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When one speaks of the neutral point in retinoscopy, one ordinarily refers to the point where the emergent rays from the patient's eye meet. This may be called the "emergent neutral" point. But there is another neutral point which concerns the incident light and may be called the "incident neutral" point. The latter neutral point is obtained when one uses a concave mirror (or a concave mirror effect) of intermediate focus. When the incident light is made to focus in the plane of the patient's pupil, there will be neutrality of motion irrespective of any refractive error the patient may have.
One can understand this phenomenon from the basic facts in retinoscopy, without elaborate tracings of rays. A plane or a long focus concave mirror always produces a "with" movement of the light patch on the patient's retina, although it may sometimes appear to move "against." A short focus concave
PASCAL JI. THE "INCIDENT NEUTRAL" POINT IN RETINOSCOPY. Arch Ophthalmol. 1948;39(4):550-551. doi:10.1001/archopht.1948.00900020558012