Validation of a set of compact and low-cost Stokes lenses aimed at refractive astigmatism measurement for optometric practice

Abstract

We describe the construction and characterization of three Stokes lenses that can be used in optometric practice to measure different ranges of refractive astigmatism using subjective routines. The proposed set of Stokes lenses is assembled from Risley prism mounts coming from a Nidek phoropter in which the optical prisms are replaced by three different sets of cylindrical lenses ( ± 0.75, ± 1.25, and ± 1.75 D) coming from a trial lens case to cover a different astigmatism range (1.5, 2.5, and 3.5 D in modulus, respectively). We present the experimental characterization of the three Stokes lenses with the power vector notation and use an automatic lensmeter (Topcon CL-300) for dioptric power measurement. The measured dioptric power profiles are in concordance with the theoretical predictions, and statistical testing reveals no differences between measured and theoretical values for the three lenses, neither in spherical nor in cylindrical components (p ≥ 0.05 for all cases). Bland–Altman plots show very good agreement between measured and theoretical values with limits of agreement below 0.12 D for both M and J components for the three lenses. These Stokes lenses can be easily constructed from regular Risley prism mounts, so they can be used in almost any phoropter model for refractive error compensation.