An interefrometric method for measuring the dioptric and prismatic power of ophthalmic lenses

Abstract

To accurately evaluate and measure the dioptric and prism power of ophthalmic lenses with an interferometric technique and correlate the results with those taken from automated focimetry. Method and materials: Optical testing of trial ophthalmic lenses, spherical and cylindrical, was carried out based on an interferometric technique in order to estimate the dioptric and prismatic power of the lenses measured. The ophthalmic lenses were inspected with laser light, using a Twyman Green interferometer, and interference patterns were acquired and processed, obtaining the dioptric and prismatic power that theses lenses presented. Comparison of the respective results was conducted with those taken from an Auto-focimeter (TOMEY TL-100) in order to check if the two types of measurement are interchangeable, and statistical analysis was carried out for both types of measurements. Results: The data showed, that the two methods Auto-focimeter and Interferometry (Twyman Green) are correlated. From the statistics the Pearsons correlation coefficient shows high statistical significant correlation between the two methods (r = 0.9996 - P<0,0001 having a 95% confidence interval for r = 0.9965 to 1,0000). Conclusions: A new method is provided for measuring the power (dioptric and prismatic) of ophthalmic lenses and this alternative method is based on interferometry. More specific a Twyman-Green interferometer was set to measure trial lenses of known power. The fringe patterns were photographed and then the power of the wave front produced due to the insertion in the set-up of the trial ophthalmic lens was measured. This is equal to the power of the trial lens. The fringes were tested compared to the plano reference wave front produced when the system did not have any lens inserted