Figure 1 – This illustration shows a side view of the cornea. The physical changes seen in keratoconus are subtle, though the effects on a patient’s vision can be tremendous.
Keratoconus is an eye disease that slowly thins the cornea at the front of the eye. The cornea is the transparent part of the eye that allows light to enter and be focused on the retina (see Figure 1). Keratoconus can cause high amounts of astigmatism and nearsightedness. In some patients with keratoconus, the only way to correct their vision is with specialty contact lenses. In advanced keratoconus, glasses alone are not enough to correct the patient’s vision. These patients need medically-necessary contact lenses. Dr. Brian Abert, O.D., FAAO fits keratoconus patients with contact lenses at Vista Eye Care using a variety of techniques and lens designs. Other treatment options include intracorneal ring segments, corneal transplantation, and the up-and-coming technique of corneal cross-linking. It is important to recognize that all treatments of keratoconus are not cures. Because keratoconus is thought to be genetic in nature, these treatments are meant only to provide better vision and comfort or to slow down the overall progression of the disease.
Figure 2 – The three parallel lines entering from the left of the illustration represents light entering the cornea. The three lines converging at a single point at the back of the eye (the retina) would correspond with a clear, sharp focus.
In a healthy, normal eye, light enters the cornea and focuses at a clean point on the retina (see Figure 2). This type of clean focus is afforded by a cornea with normal curvature (a cornea that does not have keratoconus). In this scenario, the patient may need to wear glasses or contact lenses, but that need is necessitated by the length of the eye . If the eye is too long, nearsightedness is the result. If the eye is too short, farsightedness is the result. Keratoconus is a separate disease process form the factors that normally cause a person to have a glasses prescription.
Figure 3 – This illustration shows light entering a keratoconic eye, and being mis-focused at the back of the eye. The distorted cornea is incapable of focusing light cleanly at the back of the eye. The resulting vision is completely out of focus.
When an eye has keratoconus (see Figure 3), the cornea has lost its normal curvature. Light entering the eye is incapable of focusing at a single, clean point on the retina and the result is distorted vision. Glasses will be of little help in eyes with keratoconus because even though the spectacle lens will refract light, that refracted light still has to pass through the distorted cornea. The only way for a moderate to advanced keratoconic patient to see well is to take the distorted cornea out of the equation.
Figure 4 – While the cornea in this illustration is distorted as in Figure 3, the scleral lens (in red) sitting on this cornea covers up the distortion and tears/saline (in blue) fill in the gap. The result is similar focusing as seen in an eye with a normal cornea (Figure 1).
Contact lenses are the traditional way of managing keratoconus. The uneven refractive surface of the cornea is literally bridged over with a contact lens. The patient’s tears fill in the uneven portions of the cornea, and the result is a smooth refracting surface. A hard lens (see Figure 4) is typically used because the hard lens (also call “gas-permeable,” or “GP”) is not flexible. It sits on the front of the cornea and creates the smooth refracting surface necessary to provide clear vision to the patient. Whereas soft lenses are soft, silicone based discs, GP’s are hard and custom fit to each patient’s corneal curvature, diameter, and power. Recent advances in contact lens technology have introduced specially-made custom soft lenses which can be of use in mild to moderate keratoconus. These lenses can occasionally provide better comfort than hard lenses, though because soft lenses tend to conform to the shape of the cornea, they have limited use in advanced cases.
Scleral contact lenses are the latest innovation in managing eyes with keratoconus. This is nicely illustrated in Figure 3. A scleral lens is a very large diameter GP contact lens that doesn’t move on the eye and affords great comfort and vision to the patient. Although a bit counter-intuitive, the comfort of a contact lens is actually proportional to the diameter of that lens, the reason being that a larger lens design extends beyond where the lids will interact with it. Scleral lenses nicely bridge the corneal distortions caused by keratoconus, and provide all-day comfort and vision, even in dusty or outdoor environments. Scleral lenses have the potential to literally be a life-changing visual device.
Corneal cross-linking will likely be approved soon for use in the United States. This technique is used to strengthen the protein components of the cornea in order to prevent keratoconus from continuing to thin the cornea, and thus increase the size of the corneal bulge. As the “cone” shape of the cornea progresses, the contact lens fitting process becomes more and more challenging. The idea behind corneal cross-linking is to strengthen the cornea and allow for contact lenses to be more easily fit for a longer period of time (thus delaying a potential corneal transplant). Corneal cross-linking involves use of riboflavin (Vitamin B2) applied to the internal layer of the cornea and treated with ultraviolet (UV) light. Side effects from this technique are said to include corneal haze, infections, and inflammatory diseases. Corneal cross-linking does appear to offer the advanced keratoconus patient a reasonable shot at stabilizing the progression of the disease.
Dr. Brian Abert at Vista Eye Care in Thornton, Colorado fits keratoconus patients of all ages with contact lenses. There are a variety of lenses that Dr. Abert uses for these specialty fits including hard, soft, scleral, and hybrid lenses. If you have keratoconus, feel free to contact Dr. Abert with your questions regarding contact lenses and how they can help enhance your vision, or click the button below to schedule an appointment at Vista Eye Care!
