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.
Highlights
IntroductionThe red–green duochrome (bichrome) test is based on the principles of axial chromatic aberration
The red–green duochrome test is based on the principles of axial chromatic aberration
The findings of this study showed that there was no statistical difference between the results obtained using the duochrome and unfused cross cylinder methods
Summary
The red–green duochrome (bichrome) test is based on the principles of axial chromatic aberration. The eye, like most common optical systems, displays a certain amount of axial chromatic aberration.[1,2,3,4,5,6,7,8] A yellow wavelength of approximately 570 nanometres (nm) is preferred by the eye.[3,6] The red and green wavelengths are dioptrically equidistant from the yellow wavelength.[3,6] Green light with a wavelength of 535 nm focuses 0.25 dioptres (D) in front of the retina, and red light with a wavelength of 620 nm focuses 0.25 D behind it.[8] This is because the shorter wavelength (green) is refracted more by the eye’s optics than the longer wavelength (red). 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
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
