Comparison of 6.0 mm versus 6.5 mm Optical Zone on Visual Outcomes after LASIK

Majid Moshirfar,Shannon E Mccabe,Nour Bundogji,Yasmyne C Ronquillo,Phillip C Hoopes,Thomas M Sant,William B West,Alyson N Tukan,Kirk Drennan,Rachel Huynh

doi:10.3390/jcm10173776

Abstract

Previous studies have demonstrated safety and efficacy using 6.0 and 6.5 mm optical zones in the WaveLight EX500 Excimer Laser System but have not evaluated if differing optical zone sizes influence refractive outcomes. This study examines visual outcomes between two study populations undergoing LASIK with either a 6.0 mm (1332 patients) or 6.5 mm (1332 patients) optical zone. Outcomes were further stratified by severity of myopia (low, moderate, and high) and astigmatism (low and high). Patients were matched by age and preoperative manifest sphere and cylinder. Postoperative measurements were then compared. The 6.5 mm group demonstrated better postoperative manifest refractive spherical equivalent (MRSE), manifest sphere, and absolute value of the difference in actual and target spherical equivalent refraction (|∆ SEQ|), within the total population, moderate myopia, and low astigmatism groups, but this did not lead to improved postoperative uncorrected distance visual acuity (UDVA) or best corrected distance visual acuity (CDVA). Though astigmatic correction and postoperative angle of error were similar between optical zone sizes, they were significantly worse with high myopia. Overall, this study demonstrates differences in visual outcomes between the 6.0 and 6.5 mm optical zone sizes that may warrant consideration; however, essentially, the results are comparable between them.

Highlights

Excimer laser surgery was first experimented on cadaveric eyes in 1983 [1], patented for refractive use in live corneas in 1989 [2], and used with laser in situ keratomileusis (LASIK) in 1990 [3]
We further evaluate whether preoperative severity of myopia or astigmatism contributes to the success of using a 6.0 or 6.5 mm optical zone
While the WL EX500 is approved for use with a 6.0 or 6.5 mm optical zone, the initial clinical trials showing appropriate safety and effi

Summary

Introduction

Excimer laser surgery was first experimented on cadaveric eyes in 1983 [1], patented for refractive use in live corneas in 1989 [2], and used with laser in situ keratomileusis (LASIK) in 1990 [3]. Blend zones and larger optical zones have improved visual outcomes in refractive surgery [5,6]. Post-LASIK epithelial and stromal remodeling at the transition between ablated and untreated cornea created corneal irregularities, reducing the effective optical zone and refractive outcomes while increasing the risk of myopic regression [6,7,8,9]. Implementation of blend zones created smooth transition points, decreasing corneal remodeling and aberrations [5,10], and larger optical zones reduced the chance of early myopic regression [11], hyperopic shift [12], and postoperative higher-order aberrations (HOAs) [13,14]. The use of larger optical zones (commonly 6.0 and 6.5 mm) along with blend zones have become standard practice, creating a total treatment zone around 8.5 to 9 mm in diameter

Methods

Discussion

Conclusion