An apparatus for rendering optical coherence tomography, OCT, retinal image data, acquired by an OCT scanner scanning a retina of an eye over a range of scan locations, wherein each scan location is associated with a respective coordinate in a first coordinate system, and each pixel of the rendered OCT retinal image data is associated with a respective coordinate in a second coordinate system different from the first coordinate system. The apparatus comprises a communication module arranged to receive the OCT retinal image data, and a coordinate-determining module arranged to determine values of coordinates in the second coordinate system of pixels in the received OCT retinal image using a transformation from coordinates in the first to second coordinate system. The apparatus further comprises an interpolation module arranged to interpolate between values of pixels at the determined values to calculate values of the pixels of the rendered OCT retinal image data.
