Changes in anterior chamber characteristics measured with a dual Scheimpflug analyzer and an anterior segment optical coherence tomography after laser in situ keratomileusis for myopia

In this study, all participants undergo standard laser in situ keratomileusis (LASIK) surgery in both eyes only once. The LASIK procedures are performed in each eye by first creating a superiorly hinged corneal flap using the Hansatome microkeratome with a 160 micron m head and 8.5 mm ring. The laser ablation is performed using excimer Laser with a goal of emmetropia. The surgery procedures usually takes about 20 minutes for each patient. The central anterior chamber depth (ACD), anterior chamber volume (ACV), average radius of posterior axial curvature (ARPAC) are measured using the Galilei Scheimpflug analyser. Measurements with the dual Scheimpflug analyzer are performed according to the manufacturer’s guidelines. The device is brought into focus and the subject’s eye is aligned along the visual axis by a central fixation light. The subjects are asked to sit back after each measurement, and the device is realigned before each measurement.The superior, inferior, nasal, temporal anterior chamber angles (ACAs) are respectively measured using Visante anterior segment optical coherence tomography (AS-OCT). Scans of the ACAs of each eye are obtained at the 3 and 9 o’clock positions (horizontal), and at the 6 and 12 o’clock positions (vertical). Subjects are instructed to blink prior to all measurements and open their eyes wide during scan acquisition. As the eyelids may interfere with AS-OCT image acquisition of the ACA at 6 and 12 o’clock positions, the upper and lower lids are gently moved out of the way to image the superior and inferior angle- taking care to avoid inadvertent pressure on the globe. Measurements using the Galilei and Visante AS-OCT are taken before and 2 weeks and 2 months after LASIK. Each measurement needs about 5 minutes.