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When a pediatrician examines a child, he often shines a white light into the patient's eyes along the pupillary axis and observes the color of the reflected light. Normally, the ingoing beam passes through clear cornea, aqueous, pupillary space, lens, vitreous, and retina to strike the choroid. Because of its high degree of vascularity (the choroid is considered the vasular coat of the eye), the light beam is now reflected as red. This reflected red beam passes, in reverse, the same ocular structures the white beam did to enter the eye. Upon exiting from the cornea, the beam is observed as red. A normal "red reflex" is noted. Such a reflex is comforting, but it by no means guarantees a normal eye examination. Any lesion not directly in the path of the ingoing beam would not influence the "red reflex." Such things as serious hemorrhages, tumors, retinal detachments, toxoplasmosis, and many others might be missed.
Leukokoria Hterally means "white pupil" and is generally interpreted as a "white reflex" from whatever cause. Because it is not normal, a white reflex is viewed in an ominous light. This is often justified, as retinoblastoma is generally held to be one of the five most common causes of leukokoria. Since observation of the pupillary reflex is widely used, a differential diagnosis of the white reflex is important.
Table 1 lists the causes of leukokoria. Cataracts are still the most common cause. What is a cataract? A cataract is literally any opacity of the crystalline lens of the eye. The lens is formed from surface ectoderm cells of the developing fetus. Once these cells invaginate and separate from the surface, a spherical developing lens is present. The posterior fibers elongate and fill the lens. The anterior lens cells continue to divide and elongate on the surface to lay down layer upon layer of fusiform - shaped cells throughout life. Any physical or chemical agent that damages these cells may cause a cataract to develop. This varies from a contusion injury to radiation and from chemicals and medicines to infectious and inherited causes.1 LeFe vre and Merlen estimate an observed incidence of 0.04 per cent of cataracts noticed on casual inspection at birth.2 An incidence of 11 cataracts in 2,500 live...