The red reflex from retinoscopy's point of view. Reflections on a small area.

The size of the area of retina that is involved in neutralization during retinoscopy is considerably smaller than intuition might suggest. Simple optical analysis reveals this area to be approximately 1/640 the area of the optic disc. This becomes important when retinoscoping high myopes with posterior staphylomas because even minimal misalignment with the visual axis may induce spherical error in the retinoscopic findings.