Investigation of the unfused cross cylinder test as an alternative method for the determination of spherical distance refraction end points

Abstract

Background: The duochrome test is commonly used to refine the final sphere in refraction at different stages of a subjective refraction. The unfused cross cylinder test is mainly used to determine the near reading addition with a combination of astigmatic lenses. Aim: To investigate if the unfused cross cylinder test can be adapted for distance in finding the spherical end point for distance prescription. Setting: The study was conducted at an Optometry Clinic, University of Limpopo, South Africa. Methods: Fifty-one non-presbyopic subjects aged between 18 and 25 years were examined. The duochrome and unfused cross cylinder examinations were performed monocularly under normal (bright) and dim room illumination. Results: There was no significant difference in the spherical end point determined with either the duochrome or unfused cross cylinder tests (p ≥ 0.05). The mean spherical end points as determined with the duochrome test were-0.09 ± 0.39 diopre sphere (DS) (range:-0.20 to 0.12 dioptres [D]) in bright room illumination and-0.05 ± 0.38 DS (range:-0.16 D to 0.05 D) in dim illumination. The mean spherical end points for the unfused cross cylinder tests were-0.29 ± 0.39 DS (range:-0.18 D to 0.40 D) and-0.32 ± 0.43 DS (range:-0.44 D to-0.19 D) in room dim illuminations, respectively. Conclusion: The unfused cross cylinder test results as performed in this study may provide an accurate measurement of the spherical end point in a young adult population. We recommend the unfused cross cylinder test to be used in normal (bright) room illumination as an alternative to the duochrome test in the determination of distance refractive error.