- Symptoms & Signs
What is the cornea?
The cornea is the clear tissue at the front and center of the eye. Its transparency permits light to pass into the eye, through the pupil, lens, and onto the retina at the back of the eye. The three major corneal layers are the outer layer of the cornea or epithelial layer, the middle layer termed the stroma, and finally a single layer of cells called the endothelium.
The curvature of the cornea plays an important role in focusing (refracting or bending) light. The normal cornea is smooth, clear, and tough. It helps protect the eye from infection and foreign material.
What are the different types of corneal disease?
There are several common causes of corneal disease, including the following:
- Abrasions or exposure to toxic chemicals
- Dystrophies and degenerative corneal disorders
- Autoimmune disorders
- Nutritional deficiencies
- Ectasia (thinning)
- Stevens-Johnson syndrome, a rare but serious inflammatory reaction to a medication or an infection
The cornea can also be damaged secondarily by other common eye conditions such as tear film abnormalities (dry eye), eyelid disorders, glaucoma, and iridocorneal endothelial syndrome (ICE), which may be associated with glaucoma.
What are the causes and risk factors of corneal disease?
The causes of corneal disease vary widely. The conditions listed above are due to hereditary (inherited) causes, infection, trauma, autoimmune disorders, nutritional deficiencies, allergy, secondary causes (other eye diseases that also affect the cornea), growths, and tumors among others.
Risk factors similarly vary depending on the individual's circumstances. Some risk factors are not modifiable, such as inherited genetic conditions. Others might be avoidable by limiting exposure to trauma and infection. In many people, prompt treatment of a corneal disease in its early stages will minimize the severity of the disease and its complications.
What are the signs and symptoms of corneal disease?
Signs of corneal problems can include redness around the cornea and/or corneal cloudiness. Symptoms include
- visual impairment, such as blurred or cloudy vision,
- severe pain in the eye,
- tearing, and
- sensitivity to light.
- Some patients have additional symptoms of headache, nausea, and fatigue.
Blurred vision may be the result of an irregular tear layer or epithelial layer (as seen in dry eye), scarring (following trauma or infection), cataracts, deformity of the corneal curvature (as seen in keratoconus), or swelling of the cornea (as seen in Fuchs' dystrophy). Pain and light sensitivity can be quite severe, especially in conditions affecting the outermost layer (epithelium) of the cornea. Examples include traumatic abrasions, infectious ulcers, and erosions from dryness.
What types of health care specialists diagnose and treat corneal disease?
Vision problems are diagnosed and treated by eye doctors (optometrists and ophthalmologists). For more advanced corneal conditions, particularly those requiring surgery, an ophthalmologist (medical doctor/eye surgeon) or a corneal specialist (an ophthalmologist who has undergone additional fellowship training) would provide treatment. Additional specialists such as oculoplastic surgeons (ophthalmologists who specialize in eyelid and orbital surgery), rheumatologists, infectious disease and allergy specialists, and others may be consulted when the cornea is secondarily affected by other medical conditions.
How do health care professionals diagnose corneal disease?
An eye doctor will review the person's medical history and perform a careful examination of the eyes and eyelids. The cornea is examined in detail using a slit lamp microscope. Additional medical testing that can provide information needed to make a diagnosis may include topography and keratometry (to study the shape of the cornea), pachymetry (to measure the thickness of the cornea), specialized microscopy (providing detailed pictures to assess the health of the endothelial cells, or to identify infectious agents), and assessment of the tear film. In some individuals, cultures, biopsies, or blood tests are also necessary.
What is the treatment for corneal disease?
Infections are treated with medicated eyedrops (antibiotics, antivirals, and antiparasitics) and, in some cases, oral medication. Herpetic stromal keratitis is a recurring swelling that develops after a herpes eye infection and is managed with anti-inflammatory steroid eyedrops.
Keratoconus, in which the cornea can take on a distorted cone shape, is often managed with special contact lenses. Newer treatments, including corneal crosslinking (riboflavin and ultraviolet-A) and corneal implants, are also options. Advanced keratoconus diseases are treated with anterior lamellar keratoplasty or corneal transplant surgery.
Chronic swelling from Fuchs' dystrophy or other conditions that damage the cornea's endothelial cells are managed initially with salty eyedrops or ointments that help prevent accumulation of fluid within the cornea. If the condition worsens, an endothelial lamellar keratoplasty (a type of partial thickness transplant surgery) may be indicated.
Research is under way to develop an artificial cornea for transplantation.
Autoimmune disorders are best treated by addressing the underlying disease. Corneal involvement is often managed with anti-inflammatory eyedrops such as steroids; however, steroid-sparing immune-modulating medications are sometimes preferable, particularly when other parts of the body are also involved.
A pterygium is a growth on the cornea's surface; this is most commonly seen after chronic sun exposure. They can be removed surgically if they become bothersome. Cancers of the surface of the eye are managed with surgery or in some cases, topical chemotherapy eyedrops or injections.
Dry eye is common and can result in painful erosions of the corneal surface. Aside from lubricating the eyes with artificial tears, addressing the underlying cause is important. In some individuals, dryness is due to lack of tear production, and anti-inflammatory drops such as cyclosporine (Restasis) or steroids may help. In other cases, the dryness is due to evaporation of the tears between blinks. This occurs when the eyelids' oil glands (Meibomian glands) are not functioning well. Normally, the oil from these glands coats the eye's surface and prevents tear evaporation. The oil glands' function can be improved with a combination of warm compresses, lid hygiene (for example, dilute baby shampoo lid scrubs), increased intake of omega-3 fatty acids, and in some patients, oral medication.
What are the potential complications of corneal disease?
Many corneal diseases are treatable and have a good prognosis. However, vision loss and chronic eye pain are potential complications of corneal disease so it is important to review treatment options carefully with an eye doctor.
Is it possible to prevent corneal disease?
Many corneal diseases are preventable by reducing risk factors. For example, maintaining optimal eye health (with good hygiene and regular vaccinations) is the best prevention against many infectious diseases. For example, there are vaccines available to reduce the severity and frequency of shingles, which can result in an eye herpes infection called herpes zoster ophthalmicus. Contact lens wear can make individuals especially susceptible to serious corneal infections, so people should clean contact lenses as directed. Glasses and sunglasses with 100% ultraviolet block can protect against growths that are associated with sun exposure, such as pterygium, and eye surface cancers. Safety glasses should be worn when warranted to prevent trauma. A diet rich in omega-3 fatty acids and sufficient vitamin A may help maintain a healthy tear film, thus minimizing dry eye symptoms. Reviewing one's family's ocular health history is helpful in looking for hereditary conditions. Regular eye examinations are important for detecting eye diseases at their earliest stages.
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Randleman, J.B., S.S. Khandelwal, and F. Hafezi. "Corneal cross-linking." Surv Ophthalmol 60.6 Nov.-Dec. 2015: 509-523.
Reidy, James J. Basic and Clinical Course 2010-2011 Section 8: External Disease and Cornea. Revised edition. American Academy of Ophthalmology, 2010.