44 COMPLICATIONS IN MYOPIA.
therefore often read fine print easily, although for distance and with concave glasses a diminution of normal vision to one-half or one-third is already evident.
This form of amblyopia is to be distinguished from a diminu- tion of vision which, in high degrees of myopia, often occurs as one of the symptoms of a retinal irritation. The stretching which the retina and other membranes suifer in the myopic eye is prob- ably the cause of this irritation. Aside from the diminution of vision in such cases, there are speedy fatigue in Avorking and a feel- ing of fulness and tension in the eye; often too the eye is sensitive upon light pressure ; besides this there is dazzling, subjective per- ception of light and troublesome myodesopia. The latter is often the principal inconvenience which myopes complain of; the mate- rial cause of this is always small elements in the vitreous, which are also present and visible in perfectly normal eyes. In eyes not myopic these "mouches volantes" are principally noticed when there are upon the retina no distinct images other than those cast by these elements of the vitreous, — that is, when the gaze is directed upon a uniform surface. Hence myopes not unfrequently find relief from this inconvenience in the use of concave glasses, which do away with the uniform indistinctness of their retinal images.
On the other hand, it is probable that in many cases of myopia the myodesopia is actually caused by microscopic opacities in the vitreous, since a cloudiness often develops there which is ophthal- moscopically visible. The presence of such opacities is the rule with those wide-spread choroidal changes which accompany high degrees of myopia in the latter half of life., The vitreous appears fluid and presents under the microscope small opacities, which, without possessing any determinate structure, present a fibrous, granular appearance. These are either fixed by threads which run off and end in the sound vitreous tissue, and in this case are sit- uated generally not far from the disc, or they are freely movable in the fluid substance, and swim about here and there with every movement of the head. Under these circumstances there is often also a circumscribed cloudiness at the posterior pole of the lens (cataracta polaris posterior).
In high degrees of myopia, especially in advanced age, other changes of undoubted inflammatory nature are added to the consec- utive choroidal atrophy ; they are principally in the region of the
