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Congenital Optic Nerve Malformations

Aplasia of the optic nerve is characterized by complete absence of the optic nerve, absence of retinal vessels, and no light perception vision. It was first described in 1854 by von Graefe. Only a few dozen cases have been reported in the literature. Most have been unilateral. Aplasia of the optic nerve is congenital, and its etiology remains poorly understood. There is no known sex or racial predilection. No abnormal karyotypes have been reported. Two patients with aplasia were found to have PAX6 polymorphisms, but no familial cases have been reported. Others have had in utero exposures including acetone, maternal viral infection, and maternal tobacco use. Aplasia of the optic nerve has been induced in experimental animals by treating with hypoglycemic sulfonamides, creating folic acid deficiency, exposing fetuses to x-ray radiation, and treatment with actinomycin D. Some have argued that a local failure of mesoderm leads to a lack of normal vascular development within the optic nerve. Most pathologic specimens lack retinal ganglion cells, but a 3-day-old autopsy in 1 case of bilateral aplasia showed undifferentiated ganglion cells lacking axons and dendrites. Failure of these cells to elaborate axons may be the mechanism of this malformation. Alternatively, nerve fiber misdirection and subsequent atrophy could also lead to this phenotype. Pathologic studies have shown that the neural crest-derived optic nerve sheath tends to be present and connected to the back of these eyes despite the lack of nerve tissue. The retina tends to be dysplastic with rosette formation.