The cornea is the essential outer layer of the eye. It is transparent. Light passes through it and reaches the pupil and retina. The cornea focuses your vision by refracting and focusing light. The cornea serves a second purpose, protecting the eye from invasion by infections and foreign materials.
The cornea can be vulnerable to disease and aging. Degenerations of the tissue of the cornea can harm the functioning of the cornea, which affects its ability to focus. Corneal degenerations can cause vision loss and eye pain.
One should distinguish corneal degenerations, which are usually unilateral and asymmetric, from corneal dystrophies, which are bilateral although they are sometimes spoken of in the same breath. Corneal dystrophies are genetic and progressive eye disorders that have earlier onset and eventually stabilize.
Involutional Corneal Degenerations
Age-related degenerations are known as involutional. They are the most common causes of corneal degeneration. Over 50% of the population over age 40 has White Limbal Girdle of Vogt, where the cornea’s periphery thins. This does not cause significant vision loss.
Non-Involutional Corneal Degenerations
The less common kind of corneal degenerations are caused by disease or exposure to certain conditions like heat, wind dust, dry, or chemicals, and are called non-involutional. Traumatic degeneration can cause scarring that can prevent the success of corneal transplantation. Some non-involutional degenerations cause deposits that can be vaporized off with PRK laser.
Terrien’s marginal corneal degeneration is uncommon but generally occurs in middle-aged men. It causes a progressive non-inflammatory corneal thinning that can make the cornea more opaque and leads to astigmatism, treated with glasses or contact lenses. The corneal thinning spreads circumferentially resulting in a yellow line of lipid deposits. It often presents with painless progressive blurred vision. Doctors may also prescription low dose steroids. It is more common in men and can take different progressive paths, remaining without symptoms until astigmatism results. The cause of Terrien’s is unknown.
Pellucid marginal degeneration normally has an onset between ages 20 and 40, with both sexes affected equally and no family history to indicate it is a risk except that of astigmatism. It is an avascular and uncommon form of ectasia causing central corneal thickness that can in turn cause scarring. Researchers are unsure of the exact prevalence of this condition in the population because while it seems rare, it seems to be often misdiagnosed as keratoconus. Symptoms are generally managed with glasses, contact lenses, or surgery (keratoplasty).
Lipid degeneration, or lipid keratopathy, has both a (rare) primary, or secondary form. In its primary form (LK) stromal deposit of cholesterol and phospholipids form. Serum lipids are normal and no other disease need be present. PLK may result in the requirement of penetrating or lamellar keratoplasty. The secondary form relates to the presence of corneal blood vessels from trauma, interstitial keratitis, or herpes zoster keratitis. It has a yellow opacity or fan-like cholesterol crystals on the cornea.
Dellen, also known as pathological dimples, results in dry eye and stromal thinning. Round excavations appear at the margin of the cornea. Lubrication or patching, including with amniotic membrane, is often very successful. These dimples may follow ingestion of cocaine or an operation for cataract and will often disappear within 48 hours.
Pterygium, a pink, triangular tissue growth in the cornea that often starts near the nose, is another non-involutional corneal degeneration. For more information, click here. Another non-involutional corneal degeneration is Coat’s white ring, which requires no treatment.
Band keratopathy degenerations, which are generally not hereditary, involve calcium salt deposits that build in the cornea. This can appear as a grayish white with swiss cheese-like holes. This fine dust exists in the sub-epithelium, Bowman’s layer, and the anterior stroma. There is also a uric acid form, which are brownish white. It is called bank keratopathy because the calcium settles and appears as a line across the center of the cornea from the peripheral cornea.
Bank keratopathy often stems from hypercalcemia, which is due to a systemic disease that needs to be addressed, such as:
– Automimmune conditions like rheumatoid arthritis
– Renal disease
– Crohn’s Disease
Also, some eyedrops containing phosphates such as steroid drops can cause band keratopathy, as can mercury-based preservative drops. Band keratopathy does not always require treatment, but when it does, surgery for band keratopathy removes the calcium deposits. Recurrence after this surgery, however, is common. Amniotic membrane may be used to heal wounds caused by surgery because it is anti-inflammatory, anti-fibroblastic, anti-angiogenic, anti-microbial, non immunogencic and contains important growth factors like neurotrophins and cytokines.
Another form of degeneration is Salzmann’s nodular degeneration. This is a non-inflammatory degeneration that can affect adults of any age. It often strikes both eyes. Although the condition is non-inflammatory, it can be caused by an underlying inflammatory condition, so the first line of treatment is addressing that underlying condition. You may notice symptoms in the appearance of your eye. There is usually a change in transparency of the cornea. There will be the appearance of blue nodules on the eye that are also extremely painful, and localized vision loss.
Different diagnostic tools will be used depending on symptoms. Because so many degenerations can be caused by an underlying, systemic condition, it is imperative that you provide a complete medical history to your doctor.
Some of the treatments for different kinds of degenerations are noted above and are condition-specific. In general, for pain and discomfort, doctors will prescribe lubricating eye drops. Some degeneration does not require further treatment, such as arcus senilis. Surgery is possible, including corneal transplants.
Contact one of our Eyecyte doctors to find out more about aging eyes, eye degenerations, and treatment options.