Fig. 1

Principle of ultra-widefield imaging using the confocal scanning laser ophthalmoscope developed by Optos. An ellipse has two foci, and light passing through one focus and reflecting at the inner surface of the ellipse always passes through the other focus. Thus, light emitted from one of the foci (F1) always passes through the other focus (F2) where the center of the pupil is placed. The direction of light can be changed when a galvanometer mirror is placed at F1. Taking advantage of this property, ultra-widefield retinal imaging of even a small pupil became possible