Page:Handbook of Ophthalmology (3rd edition).djvu/122

116 of the optic nerve and retina; for all other cases a good lamp-flame is all-sufficient, and in many cases more convenient.

OPHTHALMOSCOPIC DIAGNOSIS OF THE CONDITION OF REFRACTION.

The use of the ophthalmoscope for the diagnosis of the condition of refraction is as old as the use of this instrument in general. Helmholtz mentions a case in which, in a perfectly blind eye, by the help of the ophthalmoscope, he could decide the important question whether certain former difficulties of vision; which the patient complained of, depended upon myopia or incipient amblyopia. He pointed out as an advantage of this method that it makes the examiner entirely independent of the statements of the patient, since he himself sees with the patient's eye, at least with the refracting part of it. Cases in which it is desirable to be entirely independent of the statements of the patient are, in fact, frequent. Indeed, it happens often that the ophthalmoscopic examination first gives a proper direction to the functional examination.

We have already explained the manner in which the condition of refraction is disclosed by the ophthalmoscopic examination. The degree of the anomaly may be determined by the same method. Above all things the observer must be certain that both he and the patient have fully relaxed their accommodation. He can then, observing the distance from the eye under examination, determine the degree of the refraction from the number of the lens with which the fundus can be distinctly seen in the upright image. If one wish to determine exactly the condition of refraction by the ophthalmoscopic examination, it is best to paralyze the accommodation by atropine, and to use as a test-object, not the optic disc, but one of the fine retinal vessels running from it toward the macula lutea. In such a case it is well, as Coccius has proposed, to place the correcting lens close in front of the eye under examination, between it and the mirror, and to avoid the annoying reflex by slight movements of the lens. The correcting lens is then at the same distance from the eye as it would be if used as a spectacle-glass.