Registration of 2D Images from Fast Scanning Ophthalmic Instruments

Images from high-resolution scanning ophthalmic instruments are significantly distorted due to eye movement. Accurate image registration is required to successfully image subjects who are unable to fixate due to retinal conditions. Moreover, all scanning ophthalmic imaging modalities using adaptive optics will benefit from image registration, even in subjects with good fixation and anaesthetized animals. Transformation functions used to map two images could in principle be very complex. Here, we show that when the scanning in ophthalmic instruments is sufficiently fast with respect to the speed of involuntary eye movement, these mapping functions become the addition of a linear term and a single variable function. Then, based on experimental data on eye movement amplitude and speed of the fixating eye, minimum sampling frequencies for these instruments are discussed. Finally, a simple method for estimating the image transformation functions by taking advantage of the finite bandwidth of the motion signals is presented.