Posterior keratocyte density correlated with ectasia

May 1, 2008

Posterior keratocyte densities were significantly lower in ectatic eyes than in normal eyes following both histopathologic and confocal microscopic analysis in a recent small study. If further studies verify that finding, serial confocal measurements of density could be used to monitor progression of post-LASIK ectasia.

Key Points

New Orleans-A recent study has shown that posterior keratocyte density measurements could be a means of following eyes with post-LASIK ectasia. Analysis by both confocal microscopy and histopathology demonstrated that keratocyte density was significantly reduced in the ectatic regions of the posterior stroma in eyes with corneal ectasia after LASIK, leading investigators to suggest that this decreased density may contribute to the development of ectasia.

Maria A. Woodward, MD, a third-year ophthalmology resident at Emory University School of Medicine and Emory Vision, Atlanta, presented the findings at the annual meeting of the American Academy of Ophthalmology. She said that researchers and clinicians would like to have better means of identifying patients at risk for severe ectasia progression, which is currently regarded as unpredictable when postoperative ectasia first becomes manifest.

Recent research has identified several risk factors for the development of ectasia. However, some patients with risk factors do not develop the condition, while some without risk factors do, and the severity of the postoperative course can vary significantly from patient to patient.

"Overall, the keratocyte density does appear to be equivalent in normal post-LASIK and post-LASIK ectasia corneas," Dr. Woodward said. "But there are some recent studies that suggest that corneal tensile strength is not uniform throughout the cornea, with the anterior stroma being twice as strong as the posterior two-thirds of the stroma."

Expanding research

To learn more, she and co-authors J. Bradley Randleman, MD, and Daniel G. Dawson, MD, conducted a post-LASIK ectasia keratocyte density study. Their hypothesis was that keratocyte density may be diminished focally in the setting of post-LASIK corneal ectasia and that decreased keratocyte density may contribute to the development and progression of ectasia. Their goal was to compare keratocyte density between normal and ectatic post-LASIK eyes throughout various regions of the stroma.

In the case-control study, they performed histopathologic analysis on five corneal specimens with post-LASIK ectasia and five normal post-LASIK specimens, measuring keratocyte density by cell counts per high power field (C/HPF). Those specimens were evaluated with DAPI stain. Confocal microscopic analysis was performed in vivo on five ectatic and five normal eyes during patient evaluations. Masked observers unaware of the status of the eye performed the analysis.

"What we found was that in ectasia cases there was 49% less posterior keratocyte density by DAPI measurements in the ectatic regions," Dr. Woodward said. Density was 16 C/HPF in the ectasia cases versus 23 C/HPF in the normal post-LASIK cases (p = 0.004).

Results of the confocal analysis also showed a statistically significant difference. The ectatic eyes had 30% less posterior keratocyte density than the normal eyes (30 versus 58 C/HPF, p = 0.0003).

Although those findings suggest that a decrease in keratocyte density is associated with ectasia, Dr. Woodward said they also present a "chicken-and-the-egg" scenario.

"Our theory was that the keratocyte density may contribute to ectasia, but possibly another factor could contribute to ectasia and then lead to a decrease in keratocyte density," she said. "It's hard to know at this point."

She also cautioned that a limited number of eyes were examined for the study and that keratocyte density may fluctuate depending on the area chosen for analysis.