Accommodation

(ak-om-o-da'-shun). Adaptation or adjustment. Adaptation of the fetus to the uterus and birth -canal. A., Absolute, the of either eve ratcly. A., Anomalies of, depart the normal in the action of the mechanism of accommodation. A., Histological, the occurrence o I changes in the morphology and function of cells following changed conditions. A., Negative, the eye pa ive or at rest. A. of the Eye, that function of the ciliary muscle and lens whereby objects at different distances are clearly seen. It depends upon the inherent elasticity of the lens, which when the ciliary muscle of an emmetropic eye is at rest is adapted to the proper focalization of parallel rays of light, or of such rays as proceed from an infinite distance, or from the horizon of the observer. Objects nearer, to be clearly seen, require a greater refracting power on the part of the eye because the rays from such objects are more divergent. This additional refracting power is gained by an increased antero-posterior diameter of the lens, L, (illustration annexed) brought about by the contraction of the ciliary muscle, M, which occasions a loosening of the suspensory ligament and a thickening of the lens by its own elasticity. A., Paralysis of, paralysis of the ciliary muscle. A., Phosphenes, the peripheral light streak seen in the dark after the act of accommodation. A., Range of, the distance between the Punctum proxinmm, or nearest of distinct vision, and the Punctum remoti imum, or the most distant point. A. Theory, a theory that ascribes the production of myopia to a distention of the posterior portion of the sclera from the increased intra-ocular pre ure dependent upon frequently repeated accommodation of the eyes.