Ocular refraction and the shadow test . parallel. An earnest endeavor has also been made to make the subject ofconjugate foci as clear as possible, and the student is urged not topass beyond this point until he has the matter clearly in mind. Theimportance of this cannot be overestimated, because the theory andpractice of retinoscopy is founded upon the physical laws governing:conjugate foci. Let figure 129 represent an eye, E, under examination with aplane retinoscope M; the position of the operator is one metre, orforty inches distant; his eye is represented by O which is behind the O C U L
Ocular refraction and the shadow test . parallel. An earnest endeavor has also been made to make the subject ofconjugate foci as clear as possible, and the student is urged not topass beyond this point until he has the matter clearly in mind. Theimportance of this cannot be overestimated, because the theory andpractice of retinoscopy is founded upon the physical laws governing:conjugate foci. Let figure 129 represent an eye, E, under examination with aplane retinoscope M; the position of the operator is one metre, orforty inches distant; his eye is represented by O which is behind the O C U L A R REFRACTION retinoscope. Figure 129 represents the conditions that occur if theeye E be emmetropic. The parallel rays represented by the un-broken lines, are seen to be reflscted from the plane mirror M, intothe eye E. As the eye is emmetropic the rays that are reflected fromits retina emerge parallel, and some of them, represented by the dot-ted lines, reach the eye O of the observer as parallel, through thepeep-hole in the Figure 130. Emergent rays Irom an emmetropic eye brought to a focus imetre, by a convex spherical lens of one dioptre. Suppose it is desired to converge the emergent parallel raysshown in figure 129, so they will focus at the position of the observer40 inches distant. As it is known that a convex spherical lens of one dioptre willbring parallel rays to a focus at forty inches, if such a lens be placed
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