A 19-year-old female presents complaining of reduced best-corrected vision of about five years duration in the left eye. Her medical history is significant for migraine headaches with no visual symptoms. She denies a history of eye rubbing but suffers from allergies and itchy eyes.
A comprehensive exam two months earlier revealed marked asymmetry in keratometry readings and reduced best-corrected visual acuity in the left eye. The doctor diagnosed the patient with keratoconus and referred her for gas permeable contact lens fitting.
This patient, like other keratoconus patients, may be among your most challenging contact lens fits. Yet, for many keratoconus patients, contact lenses remain a mainstay of treatment. Technology and persistence can help you improve vision in these patients, as these case studies demonstrate.
A Double Challenge
By Robert L. Gordon, O.D., and Sharon S. Hiyama, O.D.
When the patient above presented to our practice, her best-corrected visual acuity was 20/25 O.D. with -0.75 -0.25 x 105 and 20/200 O.S. with -2.00 -4.25 x 155. Keratometry measurements were 46.00/ 46.37@090 O.D. (1+ distortion) and 54.00/48.00@145 O.S. (3+ distortion). Corneal topography suggested a possible diagnosis of pellucid marginal degeneration (PMD) O.D. and a definitive diagnosis of PMD O.S. Ultrasound pachymetry measured central corneal thickness of 533m O.D. and 490m O.S.
Anterior segment examination revealed no signs of striae or corneal scarring. An inspection of the tarsal conjunctiva of both upper lids demonstrated giant papillary conjunctivitis (GPC). Both eyes demonstrated normal lacrimal lakes and no evidence of keratitis sicca.
We tried fitting the patient with GP lenses, but she demonstrated poor tolerance, and the lenses moved excessively due to the GPC. Even with an 11.2mm diameter, the lenses moved excessively and decentered on vertical gaze.
We prescribed a mast cell stabilizer b.i.d. to alleviate the GPC and allow for improved contact lens tolerance. However, the patient was frustrated by poor vision O.S.
The right SynergEyes KC lens on this patient demonstrated feather touch with intermediate tear pooling.
At the dispensing visit, the lenses centered well. The right lens demonstrated feather touch with intermediate tear pooling. The left lens demonstrated slight apical vault with intermediate tear pooling. There was no bulbar conjunctival blanching or traction from the soft skirt. Equally important, there was no decentering of the lens on lateral or vertical gaze.
The patient has tolerated these lenses very well despite intractable GPC in both eyes. She has worn the lenses up to 12 hours a day for the past six months with good lens comfort, despite episodes of itchy eyes and lens coating. She often requires extended periods of treatment for her GPC but continues to wear her lenses during these periods.
Discussion. Although the etiology of PMD remains unclear, the characteristic inferior corneal thinning and collagen abnormalities appear to classify it as a variant of keratoconus.1 The incidence is unknown given that the condition is often misdiagnosed as keratoconus.2
PMD and keratoconus share several features, such as irregular astigmatism and progressive corneal thinning, leading to reduced vision. Keratoconus typically demonstrates thinning and the greatest extent of corneal protrusion at the apex of the cone, while PMD classically demonstrates corneal thinning greatest inferior to the apex of protrusion.3 Unlike keratoconus, PMD does not usually exhibit Vogts striae or Fleishers ring.4 It is important to differentiate keratoconus and PMD, as the characteristics of each guide the lens fitting process.
The SynergEyes KC lens, for which I am a clinical investigator, is a hybrid design. (The FDA granted 510k market clearance last month.) It has a GP center manufactured with Paragon HDS 100 (Dk=145) and a skirt made of a 27% water, Group 1, non-ionic hydrophilic material. The diameter of the rigid center lens is 8.4mm and the total diameter of the lens is 14.5mm. The curvature of the posterior portion of the GP is described as a prolate ellipsoid. The soft skirt is available in three curvatures for each GP base curve. The flat, median and steep curves are progressively 0.3mm steeper and vary with the GP base curve.
Ive found that SynergEyes lens tends to remain stable on the eye of keratoconus patients without decentering on rapid horizontal or vertical eye movement and that the lens has reduced problems associated with steep inferior corneal curvature, such as inferior edge lift off and corneal compression. It has resolved most lateral and vertical centering issues, as the soft skirt centers the optics of the lens over the pupil.
Patients who have moderate to severe GPC have difficulty tolerating contact lenses due to a combination of excess lens movement and lens deposition. The SynergEyes lens allows some patients to remain in contact lenses. This may be due to reduced lid-lens interaction, less lens movement against the tarsal conjunctiva and/or reduced lipid deposition on the lens surface.
Dr. Gordon is an associate professor at the Southern California College of Optometry and a founding partner in the Encino Optometric Center in Encino, Calif. Dr. Hiyama is an associate at the center.
1. Kayazawa F, Nishimura K, Kodama Y, et al. Keratoconus with pellucid marginal corneal degeneration. Arch Ophthalmol 1984 Jun;102(6):895-6.
2. Rasheed K, Rabinowitz Y. Pellucid marginal degeneration. EMedicine.com. March 24, 2005. www.emedicine.com/oph/ topic551.htm. [Accessed November 29, 2005]
3. Sii F, Lee GA, Sanfilippo P, Stephensen DC. Pellucid marginal degeneration and scleroderma. Clin Exp Optom 2004 May;87(3):180-4.
4. Szczotka LB. Use contact lenses to visually rehabilitate irregular corneas caused by surgery or disease. Contact Lens Spectrum 2003 May;18(5)34-9.
The Piggyback Approach
By Arthur B. Epstein, O.D.
This keratoconus patient (right) presented with significant central irregularity of the cornea due to superficial scarring. We used a piggyback approach to reduce corneal trauma and improve comfort. We fit the patient with a PureVision lens (Bausch & Lomb) as the soft carrier followed by an appropriate Rose-K lens (Rose K International).
The lenses centered well and showed adequate movement. The patient wears this combination for 12 or more hours a day and has a visual acuity of 20/25-, the same acuity achieved with a GP alone.
The lenses in this piggyback fit centered well and showed adequate movement.
Indications for piggyback fitting include inability to tolerate a GP lens, corneal distress (epithelial staining, epithelial and/or stromal edema, and neovascularization), and poor centration and vision with a GP alone.1 In cases of chronic corneal erosion, a piggyback system improves comfort of wearing lenses, reduces apical scarring and opacity and mitigates or delays the need for penetrating keratoplasty.2,3
When undertaking a piggyback fitting, the carrier lens should be centered, with no evident areas of fluting (localized edge lift). The soft carrier functionally flattens and elevates the cone, allowing for use of a somewhat larger, flatter GP lens for greater stability and fewer edge aberrations such as glare and flare. I usually select a low minus lens. The thinner center fits over the steeper apex, and the thicker periphery effectively fills in the periphery to stabilize the lens.
You can use corneal topography or trial fitting to choose the GP lens parameters. We typically see advanced keratoconus patients in my practice, so the median lens diameter we use is about 8.3mm (sometimes smaller). With a piggyback, it is closer to 8.7mm.
For lens care, most patients do well using a single soft lens care product alone. If additional cleaning is required, we add a GP-specific care product.
A piggyback approach adds a layer of protection and comfort for many patients, but it is not a cure-all for a poor fit. Alignment fits are somewhat easier to achieve, but excessive bearing, while less uncomfortable, will still cause epithelial staining and can lead to scarring.
Dr. Epstein is a partner in North Shore Contact Lens & Vision Consultants in Roslyn, N.Y., and director of the contact lens service at North Shore University Hospital, New York University School of Medicine.
1. Yeung K, Eghbali F, Weissman BA. Clinical experience with piggyback contact lens systems on keratoconic eyes. J Am Optom Assoc 1995 Sep;66(9):539-43.
2. Jaworski P, Wygledowska-Promienska D, Gierek-Ciaciura S. Application of duo-systems (piggy back) in correction of keratoconus. Klin Oczna 2004;106(4-5):629-32.
3. Kok JH, van Mil C. Piggyback lenses in keratoconus. Cornea 1993 Jan;12(1):60-4.
Keratoconus Fitting Pearls
The goals of keratoconus fitting are to avoid mechanical stress on the apex of the cone, spread the bearing across the cornea with the intermediate and peripheral curves, and achieve minimal apical touch and good centration with good edge lifts.
Nipple cones, which are small, paracentral cones (usually less than 5mm), can be very steep centrally but will flatten rapidly into the periphery. Because nipple cones are fairly central, you can use a smaller diameter lensgenerally, the steeper the cone, the smaller the diameterand the pupil will remain covered, allowing for good optics. The peripheral dimensions of the lens are defined by the base curve, so once you identify a nipple cone, its fairly easy to achieve a good fit.
Oval cones tend to be more inferiorly located than nipple cones, with a broader (>5mm) cone base. This type of cone is more difficult to fit because small lenses decenter inferiorly to align over the steepest portion of the cornea, and the pupil will be partially uncovered. The base curve/optic zone diameter of a standard (nipple cone) design is usually too small for these cones. Oval cones require larger-diameter GP lenses with larger optic zones.
Pellucid Marginal Degeneration (PMD)
PMD may at first appear to be high corneal astigmatism that you can manage with soft toric lenses or even glasses. As the condition progresses, however, it becomes the most difficult keratectasia to fit. Keratoconus-designed lenses do not work because the large, broad nature of the beer belly will not fit into the compact central area of the sombrero. Very large diameter lenses, such as scleral lenses or corneoscleral lenses, are often necessary in more advanced cases. Hybrid lenses may hold some hope for PMD patients who are unable to achieve acceptable contact lens fits. (For more on PMD, see Cornea & Contact Lens Q+A: Do I See Keratoconus or PMD? April 2005.)
Keratoglobus involves 70% to 90% of the cornea, yet it is surprisingly easy to fit. The lens of first choice may be an older keratoconus design, such as a Soper Cone, in which the optic zone is fairly large in comparison to the overall diameter. Adjust the periphery of the Soper Cone to tuck in around the edge of the cone. Occasionally, large scleral lenses are warranted.
Dr. Sindt is assistant professor of clinical ophthalmology and director of the contact lens service at the University of Iowa.