1.3 Anatomy

uveal tissue through translucent sclera. With age, translucency decreases and rigidity increases [13]. This age-related change in rigidity explains the observation that infantile or childhood glaucoma can lead to buphthalmos while this does not occur in adults.

In elderly individuals, scleral distensibility decreases, making stretching secondary to glaucoma very unlikely. However, ectasias (localized protrusions of thin sclera) or staphylomas (localized protrusions lined by uveal tissue) may appear in areas, where injury or inßammation has caused scleral thinning. Other age-related changes are a decrease in water content, a decrease in the amount of proteoglycans, and the subconjunctival deposition of lipids. The lipids, composed of cholesterol esters, free fatty acids, triglycerides, and sphingomyelin, give the sclera a yellowish color. Cholesterol esters and sphingomyelin show the greatest increase in volume with age [14, 15]. Calcium phosphate is deposited in small rectangular areas just anterior to the insertions of medial and lateral rectus muscles. These areas, about 1 mm wide and 6 mm high, may become translucent, revealing the bluish or brownish color due to the underlying uvea; they are called senile

scleral plaques and usually occur in individuals over 70 years of age [16].

1.3Anatomy

1.3.1Gross and Microscopic Anatomy

The scleral shell forms part of a circle averaging 22 mm in diameter [13]. Scleral thickness varies from 0.3 mm immediately behind the insertion of the rectus muscles to 1.0 mm near the optic nerve. It measures 0.4Ð0.5 mm at the equator, 0.6 mm where the tendons of the rectus muscles attach, and 0.8 mm adjacent to the limbus [17]. Traumatic scleral rupture usually occurs at the insertion of rectus muscles, at the equator, or in an area parallel to the limbus opposite from the site of the impact.

The outer surface of the sclera is smooth, except where the tendons of the extraocular muscles insert. The insertions of the rectus muscles are progressively more posterior, following a pattern described by Tillaux and hence called the spiral of Tillaux (Fig. 1.7). The medial rectus inserts 5.5 mm posterior to the limbus, the inferior rectus 6.5 mm, the lateral rectus 6.9 mm, and