MCFARLAND9: Experience with Prismatic Glasses. 479
A PERSONAL EXPERIENCE WITH PRISMATIC GLASSES. BY S. F. MC FARLAND, M.D., OXFORD, N. Y.
O?INIoNs are so various in regard to the efficiency of prismatic glasses in correcting or alleviating the distressing' annoyances resulting from muscular' paresis, that a brief statement of a long personal experience in the use of them may perhaps be admissible. During my boyhood, I had a slight divergence, occurring and disappearing at times. 'Although seldom sufficient to attract attention. Still I had the'full use of my eyes, could judge of 'distances as well as- others, and' was even expert- in many of the sports of youth requiring binocular vision. I had no inconivenience during my studies, always enjoying, the greatest comfort during the'most severe and protracted application. During the 'autumn of I862 I contracted a typho-malarial fever in the army, on recovering from which I found that I had lost the full and comfortable use of my eyes, which continued with the usual pain 'and-anndyances attending a fitile effortto use both eyes in conjunction, and I wag compelled to discontinue reading'almost entirely, until finally in January, -I866, I consulted Dr. H. D. Noyes. He gave me plane prisms of 7° each, bases-in, fot distance, and 80 each with + 36 S. for reading. At this time I had been nearly three years unable to obtain binocular vision even for a moment, and when once more I saw the beautiful landscape spread out in its true perspective, I was delighted. I have never discontinued them. They have been varied from time to time, endeavoring to obtain the 'best results, but- always adhering to the prisms.
480 MCFARLAND: Experience with Prismatic Glasses. You may ask if I suffer no inconvenience? I do. Very great inconvenience, and cannot maintain continued binocular vision, but I can obtain, and retain it long enough for an iridectomy or an extraction, and even during very protracted operations, although at the expense of pain and a distressing lassitude following the effort. Without the prisms I could not do those things, as slight differences in distance would not be appreciable. At present I wear bifocal spheroprismatic glasses, with the division one-third the width from below, instead of in the middle, and at an angle of I5' below the horizontal, thus rendering the division as nearly invisible as possible when looking through the lower portion in reading. The only inconveniences noticed were chromatism and spherical aberration, both of which disappeared after wearing the glasses a few weeks. I have been told by able ophthalmologists that prisms were of no use to me, that they did not afford me binocular vision, and inight as well be dispensed with. But after an experience of seventeen and one-half years, I consider " half a loaf better than no bread," and propose to continue their use. You may say that patients do not accept them. Neither do they cylindric glasses in many instances, although they increase the sight many fold. Patients are more likely to recognize the inconveniences than the advantages of spectacles, and do not always appreciate changes of moderate degree. When I commenced wearing prisms it required 140 to enable me to use both eyes in conjunction. I can now do so without any aid, the prisms seeming to encourage the interni rather than proving detrimental to their functions. With the bifocal sphero-prismatic glasses I am able to do all my office work without changing, and with a reasonable -amount of comfort. REMARKS.
DR. WEBSTER asked why not have the external rectus cut. DR. MCFARLAND said he had only proposed to consider the practicability of prismatic glasses.
WADSWORTH: Apparent Curvature of Surface. 48I DR. McKAY had a case present itself to him in September, 1878, occurring in a music teacher who had double vision; he stood directly in front of his class, and without moving his head made extreme excursions with his. eyes to the right and to the left, and in this way weakened the external recti. Dr. McKay ordered prisms- with bases externally (for distance only), which the patient continues to wear with comfort. Dr. McKay further stated, that when he had his case under charge he had previously read and studied closely Dr. Noyes' paper on asthenopia with reference to the use of prismatic glasses, and found the observations very comforting and beneficial at that time.
ON THE APPARENT CURVATURE OF SURFACE PRODUCED BY PRISMS. (With Woodcuts.) a
BY 0. F. WADSWORTH, M.D., BOSTON, MASS.
IT is a familiar phenomenon that a plane surface appears convex when looked at through prisms placed before the eyes with the bases inward, while the same surface appears concave if the prisms be arranged with the bases outward. The phenomenon may be explained as follows: Let the curved lines R and L (Fig. i) represent the retinas of the two eyes of an observer, k and k' the nodal points of the eyes. Let the line C D E be parallel to a line which would connect the nodal points of the two eyes. Let C and E be points on this line from which perpendiculars to the line would pass through k and k'. Let D be equidistant from C and E. Further, let lines be drawn from C, D and E through k and k' to meet the two retinas. Now, suppose the eyes to be directed toward D. The image of D will fall upon the retina of each eye in the direction of the lines D k and D k'. The separation of the image of E from that of D on the right retina will be determined by the angle a = angle D k E; and the separation of the image of E from that of D on the left retina will be determined by
A PERSONAL EXPERIENCE WITH PRISMATIC GLASSES. BY S. F. MC FARLAND, M.D., OXFORD, N. Y.
O?INIoNs are so various in regard to the efficiency of prismatic glasses in correcting or alleviating the distressing' annoyances resulting from muscular' paresis, that a brief statement of a long personal experience in the use of them may perhaps be admissible. During my boyhood, I had a slight divergence, occurring and disappearing at times. 'Although seldom sufficient to attract attention. Still I had the'full use of my eyes, could judge of 'distances as well as- others, and' was even expert- in many of the sports of youth requiring binocular vision. I had no inconivenience during my studies, always enjoying, the greatest comfort during the'most severe and protracted application. During the 'autumn of I862 I contracted a typho-malarial fever in the army, on recovering from which I found that I had lost the full and comfortable use of my eyes, which continued with the usual pain 'and-anndyances attending a fitile effortto use both eyes in conjunction, and I wag compelled to discontinue reading'almost entirely, until finally in January, -I866, I consulted Dr. H. D. Noyes. He gave me plane prisms of 7° each, bases-in, fot distance, and 80 each with + 36 S. for reading. At this time I had been nearly three years unable to obtain binocular vision even for a moment, and when once more I saw the beautiful landscape spread out in its true perspective, I was delighted. I have never discontinued them. They have been varied from time to time, endeavoring to obtain the 'best results, but- always adhering to the prisms.
480 MCFARLAND: Experience with Prismatic Glasses. You may ask if I suffer no inconvenience? I do. Very great inconvenience, and cannot maintain continued binocular vision, but I can obtain, and retain it long enough for an iridectomy or an extraction, and even during very protracted operations, although at the expense of pain and a distressing lassitude following the effort. Without the prisms I could not do those things, as slight differences in distance would not be appreciable. At present I wear bifocal spheroprismatic glasses, with the division one-third the width from below, instead of in the middle, and at an angle of I5' below the horizontal, thus rendering the division as nearly invisible as possible when looking through the lower portion in reading. The only inconveniences noticed were chromatism and spherical aberration, both of which disappeared after wearing the glasses a few weeks. I have been told by able ophthalmologists that prisms were of no use to me, that they did not afford me binocular vision, and inight as well be dispensed with. But after an experience of seventeen and one-half years, I consider " half a loaf better than no bread," and propose to continue their use. You may say that patients do not accept them. Neither do they cylindric glasses in many instances, although they increase the sight many fold. Patients are more likely to recognize the inconveniences than the advantages of spectacles, and do not always appreciate changes of moderate degree. When I commenced wearing prisms it required 140 to enable me to use both eyes in conjunction. I can now do so without any aid, the prisms seeming to encourage the interni rather than proving detrimental to their functions. With the bifocal sphero-prismatic glasses I am able to do all my office work without changing, and with a reasonable -amount of comfort. REMARKS.
DR. WEBSTER asked why not have the external rectus cut. DR. MCFARLAND said he had only proposed to consider the practicability of prismatic glasses.
WADSWORTH: Apparent Curvature of Surface. 48I DR. McKAY had a case present itself to him in September, 1878, occurring in a music teacher who had double vision; he stood directly in front of his class, and without moving his head made extreme excursions with his. eyes to the right and to the left, and in this way weakened the external recti. Dr. McKay ordered prisms- with bases externally (for distance only), which the patient continues to wear with comfort. Dr. McKay further stated, that when he had his case under charge he had previously read and studied closely Dr. Noyes' paper on asthenopia with reference to the use of prismatic glasses, and found the observations very comforting and beneficial at that time.
ON THE APPARENT CURVATURE OF SURFACE PRODUCED BY PRISMS. (With Woodcuts.) a
BY 0. F. WADSWORTH, M.D., BOSTON, MASS.
IT is a familiar phenomenon that a plane surface appears convex when looked at through prisms placed before the eyes with the bases inward, while the same surface appears concave if the prisms be arranged with the bases outward. The phenomenon may be explained as follows: Let the curved lines R and L (Fig. i) represent the retinas of the two eyes of an observer, k and k' the nodal points of the eyes. Let the line C D E be parallel to a line which would connect the nodal points of the two eyes. Let C and E be points on this line from which perpendiculars to the line would pass through k and k'. Let D be equidistant from C and E. Further, let lines be drawn from C, D and E through k and k' to meet the two retinas. Now, suppose the eyes to be directed toward D. The image of D will fall upon the retina of each eye in the direction of the lines D k and D k'. The separation of the image of E from that of D on the right retina will be determined by the angle a = angle D k E; and the separation of the image of E from that of D on the left retina will be determined by
