Design and characterization of a safe Shack–Hartmann type aberrometer for making in-vivo measurements: Heuristic approximation

The Shack–Hartmann technique is one of the most commonly used methods for measuring the optical aberrations of human eyes in−vivo. However, hazardous exposure could occur when the incident beam is focused on the retina if the illuminating system is not calibrated properly. This work describes in detail the steps taken to develop an experimental Shack–Hartmann type aberrometer with safe incident radiation for use on human eyes in−vivo. Preliminary results using a model eye indicate that the system is reliable. To ensure that no damage was done to the volunteer’s eyes, we decided in a heuristic approximation, to use only 2% of the maximum permissible radiation power suggested by the ANSI standard for the safe use of lasers. The ocular aberrations of a group of volunteers were measured with our system and the results were compared with those obtained with a commercial aberrometer. Despite the lower energy applied to the volunteer’s eyes, the experimental system showed to be efficient and accurate. The repeatability of the results was confirmed by comparing successive measurements of the aberrations of the experimental system, with smaller variations than those obtained with the Shack–Hartmann wavefront sensor.