Technological, Research or Short Note

Dark refraction shift with allowance for astigmatism

W.D.H. Gillan
African Vision and Eye Health | South African Optometrist: Vol 64, No 1 | a206 | DOI: https://doi.org/10.4102/aveh.v64i1.206 | © 2005 W.D.H. Gillan | This work is licensed under CC Attribution 4.0
Submitted: 19 December 2005 | Published: 19 December 2005

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W.D.H. Gillan, Optometric Science Research Group, Department of Optometry, University of Johannesburg, PO Box 524, Auckland Park, 2006 South Africa, South Africa

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Abstract

Purpose: To show that the dark refraction shift (dark focus) is a more complicated phenomenon than implied when presented as spherical. Methods: Fifty autorefractor measurements of refractive state of the right eye were obtained in light  and  dark  conditions.  Multivariate  methods were used to analyze the data and stereo-pair scat-ter plots, polar meridional profiles and other means of presenting results are used to show important characteristics of the dark refraction shift. Results: The complexity of the dark refrac-tion shift is indicated by stereo-pair scatter plots showing the amount of stigmatic and antistigmatic variation that occurs in light and dark conditions. The mean dark refraction shift is presented in a complete manner including all three components of refractive state. The greater variance and covari-ance under dark conditions is clearly shown by the term-by-term dark-light variance-covariance ratio and polar profiles  of variance and covariance.Conclusions: The  dark  refraction  shift  is  a more complicated phenomenon than implied by representations as purely spherical in nature.

Keywords

dark refraction shift, dark focus, multivariate methods, stigmatic, antistigmatic, polar profiles

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