Systems, devices, and methods used to diagnose visual problems are disclosed. Diagnosing visual problems can be implemented using a fundus camera, for example. The camera focuses an image of an interesting portion of an eye being viewed. The image can be an intermediate real image of the fundus. Once the portion of the eye is in focus, the settings or the position of the focusing mechanism is determined. An optical error of an eye can be determined based on the determined settings or the determined position of the focusing mechanism. Once in focus, an image of the interesting portion of the eye can be taken or captured. A size of any feature of the eye can be determined, in absolute units based on determining an area occupied by the feature of the eye in the picture or the image, and the determined optical error of the eye.
