Dispelling Myths in Refractive Surgery

American Society of Cataract and Refractive Surgery (ASCRS) 2012 Symposium on Cataract, IOL and Refractive Surgery

William B. Trattler, MD


May 04, 2012

Refractive surgery continues to be a strong focus of the American Society of Cataract and Refractive Surgery (ASCRS), and during its 2012 meeting, held in Chicago, this was no exception. A very popular symposium, the EyeWorld Symposium on Refractive Surgery, helped to kick off the ASCRS meeting.

One of the most influential lectures was given by Steven Schallhorn, MD, titled "Myth Busters -- Re-examining Modern Patient Selection Criteria."[1] Dr. Schallhorn focused his talk on exploring a number of commonly held beliefs of refractive surgeons that appear to be more myth than reality. Dr. Schallhorn based his talk on data developed from Optical Express, a large chain of laser vision-correction centers based in Europe.

The first myth evaluated by Dr. Schallhorn was the issue of whether patients with thin corneas were appropriate candidates for LASIK. Although multiple studies in the peer-reviewed literature have reported on the successful outcomes of LASIK in patients with thin corneas, some surgeons continue to advocate not performing surgery on patients with a corneal thickness below a certain level, such as 500 microns. Dr. Schallhorn analyzed the results of 81,715 eyes on which LASIK was performed from April 1, 2008 to March 31, 2009. More than 2000 of these eyes had a central corneal thickness of < 500 microns, and these eyes were compared with more than 79,500 eyes with a central corneal thickness > 500 microns. All eyes with abnormal preoperative corneal topography were excluded from surgery.

Dr. Schallhorn analyzed the relationship between corneal thickness and both refractive error and age. In the dataset that he reported on, the proportion of eyes in both the thick and thin cornea groups were virtually the same.[2] Furthermore, during the 3 years of follow-up for this group, only 3 patients developed post-LASIK ectasia -- and all 3 of these patients had a corneal thickness > 500 microns. In summary, Dr. Schallhorn maintained that there still does not appear to be any scientific evidence that eyes with thin corneas and normal topography are at increased risk of developing post-LASIK ectasia.

A second series of myths explored by Dr. Schallhorn focused on whether patients with 3 diopters (D) or more of hyperopia, or patients with higher levels of preoperative astigmatism, are less likely to be satisfied with the results of their LASIK procedures. Research shows that less than 2% of patients with preoperative hyperopia of ≥ 2.75 D are dissatisfied, and this is the same for patients with < 1.5 D of hyperopia. Similarly, patients with ≥ 3 D of astigmatism have a very low likelihood of being dissatisfied with their laser vision correction results, which is similar to patients with ≤ 1 D of astigmatism.

Dr. Schallhorn stimulated the most interest with his analysis of patients with large pupils.[3] It has long been held by some that patients with large pupils (≥ 8 mm) are at increased risk for night-vision complaints following LASIK. Dr. Schallhorn analyzed more than 30,000 eyes with a patient questionnaire and found that patients with large pupils were extremely unlikely to be dissatisfied with their vision in low light. Patients with a pupil size of ≥ 8.0 mm (representing more than 5000 eyes, or < 1%) reported that they were unlikely to be dissatisfied with their night vision. When queried specifically about driving at night, only 2.9% of patients with large pupils reported dissatisfaction vs 3.1% of patients with a pupil size of ≤ 5 mm.

In summary, Dr. Schallhorn's research has helped refractive surgeons better understand that some commonly held beliefs are actually not grounded in science. Refractive surgeons can adjust their treatment parameters based on this work.