The eye is the primary organ of vision. Each one of the two eyeballs is located in the orbit, where it takes up about one-fifth of the orbital volume (Figure 2.1). The remaining space is taken up by the extraocular muscles, fascia, fat, blood vessels, nerves and the lacrimal gland.
The eye is embryologically an extension of the central nervous system. It shares many common anatomical and physiological properties with the brain. Both are protected by bony walls, have firm fibrous coverings and a dual blood supply to the essential nervous layer in the retina. The eye and brain have internal cavities perfused by fluids of like composition and under equivalent pressures. As the retina and optic nerve are outgrowths from the brain, it is not surprising that similar disease processes affect the eye and central nervous system. The physician should constantly remind himself or herself of the many disease conditions that can simultaneously involve the eye and the central nervous system.
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