Keratoconus: Better Treatment and Better Prognosis
From the Greek words “kerato,” which means cornea and “konus,” meaning cone-shaped, keratoconus is a progressive condition which causes the normally dome-shaped clear cornea to become thinner and irregularly-shaped. Because the cornea is the main refractive surface of the eye, any irregularities in its shape or curvature cause vision to become distorted and blurry.
In figure 1, the photo simulates what someone with uncorrected keratoconus might see; some objects may be clear, while others are blurred or distorted.
Keratoconus is not caused by inflammation or infection, but may have a genetic component, although not all patients are able to trace any family history of the condition. Most keratoconus cases affect both eyes, but the two eyes may not be distorted in a symmetrical way, and it is common for one eye to progress faster than the other. Incidence of keratoconus is usually considered to occur in about one out of every 2000 people. Changes in corneal shape due to keratoconus can begin in the late teen years and progress into the 40s or 50s. It is often seen that keratoconus progression may be episodic, with periods of stability interspersed with other periods of rapid change.
Corneal tissue is made up of collagen strands, laid out in a geometric pattern which is kept in a relatively dehydrated state by cells lining its inner surface; this maintains its clarity and regular shape. In keratoconus, the tissue becomes thinner and unable to sustain its normally smooth, regular surface. Corneal ectasia may occur, which is seen when the thin corneal tissue bulges outwards.
Symptoms and Signs
People with early keratoconus may notice that their vision changes more rapidly than would normally be expected, requiring frequent eye exams and changes in spectacle lens prescription. They may notice that their vision is not just blurred, but distorted so that lines become wavy or bent, and there may be haloes around lights at night. Light sensitivity and glare may be present and the eyes may water more than normal.
During a vision examination, an eyecare practitioner may see rapid changes in the amount of refractive error, especially myopia (nearsightedness) and astigmatism. Astigmatism in most people is relatively predictable and correctible by spectacle lenses, but in keratoconus, the astigmatism may be much more irregular, making it impossible to fully correct with eyeglasses. Mapping of the corneal surface will show the irregularities in the surface tissue, with irregular changes in the steepness of curvature which vary across the area, perhaps steeper in one area but flatter in another.
Contact lenses have long been a mainstay of keratoconus treatment; the goal of fitting contact lenses in this condition is two-fold: first, to give the patient better vision, and second, to help stabilize the cornea and slow down progression of the condition. As keratoconus progresses, spectacle lenses become less useful for vision correction, because they cannot overcome the irregular shape of the cornea. Contact lenses in keratoconus are used to provide a “new” front surface for the eye, with a smooth, regular shape, while the tears fill in behind it, becoming part of the optics for better vision.
Contact lenses used in keratoconus may be rigid lenses with improved oxygen flow; larger lenses that use the sclera (the white of the eye) for support; hybrid lenses with some characteristics of both rigid and soft lenses; and specialty soft lenses. Each of these types has advantages, and a patient with keratoconus may, at different times and stages of the condition, have need for each type in succession. Fitting contact lenses for keratoconus is very complex and requires frequent office visits and frequent new lenses as the cornea’s shape changes over time.
However, contact lenses do not stop the progression completely, and unfortunately, about 10% to 20% of keratoconus cases would require surgery, in the form of a corneal graft, or a full-thickness corneal transplant from a donor eye. Now, there is a better option.
Breakthrough: Corneal Collagen Cross-Linking
Recently, a procedure called corneal collagen cross-linking, often referred to as CXL or CR3 has been used very successfully in cases of keratoconus and other
CXL involves the use of riboflavin eye drops and ultraviolet light. The riboflavin, a form of vitamin B-2, penetrates the corneal tissue, which is then exposed to ultraviolet-A (UV-A) light. The light stimulates the cornea to form more links between the collagen fibers, thus giving the cornea more strength and stability.
CXL is much less invasive than corneal grafting or transplantation, and the results are quite good; it has been shown in studies that up to 99% of patients with keratoconus treated in this way have corneas that either remain stable or even improve in terms of shape and curvature. This is an exciting finding for people who have been diagnosed with keratoconus that could have led to blindness not that long ago.
The increased numbers of links between the collagen fibers in the cornea provide both better strength and more thickness, as would be seen in normal corneal tissue. After CXL, most patients can see better with spectacles and can better tolerate contact lenses as well. The improvement in corneal stability also seems to be a lasting effect as well and has been demonstrated itself to be a long-term solution.
CXL is indicated in any patient with keratoconus or other degeneration which causes weakening and shape changes. The earlier in the process of the condition, the better the outcome is expected to be and the better the long-term prognosis for the patient’s vision.
Other Uses for CXL
CXL has also been shown to be very useful in other conditions, such as pellucid marginal degeneration another condition that deforms the shape of the cornea, as well as induced corneal weakness from refractive surgeries such as LASIK.
During the 1980s and into the 1990s, a type of refractive surgery known as radial keratotomy (RK) was widely available in Europe and North America; RK was done by using incisions in a radial pattern on the front surface of the cornea in an effort to purposely make it weaker in order to flatten it out and reduce myopia (nearsightedness) and astigmatism. Unfortunately, in many patients, the results were not predictable and sometimes led to daily fluctuations in vision; in others, the weakened cornea could not withstand normal intraocular pressure and became ectasic, or bulged outward.
Some surgeons have successfully used CXL to achieve improved corneal stability and treat ectasia in post-RK patients.
Another potential area of interest for CXL is in the treatment of bacterial corneal ulcers that are not responsive to antibiotics. The riboflavin and UV-A light form an effective team for the eradication of bacteria that cause a variety of infections, and may become especially useful in those caused by “superbugs” that are resistant to most available antibiotics.
It is possible that people who are considering refractive procedures like LASIK might undergo CXL as a pre-treatment to strengthen the cornea beforehand.
Currently, studies are being done with CXL in combination with tiny, implanted rings meant to flatten the cornea for myopia reduction, as well as a developing technique using microwave energy to the same end. Both of these benefit from the added strength and stability of the cornea.
What to Expect
After a thorough vision examination and general ocular health evaluation, the thickness of the cornea will be measured and its contours mapped in a procedure called corneal topography.
The patient is placed in a reclining chair and the riboflavin eye drops are applied over a period of time to allow them to penetrate the tissue. Then, the UV-A light source will be used for a period of time of up to 30 minutes. Afterwards, depending on the specific technique used, a bandage soft contact lens may be applied, and prescriptions for topical antibiotics and topical anti-inflammatory drops will be provided.
CXL: A Better Future
Any family history of keratoconus should signal the need for a visit to an eyecare practitioner for an evaluation and regular eye exams should follow to diagnose and treat keratoconus in its earliest stages, before major damage occurs.
Patients who would have been facing almost certain visual impairment and possible functional blindness because of progressive keratoconus can now look forward to a much more optimistic view of the future. It appears that CXL, useful in several conditions, is providing the possibility of improvement of vision, instead of a progressive worsening of it over a period of years.