. A treatise on the diseases of the eye. of accommodation. (Hensen andVolckers^ Experimental-TJntersuchung iiber den Mechanism der , 1868.) 2 It was found, with the ophthalmometer, that the position of the reflection imagesof a candle, produced by the cornea and the anterior and posterior surfaces of the lens,undergo a change during accommodation for near objects. While the reflex imagefrom the cornea remains unchanged, that from the anterior surface of the lens approachesthe corneal image and diminishes in size; the image from the posterior surface ofthe lens also diminishes
. A treatise on the diseases of the eye. of accommodation. (Hensen andVolckers^ Experimental-TJntersuchung iiber den Mechanism der , 1868.) 2 It was found, with the ophthalmometer, that the position of the reflection imagesof a candle, produced by the cornea and the anterior and posterior surfaces of the lens,undergo a change during accommodation for near objects. While the reflex imagefrom the cornea remains unchanged, that from the anterior surface of the lens approachesthe corneal image and diminishes in size; the image from the posterior surface ofthe lens also diminishes very slightly in size, but undergoes no appreciable change ofposition. 624 ANOMALIES OF REFKACTION AND ACCOMMODATION. modiition. The anterior portion of the eye is divided into two equal one half, f, shows the position of the parts when the eye is adjusted fordistance, the other, n, when it is accoramodated for near objects. When theeye is in a state of rest, the iris forms a curve (a) in the vicinity of Schlemnis. Fiic. canal (s) ; but when accommodated for near objects, the fibres of the irissuffer contraction, the periphery of the iris becomes straigiitened (6), andthe anterior chamber lengthened, so that its diminution in depth is compen-sated for by the advance of the anterior surface of the lens. The question now arises, in what manner is this change in the form of thelens produced? There can be no doubt now that it is entirely due to theaction of the ciliary muscle. Cramer, Donders, Helmholtz, Miiller, as wellas many other observers, considered that whilst the ciliary muscle played themost important part in the mechanism of the accommodation, it was materi-ally assisted by the iris. Indeed, it was impossible to determine with accu-racy, even after the most careful dissections and most elaborate investigations,the relative amount of importance of the iris and ciliary muscle. Thisquestion has now, however, been definitely set at rest by a case which oc-cur
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