In direct ophthalmoscopy, before the fundus is examined with the instrument held close to the subject's eye, it is customary to observe the fundus reflex in the pupillary area for opacities in the media, especially the lens. This is done at a distance of 12 in. (300 mm.) or so. However, with the modern electric ophthalmoscope, even when there are no intervening opacities in the media the fundus reflex almost never is uniform in brightness. One portion of the pupillary area usually is much brighter than the remainder, and the boundary between these two areas is a curved one with the concavity upward. The position and extent of these two areas, the brighter area and the darker area, vary with the refractive state of the eye. The description and explanation of this phenomenon will be attempted in general terms. Although rough numerical examples will be worked out, chiefly to clarify
EGGERS H. Variations of the Fundus Reflex in Ametropia. AMA Arch Ophthalmol. 1957;57(6):801–814. doi:10.1001/archopht.1957.00930050813002
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