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Y.-L. Chen, L. Shi, B. Tan, J. W. L. Lewis, M. Wang; Astigmatism in Dynamic Infrared Photorefraction (DIP). Invest. Ophthalmol. Vis. Sci. 2009;50(13):1580.
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Previously we showed that the photorefraction-based DIP technique is a low cost method of detecting high-order aberration and demonstrated the method with keratoconus eyes. The relative contribution in each order aberration can be obtained using Zernike analysis. In this study, we examined and differentiated the detection of the second-order aberration including the cylindrical defocus.
The near-infrared(NIR), multi-meridian and -eccentric sources of DIP were used to obtain retinal reflex images of a small number of eyes with various degrees of refractive errors. In this mode of operation, DIP functions as an infrared spot retinoscope that enables digital registration and image analysis for the examiner’s visualization. Each acquired photorefraction reflex image is processed, color-coded, and presented at the corresponding meridian and eccentricity of the NIR illumination to form an inclusive DIP map.
Hyperopic, myopic, and astigmatic eyes yield DIP color maps with distinguishable characteristic patterns. For ametropic eyes with only spherical refractive errors, as the NIR sources at a specific eccentricity illuminate the eye at various meridians, the multi-frame maps yield rotationally symmetric patterns. A centripetal or centrifugal map illustrates a hyperopic- or a myopic-shifted eye, respectively, as shown in the two left-most maps in the Figure. Depending on the known degree of defocus calculated from the neutralization of the device, astigmatic eyes present either elliptical appearances (the third and fourth maps in the Figure) that are aligned to the two principle meridians or the specific X-shaped pattern as shown in the right of the figure.
Astigmatism presents unique features in direct DIP measurements.
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