Roe L D, Guyton D L
Surv Ophthalmol. 1984 Mar-Apr;28(5):405-8. doi: 10.1016/0039-6257(84)90245-5.
Both the retinoscope and the ophthalmoscope allow observation of the fundus and of the "red reflex." Retinoscopy, however, requires an effective light source that may be quickly moved off the visual axis. The ophthalmoscope is unable to provide this type of illumination. On the other hand, the retinoscope is unable to provide sufficient illumination of the retina to make it useful for ophthalmoscopy . Ophthalmoscopy requires the examiner's retina to be conjugate to the retina being examined, whereas the examiner's retina becomes conjugate to the peephole of the retinoscope in retinoscopy. The "red reflex" seen with either the retinoscope or the ophthalmoscope may be clear or blurred. The clear red reflex is more useful for ophthalmoscopy , while the blurred red reflex is primarily used for retinoscopy.