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JA Potter, NC Strang, BT Barrett; Psychophysical Estimation of Axial Length in Myopic Eyes . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2027.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Simple optical modelling has shown that the size of the myopic defocus blur-circle on the retina is related to the pupil size, axial length and refractive error of the eye. Studies manipulating defocus blur in individuals have confirmed this relationship experimentally. However, the relationship has yet to be investigated in uncorrected myopic subjects where anatomical variations resulting from myopic growth could potentially modify the perceived size of the blur-circle. In this study we use a simple psychophysical method to estimate the blur-circle diameter in a group of myopic subjects. Methods: Subjects (n=25) with refractive errors ranging from -0.50DS to -8.50DS (<0.75DC) viewed two luminous circle targets from a distance of 4m. A beam splitter was used to present the two spatially adjacent circles simultaneously. The size of the reference circle remained constant and was viewed with no refractive correction in place (blurred circle), whilst the other circle could be varied in size and was viewed with full refractive correction through a Badal optical system (in-focus circle). Both circles were viewed through a fixed pupil (4mm). The task of the subject was to match the size of the in-focus circle to the size of the blurred circle using a method of adjustment. Biometric data were collected on all subjects. The results were compared to a simple predictive model of blur circle size. Results:A strong relationship (r=0.97) existed between blur circle diameter and level of uncorrected myopia. The increase in blur-circle diameter with increased uncorrected myopia was in line with simple model predictions. Axial length was found to increase by ∼0.46mm per dioptre of myopia. Conclusion:Anatomical variations in myopic eyes do not disrupt the relationship between blur-circle diameter and refractive error. This technique has the potential to provide a simple, non-invasive method of estimating refractive error and axial length in myopic eyes.
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