Strategy for Boosting Visual Acuity in Keratoconus Patients

Acorneal condition characterized by unpredictable progression, keratoconus requires a flexible management strategy to ensure that treatment options are available for the various stages and severity of disease that can be seen. By convention, the first line of treatment is the restoration of good visual quality and clarity using a nonsurgical technique, namely prescription of rigid contact lenses.

Some keratoconic patients experience little disease progression and can be effectively managed on a longterm basis with contact lenses. Others, however, experience unpredictable disease progression in which the cornea becomes thinner and steeper, and preexisting myopia and astigmatism worsen. Once a patient’s visual requirements can no longer be met with contact lenses, surgical options must be considered.

PAST AND PRESENT SURGICAL OPTIONS

In the past, surgical options were limited to corneal transplant, an option less desirable than those available today given the inevitable wait for a suitable donor and the risk of graft rejection. Today, several straightforward and noninvasive surgical procedures are available for keratoconic patients, including intrastromal corneal ring segment (ICRS) implantation, topography-guided PRK, and corneal collagen crosslinking (CXL). These three approaches address different aspects of the mechanism of keratoconus progression, and as such they can be remarkably effective when used in combination.

In topography-guided PRK, an excimer laser is used to ablate topographically identified points on the cornea. These points are smoothed to produce a flatter and more even cornea. This restoration of the spherical shape of a normal cornea results in correction of the astigmatism and myopia that typically trouble keratoconus patients. CXL involves the application of riboflavin drops to the cornea, followed by ultraviolet light exposure to trigger the crosslinking of corneal collagen. Crosslinking helps to minimize the corneal steepening that usually worsens as keratoconus progresses.

ICRSs, such as the Keraring (Mediphacos), are crescentshaped plastic rings that flatten the steepened keratoconic cornea when placed on its periphery. I have been implanting the Keraring in keratoconic patients for several years and have found that this simple, noninvasive procedure preserves corneal integrity, stabilizes the cornea, and corrects a wide variety of keratoconic severities. The peripheral positioning of the rings adds structural integrity to the cornea and ensures that the corneal apex is relocated closer to the central pupil, eliminating myopic refractive error.

SYNERGISTIC EFFECT

When CXL is combined with implantation of the Keraring, a highly effective outcome is produced by the synergistic effect of the two treatments to achieve a high level of corneal flattening.

The first step in reestablishing functional vision in a keratoconic patient is to determine his or her current visual acuity. If the BCVA is 20/32 or better—a feature of less advanced keratoconus—topography-guided PRK in combination with CXL is an appropriate option. In eyes with a BCVA worse than 20/32—as is often seen in advanced keratoconus—ICRS implantation is my preferred primary strategy. I will be prepared to perform PRK and CXL 3 to 4 months later if needed.

EFFICACY STUDY

My colleagues and I performed a study to evaluate the efficacy of treating keratoconus with combined topography-guided PRK and CXL as a primary treatment strategy or secondary to Keraring implantation.

The first study group included 23 eyes of 23 patients whose mean age was 33 years. I have found that patients with thin corneas are unsuitable for PRK; therefore, all participants had a corneal thickness of at least 450 μm before PRK. The ablation performed during the procedure was limited to ensure that corneal thickness was not reduced by more than 50 μm. Topography-guided PRK was performed first, followed by conventional CXL, after which all patients were monitored for 6 months.

found that all eyes experienced an improvement of visual acuity, with an average gain of 3.6 and 1.4 Snellen chart lines for UCVA and BCVA, respectively.

In a second group of 21 eyes of 21 patients whose mean age was 27.3 years, we implanted Kerarings. By 3 months after implantation, however, all eyes showed potential for further visual improvement. All patients underwent topographyguided PRK plus CXL as a secondary procedure. After 6 months, no significant side effects had occurred in the group; UCVA and BCVA were improved by a mean 2.7 and 1.8 lines, respectively; and mean spherocylindrical refraction was significantly reduced from preoperative level.

CASE PRESENTATION

The following case study illustrates the potential efficacy of this triple procedure in improving the refractive outcomes of keratoconic patients.

Mr. M, a 26-year-old keratoconic patient, had a baseline UCVA of 1/20 and a refraction of -8.50 D. At 6 months following implantation of the Keraring, his UCVA and refraction improved to 2/10 and -4.50 D, respectively. At this point, he underwent topography-guided PRK plus CXL and achieved further improvement. Three months after PRK plus CXL, Mr. M had UCVA of 7/10 and refraction of +0.50 D (Figures 1 and 2).

I believe that the case presentation and the findings of our study show that a triple procedure, in which topography-guided PRK is combined with CXL in patients previously implanted with the Keraring, is safe and effective for improving visual acuity. I prefer to offer patients the opportunity to achieve the maximum visual acuity possible; therefore, when I implant a Keraring, I ensure that the patient will be able to have PRK and CXL at a later date if he or she needs a boost in visual acuity. To keep this option open, I always try to use a size 6 Keraring.

The Keraring is available in two sizes with inner ring diameters of 5 mm (SI- 5) or 6 mm (SI-6). These size options ensure that I can tailor the Keraring procedure to meet each patient’s specific needs, as reflected by his or her degree of ectasia, refraction, and topographic results. I prefer an SI-5 when larger segments of the eye require flattening. My experience has shown that the SI-5 is highly effective in correcting spherical refraction. The larger SI-6 allows greater optical room for PRK; therefore, I implant this size in patients in whom I hope to perform PRK and CXL at a later date.

CONCLUSION

I believe that keratoconic patients today are in the best clinical position such patients have ever been in. No longer is a corneal transplant the only effective surgical option. The use of topography-guided PRK and CXL has revolutionized the surgical management of these patients. The synergistic action of the Keraring in combination with these procedures ensures that a high level of visual clarity is a possibility for all patients, including those with advanced keratoconus.

TAKE-HOME MESSAGE

Implantation of ICRSs can preserve corneal integrity, stabilize the cornea, and correct a wide variety of keratoconic severities.

A high level of corneal flattening can be achieved when topography-guided PRK and CXL are combined with implantation of the Keraring.

Dominique Pietrini, MD, practices at the Clinique de la Vision, Paris. Dr. Pietrini states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +33 1 58 05 2000; fax: +33 1 58 05 2001; e-mail: dpietrini@club.fr.

Tony Guedj, OD, ORTHO, is an optometrist at the Clinique de la Vision, Paris. Dr. Guedj states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: tony.guedj@yahoo.fr.