A method of determining a geometrical measurement of a retina of an eye, comprising obtaining a two dimensional representation of at least a portion of the retina of the eye 34, deriving a geometrical remapping which converts the 2D representation of the portion to a three dimensional representation of the portion 36, using one or more coordinates of the two dimensional representation of the portion to define the geometrical measurement to be taken on the 2D representation 38, using the remapping to convert the coordinates of the 2D representation of the retinal portion to equivalent coordinates of the 3D representation of the retinal portion 40, and using the equivalent coordinates of the 3D representation of the portion to determine the geometrical measurement of the retina 42. The method also comprises determining a correction for distortion in the 2D image by using an imaging device used to capture the 2D representation to capture a distorted image of a target and comparing the distorted image to a computed image of the target. The measurement may be a distance, an area or an angle between structures on the retina.
