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Refraction and accommodation in the dog's eye: A correction
NOTES REFRACTION
FROM AND
NELA
RESEARCH
ACCOMMODATION A CORRECTION.
LABORATORY.':; IN T H E
DOG'S
EYE:
By H. M. Johnson.
IN a note which recently appeared in this journal i the writer asserted, on the authority of Freytag, that the refractive indices of the lens and fluid media of the dog's eye are practically identical, and that several other species of infra-primate mammals suffer under the same condition. If this assertion were true, its significance would be very great indeed, since in such case the animals concerning which it is made could not change the focal distance of the eye by any mechanism of accommodation which mammals are known to possess. At the time my note was published, 1 had been unable to procure a copy of Freytag's original article." My assertion was based on my acceptance of a reference made by an American compiler to Freytag's work, in which a series of values were presented in tabular form as Freytag's. A comparison of the latter with the original article, which I have since obtained, shows that Freytag was incorrectly quoted by his reviewer, although the error is clearly unintentional. Freytag actually gives as mean values of the refractive indices in young and old dogs: for the aqueous humor, 1.3349 ; for the vitreous humor, 1.33483; and for the lens, values ranging between 1.4498 and 1.4666, depending on age. These differences are greater than those obtaining between the refractive indices of the lens and fluid media in the human eye, and are comparable with the differences found in the other mammals which Freytag studied. In the individual dog which I studied no clear evidence of * Communicated by the Director. 1 ,, Visual Pattern-discrimination in the V e r t e b r a t e s - - V . A Demonstration of the Dog's Deficiency in Detail Vision," in " Notes from the Nela Research Laboratory," JOURNAL OF THE FRANKLIN INSTITUTE, December, 1915. 2 Freytag, G. : " Die Brechungsindices der Linse und der fliissigen Augenmedien bei der Katze nnd beim Kaninchen." Arch. f. vergl. Ophthahnologie, vol. i, 19o9-1o. 575
576
NELA RESEARCIt LABORATORY NOTES.
[J. F. I.
accommodation could be obtained. Momentary fluctuations in refraction varying from o.25 to o.75 D occasionally appeared during a prolonged examination. These may have been caused by accommodation, but they are as readily explainable on other assumptions. The facts are quite consistent with the results obtained by Boden, a who refracted the eyes of Ioo dogs both before and during mydriasis. These individual dogs apparently make little or no use of their mechanism of accommodation. If this is generally true of dogs as a class, it would seem that the defect is retinal rather than in the accommodatory apparatus itself. If it may be assumed that the stimulus to accommodation is indistinctness of the retinal image, it is evident that an animal whose retina is relatively insensitive to detail would have relatively slight stimulus to accommodation. As regards the conclusions which I drew from the experiments reported in the above note, I still feel quite safe in applying them to the dog. They cannot properly be extended to cover other infra-primate mammals, however, until more is known about the extent and range of accommodation in the latter. A FORM OF T H E H O L B O R N - K U R L B A U M O P T I C A L PYROME T E R A D A P T E D TO A W I D E RANGE OF L A B O R A T O R Y USES. By W. E. Forsythe.
THERE has been constructed for use in Nela Research Laboratory an optical pyrometer that is thought to have some advantages over existing forms. In this pyrometer are used tungsten pyrometer lamp filaments, and, as these are quite small (diameters o.ool 5 to 0.0025 inch), an eye-piece with quite large magnifying power had to be employed. The mounting of the pyrometer lamp is so constructed that all possible adjustments, such as raising and lowering, moving the filament across the field of view, turning and tipping the bulb, can be easily obtained. The holder of the pyrometer lamp is so arranged that it can be rotated in a collar 8Boden, Rudolf: " Ueber den Refraktionszustand des Hundeauges," Arch. f. vergl. Ophthalmologie, vol. i, I9o0-Io.
FROM AND
NELA
RESEARCH
ACCOMMODATION A CORRECTION.
LABORATORY.':; IN T H E
DOG'S
EYE:
By H. M. Johnson.
IN a note which recently appeared in this journal i the writer asserted, on the authority of Freytag, that the refractive indices of the lens and fluid media of the dog's eye are practically identical, and that several other species of infra-primate mammals suffer under the same condition. If this assertion were true, its significance would be very great indeed, since in such case the animals concerning which it is made could not change the focal distance of the eye by any mechanism of accommodation which mammals are known to possess. At the time my note was published, 1 had been unable to procure a copy of Freytag's original article." My assertion was based on my acceptance of a reference made by an American compiler to Freytag's work, in which a series of values were presented in tabular form as Freytag's. A comparison of the latter with the original article, which I have since obtained, shows that Freytag was incorrectly quoted by his reviewer, although the error is clearly unintentional. Freytag actually gives as mean values of the refractive indices in young and old dogs: for the aqueous humor, 1.3349 ; for the vitreous humor, 1.33483; and for the lens, values ranging between 1.4498 and 1.4666, depending on age. These differences are greater than those obtaining between the refractive indices of the lens and fluid media in the human eye, and are comparable with the differences found in the other mammals which Freytag studied. In the individual dog which I studied no clear evidence of * Communicated by the Director. 1 ,, Visual Pattern-discrimination in the V e r t e b r a t e s - - V . A Demonstration of the Dog's Deficiency in Detail Vision," in " Notes from the Nela Research Laboratory," JOURNAL OF THE FRANKLIN INSTITUTE, December, 1915. 2 Freytag, G. : " Die Brechungsindices der Linse und der fliissigen Augenmedien bei der Katze nnd beim Kaninchen." Arch. f. vergl. Ophthahnologie, vol. i, 19o9-1o. 575
576
NELA RESEARCIt LABORATORY NOTES.
[J. F. I.
accommodation could be obtained. Momentary fluctuations in refraction varying from o.25 to o.75 D occasionally appeared during a prolonged examination. These may have been caused by accommodation, but they are as readily explainable on other assumptions. The facts are quite consistent with the results obtained by Boden, a who refracted the eyes of Ioo dogs both before and during mydriasis. These individual dogs apparently make little or no use of their mechanism of accommodation. If this is generally true of dogs as a class, it would seem that the defect is retinal rather than in the accommodatory apparatus itself. If it may be assumed that the stimulus to accommodation is indistinctness of the retinal image, it is evident that an animal whose retina is relatively insensitive to detail would have relatively slight stimulus to accommodation. As regards the conclusions which I drew from the experiments reported in the above note, I still feel quite safe in applying them to the dog. They cannot properly be extended to cover other infra-primate mammals, however, until more is known about the extent and range of accommodation in the latter. A FORM OF T H E H O L B O R N - K U R L B A U M O P T I C A L PYROME T E R A D A P T E D TO A W I D E RANGE OF L A B O R A T O R Y USES. By W. E. Forsythe.
THERE has been constructed for use in Nela Research Laboratory an optical pyrometer that is thought to have some advantages over existing forms. In this pyrometer are used tungsten pyrometer lamp filaments, and, as these are quite small (diameters o.ool 5 to 0.0025 inch), an eye-piece with quite large magnifying power had to be employed. The mounting of the pyrometer lamp is so constructed that all possible adjustments, such as raising and lowering, moving the filament across the field of view, turning and tipping the bulb, can be easily obtained. The holder of the pyrometer lamp is so arranged that it can be rotated in a collar 8Boden, Rudolf: " Ueber den Refraktionszustand des Hundeauges," Arch. f. vergl. Ophthalmologie, vol. i, I9o0-Io.