Effective optical zone after corneal lenticule extraction with the CLEAR femtosecond laser application

Abstract

Laser vision correction of myopia induces an effective optical zone (EOZ) smaller than the programmed optical zone (POZ) by 16 to 26%. We evaluated the EOZ after corneal lenticule extraction for myopia with astigmatism ≤1 diopter (D) with a new femtosecond laser application (CLEAR), compared to POZ in a retrospective, consecutive, comparative case series study. Forty eyes of 40 patients underwent lenticule extraction with the Ziemer CLEAR® application; the control group was composed of 40 eyes of 40 patients receiving myopic femtosecond laser in situ keratomileusis (LASIK); EOZ was calculated on difference tangential maps at 6 months. For lenticule extraction, mean preoperative spherical equivalent (SE) was -6.03±2.48 D; mean POZ was 6.43±0.27 mm; EOZ 5.55±0.45 mm; mean difference between POZ and EOZ was 0.88 ± 0.28 mm (p=0.00); the mean reduction of EOZ compared to POZ was 13.60%±4.75; a positive correlation between preoperative SE and percent reduction of EOZ was found (r=0.63). For LASIK, mean preoperative SE was -5.89±2.14 D; mean POZ was 6.57±0.34 mm; EOZ 5.16±0.53 mm; the mean difference between POZ and EOZ was 1.41±0.35 mm (p=0.00); the mean reduction of EOZ compared to POZ was 21.46%±5.20. The mean difference between EOZ of the 2 procedures was 0.39 mm (p=0.0008). The mean difference between the reduction in optical zone (POZ-EOZ) of the 2 procedures was -0.53 (p=0.00). In conclusion, in myopia with low astigmatism, the CLEAR application for lenticule extraction provided a limited reduction in EOZ, compared with existing platforms. A positive correlation exists between corrected SE and reduction of the EOZ.