Original Research

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

Nkalebetja T. Makgaba, Solani D. Mathebula
African Vision and Eye Health | Vol 79, No 1 | a514 | DOI: https://doi.org/10.4102/aveh.v79i1.514 | © 2020 Nkalebetja T. Makgaba, Solani D. Mathebula | This work is licensed under CC Attribution 4.0
Submitted: 07 June 2019 | Published: 30 September 2020

About the author(s)

Nkalebetja T. Makgaba, Department of Optometry, University of Limpopo, Sovenga, South Africa
Solani D. Mathebula, Department of Optometry, University of Limpopo, Sovenga, South Africa


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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.


Keywords

duochrome; bichrome; unfused cross cylinder; spherical end point; chromatic aberration

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