MYOPES. Those, who by a natural defect have the cornea and crystalline !'ntnour too convex, are called rnyopes. 'I his figure, which increases the quantity of refraction, tends to render the rays of such pencils as are formed in the eye more convergent, so that the point where these same rays meet is on this side of the retina. Myopes see distinctly those objects only which are near, which send towards the eye rays more divergent, and thereby less disposed to converge, through the effect of refraction in the crystalline and other humours. This im perfection, being the reverse of that which affects the eye of presbyta, is re medied by the use of a glass slightly con cave; which, increasing the divergence of the rays received by the eye, prolongs the pencils that are formed in the organ, and causes their summits to fall more ex actly on the retina. Myopes seem to have a fondness for minute objects: in general they write a very fine hand, and read in preference works that are printed in a small type, because, by choosing dimen sions suited to the narrow scope of their sight, they continue to embrace a greater number of objects at once. They have
the habit also of closing, in a certain de gree, the eyelids, when they wish to see objects distinctly that are otherwise dis tant from them. Two advantages have been ascribed to this natural motion. On the one hand, by contracting the lid, as is given to a smaller portion of light. Now those who are myopes see objects that are situated at a distance indistinctly, merely because the cones that are form ed in the eye, aswe have observed in the preceding paragraph, have their summit on this side the retina ; so that the pro longations of the rays, of which these cones are the assemblage, give rise to new cones, whose base meeting the bottom of the eye, depicts a small circle there, instead of a simple point. Accord ingly, when the number of rays introduc ed into the eye is diminished, that small circle is contracted, and the vision becomes less confused. On the other hand, the eye-lids, by closing, exert a pressure on the organ, that diminishes its convexity, and in part restores it to the form most favourable to clearness of vision.