Keratitis it may cause corneal scarring-so prompt diagnosis and treatment of Ocular Herpes is important. We may prescribe both oral medications and eye drops to try and resolve the infection and prevent serious damage from occurring. Prompt diagnosis and medication are the keys to preventing any vision loss.
Fuchs Dystrophy is a slowly progressive disease of the cornea that can be found in both eyes and is slightly more common in women than men. While it is possible to observe Fuchs Dystrophy in people in their 30’s and 40’s, it usually does not compromise vision until people are in their 50’s or 60’s. The innermost layer of cells in the cornea, called the endothelium, is a single layer of non-regenerating cells. The endothelial cells are responsible for pumping water out of the cornea and helping to maintain the corneal transparency. While the reason is poorly understood, in Fuchs Dystrophy, the endothelial cells die, which make the endothelium less efficient in its pumping activity. This results in the cornea swelling and distorting vision. In its later phases, Fuchs Dystrophy is often associated with considerable pain as the epithelium “blisters” by forming “bullae”, which actually begin to burst open. Early in the course of Fuchs Dystrophy patients will wake up with blurry vision that gets progressively clearer as the day passes. As the Fuchs Dystrophy disease worsens, the vision does not clear we will attempt to help reduce the corneal swelling each day with eye drops and ointments. However, when these measures fail to provide comfort and clear vision, it may be necessary to have a corneal transplant procedure called DSEK or DMEK to transplant endothelial cells, which may help certain Fuchs Dystrophy patients overcome their discomfort and vision problem.
The outermost layer of the cornea, called the epithelium, is attached or anchored to an underlying basement membrane, called Bowman’s Membrane, in order to remain healthy. Sometimes the epithelial basement membrane develops abnormally making it difficult or impossible for the epithelium to adhere properly to the basement membrane. If the epithelium does not adhere properly, Recurrent Corneal Erosions will occur. Recurrent Corneal Erosions are painful and cause the corneal surface to become irregular resulting in intermittent blurry vision along with the discomfort and foreign body sensation. Map-Dot-Fingerprint Dystrophy is also known as Epithelial Basement Membrane Dystrophy because it is caused by a lack of the healthy formation of the Basement Membrane. It affects adults between the ages of 40-70 and can sometimes begin earlier. As the name implies, its appearance is of a map of gray areas, which may also be accompanied by opaque dots, and fingerprint like whirls or lines. We will often discover Map-Dot-Fingerprint Dystrophy during a routine eye examination in patients who do not have any noticeable symptoms. If treatment is required to control the pain for those patients who are symptomatic, we may prescribe lubricating eye drops, patch the eye, apply a soft bandage contact lens or in more severe cases, scrape the cornea to attempt to achieve better adhesion of the epithelium. In some cases, we may suggest that the best results can be achieved using Excimer Laser Phototherapeutic Keratectomy (PTK) to smooth the surface of the cornea.
Lattice Dystrophy occurs as a result of the accumulation of abnormal protein fibers, or amyloid deposits in the middle cornea layer called the corneal stroma. If these deposits become dense enough they will become opaque and affect the corneal transparency so that vision is reduced. If these deposits occur under the outermost layer, the epithelium, they can cause recurrent erosions of the cornea, which can be painful and disturb the normal corneal curvature, effecting vision.
In instances where there are recurrent corneal erosions and pain, we may prescribe eye drops, ointments and occasionally an eye patch or bandage soft contact lens. Early Lattice Dystrophy seems to respond well to Excimer Laser Phototherapeutic Keratectomy (PTK) whereas more serious cases may require a corneal transplant.
Keratoconus is a non-inflammatory “ectasia” of the cornea in which the normally round dome-shaped cornea progressively thins causing a cone-like bulge to develop resulting in significant visual impairment. Keratoconus has been estimated to occur in 1 out of every 1-2,000 persons in the general population. Keratoconus is generally first diagnosed in young people at puberty or in their late teens and progresses through the third or fourth decade of life. It tends to progress more rapidly in young patients. Keratoconus occurs about equally in men and women. It is found in all parts of the United States and the rest of the world. It has no known significant geographic, cultural or social pattern. The signs and symptoms of Keratoconus may change as the disease progresses and may include a) blurred or distorted vision b) monocular double vision c) rapidly changing eyeglass prescriptions especially with high degrees of astigmatism d) increased sensitivity to bright light and glare e) problems with night vision f) headaches from eyestrain and in the most severe situation e) hydrops, a painful condition in which the back of your cornea ruptures and fills with fluid, causing a sudden clouding and loss of vision.
Management & Treatment of Keratoconus
Eyeglasses & Contact Lenses-Eyeglasses and soft contact lenses may be well tolerated and provide satisfactory comfort and vision when Keratoconus is mild. Most often, the quality of vision tends to decline so that patients require Rigid Gas Permeable Lenses (RGP) for vision correction. Other contact lens options for Keratoconus include piggyback lens systems where an RGP lens in worn over a soft silicone hydrogel lens, hybrid contact lenses such as SoftPerm® and SynergEyes® and even very large gas permeable contact lenses that fit over the sclera or white of the eye, called a Scleral Lens. With comprehensive contact lens care, typically only 10-20% of patients progress to the point of needing medical or surgical intervention.
Collagen Cross Linking-Corneal Collagen Cross Linking is a non-invasive treatment that has been proven to strengthen the weak corneal structure in Keratoconus. This treatment method works by increasing collagen cross-linking, which serve as the natural “anchors” within the cornea. These anchors are responsible for preventing the cornea from bulging and becoming steep and irregular and thus causing Keratoconus. Corneal Collagen Cross Linking is administered by placing riboflavin eye drops onto the surface of the eye and exposing the surface to a precise amount of ultraviolet light. Corneal Collagen Cross Linking offers a possible solution for many Keratoconus patients who have progressed to a significant amount of visual disturbance but not so much so as to require a cornea transplant.
Corneal Transplantation-When Keratoconus has progressed to the point that contact lenses are no longer well tolerated and Corneal Collagen Cross Linking cannot provide good vision correction, a cornea transplant is the best choice. In many cases of Keratoconus a Penetrating Keratoplasty (PK) is the preferred surgical solution although today cornea surgeons may recommend a Lamellar Keratoplasty (LKP). With PK the cornea surgeon removes the central portion of the damaged cornea with a “cookie cutter” like instrument called a trephine and replaces it with a clear cornea obtained from the eye bank. The donor cornea is very carefully sewn into place using sutures that are thinner than a human hair. When the new cornea has healed properly, the fine sutures or stitches can be removed right in the office in most cases. PK is the most common type of cornea transplant as it has the potential to provide the clearest vision after healing because there is no interface (layer) to look through. However, the healing time is somewhat long and the use of a contact lens might be required for the clearest vision. Sometimes Lamellar Keratoplasty (LKP) may be used if the damaged corneal tissue is mainly located in the outermost 50% of the cornea. In LKP the outermost half of the cornea is carefully dissected and removed along with any damaged tissue. Then a new donor cornea is gently sewn into place. This type of corneal transplant is less invasive and will allow your eye to be stronger after surgery than it would be with a regular full thickness transplant, or Penetrating Keratoplasty. However, in some cases there can be some loss of clarity from the interface between the new and remaining layers of the cornea.
Recurrent Corneal Erosion or Scratched Cornea
Recurrent Corneal Erosion is a condition of the cornea whereby there is a poor attachment of the outermost layer of the cornea, the epithelium, to the underlying basement membrane layer, called Bowman’s Membrane. Patients who experience Recurrent Corneal Erosion may experience sharp pain, light sensitivity, tearing and watering of their eyes, and a gritty sensation. Often this occurs upon awakening or rubbing the eyes. Recurrent Corneal Erosion is a condition that may be associated with Map-Dot-Fingerprint Dystrophy. We may initially prescribe salt solution eye drops or ointment as the first line of treatment. This medication helps the epithelium to adhere more firmly to Bowman’s Membrane. Usually artificial tears are also recommended to keep the cornea moist. Sometimes, a soft bandage contact lens will be used to help the healing process. Those patients who have a corneal dystrophy may require additional treatment. This usually includes an in-office procedure where the epithelium is either gently removed, or microscopic “spot welds” are made on the cornea to encourage the epithelial layer to bond securely to Bowman’s Membrane. Patients, who continue to suffer from Recurrent Corneal Erosions despite the treatments described, may benefit from Phototherapeutic Keratectomy (PTK). This involves removal of the superficial layer of corneal cells using the Excimer Laser to encourage proper healing.
A pterygium is a fleshy triangular growth of tissue on the cornea that may grow slowly throughout a person’s life. Rarely, a pterygium can grow across the cornea and block the pupil. People who live in sunny climates where they are exposed to more sunlight and UV light are more prone to developing pterygia. Pterygia may become red, swollen and inflamed. Occasionally they need to be removed. Removal of a pterygium is a surgical procedure that has recently undergone medical advances. Our eye surgeons use a surgical technique called Amniotic Membrane Graft in order to prevent recurrences and obtain the best possible results for Pterygium surgery.