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Y.-L. Chen, L. Shi, B. Tan, J. W. L. Lewis, M. Wang; Analysis of High-Order Aberrations in Low-Cost Photorefraction. Invest. Ophthalmol. Vis. Sci. 2008;49(13):983.
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To demonstrate the detection and quantitative analysis of high-order ocular aberrations using photorefraction.Background: Photorefraction (PR) is a viable large-scale screening technique that has been used primarily to measure refractive errors and ocular alignment in small children. However, the PR reflex carries double-pass wavefront information including aberrations from diffraction and scattering.
The near-infrared, multi-meridian-eccentricity, adaptive PR technique (APR) is employed to image eyes with normal and abnormal degrees of high-order (HO) aberrations including keratoconus (KC) and ectasia. Pupil areas in APR images are located and rotated to the corresponding detection meridian. Excluding the first Purkinje reflection, the pupil images are then rescaled to their maximum and minimum intensity and are decomposed into Zernike components up to the 6th order. Percentage contribution from each order is calculated, and the results are classified into normal and abnormal groups.
The images of each group of patients show distinguishable characteristic patterns in. Fig.1 shows the analysis result. The spherical refraction gives the major contribution to the P1+1 coefficient. The sign of this coefficient indicates convergent and divergent refraction. P1-1 coefficient is the indication of cylindrical refraction. Significant levels of higher order contribution are observed in keratoconus patients (shown in table and figure). The major problem of false negatives are attributed to small pupil size (KC #18) and a high level of refraction (KC #17; -17 diopter). Gaze angle does not seem to influence the result.
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