On the pathogeny of squint / by Professor Donders ; translated from the German, with a preface, by E. Perceval Wright.

  • Donders, F. C. (Franciscus Cornelis), 1818-1889.
Date:
1864
Catalogue details

Licence: Public Domain Mark

Credit: On the pathogeny of squint / by Professor Donders ; translated from the German, with a preface, by E. Perceval Wright. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    The researches which I made conjointly with Dr. Doyer, establish that the centre of motion is situated behind the centre of the optic axis, so that the portion of this axis situated in front of the centre of rotation is to that behind, as 15 : 11. (Vide the annexed table given from the French.) Table of the mean obtained by the examination of 19 emmetropic eyes. 19 myopic eyes, M = 1 : 16 up to M = 1 : 2-25 12 emmetropic eyes, H == 1 : 16 „ H = 1 : 3*75 Hean length of the visual axis Situation of centre of motion Angle a between the axis of cornea and line of vision Behind the cornea In front on tho posterior of the sclerotic Proportion per cent. Behind the middle of the visual axis Millimetres Millimetres Millimetres E 23-53 13-54 : 9-99 = 57-54 : 42-46 1*77 5°-082 M 25-55 14-52 . 11-03 = 56-83 : 4317 1-75 2° H 22-10 13-22 : 8-88 - 59-8 : 40-2 2*17 7°-55 About the same proportions, however, were also found in the case of the longer axes of myopic people; here, consequently, the centre of motion lies further away from the posterior surface of the sclerotic. The excursions are therefore, in these cases, for equal degrees of rotation larger, and the movements necessarily limited; this limitation would be still greater were not the entrance of the optic nerve, on account of the disproportionate extension of the external posterior portion of the seg- ment, moved further inwards, and thus removed considerably less from the centre of motion. To this limitation, moreover, the greater distance between the centre of motion and the insertion of the muscles may help to contribute, to which distance, the' arc of rotation, obtained with a given shortening of the muscles, stands in inverse proportion. Apart from the consideration of all this, the elongation of the axis of the eye gives of itself a sufficient explanation of the diminution of the movements of the globe; this latter affects the movements inwards as well as outwards. With myopic people it is so general that out of seven- teen eyes examined, nine could not turn themselves sufficiently far so as to bring, without modification, our method for ascertaining the centre of motion, into use—a method which requires an excursion of not more