Abstract
The high power of the eye and optical components used to image it result in "static" distortion, remaining constant across acquired retinal images. In addition, raster-based systems sample points or lines of the image over time, suffering from "dynamic" distortion due to the constant motion of the eye. We recently described an algorithm which corrects for the latter problem but is entirely blind to the former. Here, we describe a new procedure termed "DIOS" (Dewarp Image by Oblique Shift) to remove static distortion of arbitrary type. Much like the dynamic correction method, it relies on locating the same tissue in multiple frames acquired as the eye moves through different gaze positions. Here, the resultant maps of pixel displacement are used to form a sparse system of simultaneous linear equations whose solution gives the common warp seen by all frames. We show that the method successfully handles torsional movement of the eye. We also show that the output of the previously described dynamic correction procedure may be used as input for this new procedure, recovering an image of the tissue that is, in principle, a faithful replica free of any type of distortion. The method could be extended beyond ocular imaging, to any kind of imaging system in which the image can move or be made to move across the detector.
Highlights
Raster-based scanning systems such as scanning light ophthalmoscopy (SLO) and optical coherence tomography (OCT) have become ubiquitous in both clinical practice [1,2,3] and ophthalmic research [4,5,6]
To mimic the behaviour of raster systems whereby minimal dynamic distortion is expected along the “fast” scan axis, for dynamic distortion we modelled variation of the distorting functions only in the y direction (i.e. Dx(y) and Dy(y))
Four frames were simulated with mean position given by the coloured crosses; two example frames are shown (Fig 3A and 3B)
Summary
Raster-based scanning systems such as scanning light ophthalmoscopy (SLO) and optical coherence tomography (OCT) have become ubiquitous in both clinical practice [1,2,3] and ophthalmic research [4,5,6]. The method makes a key assumption that the fixational motion of the eye is random in nature, so that if a sufficient number of frames are observed there should be no expected bias in the distortion seen for any particular piece of tissue compared with the rest of the tissue. Where this assumption holds true, this procedure can be expected to remove dynamic distortion entirely. The method has been adopted by several imaging groups [12,13,14,15,16,17]
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