Growth and Development
Chapter 610 Growth and Development
The eye of a normal full-term infant at birth is approximately 65% of adult size. Postnatal growth is maximal during the 1st yr, proceeds at a rapid but decelerating rate until the 3rd yr, and continues at a slower rate thereafter until puberty, after which little change occurs. The anterior structures of the eye are relatively large at birth but thereafter grow proportionately less than the posterior structures. This results in a progressive change in the shape of the globe; it becomes more spherical.
In an infant, the sclera is thin and translucent, with a bluish tinge. The cornea is relatively large in newborns (averaging 10 mm) and attains adult size (nearly 12 mm) by the age of 2 yr or earlier. Its curvature tends to flatten with age, with progressive change in the refractive properties of the eye. A normal cornea is perfectly clear. In infants born prematurely, the cornea may have a transient opalescent haze. The anterior chamber in a newborn appears shallow, and the angle structures, important in the maintenance of normal intraocular pressure, must undergo further differentiation after birth. The iris, typically light blue or gray at birth in white children, undergoes progressive change of color as the pigmentation of the stroma increases in the first 6 months of life. The pupils of a newborn infant tend to be small and are often difficult to dilate. Remnants of the pupillary membrane (anterior vascular capsule) are often evident on ophthalmoscopic examination, appearing as cobweb-like lines crossing the pupillary aperture, especially in preterm infants.
The lens of a newborn infant is more spherical than that of an adult; its greater refractive power helps to compensate for the relative shortness of the young eye. The lens continues to grow throughout life; new fibers added to the periphery continually push older fibers toward the center of the lens. With age, the lens becomes progressively denser and more resistant to change of shape during accommodation.
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