Technical Requirements For Adapting A Corneal Femtosecond Laser Workstation To Perform A Lenticular Capsulotomy

Abstract

Purpose: : To determine the technical capabilities required for adapting corneal femtosecond laser workstations to perform a capsulotomy for cataract procedures.

Methods: : Critical functions for locating the lens and focusing deeper into the eye with a high quality focused beam of sufficient energy are investigated and measured. Beam delivery capabilities are extended to reach the lens and quantified with focused spot measurements through the scan range in three dimensions. Threshold energy and laser spot measurements for a successful capsulotomy are determined. Beam distortions and losses due to the cornea and different patient interface techniques are evaluated. A laser range finding technique is investigated that uses the scanning femtosecond laser at low power to simultaneously locate the lens capsule and calibrate the scanning system to its location. Capsulotomy procedures on cadaver eyes and rabbits were completed to confirm the adapted system’s performance.

Results: : The depth scanning range was verified to increase from 1.2 mm to 6 mm with incremental modifications to the optical delivery system. The threshold energy for a successful capsulotomy was determined to be less than 2μJ for a 1/e² spot diameter of less than 4μm. The focused beam spot size was measured through a 6 mm depth and 6.5 mm diameter range and found to be sufficient for a capsulotomy. A hybrid liquid patient interface based on the existing design was shown to minimally degrade the focused beam through the cornea enabling capsulotomy. Laser range finding for locating the anterior surface of the capsule was evaluated in wet labs and found to be repeatable and accurate to better than ±20μm, well within surgical scan range. A series of cadaver and rabbit studies were done to confirm successful capsulotomy procedures. An analysis for laser exposure at the retina in rabbits was performed to demonstrate the exposure is well below the American National Standards Institute’s eye safety standards.

Conclusions: : Corneal femtosecond laser systems can be successfully modified to perform lenticular capsulotomy procedures by extending the focal depth range, adding the ability to locate the lens, and by using liquid interface to ensure the quality of focus at the anterior surface of the capsule.

Keywords: cataract • laser