Scanning laser measure of optical quality of the cultured crystalline lens

Abstract

An apparatus has been designed to automate the laser measuring technique and make it possible to monitor lens refractive function (spherical aberration) as well as change in lens transmittance during lens culture. A scanning laser beam (helium–neon) is used so that a number of beams puss through different spots on the lens to determine lens spherical aberration compared over time. Each refracted beam, received by two video cameras (X and Y directions), is digitized. The system first locates the optical centre of the lens by determining the beam position providing the least deflection for both the X and Y directions. The beam is then moved in predetermined steps on either side of the centre, and focal lengths are determined relative to the optic axis for each position. A measure of beam scatter is noted from post-refraction pixel excitation for each beam position. Improvements to the scanning laser system have led to greater accuracy and speed as well as to improved culture cells. Accuracy was increased by using high resolution (1 μm) stepping motors to move the scanning helium neon laser. A new alignment process involving the superposition of the incident beam reflected on it self ensures that the incident beam is perpendicular to the lens equatorial axis. Scanning speed has been improved through a variety of hardware and software changes. Scanning time for a lens, including locating the optical centre and measuring focal length for 20 lens positions along the X and Y directions, takes about 60 seconds. Long-term studies on the degradation of lens optical performance frequency yield diffuse beams of very low intensity. An option now exists to build an image using repeated frame grabs until a pre-set level of intensity is reached. New lens cells consist of a flexible silicon rubber base enclosing a flat face plate, a lens carrier and a four-sided, upper glass chamber.