2D reverse Shack-Hartmann ocular refraction measurement

摘要

Traditional refraction measurement equipment is expensive, cumbersome and requires professional training for its operation. Therefore, refraction measurements are usually performed by eye care professionals, requiring an in-office visit. A handheld, low-cost and simple refraction measurement device based on the reverse Shack Hartmann technology is aimed for consumers, telehealth and at-home measurements. The device attaches to a smartphone where patterns on the screen are aligned by the user looking through the optics of the device. The optical train consists of chromatic separation into two channels that then combine in the user's eye. The measurement consists of repeated alignment of the patterns by the user at different meridians of the pupil to allow for refraction mapping. The formulation of a 2D pattern and alignment scheme is presented for achieving optometric refraction values. In this case, the method maintains a low number of required measurements by the user. On the other hand, higher order aberrations may be measured using this method and the general terms of the measurement formulation is presented using the Zernike polynomials. The derivation is based on a model of the eye with an angular deviation field as the source of refraction. The paraxial approximation is used as the angular deviations are shown to be small for any ophthalmic condition. The model and formulation are then validated by a series of experiments in a calibrated model eye. Results show that two measurements are sufficient for producing accurate optometric refraction measurement values.