To investigate the changes of corneal biomechanics of intrastromal correction (INTRACOR) femtosecond technique to treat presbyopia.

A prospective, clinical self-control clinical trial was designed.Twenty-four presbyopic patients with emmetropia or mild hyperopia were enrolled in this study.The INTRACOR procedure was performed using the Technolas femtosecond laser in the nondominant eye.Uncorrected distance visual acuity (UCDVA), uncorrected near visual acuity (UCNVA) and spherical equivalent (SE) were recorded in preoperation and postoperative 12 months, and the quality of life of postoperative patients was evaluated.The corneal deformation parameters including highest concavity deformation amplitude (HC-DA), highest concavity peak distance (HC-PD), highest concavity radius (HC-R), non-contact intraocular pressure and the central corneal thickness (CCT) were measured using the Corvis ST visualization biomechanical analyzer in preoperation and postoperative 1 month, 3, 6 and 12 months, respectively.This study followed the Declaration of Helsinki.Written informed consent was obtained from each subject prior to entering study cohort.This study protocol was approved by Ethic Committee of Affiliated Eye Hospital of Shandong University of Traditional Chinese Medicine (No.SDZYYDXYKYYLL2011.06).

Compared with preoperation, UCNVA of all 24 (100%) eyes was improved at 12 months postoperatively with minimal or no change in UCDVA.The mean spherical equivalent was (+ 0.35 ± 0.29)D and (-0.37 ± 0.29)D before and 12 months after operation, with a significant difference beteeen them (t=-7.39, P<0.01). No significant differences were seen in the intraocular pressure, CCT and HC-PD values between preoperation and postoperative 1 month, 3, 6, 12 months (F=1.273, 1.347, 2.434; all at P>0.05). Compared with preoperation, the postoperative 1 month, 3, 6, 12 months HC-R values were significantly declined, HC-DA values were significantly increased, with significant differences between them (all at P<0.05), and no significant differences were found in HC-R and HC-DA between the postoperative adjacent time points (all at P>0.05). Corneal aspherical index (Q Value) was -0.28±0.10 at 12 months postoperatively, which was increased compared with the preoperation, and the maximum value added value (diff-K) of the central corneal curvature was (2.55±0.81)D.

INTRACOR treatment of presbyopia can effectively improve near vision, increase postoperative corneal biomechanical maximum HC-R and HC-DA, negatively increase the corneal central curvature increased aspheric index, which suggests that corneal biomechanics of central cornea is weakened after intrastromal femtosecond presbyopic treatment, and the hyperprolate mutifocal corneal shape is formed under normal intraocular pressure.

Presbyopia; Femtosecond laser; Intrastromal correction; Perspective study; Corneal biomechanics; Corneal aspherical index