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 primary corneal layers are the cornea or epithelial layer’s outer layer, the middle layer termed the stroma, and a single layer of cells called the endothelium.
The curvature of the cornea plays a vital 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.
Different types of Corneal Disease
There are several common causes of corneal disease, including the following:
- Bacterial, fungal, or viral keratitis, as well as parasitic diseases
- Abrasions or exposure to toxic chemicals
- Dystrophies and degenerative corneal disorders
- Fuchs’ dystrophy, map-dot-fingerprint dystrophy, or lattice corneal dystrophy
- Autoimmune disorders
- Wegener’s disease, rheumatoid arthritis, or lupus
- Nutritional deficiencies
- Vitamin A deficiency
- Vernal and atopic keratoconjunctivitis
- Pterygium or benign or malignant cancerous growths on the eye’s surface
- Ectasia (thinning)
- Keratoconus, or thinning of the cornea following refractive laser surgery
- Stevens-Johnson syndrome, a rare but inflammatory severe 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) be associated with glaucoma.
Corneal Disease Symptoms
Blurred vision refers to a lack of sharpness of vision resulting in the inability to see fine detail. Blurred vision may result from abnormalities present at birth, such as nearsightedness or farsightedness that require corrective lenses (glasses), or it may signal the presence of eye disease.
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 corneal disease will minimize the severity of the disease and its complications in its early stages.
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 the 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 cornea’s outermost layer (epithelium). Examples include traumatic abrasions, infectious ulcers, and erosions from dryness.
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. Different 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.
Diagnosing 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 the 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.
Treatment for Corneal Disease
Treatment is tailored to the individual disease and the individual patient. Treatments might include medications, laser treatment, or surgery, depending on the condition.
Infections are treated with medicated eye drops (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 eye drops.
An abrasion might require temporary patching or a bandage contact lens, depending on the injury’s cause and extent.
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 is managed initially with salty eyedrops or ointments that help prevent fluid accumulation within the cornea. If the conditions worsen, an endothelial lamellar keratoplasty (a type of partial-thickness transplant surgery) may be indicated.
Research is underway 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.
Eye problems caused by vitamin A deficiency can be seen in patients who have had certain types of bariatric (weight loss) surgery and can be corrected with supplements.
Allergic eye disease responds well to both topical and oral allergy medication.
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 eye’s surface are managed with surgery or, in some cases, topical chemotherapy eye drops 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 essential.
In some individuals, dryness is due to lack of tear production, and anti-inflammatory drops such as cyclosporin (Restasis) or steroids may help. In other cases, the dryness is due to the evaporation of the tears between blinks. This occurs when the eyelids’ oil glands (meibomian glands) are not functioning well. Typically, 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.
Complications of Corneal Disease
Many corneal diseases are treatable and have a good prognosis. However, vision loss and chronic eye pain are potential corneal disease complications, so it is essential to review treatment options carefully with an eye doctor.