of a house surgeon at the Manhattan Eye and Ear Hospital, Dr. C. H. Johnson. Ordinarily this gentleman had half a diopter of astigmatism in each eye; but he could, at will, increase this to two diopters in the right eye and one and a half in the left. He did this many times, in the presence of a number of members of the hospital staff, and also did it when the upper lids were held up, showing that the pressure of the lids had nothing to do with the phenomenon. Later he went to Louisville, and here Dr. J. M. Ray, at the suggestion of Dr. Davis, tested his ability to produce astigmatism under the influence of scopolamine (four instillations, 1/5 per cent solution). While the eyes were under the influence of the drug the astigmatism still seemed to increase, according to the evidence of the ophthalmometer, to one and a half diopters in the right eye and one in the left. From these facts, the influence of the lids and of the ciliary muscle having been eliminated, Dr. Davis concluded that the change in the cornea was "brought about mainly by the external muscles." What explanation others offer for such phenomena I do not know.
1. Johannes Kepler (1571-1630). German theologian. astronomer and physicist. Many facts of physiological optics were either discovered, or first clearly stated, by him.
2. Donders: On the Anomalies of Accommodation and Refraction of the Eye. English translation by Moore, 1864, p. 10. Frans Cornelis Donders (1818-1889) was professor of physiology and ophthalmology at the University of Utrecht, and is ranked as one of the greatest ophthalmologists of all time.
3. Edmund Landolt (1846-) Swiss ophthalmologist who settled in Paris in 1874, founding an eye clinic which has attracted many students.
4. On the Mechanism of the Eye, Phil. Tr. Roy. Soc., London, 1801.
5. On the Anomalies of Accommodation and Refraction of the Eye, pp. 10-11.
6. Maximilian Adolf Langenbeck (1518-1877). Professor of anatomy, surgery and ophthalmology at Gottingen, from 1846 to 1851. Later settled in Hanover.
7. Johannes Evangelista von Purkinje (1787-1869). Professor of physiology at Breslau and Prague, and the discoverer of many important physiological facts.
8. Antonie C. Cramer (1822-1855). Dutch ophthalmologist.
9. Handbuch der physiologischen Optik, edited by Nagel, 1909-11, vol. i, p. 121.
10. Ibid. vol. i, p. 122.
11. The Refraction and Accommodation of the Eye and their Anomalies, authorized translation by Culver, 1886, p. 151.
12. Physiologic Optics, authorized translation by Weiland, 1904, p. 163. Marius Hans Erik Tscherning (1854 - ) is a Danish ophthalmologist who for twenty-five years was co-director and director of the ophthalmological laboratory of the Sorbonne. Later he became professor of ophthalmology in the University of Copenhagen.
13. The Hygiene of the Eye in Schools, English translation edited by Turnbull, 1886, p. 23. Hermann Cohn (1838-1906) was professor of ophthalmology in the University of Breslau, and is known chiefly for his contributions to ocular hygiene.
14. Lessons in Elementary Physiology, sixth edition, 1872, p. 231.
15. On the Anomalies of Accommodation and Refraction of the Eye, p. 13.
16. Krankheiten des Auges, 1853-56, vol. iii, D. 219, et seq.
17. Ueber die Ursachen und die Entstehung der Kurzsichtigkeit, 1876. Vorwort.
18. Handbuch der physiologischen Optik, vol. i, pp. 124 and 145.
19. Ibid, vol. i. P. 144.
20. Physiologic Optics, p. 166. Herman- Ludwig Ferdinand von Helmholtz (1821-1894) whose observations regarding the behavior of images reflected from the front of the lens are supposed to have demonstrated that the curvature of this body changes during accommodation.
21. Absence of the lens.
22. On the Anomalies of Accommodation and Refraction of the Eye, p. 320.
23. Archiv. f. Ophth., 1855, vol. ii, part 1, p. 187 et seq. Albrecht von Graefe (1828-1870) was professor of ophthalmology in the University of Berlin, and is ranked with Donders and Arlt as one of the greatest ophthalmologists of the nineteenth century.
24. Klin. Montasbl. f. Augenh., Erlangen, 1872, vol. x, p. 39, et seq.
25. Archiv. f. Ophth., 1873, vol. xix, part 3, p. 107.
26. Flint: Physiology of Man, 1875, vol. v, pp. 110-111.
27. Davis: Accommodation in the Lensless Eye, Reports of the Manhattan Eye and Ear Hospital, Jan., 1895. The article gives a review of the whole subject.
28. An instrument for measuring the curvature of the cornea.
29. Nov., 1893, p. 932.
30. Inasmuch as the eye is inextensible, it cannot adapt itself for the perception of objects situated at different distances by increasing the length of its axis, but only by increasing the refractive power of its lens. - De Schweinitz: Diseases of the Eye, eighth edition, 1916, pp. 35-36.
CHAPTER IV - THE TRUTH ABOUT ACCOMMODATION AS DEMONSTRATED BY EXPERIMENTS ON THE EYE MUSCLES OF FISH, CATS, DOGS, RABBITS AND OTHER ANIMALS
THE function of the muscles on the outside of the eyeball, apart from that of turning the globe in its socket, has been a matter of much dispute; but after the supposed demonstration by Helmholtz that accommodation depends upon a change in the curvature of the lens, the possibility of their being concerned in the adjustment of the eye for vision at different distances, or in the production of errors of refraction, was dismissed as no longer worthy of serious consideration. "Before physiologists were acquainted with the changes in the dioptic system,1 says Donders, "they often attached importance to the external muscles in the production of accommodation. Now that we know that accommodation depends on a change of form in the lens this opinion seems scarcely to need refutation." He states positively that "many instances occur where the accommodation is wholly destroyed by paralysis, without the external muscles being the least impeded in their action," and also that "some cases are on record of paralysis of all or nearly all of the muscles of the eye, and of deficiency of the same, without diminution of the power of accommodation."2
If Donders had not considered the question settled, he might have inquired more carefully into these cases, and if he had, he might have been less dogmatic in his statements; for, as has been pointed out in the preceding chapter, there are plenty of indications that the contrary is the case. In my own experiments upon the extrinsic eye muscles of fish, rabbits, cats, dogs and other animals, the demonstration seemed to be complete that in the eyes of these animals accommodation depends wholly upon the action of the extrinsic muscles and not at all upon the agency of the lens. By the manipulation of these muscles I was able to produce or prevent accommodation at will, to produce myopia, hypermetropia and astigmatism, or to prevent these conditions. Full details of these experiments will be found in the "Bulletin of the New York Zoological Society" for November, 1914, and in the "New York Medical Journal" for May 8, 1915; and May 18, 1918; but for the benefit of those who have not the time or inclination to read these papers, their contents are summarized below.
There are six muscles on the outside of the eyeball, four known as the "recti" and two as the "obliques." The obliques form an almost complete belt around the middle of the eyeball, and are known, according to their position, as "superior" and "inferior." The recti are attached to the sclerotic, or outer coat of the eyeball, near the front, and pass directly over the top, bottom and sides of the globe to the back of the orbit, where they are attached to the bone round the edges
