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VISANTE OPTICAL COHERENCE TOMOGRAPHY

Dr. Edward Boshnick
8479 Coral Way
Miami, FL 33155
(305) 264-4400
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Keratoconus

Keratoconus is a non-inflammatory ectasia or protrusion of the cornea. It is characterized by progressive thinning and steepening of the central cornea. As the cornea steepens and thins, the patient experiences a decrease in vision which can be mild or severe depending on the amount of corneal tissue affected. The onset of keratoconus usually starts in the teenage years or early 20s. It rarely develops after the age of 35. Keratoconus shows no gender predilection and is bilateral in over 90% of cases. In general, the disease develops asymmetrically. Diagnosis of the disease in the second eye usually lags 6 or 7 years after diagnosis in the first. The incidence of keratoconus is about 2 to 3 people per 1000 population.

As the condition progresses, the distorted cornea will require a contact lens, usually rigid gas permeable. The progression of keratoconus is unpredictable. While keratoconus interferes with the clarity of a persons sight, it rarely causes blindness. With the latest contact lenses specifically designed for keratoconus, the need for a corneal transplant is extremely remote. Recently, several soft lens have been introduced for the treatment of keratoconus, including the Soft K lens and the Flex lens.

What Causes Keratoconus?

The characteristics of keratoconus have been known for at least 200 years, but the specific causes are still undetermined. Several theories have been proposed. One theory is that keratoconus is genetic in origin. About 7% of patients have other family members with the disease. Another view holds that keratoconus is secondary to some disease process. While there are many theories, research into keratoconus continues.

Standard lens designs with fixed optical zones (OZ) do not ideally fit the cone shape of keratoconus patient's. This shows a standard lens that will yield unwanted pooling at the base of the cone and peripheral bearing that can seal off and cause corneal problems.

How is Keratoconus treated?

As keratoconus advances, rigid gas permeable lenses are the first choice to correct vision adequately. Most of the time this is a permanent remedy. Because of the progression of the disease, it is important that the lenses are fitted with great care and are reassessed at least annually by eye care professionals. The lenses that we use have a complex geometry that takes into account the conical shape of the cornea for all stages of the condition. The lenses have multiple curves which are custom designed to fit each individual cone correctly without traumatizing the delicate compromised corneal tissue. For almost all patients, this means better comfort and optimum visual acuity. Additional features of these newest of keratoconus lens designs include:

This demonstrates the benefits of a smaller optical zone to fit the cone contour. The design results in little tear pooling at the base of the cone and shows an even distribution of tears under the lens.

1. The complex geometry of the lens can be customized to suit each eye and correct all of the myopia and astigmatism associated with the keratoconus.

2. They are easy to insert, remove and clean.

3. They provide excellent health to the eye, because they allow the cornea to “breathe” oxygen directly through the lens.

4. The central zone of the lens fits directly over the cone. Consequently, the lens will not slide around on the cornea causing ocular irritation or scarring. The concept of this unique fit is similar to the manner in which a bra is fitted over a breast.

Why is it that I always have pain in my eyes and the sunlight “kills” me?

The lenses that you are wearing are probably not fit correctly. We see this often when the lenses are fit too flat, and the design of the lens is not appropriate. The lenses are moving excessively over the cornea with each blink causing abrasions to the apex of the cone. If this continues, irreversible scarring will result and visual acuity will diminish. When I get to see a cornea like this, I often have to refit with a new rigid lens over a special soft lens which acts as a bandage. The soft lens allows the cornea to heal, while the rigid lens provides vision. Typically, this “piggy back” combination lasts no more than a few weeks. As the cornea heals, new measurements of the corneal curves are taken. It is not unusual to encounter changes in the curves and contour of the healed cornea. As this takes place, new rigid lenses are ordered to fit the healed cornea.

Corneal Ectasia

Known Risk Factors For Ectasia

Corneal ectasia is a condition resembling keratoconus but comes from a different origin. Almost invariably the cause is refractive eye surgery, specifically LASIK. After LASIK, the cornea has been made thinner. Because the corneal “wall” has been made thinner, internal pressure from within the eye can cause expansion or distension of the cornea. The resultant distorted corneal surface will usually make it impossible to have clear vision with eyeglasses or soft contact lenses. Most of the time a special gas permeable contact or scleral lens will be needed to restore lost vision. These special high tech lenses (which have only recently become available) will act to create a new corneal surface allowing the patient to regain clear, comfortable vision.

Right cornea with post-rk ectasia

Right cornea with post-rk ectasia

This patient underwent an early form of refractive surgery known as Radial Keratotomy (R-K) in 1988. In 1990 patient began losing vision. We recently fit this patient with a scleral lens which has greatly improved his vision while at the same time providing excellent comfort. This is the first time patient has had quality vision and comfort in 18 years.

Patient RM with post-lasik corneal ectasia right eye

Patient RM with post-lasik corneal ectasia left eye

This 76 year old patient underwent Lasik in 1997. Several years later he started losing his vision very rapidly in a short time span. In 2009, we fit him with scleral lenses which have enabled him to regain quality vision with excellent comfort. Patient was legally blind with best correction until he received his new lenses.

Pellucid Marginal Degeneration

Pellucid Marginal Degeneration is a sub-category of keratoconus. Pellucid corneas involve a larger distorted geographic area usually extending from the inferior corneal margins up to the center of the cornea. It is not unusual for 50% or more of the corneal surface to be involved. Because so much of the cornea can be affected, fitting this type of cornea can be more challenging. The problem we face as eyecare practitioners is fitting the steep areas if the cornea without adversely affecting the flatter areas. Typically what is needed is a much larger gas permeable lens than would be used when fitting a "nipple" cone. Smaller lenses tend to be very unstable on a pellucid cornea and may wobble on the cornea with each blink causing a great deal of irritation. Very often, even the larger lenses will not work and we are forced to use a gas permeable scleral lens. Scleral lenses vault the entire cornea and are supported by the white portion of the eye (the sclera). A special liquid fills the space between the back surface of the lens and the front surface of the cornea. This liquid acts as a buffer and protects the compromised corneal tissue. These lenses are almost always very comfortable and the vision provided by them is extremely good. The great majority of patients are able to wear their scleral lenses almost all of their waking hours without problems.

Vision Loss and Corneal Transplant Surgery

Many keratoconus patients fear that their keratoconus will keep on progressing causing further vision loss or ultimately corneal transplant surgery. This is not necessarily true. There have been many new advances in contact/scleral lens technology. This has allowed the overwhelming majority of keratoconus (ectasia, pellucid marginal degeneration) patients to wear these specialty lenses safely, comfortably and with good to excellent vision for almost all of their waking hours. Please understand that for the overwhelming majority of keratoconus patients, the active progressive stage of this disease seldom exceeds 5 years. I have seen many keratoconus patients over a 30 year period have virtually little or no change in the status of their corneas.

Corneal transplant surgery is not without risk. Infection and/or rejection of the graft can occur. In addition, the long term use of anti-inflammatory drugs used after this surgery can have undesirable side effects. The great majority of the post-corneal transplant patients who I have seen over the years have had irregularly curved corneas which required the use to special gas permeable contact lenses to restore useful vision. The fitting of a contact lens on a transplanted cornea can be even more challenging than on a keratoconic cornea.

To sum up, everything should be done to avoid a corneal transplant. Every year, new materials and technologies are appearing to make it easier for the keratoconus patient to be fit so as to allow better vision and comfort while maintaining ocular health.

A few words about Hydrops:

Hydrops is a rare complication of keratocunus, generally occurring in advanced keratoconus. It is caused by a fissure or split within the internal layers of the cornea. Fluid then enters the cornea from within the eye. When it occurs, the cornea becomes acutely swollen and opaque (cloudy/white).

There is no specific treatment. The condition will clear over a period of several weeks to months. The cloudy vision should improve over time. Hydrops typically results in corneal scarring. If the split is in the central part of the cornea, vision may be impaired, no matter what type of correction is attempted. Occasionally, hydrops can benefit keratoconus patients who have extremely steep corneas. As the cornea heals, a flattening of the cornea often results, making it easier to fit with a contact or scleral lens.

When hydrops causes extreme pain and/or light sensitivity, scleral lenses should be fit as soon as possible. This is because the scleral lens promotes healing and protects the irritated corneal tissue. In addition, vision and comfort is usually very good.

Developing hydrops in one eye does not necessarily mean that you will develop it in the other eye. Keratoconus, is often a very asymmetrical condition in that one eye is often much more advanced than the other.

Cross-Linking Studies For Keratoconus And Ectasia Begin In The United States

Clinical trials have begun in the United States to study the safety and effectiveness of corneal collagen cross-linking (CXL) in patients with progressive keratoconus and corneal ectasia after corneal refractive surgery. Corneal collagen cross-linking is a procedure that stiffens the cornea by exposing it to ultraviolet (UVA) light after it is saturated with riboflavin (vitamin B32). In the United States, the UVA light (UV-XTM Illumination System; IROC, Zurich, Switzerland) and riboflavin (MedioCroSSTM; Peschke Meditrade GmbH; Huenenberg, Switzerland) are regulated as a combination product under the jurisdiction of the Center for Drug Evaluation (CDER) of the U.S. Food and Drug Administration (FDA). FDA recently completed it review of the keratoconus and ectasia clinical study protocols and gave permission to begin enrollment of 160 patients into each study at up to 20 investigative sites in the United States.

The corneal collagen cross-linking procedure was developed at the University of Dresden in Germany, and has been under investigation there since 1998. The cross-linking procedure is performed by instillation of riboflavin drops onto the eye over a period of 30 minutes to saturate the cornea. Riboflavin drops are then continued for another 30 minutes as the eye is exposed to a UVA light positioned above the cornea to deliver a carefully determined dose of UVA light. As the UVA light interacts with the riboflavin, chemical bonds (cross-links) form between the corneal collagen molecules and make the cornea stiffer. As a result, the corneal collagen tissue is stronger and can more uniformly retain its natural curved shape, rather than bow forward into the cone-like shape that is the hallmark of keratoconus and ectasia.

Keratometry results from an ongoing CXL clinical study in Dresden, where over 800 eyes have been treated, showed a 1.25 diopter reduction in the maximum corneal curvature at 6 months after the CXL procedure and that corneal curvature continued to flatten for up to 7 years after treatment in the cross-linked eyes.] Eyes treated in an ongoing study in Australia showed a similar flattening effect and more than a 2-line improvement in best spectacle corrected vision. 2 Most importantly, none of the patients treated in either the Dresden or Australian clinical trials have had their keratoconus or ectasia progress to corneal transplantation, which is the traditional treatment for these conditions when all other treatment options fail.

The combination of riboflavin concentration and UVA light exposure parameters that are being used in the Dresden, Australian, and U.S. studies have been carefully selected such that -95% of the UVA light is absorbed in the first 400 microns of the cornea. This minimizes the passage of the UVA light through the entire cornea and protects the remainder of the eye from damage. There is only one report of endothelial cell dysfunction in the international clinical trials and in the published literature on crosslinking, which occurred in an eye with a thinner cornea than is now recommended. In the U.S. clinical trial, corneal thickness at the thinnest point on the cornea must be at least 400 microns before the UVA light treatment can start to assure safety of the treatment.

The U.S. studies are randomized, controlled, prospective clinical trials. One eye of each subject will be randomized to receive either the cross-linking treatment with riboflavin and UVA light (with epithelium removal) or treatment with riboflavin alone (without epithelium removal). After three months, the results in the two groups will be compared. Then, the riboflavin only eyes that show no effect and untreated fellow eyes can receive the cross-linking treatment with riboflavin and UVA light, if the physician and the subject feel this is appropriate, based on the information available at the time. The cross-linking procedure used in the U.S. studies requires removal of the epithelium (the outer layer of cells covering the surface of the cornea) before the start of the riboflavin administration. Although some surgeons advocate performing the procedure without removing the epithelium, experimental work recently reported by Asota et al. demonstrated that corneas with the epithelium removed had complete riboflavin saturation, whereas, riboflavin showed little to no penetration in corneas with intact epithelium. These experiments confirmed that removal of the epithelium is necessary to achieve riboflavin diffusion across the cornea and corneal saturation can be achieved using the riboflavin dosage regimen from the U.S. clinical studies.

In order to be included in the U.S. study, potential subjects must have a well-established diagnosis of keratoconus that has progressed within the past two years or a diagnosis of ectasia after LASIK or PRK. There may not be any other diseases that might affect the outcome of treatment, and the cornea must be thick enough to allow treatment without damage to the endothelial cells, which are on the posterior surface of the cornea. Subjects must also have best corrected vision that is worse than 20/20 and must be available for follow-up at the investigational site for one year after the cross-linking treatment. The study description can be found at http://www.clinicaltrials.gov/ct2/ search keyword: cross-linking. Further information on becoming a study participant can be obtained by contacting one of the investigators listed below or by sending an email to crosslinking@crc-regulatorv.com .

US Investigational sites are:
Emory University (Drs. Doyle Stulting and Bradley Randleman; Atlanta, GA)

Gordon Binder Weiss Vision Institute (Drs. Perry Binder; Michael Gordon, and Jack Weiss; San Diego, CA)

Ophthalmic Consultants of Long Island /TLC Laser EyeCenter (Drs. Eric Donnenfeld and Marguerite McDonald; Garden City, NY)

Cornea and Laser Eye Institute (Dr. Peter Hersh; Teaneck, NJ)

Price Vision (Dr. Frank Price, Jr.; Indianapolis, IN)

Columbia University (Dr. Stephen Trokel; New York, NY)

DurrieVision (Dr. Daniel Durrie; Overton, Kansas)

Minnesota Eye Consultants (Drs. David Hardten, Richard Lindstrom, Elizabeth Davis, and Sherman Reeves; Minneapolis, MN)

Center for Excellence in Eye Care (Dr. William Trattler; Miami, FL)

Wilmer Eye Institute, Johns Hopkins Medical Center (Drs. Walter Stark, Albert Jun and Roy Chuck).

References:
1 Seiler T. Corneal collagen cross-link:from the basics to the clinical use. European Society of Cataract and Refractive Surgery (ESCRS) Winter Refractive Meeting (Barcelona, Spain): February 8, 2008.

2 Snibson, G. (Principal Investigator), Wittig C. A prospective, randomized clinical trial of cornea] collagen cross-linking in progressive keratoconus. 2008 Corneal Collagen Cross-Linking Congress< (Zurich; Switzerland); December 8, 2008.

3 Asota IM, Stulting RD, Fant BS, Edelhauser H. Corneal Stroma Riboflavin Uptake to Establish Steady-State Concentrations for Ultraviolet-A Crosslinking. American Society of Cataract and Refractive Surgery Symposium and Congress (Chicago, ILL); April 5, 2008.