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Emerging treatments address various stages of keratoconus
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While a number of treatment modalities currently exist for keratoconus, new options such as improved lens designs, Intacs corneal inserts, PRK and wavefront technology are entering the arena.
Contact lenses for keratoconus
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Gas-permeable lenses are the predominant modality used to correct vision in keratoconus patients. They are generally spherical in curvature and can achieve excellent fitting profiles with sharp, clear visual results.
Aspheric lens designs gradually flatten from the center toward the periphery, approximating the steep cone vs. flat periphery curvature relationship seen in keratoconus. These designs are indicated for small to moderate cones. The goal of this type of lens is to vault the apex of the cone, or lightly touch it, and align the more normal peripheral cornea.
According to Christine W. Sindt, OD, a practitioner and assistant professor at the University of Iowa Department of Ophthalmology, choosing a contact lens for a keratoconic patient is very specific to the progression of the disease and the needs of the patient. “My lens choice depends on the size of the cone and the patient’s individual needs,” she told Primary Care Optometry News. “For example, dry eyes, problems with glare, occupational needs, past experience with lenses and so forth will help me determine how I will approach a keratoconus fit. I use many standardized fitting sets, but I often alter the parameters as I go along.”
Dr. Sindt said she most often uses the Rose K lens (Lens Dynamics, Golden, Colo.). “I like the reproducibility of the lens and the even weight distribution without harsh points of touch,” she said. “I also use a large number of dyna-intralimbals and corneo-scleral lenses, especially in cases of pellucid marginal degeneration.”
Dr. Sindt said successful fitting of a keratoconus lens requires knowledge and experience working with a particular lens design. “The key to fitting keratoconus is to choose a design and to work with it enough to know how to manipulate the parameters to get the desired effect,” she said. “I don’t believe there is a standardized design to fit everyone, but designing a lens from the ground up, at least for me, seems like an awful lot of work to me.”
New bi-aspheric lens
The Keratoconus Bi-Aspheric lens (BE Enterprises, Vancouver, B.C.), is a GP design lens for keratoconus. Designed by John Mountford, OD, and Don Noack, OD, practitioners in Brisbane, Australia, the KBA features a high-eccentricity value back surface that is designed to approximate the significantly changing curvature of the keratoconic cornea.
The front surface asphericity neutralizes radial astigmatism created by the back, providing a purely optical lens without zonal junction points to hinder vision. “The result is a lens-to-cornea relationship with superb alignment and, therefore, comfort, centration and vision,” said Randy Kojima, director of technical affairs for BE Enterprises.
Mr. Kojima said KBA lenses are large, typically 10.2 mm in diameter. He told Primary Care Optometry News the fitting procedure is simple, predictive and scientific.
“Using a KBA trial fitting set, determine the trial lens that creates clearance over the cone. KBA lenses are designed to protect the epithelium from scarring or damage, so lenses should not be in touch with the cone,” he said. “Second, determine the trial lens that produces the ideal peripheral alignment with the cornea. Employing the KBA software, a mathematically determined, custom KBA will be calculated from the best fitting lens in an apical/cone clearance and the best fitting lens in peripheral alignment.”
Mr. Kojima said the software will calculate the required base curve and eccentricity value of a custom-order lens to maintain sagittal clearance and the ideal corneal alignment.
Hybrid lens design
Jerome Legerton, OD, discussed the advantages and disadvantages of “piggyback” contact lens systems. “The piggyback lens may function as a bandage soft contact lens, shielding the cornea from insult, epithelial staining and, therefore, pain,” Dr. Legerton said. “This system suffers from the need to handle and care for two pairs of lenses.”
Dr. Legerton cited four CLEK study clinics that enrolled 10 non-CLEK keratoconus patients each and attempted to fit them with a standardized piggyback contact lens system. “Of these 40 patients, almost a third of them discontinued the piggyback treatment within the first month of fitting,” Dr. Legerton said.
According to Dr. Legerton, one possible alternative is a new high-Dk hybrid lens for keratoconus — SynergEyes KC by Quarter Lambda Technologies Inc. (San Marcos, Calif.). The lens recently received IRB approval for 510(k) clinical trials, Dr. Legerton said in an interview. “SynergEyes KC incorporates a 150-Dk gas-permeable center with a hydrogel skirt,” Dr. Legerton said. “The lens features increased strength, along with vastly increased oxygen permeability.”
Dr. Legerton said the goal of this lens is to provide a lens platform that easily facilitates custom vision correction for the purpose of optimizing visual performance. “The high-Dk hybrid lens is intended to provide the optical advantages of gas-permeable lenses with the comfort advantages of soft lenses,” he said. “The stability and centration provided by the soft skirt appear to provide a foundation for the rigid center to correct the full refractive error of eyes suffering from keratoconus.”
The SynergEyes KC lens is designed specifically for mild to moderate keratoconus. Quarter Lambda Technologies has an additional patent pending design for severe keratoconus and post-surgical applications.
Intacs inserts
Another promising development in keratoconus treatment is the use of Intacs prescription inserts (Addition Technology, Des Plaines, Ill). Intacs are clear, thin inserts that are placed in the periphery of the cornea. They reshape the curvature of the cornea, thereby correcting mild myopia. The manufacturer recently received European regulatory approval — a CE mark — for using Intacs to treat keratoconus.
Brian S. Boxer Wachler, MD, director of the Boxer Wachler Vision Institute in Beverly Hills, Calif., has been using Intacs for the past several years and believes this treatment – currently an off-label use in the United States — to be an excellent option for keratoconus patients. “Since my first report of Intacs for the treatment of keratoconus in the United States in 1999, it has become a mainstream surgical treatment,” he said. “It has found a perfect place between contact lens and corneal transplant options.”
Dr. Boxer Wachler said the unique approach of Intacs effectively thwarts the progression of the disease. “Intacs reduce astigmatism as well as myopia, which ‘turns back the clock’ on the disease,” he said. “No other procedure can partially reverse keratoconus by modifying the full thickness of corneal architecture.”
Intacs is performed as a 10-minute, outpatient procedure with topical anesthetic drops, Dr. Boxer Wachler said. “If contact lenses are fitted after surgery, I recommend waiting 1 month if possible for the cornea to stabilize,” he said. “Glasses may be dispensed within 1 week, but there may be a prescription update at the 1-month follow-up visit.”
Dr. Boxer Wachler said with proper patient expectations, Intacs has a high patient satisfaction rate. He said optometrists who have both contact lens tolerant and intolerant patients may consider adding Intacs to their comanagement practices. “I have found that optometrists provide important postoperative care to these patients after surgery, as well as fitting contact lenses and glasses for residual refractive error in most cases,” he said.
PRK and keratoconus
The efficacy of PRK for keratoconus continues to be studied by clinicians, with some favorable results. A 6-year Russian study published in the March-April 2003 issue of the Journal of Refractive Surgery studied the use of PRK combined with phototherapeutic keratectomy (PTK) for patients with primary keratoconus.
In the study, 41 patients (70 eyes) underwent PRK and PTK with a Nidek (Fremont, Calif.) EC-5000 excimer laser. PRK included spherical or cylindrical ablations, or both. PRK ablation zone diameter was 6 mm.
PTK was performed with an ablation zone diameter of 8 mm and a transition zone of 9 mm. The ablation zone was decentered toward the cone apex as indicated by corneal topography.
According to the findings, uncorrected visual acuity increased from 0.07 ± 0.0003 D to 0.76 ± 0.03 D. Mean best spectacle-corrected visual acuity increased from 0.70 ± 0.03 D to 0.83 ± 0.04 D; myopia decreased from a mean 5.32 ± 0.62 D to 1.55 ± 0.30 D and astigmatism decreased from a mean 3.25 ± 0.53 D to 1.75 ± 0.25 D. Therapeutic results showed that keratoconus progression was stopped in 91.43% of eyes with a mean follow-up of 3.5 years and maximum follow-up of 6 years.
The conclusion of the study was that PRK and PTK with the Nidek EC-5000 excimer laser was an excellent option for patients with primary keratoconus.
Wavefront technology for diagnosis
Wavefront analysis can be a very useful tool in detecting subtle forms of keratoconus, according to Joseph Stamm, OD, FAAO, director of clinical services for StrongVision Refractive Surgery Center at the University of Rochester in New York.
“As keratoconus creates an inferior-steep power pattern on the cornea as detected with corneal topography, there is a corresponding elevation of vertical coma in the wavefront,” Dr. Stamm said. “Coma may be considered an aberration of the wavefront in which a portion of the wavefront is advanced and an adjacent portion retarded.”
Dr. Stamm said the advanced portion corresponds to a higher surface power and vice versa for the retarded portion. “Looking at the keratoconic cornea, the ectasia is inferior with more power in the lower quadrant of the cornea as compared to the superior,” he said. “This induces the coma.”
Although most corneal topographers currently on the market are sensitive enough to detect even forme fruste keratoconus, Dr. Stamm said the Orbscan II (Bausch & Lomb, Rochester, N.Y.) can detect the more subtle variant known as posterior keratoconus. “In this variant, the ectasia is present in the posterior cornea, but does not manifest itself in the anterior cornea,” he said. “Wavefront analysis will identify the coma that this will induce.”
Dr. Stamm said one problematic aspect of wavefront analysis with keratoconus is its difficulty in recording higher-order aberrations in a scarred or ectatic cornea. “New, more robust wavefront devices with larger dynamic ranges are currently under development to address this issue,” he said.
Wavefront for lens design
Wavefront-designed contact lenses can also be used to treat keratoconus, according to Garold L. Edwards, OD, FAAO, senior technology consultant for Optical Connection Inc.
“In keratoconus, the protruding cornea creates irregular astigmatism and induces higher-order aberrations,” he said in an interview. “A wavefront analyzer can measure both lower-order aberrations and higher-order aberrations. When the aberrations are measured, a soft lens can be designed and manufactured to correct them.”
Optical Connection has announced plans to develop wavefront-designed contact lenses that correct higher-order aberrations.
For Your Information:
- Christine W. Sindt, OD, is an assistant professor at the University of Iowa. She can be reached at Hospitals and Clinics Department of Ophthalmology and Visual Sciences, 200 Hawkins Dr., Iowa City, IA 52242; (319) 356-4816; fax: (319) 356-0363; e-mail: christine-sindt@uiowa.edu. Dr. Sindt has no direct financial interest in the products mentioned in this article, nor is she a paid consultant for any companies mentioned.
- Randy Kojima is director of technical affairs for BE Enterprises, 866 E. Cordova Street, Vancouver, BC V6A 1M4 (604) 215-1467; fax: (604) 215-1476.
- Jerome Legerton, OD, is a Primary Care Optometry News Editorial Board member based in San Diego. He can be reached at 874 Harbor View Place, San Diego, CA 92106; (619) 758-9140; fax: (619) 758-9141; e-mail: jlegerton@aol.com. Dr. Legerton has a financial interest in Quarter Lambda Technologies Inc.
- Brian S. Boxer Wachler, MD, is director of the Boxer Wachler Vision Institute in Beverly Hills, Calif. He can be reached at RoxSan Medical Building, 465 N. Roxbury Dr., Beverly Hills, CA 90210; (310) 860-1900; fax: (310) 860-1902; e-mail: bbw@boxerwachler.com. Dr. Boxer Wachler has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Joseph Stamm, OD, FAAO, is director of clinical services for StrongVision Refractive Surgery Center at the University of Rochester. He can be reached at 100 Meridian Centre, Ste. 125, Rochester, NY 14618; (585) 341-7815; fax: (585) 756-1975; e-mail: joseph_stamm@urmc.rochester.edu. Dr. Stamm has no direct financial interest in the products mentioned in this article, nor is he a paid consultant for any companies mentioned.
- Garold L. Edwards, OD, FAAO, is senior technology consultant for Optical Connection Inc. He can be reached at 3315 Almaden Expressway, Suite 25, San Jose, CA 95118; (408) 265-8644; fax: (408) 265-8639; email: gedwards@opticalconnection.com.