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Contact Lens Options for Keratoconus and Other Corneal Disorders
The normal cornea (the front clear lens of the eye) supplies about 75% of the eye's focusing power. In keratoconus, the cornea becomes thinner and loses its structural integrity. As a result, it loses its uniform, domelike configuration and develops irregular astigmatism. It, thus, is unable to produce a clear image inside the eye.
Because the optical surface of the cornea is irregular in keratoconus, glasses cannot give crisp focused vision. Contact lenses, in particular rigid gas permeable contacts (RGP) and a variety of specialty KC and therapeutic contact lenses, can cover these irregularities and better focus incoming light. Applying a rigid lens allows tears to fill the space between the contact lens and the cornea. This layer of fluid optically neutralizes the irregularities of the cornea such that, for all practical purposes, the cornea itself ceases to have any optical effect. The front surface of the contact lens now effectively becomes a new corneal surface... but a surface that we can control, being perfectly smooth, clear, and regular, and also containing the patient's prescription. The contact lens produces a clear image in the eye, often with a dramatic visual improvement for the keratoconus patient.
Adapting lenses of this type is challenging and rewarding for both doctor and patient. These highly specialized lenses feature a complex series of curves to enable us to fit the lens such that patients may enjoy vast improvements in vision and be able to utilize the lenses throughout their active day. These lenses range from the very tiny (6 mm) to quite large (14 mm).
Hybrid or Synergeyes lenses are sometimes used for proper centration and for sensitive eyes. These lenses have a rigid gas permeable center with a soft skirt around the lens edge. Synergeyes lenses have the advantage of excellent oxygen permeability combined with comfort and availability in a number of configurations for unusual corneal shapes. Recently, we introduced new Synereyes lens designs to our practice, allowing fitting of some previously difficult to fit corneas. Please go to www.treatkeratoconus.com to read about these hybrid contact lenses.
Some special cases require a "piggy-back" fitting, an RGP lens fitted over a soft contact lens. Other patients with KC and other corneal and ocular surface disorders may be helped with scleral and mini-scleral lenses, which are large, compound curve lenses, which extend beyond the iris onto the white of the eye.
A variety of keratoconus lenses is necessary to fit all the varied shapes and requirements of the keratoconic cornea. Because of this, the CLEI Center for Keratoconus has available every modern technology for the diagnosis and treatment of this disease and a vast specialized KC contact lens inventory (including our own Hersh Palpebral Traction Lens). This gives us the tools to meet the challenge of the keratoconic cornea and restore the patient to useful vision.
Led by Dr. Clark Chang, the contact lens division of the CLEI Center for Keratoconus strives to achieve success with even the most difficult KC challenges. Though not always successful, we will spare no effort in assuring that you get the best result possible.
Dr. Chang has been asked to join the Expert Panel on a new Keratoconus treatment website. This website is meant to act as a resource center for keratoconus patients and introduce the new hybrid contact lens technology. Please feel free to ask Dr. Chang your questions:
Current Non-Surgical Management Concepts for Keratoconus
Clark Chang, O.D.
Keratoconus is a non-inflammatory, progressive corneal condition associated with corneal thinning, weakening, and steepening, resulting in corneal optical irregularities and poor vision. An incidence rate of 1:2000 has been reported with no known sexual or ethnic predilection. In addition, familial inheritance has been reported in 6-24% of cases and co-morbidities such as atopic disease and connective tissue diseases have also been reported in the literature. Thus, genetic predisposition, enzyme imbalance on ocular surface, and eye rubbing as an exaggerated allergic response have all been proposed as potential underlying causes to keratoconus development. However, no definite causative factor(s) have been proven.
The increasingly irregular corneal contour, as keratoconus progresses in severity, causes optical side effect known higher order aberrations (think of static noise for TV signals). The resultant aberrations are primarily responsible for the reduction in one’s visual functions. Corneal transplant has traditionally been utilized as the choice of medical treatment for the misshapen cornea. However, the reconstructed tissue interface does not always permit full restoration of a regular corneal contour, which still necessitates contact lens rehabilitation after corneal transplantation. Therefore, with the recent advancements in contact lens technology, non-surgical management methods have been recognized as the leading treatment choice in visual rehabilitation in keratoconus population. Surgical interventions are currently being preserved for individuals who either can not tolerate contact lenses or can not achieve satisfactory vision with contact lenses.
Rigid Gas Permeable Lens (RGP) provides good safety profile and visual outcome, making this lens option the most widely utilized method in rehabilitation of an irregular corneal surface. The firm structure of a RGP lens permits accumulation of tear fluid beneath the lens; the combination of a smooth outer lens surface with fluid filling the irregular space between lens and cornea result in the neutralization of a distorted corneal surface. The reformed anterior ocular surface leads to a significant reduction in optical aberrations induced by a keratoconic cornea. The advantages of good visual outcome and ease of lens handling may not always outweigh the relatively lengthy adaptation period required for RGP lenses. Hence, alternative non-surgical options have been developed to overcome such occasions.
The flexible nature of most soft lens materials does not allow sufficient tear accumulation to restore a smooth anterior corneal surface; hence, this corrective modality is only utilized in patients with mild keratoconus and when functional vision can still be supported with regular ophthalmic lenses. Nonetheless, recent custom soft keratoconus lens designs employ enhanced lens thickness profile in attempt to mimic the optical benefits offered by RGP lenses. While oxygen permeability may be a concern until new material becomes available, the soft keratoconus lens provides a viable alternative for RGP intolerant wearer with mild to moderate keratoconus.
RGP intolerance mainly stems from heightened corneal sensitivity stimulated by lens movements and its weight distribution across the corneal surface. A carefully selected bandage soft lens can be placed under the RGP lens in a piggyback system, which decreases neural stimulation and stabilizes RGP lens on the cornea. However, the two-lens system can potentially increase the complexity in lens handling and maintenance as well as reduce oxygen supply to the eye.
Hybrid lens technology has enabled the binding of a RGP lens to a soft lens cut-out so that a single lens system can satisfy both the demands for improved visual quality and wearing comfort. The recent advances in the fourth generation hybrid lens, SynergEyes ClearKone®, utilize an uniquely designed RGP lens contour to facilitate expansion of its previous fitting parameters to include patients through all stages of keratoconus. A fitting success rates up to 86.9% has been reported utilizing hybrid lens platforms in keratoconus population.
Recently improved oxygen permeability in RGP lens material led to the clinical resurgence of scleral lenses. Scleral lenses comprise the largest diameter lenses within the family of non-surgical rehabilitation options. Although counterintuitive, a sclera lens design often can be more comfortable than its smaller RGP counterpart. This is because a sclera lens design allows its lens edge to rest on sclera (white part of the eye), which has much lower sensitivity level than one’s cornea. In addition, similar to the fourth generation hybrid lenses, sclera lenses are designed to avoid interaction between posterior lens surface and corneal surface, which minimize stimulation of corneal sensitivity. Up to a 93% of keratoconus fitting success rate has been described with modern scleral lens designs.
Owing to the larger lens diameter in both the hybrid and scleral lenses, in comparison to the conventional RGP lenses, the insertion and removal process require good techniques and much practice during the initial adaptation period. This can hold true even for experienced users of other lens modalities.
A well fitted lens not only defers the need for more invasive surgical procedures but also significantly improves the quality of one’s vision and life. However, this process requires the combined ingredients of a physician’s clinical expertise and a patient’s determination. Further, it is essential for both the physician and patient to recognize that no single lens design currently encompasses the complexity of all fitting situations. An open and honest discussion regarding one’s visual expectations and daily functional activities performed in real life environment can be meaningful in the selection of a tailored management choice from the many non-surgical options that exist today.
Dr. Chang gives contact lens webinar
May 11, 2011
Dr. Chang will share his extensive knowledge of fitting the ClearKone® lens on several types of irregular cornea patients. Strategies for troubleshooting common fitting problems, case studies and tips for simplifying the hybrid fitting process will be discussed. Attendees will have the opportunity to ask questions and share experiences.