Optic nerve abnormalities are frequent causes of pregeniculate visual impairment (see also Chapter 26). The most common of these is optic nerve hypoplasia, which may be associated with central nervous system anomalies such as septo-optic dysplasia and schizencephaly. Other optic nerve disorders are optic atrophy, morning glory disc anomaly, optic disc coloboma, and staphyloma. Causes of optic nerve atrophy include hydrocephalus, brain tumors, trauma, hypoxic–ischemic injury, metabolic storage diseases, and inherited optic neuropathies such as Behr optic atrophy.
Inherited retinal disorders are also common causes of pregeniculate visual impairment and should be considered in infants with poor vision, nystagmus, and no obvious abnormality on ophthalmic examination. Inherited retinal diseases include Leber congenital amaurosis, achromatopsia, blue-cone monochromatism, and congenital stationary night blindness (see Chapter 25). Fundus examination in an infant with a retinal dystrophy is often normal because the associated retinal pigmentary changes may not appear until later. Subtle retinal vessel attenuation and optic disc pallor may be present. Electroretinography (ERG) can aid in the diagnosis of these disorders. Foveal hypoplasia can also cause pregeniculate visual impairment. It can be isolated but is more commonly associated with albinism and aniridia.
Retrogeniculate Visual Impairment, or Cerebral Visual Impairment
Cerebral visual impairment (CVI; also termed retrogeniculate visual impairment) is the most frequent cause of childhood visual impairment in developed countries. It denotes visual deficits resulting from pathology posterior to the lateral geniculate nucleus (the retrogeniculate visual pathways). CVI is also often referred to as cortical visual impairment, but the former term is preferred because subcortical visual impairment causes vision problems that are difficult to differentiate from those due to cortical visual impairment. The pathology may involve the optic radiations as well as the occipital cortex. Depending on the etiology, the visual impairment can be transient or permanent and can be an isolated finding or associated with multiple neurologic deficits.
The causes of CVI can be congenital or acquired. Prenatal and perinatal causes include periventricular leukomalacia (a prominent cause of visual impairment in premature children), intrauterine infection, hypoxia, intracranial hemorrhage, structural central nervous system abnormalities, seizures, and hydrocephalus. Acquired causes include accidental trauma, abusive head trauma, meningitis, and encephalitis.
Infants with CVI show varying degrees of visual inattentiveness. Both the family and the ophthalmologist may be uncertain as to whether the baby can see. Examination reveals normal ocular structures, normal pupillary responses, and variable levels of visual fixation, from mildly decreased to roving eye movements. Nystagmus is typically not present. Descending optic atrophy (from transsynaptic degeneration) may coexist. In preterm infants, optic disc cupping resembling that seen in glaucoma can occur as a result of transsynaptic degeneration, most commonly secondary to periventricular leukomalacia.
ERG results are normal. VEP results may be normal or subnormal. Neuroimaging studies may be normal or may reveal changes such as cerebral atrophy, porencephaly in the occipital (striate or parastriate) cortex, damage to the optic radiations, or periventricular leukomalacia. Children with normal neuroimaging studies tend to have a more favorable prognosis.
Khetpal V, Donahue SP. Cortical visual impairment: etiology, associated findings and prognosis in a tertiary care setting. J AAPOS. 2007;11(3):235–239.
Pediatric Low Vision Rehabilitation
Vision rehabilitation should be recommended when a child has a visual impairment that affects his or her ability to perform visual tasks (as occurs with best-corrected visual acuity worse than 20/40 in the better-seeing eye, decreased visual field, central field loss, or reduced contrast sensitivity). At the time of diagnosis and throughout the subsequent years, the ophthalmologist plays an important role in recommending that children with low vision receive comprehensive vision rehabilitation. Early referral is essential for setting the family and child on a course to achieve optimal visual performance and to make a successful adjustment to vision loss.
Vision rehabilitation for children often involves pediatric ophthalmologists, vision rehabilitation clinicians, occupational therapists, teachers, orientation and mobility specialists, technology experts, state societies, and other professionals and organizations. An Individualized Education Plan (IEP) outlines the needs of an individual child in the school setting. The child’s needs in the home and in other nonacademic settings must be considered as well. A variety of aids are available to assist patients with low vision, ranging from simple telescopes to Braille literacy. Because most children have large accommodative amplitudes that allow them to hold an object closer than normal to enlarge its image, magnifiers may not be necessary for pediatric patients with low vision. Existing and future technologies, including e-readers, audio books, and text-to-speech technology, offer continually expanding opportunities for these children.
The American Academy of Ophthalmology’s Preferred Practice Pattern on vision rehabilitation (see references) outlines the rehabilitation process for preschool-aged children to young adults. The availability of rehabilitation resources varies across communities, but the following online resource, which can be searched by location, may be helpful for clinicians and families in identifying such services in their community: http://www.afb.org/directory.aspx. Other useful information can be found in the SmartSight Patient Handout (one.aao.org/smart-sight-low-vision), available on the Academy’s website. See also Table 16-1, which lists resources for further information, and BCSC Section 3, Clinical Optics, for detailed discussion of low vision aids.
Table 16-1
American Academy of Ophthalmology Vision Rehabilitation Committee. Preferred Practice Pattern Guidelines. Vision Rehabilitation. San Francisco: American Academy of Ophthalmology; 2013. Available at: www.aao.org/ppp.
Markowitz SN. Principles of modern low vision rehabilitation. Can J Ophthalmol. 2006;41(3):289–312.