American Journal of Ophthalmology Series 3, Vol. 4, No. 9 September, 1921

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MONOCULAR DIPLOPIA. A simple form of monocular diplopia The patient's complaint of double is produced in the Schreiner experi­ vision should lead promptly to the test­ ment. A card held before the eye, with ing of whether it is binocular or mon­ two pin holes in front of the pupil, will ocular, by covering each eye in succes­ make a distant light look double, if sion to see if this leaves diplopia with its rays are not perfectly focussed on a single eye in use. This begins the the retina. .This anyone can try by diagnosis; but it is only complete when imitating in his eye hyperopia or the exact cause of the doubling has myopia by the use of a concave or been determined for each particular convex lens before it. Only when the case, and the significance of what the light is perfectly focussed on the retina diplopia implies has been worked out. do the two images fuse into one. This condition has been rather in­ Another very simple form of monoc­ adequately explained in the text books; ular diplopia is produced by placing and the lists they give of possible the edge of a prism before the pupil so causes are often confusing. It is pos­ that some of the light reaching the re­ sible for the symptom to arise from tina comes along side of the prism, conditions of the refracting media and while some is deflected by coming thru surfaces; from peculiar displacements it. The same thing is done by looking of the retina; or, perhaps, as a symp­ thru the edge of a correcting glass, tom of disease of the central nervous where a prismatic effect is produced. system. Such conditions as opacities The monocular diplopia, produced of the cornea or lens or polycoria are by imperfections of the dioptric sur­ associated with monocular diplopia; faces or media of the eye or by poly­ but the cause of it is the accompanying coria, is like that of the above experi­ disturbance of regular refraction, not ments. An irregular cornea has por­ the opacity or multiplicity of pupils tions which are so inclined as to deflect in itself. the rays passing thru them, as does the 697 698 EDITORIALS

prism held partly in front of the pupil. most cases; the occurrence of such The opacities, that accompany such ir­ images has not been shown to have regularities, tend to render the sep­ any definite relation to the anatomy arate images more distinct. The same and physiology of the visual centres. is true of irregularities in the crystal­ In this the double vision closely resem­ line lens, whether these are irregulari­ bles the paresfhesias of hysteria, and ties of surface or of refractive index, probably in most cases the diplopia is and the opacities that appear with hysteric in character. It is well known them. In polycoria, the different open­ that in connection with organic brain ings in the iris correspond to the dif­ disease, hysteric symptoms are apt to ferent pin holes of the Schreiner ex­ arise. But these cases should be periment, producing diplopia when the studied in minute detail to ascertain light entering the eye is not perfectly if there is any basis other than that of focussed on the retina. And in poly­ suggestion to account for them. coria, one or more of the pupils is gen­ All cases of monocular diplopia are erally situated so far toward the peri­ worthy of close study, and they may phery of the iris that the focussing of help to throw important light on the the light, entering thru it, is certain to origin and prognosis of the conditions be imperfect. on which the diplopia depends, or with It is not generally realized how which it is associated. In a large pro­ marked a monocular diplopia may arise portion of instances, there are more from imperfect focussing (diffusion than two images present, polyopia; but phenomena) thru a normal pupil of not the fewer the images the more readily unusual size. Looking at a white line they can be studied. A first step toward on a black ground with a strong spher­ finding the full significance of the di­ ical lens or cylinder with its axis paral­ plopia is to ascertain in which part of lel to the line, will serve to bring out the pupil each particular image takes this kind of diplopia; which appears as its origin. In a case of partial cataract, a duplication of outline, rather than the as that reported on page 673, this one perception of separated distinct im­ fact may indicate swelling or shrinking ages. This kind of diplopia is com­ of the crystalline lens, and thus add plained of by patients suffering from definiteness and certainty to the uncorrected ametropia of high degree, prognosis. and is more noticed when the regular error is supplemented by irregular as­ The connection with a particular tigmatism. part of the pupil is established by cov­ ering that part with a corner of a card, The diplopia, that may arise in de­ and having the patient notice that the tachment of the retina, may be binoc­ image in question disappears. Changes ular, due to displacement of one retina in the images, and therefore in the con­ so that it receives on an abnormal por­ ditions of the cornea or crystalline lens tion an image, the counterpart of that cause them, may often be discov­ which is normally received on the re­ ered by placing the patient in a certain tina of the other eye. It may, how­ definite, easily reproduced position ever, be monocular, the light impress­ with regard to a point of light; and ing both layers of a folded retina, one having him make a drawing of the layer lying behind the other; or fall images he sees. The change in such upon two folds that are in close jux­ images, produced by viewing them taposition. In either case, the double thru different convex and concave images are so faint or indefinite that lenses, will sometimes help to deter­ they are not much noticed unless the mine their significance. Studies of sight is very defective in both eyes. such multiple images, made with care About the double vision noticed in and accuracy, will generally be found connection with cerebral disease, our interesting, and often afford important knowledge is not very definite. In practical help. E. J.