1. A method to register retinal images, the method comprising: determining a first tracing of a blood vessel in a first retinal image acquired at a first optical wavelength; determining a second tracing of the blood vessel in a second retinal image acquired at a second optical wavelength; identifying features common to the first tracing and the second tracing to obtain identified features; determining a feature displacement vector for each identified feature of the second tracing with respect to a corresponding identified feature of the first tracing; calculating, in accordance with the feature displacement vectors, a pixel displacement vector for pixels of the second retinal image; and transforming the second retinal image in accordance with the pixel displacement vectors to obtain a transformed second image registered to the first retinal image.