Comparison between an Interefrometric Technique and an Autorefractometer for Dioptric and Prismatic Power Measurement of Ophthalmic Lenses

Objective 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 Testing of trial ophthalmic lenses, spherical and cylindrical, was carried out using an interferometric technique in
order to estimate the dioptric and prismatic power of these lenses. The ophthalmic lenses were measured with a laser light, using a
Twyman Green interferometer, and interference patterns were acquired and processed, obtaining the dioptric and prismatic power of
these lenses. Comparison of the interferometric technique results was conducted with those taken from an Auto-focimeter (TOMEY TL-
100) in order to check if the two techniques of measurement are interchangeable, and statistical analysis was carried out for both types of
measurements.
Results The two methods Auto-focimetery and Interferometry (Twyman Green) are correlated. From the statistics of the comparison of
the two methods the results were a) the Pearson (precision) correlation coefficient showed that there is a high statistical significant
correlation between the two methods (r = 0,9992 - P<0,0001 having a 95% confidence interval for r = 0,9964 to 0,9981), b) also the
Correlation coefficient r showed that there is a high statistical significant correlation between the two methods r = 0,9992 - P<0,0001
having a 95% confidence interval for r = 0,9987 to 0,9996) and c) the Spearman's coefficient of rank correlation (rho) showed that there
is a high statistical significant correlation between the two methods r = 0,998 P<0,0001 having a 95% confidence interval for r =
0,997 to 0,999).
Conclusions A method for measuring the dioptric and prismatic power of ophthalmic lenses based on interferometry, and more specific a
Twyman-Green interferometer was proven to be as accurate as Auto-focimetery. 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 was equal to the
power of the trial lens used to measured. The fringes were tested compared to the plano reference wave front produced when the system
did not have any lens inserted.