Definition and Overview
Keratoconus is a progressive disease of the eye characterized by the outward bulging of the cornea making it appear like a cone rather than round. When this happens, the eyes fail to focus on images properly.
The eyes are coated by the sclera, and part of is it the cornea, a thin transparent film or “window” where light enters and begins its journey into the eyes. It is composed of several layers, and its mission is to bend the light rays so they can pass through the pupil, which forms part of the iris. The iris, meanwhile, is responsible for controlling the amount of light by shrinking or enlarging. The light then goes through the crystalline lens and into the vitreous until it reaches the retina, which converts all the rays of light it receives into electrical impulses that can be interpreted by the brain.
The cornea’s normal shape is round. However, for a number of possible reasons, it thins out that it begins to take another shape, which is cone. Because of this, the light seems “dispersed” rather than focused once it reaches the retina. The brain can then “look at the object” as if it is distorted or blurry.
As a progressive disease, any damage to the cornea can never be corrected but it can be stabilized. Further, usually the progression is slow, spanning a decade or more before the symptoms appear or it begins to worsen again. It is usually treated with the right contact lenses or prescription glasses, which should be changed often depending on the progression of the treatment or the condition. This does not cause blindness, but the distortion can be severe, it can compromise the patient’s quality of life. The cornea can also develop scarring.
It can appear among young adults, but many cases have also happened among adolescents and children. Although the disease can affect both eyes, the degree of the condition is different for each.
Causes of Condition
There is no definite cause of keratoconus. One of the long-held theories is that it is genetic as there are patients who have immediate family members like parents or siblings diagnosed with the condition. For this reason, children as early as 10 years old are already encouraged to have their eyes tested for the disease. On the other hand, some experts suggest that familial association is actually low at 6%.
Some believe that it is caused by the poor presence of antioxidants in the eye. Collagen is also present in the eye, primarily in the cornea, where it helps support its shape. Meanwhile, the cells of the cornea release certain by-products of cellular function, which should be removed away from these cells by antioxidants. When the antioxidants of the eyes are low, the by-products remain, causing damage to the collagen. This then leads to the progressive change in the shape of the cornea.
Some kinds of evidence have established a strong link between allergies and keratoconus—that is, those who are prone to eczema, hay fever, and asthma are also more likely to develop the eye disease.
Prolonged sun exposure has also been cited as one of the possible causes, along with recurrent irritation of the eyes. Poor-quality lenses are also believed to be a cause since these appliances come in contact with the cornea.
Other theories do not have enough evidence or simply anecdotal that they remain debatable or not fully accepted in the field of medicine. These include rubbing one’s eyes and hormonal imbalances.
- Blurry or distorted vision
- Sensitivity to light
- Chronic eye irritation
- Tendency to change contact lenses or prescription glasses often
- Presence of glare or halo in images
- Eye pain
- Eye rubbing
- Strain in the eyes
- Difficulty in seeing especially at night
- Refractive errors such as nearsightedness, astigmatism, and farsightedness
During the early stages of the disease, the patient doesn’t experience any symptom or the symptoms are so subtle that they are often ignored. Further, the disease shares similar symptoms with other eye problems. Only an eye doctor called an ophthalmologist would be able to tell the difference through different tests.
Who to See & Types of Treatment Available
An ophthalmologist is a specialist trained to assess, diagnose, treat, and manage a variety of eye diseases including keratoconus. If the doctor suspects the eye disease, standard tests such as keratometry will be performed. This tells the shape, particularly the curvature of the cornea by looking into the light’s reflected pattern. For a more comprehensive examination, however, the doctor may conduct a 3D mapping of the eye’s cornea.
Usually, the first line of treatment involves using soft contact lenses and prescription glasses. As the disease progresses, these devices should also be adjusted.
The complication, however, sets in once the shape change has become more pronounced as the soft contacts may not work anymore. The next step is to use RGP (rigid gas permeable) contact lenses, which have the ability to “vault” into the cornea so it compensates for its thinning. While this is effective, it is uncomfortable for many wearers. Hence, some doctors recommend hybrid lenses, lenses for the sclera (semi or scleral), or the use of both soft and RGP (a process known as piggybacking), in which the soft lens acts as cushion for the RGP.
If the disease has become worse that contact lenses including RGP are no longer effective, surgery becomes an option. These include implantation of Intacs, which are inserts made of plastic. They are placed within the cornea’s periphery to help clear the vision.
Corneal cross-linking is also recommended especially if there’s still enough tissue left in the cornea. The purpose of the procedure is to reinforce the tissue so it won’t bulge anymore. In cross-linking, riboflavin, a B vitamin, is introduced into the cornea, aided by UV light. The doctor may remove the outer layer of the cornea called the epithelium during the procedure.
If all other methods fail and the condition has turned for the worse, a corneal transplant may become necessary. Also known as keratoplasty, the patient receives a healthy cornea from a deceased donor. It’s expected that the vision will improve significantly, although in some instances, it still needs to be supported by soft contact lenses or prescription glasses.
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Sugar J, Batta P. Keratoconus and other ectasias. In: Yanoff M, Duker JS, eds. Ophthalmology. 4th ed. St. Louis, MO: Elsevier Mosby; 2013:chap 4.18.