. The hygiene of the schoolroom. When an eye turns in or out or away from its fellow,the danger is that the power of sight will begin to fail inthe eye and will continue to fail. Every case of squintdiscovered, then, should be referred to the eye specialist. In studying the eye as shown in Fig. 12 from the frontto the back, we see the cornea, the aqueous humor, thepupil, the iris, the crystalline lens, the vitreous humor, andthe retina. The cornea, perfectly transparent, is the firststructure through which the light passes. The aqueoushumor fills the space between the back of the cornea andthe
. The hygiene of the schoolroom. When an eye turns in or out or away from its fellow,the danger is that the power of sight will begin to fail inthe eye and will continue to fail. Every case of squintdiscovered, then, should be referred to the eye specialist. In studying the eye as shown in Fig. 12 from the frontto the back, we see the cornea, the aqueous humor, thepupil, the iris, the crystalline lens, the vitreous humor, andthe retina. The cornea, perfectly transparent, is the firststructure through which the light passes. The aqueoushumor fills the space between the back of the cornea andthe lens. The iris divides this space into two chambers,the anterior and the posterior. The colorless, transparent,bi-convex, crystalline lens serves to focus the light enter-ing the eye. The vitreous humor is a soft, jelly-like sub-stance, clear and transparent. The retina is the innermostlining of the eyeball, and is the sensitive area upon whichthe images from external objects are refracted. 72 The Hygiene of the Schoolroom. k A. FIG. 13. SHOWS THE MUSCLES OF THE EYEBALL IN NORMAL POSITION. A, A. The parallel optic axes. C, C. The centres of motion of theglobes. B, B. Axes of rotation of the oblique muscles. D, D. Axesoi rotation of the superior and inferior muscles. n, n. Externalstraight muscles. /, /. Internal straight muscles. &, o. Superioroblique muscles, running through pulleys at D, D. s. Superior straightmuscle of one eye. This muscle is removed in the other eye to showthe optic nerve. »/, ni. Attachments of the inferior oblique muscles,which cannot be seen in this view from above. The space betweenD, D, is the cavity of the nose. If we look at a house a mile distant and then look atone of the fingers placed before the eyes, we find it canonly be done with a distinct sense of muscular effortsomewhere in the eye. This effort, spoken of as accommo-dation, is the same act as is accomplished by the screw in The Hygiene of the Eye. 73
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