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What eye problems are you trying to address in this clinical trial?
Dr. Stulting: There are some problems that we see when the cornea is not strong -- when the cornea is too elastic, so that it stretches. When it stretches it bulges forward. The curvature change occurs and the cornea, because it is an optical element that bends light to focus objects for us, causes blurred vision. There are two diseases that we are looking at in the clinical trials. The first is keratoconus. That is a naturally occurring disease in which the cornea stretches and becomes cone shaped instead of hemispherical. The other is called ectasia, which is a similar stretching that occurs after refractive surgery like Lasik or photorefractive keratectomy otherwise known as PRK.
You found in some of the patients who have Lasik, there can actually be an unexpected and undesirable result?
Dr. Stulting: Right. These are people who had a propensity to develop keratoconus probably and simply developed it quicker or perhaps when they might not have developed it otherwise after they had Lasik. In other words, their corneas were abnormally weak and the removal of tissue with Lasik caused them to develop this stretchy condition and the abnormal cornea curvature.
How common are these conditions?
Dr. Stulting: Keratoconus occurs in about one in 2,000 people and as the disease progresses and gets severe it requires corneal transplantation. Keratoconus is responsible for about 15 percent of the roughly 37,000 corneal transplants performed each year in this country.
How common is the eye condition that occurs as a result of?
Dr. Stulting: It's difficult to estimate the eye condition that is the consequence of Lasik, but it is probably about one in 2,000 as well.
What is the result for the person who has this condition? What do they experience because the shape of their cornea is not the way it should be?
Dr. Stulting: They become nearsighted because the cornea steepens. Then they develop a stigmatism, which is blurred vision because the curvature of the cornea is not equal around its circumference. As it gets worse, they develop scarring and a very irregular corneal curvature that makes it so that they do not see well even with glasses. Contact lenses are required for good vision at that point. Then if it progresses even further, they get to the point where they either cannot be corrected adequately; that is they do not have good vision with the contact lens or they physically cannot wear the contact lens because of discomfort. At that point they require corneal transplantation.
What do you specifically do in the experimental procedure?
Dr. Stulting: In this country, it is experimental. Outside of the United States there are countries in which it has already been approved. The procedure consists of exposure to riboflavin, which is vitamin B2. We give in a form of a drop. It takes about 30 minutes for us to give enough drops to saturate the cornea. In order for the riboflavin to enter the cornea, we have to remove the surface layer of cells that covers the cornea, called the epithelium. Once the cornea is saturated with riboflavin we then expose the eye to ultraviolet light at a specified strength for a specified duration of time … 30 minutes in the clinical trials. During that time there is a reaction between the ultraviolet light and the riboflavin, which joins or links the collagen molecules in the cornea, and in doing so makes it stiffer than it otherwise would be. The stiffness makes it resistant to stretching and in fact, data from international trials has shown us that there is actually a little bit of improvement in terms of flattening of the corneal curvature and an increase in vision, so we get a little bit improvement and protection against progression of keratoconus to the point that contact lens or corneal transplants are necessary. At least that is what the data from the international trials appears to tell us.
What do you hope this new procedure will mean for patients with these conditions?
Dr. Stulting: We hope it will mean avoiding poor vision because of keratoconus or ectasia, avoiding the need for glasses in people who might see well otherwise, avoiding the progression to the need for contact lenses or corneal transplant. There is a tremendous amount of disability and loss of productivity related to either of these diseases and, as I said before, it is responsible for about 15 percent of the corneal transplants performed each year in this country, so it will make a big difference for patients with either of those two diseases. In fact, as we move forward, I can envision a day where we will diagnosis keratoconus very early -- as soon as there are any abnormalities in the shape of the cornea. We will cross-link those eyes and then they won't progress. Patients who are at risk for ectasia who can be identified before they have Lasik can then be cross-linked and can undergo those procedures safely. There are actually some other uses for cross-linking going forward. First of all, cross-linking makes the cornea resistant to the uptake of fluid. The cornea is a very compact and clear structure, but there are some diseases that cause it to absorb water. When it absorbs water it swells and becomes cloudy and the vision also becomes cloudy. Those diseases can be treated as well with collagen cross-linking so that the cornea doesn't absorb water as easily.
When you say collagen cross-linking, are you talking about using the riboflavin and the ultraviolet light combination?
Dr. Stulting: Yes.
How long have you been an eye surgeon and how exciting is this prospect in terms of treating eye conditions?
Dr. Stulting: I've been an eye surgeon for about 26 years and this is a very exciting prospect. It is not very often in your career where you have an opportunity to treat a disease that had no treatment available and keratoconus is certainly one of those diseases, as is ectasia. There are actually some other exciting uses for cross-linking that we may be able to put to good use as time goes on. Stiffening of the cornea and cross-linking of the molecules makes the cornea resistant to in somatic activity that can degrade the cornea. There are some types of corneal ulcers that cause disability, can cause corneal perforations, and cross-linking makes them resistant to that. It can also be used to treat certain kinds of infections because the reaction between the ultraviolet light and the riboflavin generate oxygen and the oxygen is toxic to microbial, to microbes like acanthamoeba and fungus that often is hard to treat with medications.
