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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    an effort of accommodation, to overcome the hypermetropia; and in pro- portion as the object gets nearer, so must he add to this effort that which would be required if the eye were a normal (emmetropic) one, so that looking at near objects requires a great deal of effort. Now, there exists a certain connexion between accommodation aud the convergence of the lines of vision. The stronger one can converge the more powerfully can he bring into operation his faculty of accommodation. A certain tendency to increased convergence cannot be, therefore, altogether absent in the case of any exertion of the accommodation. This tendency exists in every hypermetropic eye. One can be easily convinced of this by holding negative glasses before emmetropic eyes, and bringing them thereby into a hypermetropic condition. It will then be found that, at each effort to see distinctly, double images threaten simultaneously to present themselves, and that there is, in short, only the choice between indistinct vision and squinting: this conflict probably existed in all hypermetropic eyes, without their being conscious of it. Hypermetropia is a very widely diffused anomaly. I am persuaded that it occurs still more frequently than myopia. If then converging strabismus be, as a rule, a consequence of hypermetropia, it is evident that hypermetropia very frequently exists without causing squint. One might even say that strabismus develops itself but in a comparatively very small number of cases of hypermetropia. This need, however, by no means surprise us. In fact, the desire to see an object, simply with both eyes, at the same moment, makes itself, as a general rule, energeti- cally felt; the direction of the lines of vision is thereby strongly marked. Many years ago I convinced myself of this fact by my experiments on the effects of prismatic glasses.14 If we place before a normal eye a weak prismatic glass, with the refracting edge turned inwards, then looking at a fixed object, it at first appears double; but then an increased convergence is at once and involuntarily called into play, which causes an union of the double images; if, in a moment or two, we now remove the glass, double images again make their appearance, and as speedily, through a diminution of the convergence, disappear, coalescing, so to speak, of themselves. The movements here alluded to take place, in fact, so spontaneously, that the person is not even conscious of it. This aversion to double images, or rather this instinctive clinging to single binocular vision, preserves the hypermetropic eyes of most people from squinting, they preferring rather to sacrifice pleasant, easy, and sharp vision than Nederlansch Lancet, 2 Ser, D. HI., bl. 233. 'S. Hage, 1845.