Congenital Stationary Night Blindness

This condition is clinically classified into two subtypes: one with a normal fundus appearance and another with an abnormal fundus.414 Subtypes of CSNB with abnormal fundi include Oguchi disease and fundus albipunctatus. Vision of affected children ranges from 20/20 to 20/200 and does not deteriorate with time. Those with X-linked recessive CSNB have reduced vision with a myopic refractive error and typically show nystagmus. The autosomal recessive or dominant cases generally do not show nystagmus. Typically, the ERG shows a normal a wave and an attenuated b wave under scotopic conditions. The dark adaptation curve is usually 2–3 log units higher than normal. The recognized genetic subtypes of CSNB are detailed in Chap. 8.

Achromatopsia

This is a congenital, nonprogressive defect of the cone photoreceptors. Affected children present with nystagmus, decreased vision, defective or absent color discrimination, photophobia, and paradoxical pupils (initial constriction upon dimming ambient light). The fundus appears normal. Achromatopsia has been subdivided into two categories: complete (autosomal recessive), in which cone function is absent and vision ranges from 20/200 to 20/400, and incomplete

(X-linked), in which residual cone function is present and vision may range from 20/40 to 20/400. The incomplete variety may be further subdivided on the basis of residual sensitivity to one or a combination of red, green, or blue light stimuli. The associated nystagmus in some incomplete cases may improve with time or may disappear altogether. The ERG is characterized by diminished or absent cone response and a normal rod response.

Congenital Optic Nerve Disorders

Some congenital disorders of the optic nerves should be mentioned in the context of infant blindness, although these disorders are discussed at length in other chapters. The most relevant for this discussion is bilateral optic nerve hypoplasia (Chap. 2) and congenital, or early-onset, optic atrophy (Chap. 4). Neuroimaging studies are generally required in patients with optic nerve hypoplasia as a part of both a neuroendocrinologic workup (i.e., the presence of posterior pituitary ectopia on MRI is a useful marker for associated pituitary gland dysfunction) and a neurodevelopmental evaluation (i.e., the presence of hemispheric abnormalities on computed tomography [CT] or MRI scanning is a clinical marker for associated developmental abnormalities).77,78,529 Congenital or early-onset bilateral optic atrophy always warrants neuroimaging to look for supra-sellar tumors (craniopharyngioma, glioma) or hydrocephalus.475