Analysis of best corrected visual acuity following corneal refractive surgery comparing low and standard predicted postoperative keratometry
Drake, Ryan Carpenter
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BACKGROUND: It is a commonly held view in the ophthalmologic community that eyes with sufficiently low calculated postoperative corneal keratometry, less than 35 diopters, should not undergo corrective refractive laser surgery (CRLS) due to the increased risk of best corrected visual acuity (BCVA) loss. Typical CRLS include Laser In-Situ Keratomileusis (LASIK), Photorefractive Keratectomy (PRK), and Laser-Assisted Sub-Epithelial Keratectomy (LASEK). Evidence for this claim in currently available literature is sparse and inconsistent. PURPOSE: To further elucidate the relationship between calculated “flat” postoperative corneal keratometry and loss of BCVA. Additionally, to investigate the role of procedure type (LASIK, ASA, or LASEK) and degree of calculated postoperative corneal flatness on visual outcomes following CRLS. METHODS: 222 eyes (111 candidates and 111 controls) were retrospectively analyzed and matched based on calculated postoperative keratometry compared to control subgroups with calculated postoperative keratometries ≥38 D and further stratified into subgroups 1b (K=38-38.99 D), 2b (K=39-39.99 D), 3b (K=40-40.9 9D), and 4b (K≥41 D). All of the eyes had undergone LASIK, PRK, or LASEK between December 2008 and November 2016 at Boston Eye Group/Boston Laser in Brookline, MA. RESULTS: Statistical analyses showed no significant differences between candidates and controls in preoperative BCVA (p=0.650) and postoperative BCVA (p=0.081). Subgroup matching showed no significant differences in the amount of tissue ablated in 1a & 1b (p=0.946), 2a & 2b (p=0.694), 3a & 3b (p=0.989), and 4a & 4b (p=0.986). There was also no significant change between preoperative and postoperative BCVA in subgroups 1a (p=0.367), 2a (p=0.297), 3a (p=0.576), 4a (p=0.669), 1b (p=0.458), 2b (p=0.227), 3b (p=0.071), or 4b (p=0.703). 3 of 111 (2.70%) candidate eyes and 1 (0.90%) control eye lost 1+ lines of BCVA following surgery. There was no statistical difference in 1+ lines of BCVA lost between these groups (p=0.313). Similarly, the type of CRLS undergone did not affect the rate of BCVA line loss (p=0.793). CONCLUSION: Our evidence suggests that in a matched comparison of flat and normal mathematically predicted postoperative keratometries, there was no increase in BCVA lost due to flat keratometry.
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