WHAT HOLDS AND SURROUNDS
THE LENS
The lens is slung in a ligament that is a part of the “ciliary body,” which is a continuation of the choroid coat of the eyeball. This ciliary body is a ring of tissue lying behind the iris connected with the anterior portion of the choroid coat of the eye.
Between the iris and the underlying lens on the one hand and the inner surface of the bulging cornea on the other is a small space or cavity filled with a clear transparent fluid called the aqueous humor.
THE COATS OF
THE EYE
Looking at the white of the eye, the first coat is the transparent conjunctiva, which is reflected back on to the eyeball from the eyelids. Next comes the sclerotic coat, formed of dense whitish tissue, which seen through the transparent conjunctiva makes up the “white of the eye.” The sclerotic coat covers the whole globe of the eyeball with the exception of the transparent bulging cornea in front (which, however, is practically a continuation of the sclerotic), and the back of the eye where the optic nerve enters. The sclerotic is the thickest and densest coat of the eye.
Within the sclerotic coat, and so to speak lining it, comes the choroid coat. Countless blood vessels run through this coat, supplying both the one above it and that beneath it. As this coat approaches the front of the eye under the circumference of the cornea, it thickens into the ciliary body, forming a dense ring of tissues underneath the junction of the cornea and the sclerotic coat.
THE WORK OF THE
RETINA
The innermost coat of the eye is called the retina. This coat contains the nerve endings of the optic nerve which, coming through the opening in the bony orbit, passes through the sclerotic and choroid coats. After entering the eye, the optic nerve divides into myriads of fibers, which, spreading from the point of entrance at the back of the eye, form a fibrous network all over its inner surface. In addition to this network of nerve fibers and highly specialized nerve cells, tiny blood vessels entering with the optic nerve branch out on all sides over the retina.
THE RODS AND
CONES
The retina is a comparatively thick membrane composed of eight layers of different kinds of nervous tissue. The essential layer, that of the “rods and cones,” is the seventh from within outward. Thus a ray of light on entering the eye must pass through six superficial layers before it reaches the “rods and cones.”