Study on change in corneal biomechanics and effect of percent tissue altered in myopic laser-assisted keratomileusis.

Purpose: To evaluate corneal biomechanical changes and their correlation with the percentage of tissue altered (PTA) in myopic femtosecond (FS)-flap LASIK.

Methods: Prospective longitudinal observational study of 80 eyes of FS LASIK. Demographic details, LASIK parameters, preoperative and postoperative (day 1, month 1, 3, and 6), UCVA, BCVA, refraction, corneal topography, corneal hysteresis (CH), and a corneal resistance factor (CRF) were noted. Change in CH and CRF and its correlation with PTA were analyzed. Data were analyzed in three subgroups [subgroup 1: PTA 23 to <27%; subgroup 2: 27 to <33%; subgroup 3: 33 to <40%].

Results: FS LASIK for MRSE -3.5D ± 1.6D with mean PTA of 31.6 ± 4.4% (range 23.8-39.8%), showed statistically significant decrease in CH and CRF. Mean CH decreased from a preoperative value of 10.4 ± 1.9 to 8.1 ± 1.1; mean CRF from 10.5 ± 1.6 to 7.5 ± 1.3 at 6-months postoperative period, respectively. Mean preoperative CH decreased by 25%, 24%, 23%, and 21% and mean preoperative CRF decreased by 34%, 28%, 28%, and 28% at postoperative day 1, month 1, 3, and 6 follow-ups. Mean CH and CRF showed a significant negative correlation with PTA (CH: r = - 0.33 [P = <0.0001], CRF: r = -0.34 [P = <0.001]. Subgroup analysis noted greater decrease in CRF and CH in eyes with higher PTA (subgroup 3).

Conclusion: Myopic FS LASIK causes a decrease in corneal biomechanics with a significant negative correlation with PTA indicating a greater decrease in corneal biomechanics with higher PTA.