Corneal topography stability after crosslinking is demonstrated by comprehensive analyses
March 1, 2009
Results from visual acuity testing, refraction, and corneal topography analysis using Scheimpflug imaging (Pentacam, Oculus) in a series of 48 eyes with progressive keratoconus demonstrate the benefits of corneal collagen crosslinking for halting keratoconus progression. More research is needed to provide answers to questions about the long-term stability of collagen corneal crosslinking and to refine its indications and contraindications.
Atlanta-Outcomes from multiple assessments demonstrated that stability of corneal topography was achieved for at least 1 year following treatment of keratoconus using corneal collagen crosslinking with riboflavin and ultraviolet A (UVA) light, reported Dilraj Singh Grewal, MD, at the annual meeting of the American Academy of Ophthalmology.
"These results indicate that corneal collagen crosslinking is effective for halting progression of keratoconus and suggest that it holds promise as a viable modality for the management of progressive ectatic corneal disorders," he said. "However, as with all new therapies, further studies are needed to provide answers to questions about the long-term stability of collagen corneal crosslinking and to refine its indications and contraindications."
Dr. Grewal is a research fellow at the Grewal Eye Institute, Chandigarh, India, and also is a postdoctoral research fellow at the Bascom Palmer Eye Institute, Palm Beach Gardens, FL.
To investigate the hypothesis that the corneal collagen crosslinking procedure stabilizes changes in corneal curvature in eyes with progressive keratoconus, he and colleagues analyzed data collected in a case series of 48 eyes of 48 patients followed for up to 1 year post-crosslinking. Progressive keratoconus was identified as an increase in the maximum keratometry reading of at least 1 D in the previous year or the need for more than one new contact lens in the previous 2 years.
Patients were eligible for crosslinking if they were aged at least 18 years and had a central corneal thickness of at least 400 μm. They were excluded if they had a history of corneal surgery, intracorneal ring implants, or delayed wound healing. In patients who underwent crosslinking in both eyes, one eye was randomly selected for inclusion in the study.
The crosslinking procedure was performed with the patient under topical anesthesia. A 7.0-mm circle of epithelium was removed with a blunt spatula, and 0.1% riboflavin in 20% dextran was instilled at a rate of two drops every 5 minutes for 30 minutes. The UV treatment was performed with the UVA lamp focused on the apex of the cornea at a distance of 5 cm in order to deliver a radiation dose of 3 mW/cm2 . During the 30-minute period of UVA exposure, instillation of the riboflavin drops every 5 minutes was continued.
Patients were examined before crosslinking and post-crosslinking at 1 week and 1, 3, 6, and 12 months. They underwent subjective refraction, measurement of best-corrected visual acuity (BCVA), and Scheimpflug imaging (Pentacam, Oculus) to determine corneal thickness; corneal volume; mean, horizontal, and vertical anterior and posterior corneal curvature; and anterior and posterior corneal elevation.
Mean BCVA (logMAR) was 0.22 at baseline and worsened initially to 0.24 at 1 week and 1 month. It improved thereafter, however, reaching 0.20 at 6 months, and it remained stable at that level at 1 year, although the change was not significant.
Changes in mean spherical equivalent (SE) showed a similar pattern of initial worsening followed by improvement. From baseline to 1 year, mean SE changed from –6.3 to –4.9 D.
"The mean change of about 1.4 D was not statistically significant, but it is within the range that has been reported in previous studies and reflects corneal flattening, which occurs secondary to stiffening of the corneal collagen fibers as a result of crosslinking," Dr. Grewal said.
Mean central corneal thickness decreased slightly from baseline through 1 month (459 versus 436 μm) but then began to increase and was unchanged from baseline at 1 year (455 μm). Mean IOP also was unchanged based on the levels at baseline and 1 year, 12.6 versus 13.4 mm Hg, respectively.
Mean corneal volume essentially was unchanged throughout follow-up, and mean anterior corneal curvature and mean horizontal and vertical anterior corneal curvature also were stable through 1 year.
"Mean anterior corneal curvature decreased by about 2.0 D, from 50.55 to 48.58 D," Dr. Grewal said. "This change was not statistically significant and is similar to what has been reported by other investigators."
Mean posterior corneal curvature was decreased slightly from its baseline level of –7.7 D at all follow-up visits (–7.31 to –7.52 D), but none of the changes from baseline were statistically significant. Also, no significant differences were seen comparing the baseline and 1-year values for mean apex anterior corneal elevation (30.5 versus 28.63 μm) and posterior elevation (66.3 versus 62.5 μm).