Effective optical zone after corneal lenticule extraction with the CLEAR femtosecond laser application
Accepted: 15 November 2023
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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.
School of Biomedical Sciences, Ulster University, Coleraine, UK
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