Visual Disability: Developmental and Behavioral Consequences
Michael E. Msall
I. Description of the problem. Legal blindness is defined as central visual acuity in the best eye with corrective lenses of 20/200 or worse, or a restriction in the visual field so that the widest diameter of vision subtends an angle of 20 degrees. The term legal blindness is a misnomer as approximately 75% of individuals with legal blindness have some residual visual function. In addition, the majority of adults with legal blindness can read large print. For children with vision worse than 20/400, ophthalmologists use functional descriptors such as child’s ability to count fingers or detect hand motion, nearby large objects, the direction of a light source or its presence. Students can be classified as educationally visually impaired if their corrected vision is 20/70 or worse. The World Health Organization (WHO) classifies visual disability into five categories described in Table 87-1.
A. Epidemiology. The epidemiology of severe visual impairment is changing. Both laser surgery for severe threshold retinopathy of prematurity and advances in the prevention of congenital rubella, measles, Hemophilus influenza, pneumococcal, and group B β-streptococcal meningitis have substantially decreased their contributions to visual and multiple disabilities. Current estimates of the prevalence of childhood blindness are 6 per 1,000. Congenital blindness occurs with a frequency of 30 per 100,000. In developing countries, the major contributors to visual disability include gonoccocal ophthalmia neonatorum, trachoma, vitamin A deficiency, and measles. Worldwide, there are 1.5 million children who are legally blind. The United States does not keep a registry for children with severe visual disability, but 50,000 children are considered visually impaired by school systems of which 20,000 require Braille as a reading medium. Children with combined deafness and blindness number 500 per year and include 10,000 children from birth to age 21 years.
B. Etiology. Table 87-2 describes the major known etiologies of severe visual impairment in childhood. The timing of these etiologies is prenatal in 43%, perinatal in 27%, postnatal in 8%, and unknown in 22%. Several multiple malformation syndromes involve visual impairment and include chromosomopathies, CHARGE association (coloboma, heart disease, choanal atresia, intellectual disability, growth and genital anomalies, ear anomalies), Lowe syndrome (intellectual disability, cataracts, renal tubular dysfunction), neurocutaneous disorders (tuberous sclerosis, optic gliomas in Neurofibromatosis-1), metabolic (homocystinuria) and neurodegenerative disorders (leukodystrophies and optic atrophy, gangliosidosis and cherry red macula, Batten’s disease).
1. Many syndromes affect both vision and hearing. These include Alport’s, Usher’s, Cockayne’s, Stickler’s, and Refsun’s syndromes as well as congenital infections, lysosomal storage disease, and leukodystrophies.
2. Postnatal causes of blindness account for 8% to 11% of all childhood blindness. Etiologies include infections, trauma, complicated hydrocephalus, retinoblastoma, craniopharyngioma, demyelinating diseases, and leukemia with CNS (central nervous system) involvement.
3. Blindness and associated developmental disabilities. It is important to recognize that in more than 50% of children with visual disability, there are additional major disorders including cerebral palsy, cognitive-adaptive developmental disability, autistic spectrum disorders, recurrent seizures, hearing impairments, and learning disabilities. Among children with visual disability in a comprehensive community registry, 65% had additional disabilities. Of the children with multiple disabilities, cortical visual impairment (CVI) occurred in 50%.
C. Developmental aspects of vision. Pupillary light reactions and lid closure to bright light are present at 30 weeks gestation. Brief visual fixation is present at birth including brief saccades to a moving person, moving face, and dangling ring. At birth, acuity has been assessed as approximately 20/400 by optokinetic nystagmus (OKN), forced preferential looking (FPL), and visual evoked potentials (VEP). By three weeks, watching a mother speak occurs. The presence of strabismus is easily identified by an off-center asymmetry of
reflected light, the Hirshperg reflex. Eyes that do not see well tend to deviate or drift, and this along with nystagmus may be the first indication of poor vision. Pupillary responses, an intact red reflex, and the ability of a child to track 360 degrees are indicators of globally adequate vision. Developmental consequences of these core visual skills impact on motor, manipulative, communicative, social and adaptive skills and are shown in Table 87-3.
Table 87-1. WHO classification of visual disability
Category 1
Impaired
20/60 to 20/200
Category 2
Severe impairment
20/200 to 20/400
Category 3
Blind
20/400 to 20/2,400
Category 4
Blind
<20/2,400 and light perception
Category 5
Blind
No light perception.
II. Making the diagnosis.
A. Clinical Presentation. Infants with visual disability present in one of three clinical scenarios.
1. In the first scenario, parents are concerned that their child is not seeing. At 6 to 10 weeks, the child is not smiling reciprocally and does not follow faces or rings but does have a normal papillary response, red reflex, and intact globe. These children either have cortical visual impairment (CVI), delayed visual maturation (DVM), or evolving developmental disability. Both CVI and DVM have high rates of motor, cognitive, and communicative disability. However, in DVM, functional visual recovery occurs, while in CVI, some visual improvement may occur but low vision is a common sequelae. In children with severe evolving developmental disability, the children stare and are inattentive because of disorders of nonvisual higher cortical function impacting on learning, perception, communicating, and social skills.
2. In the second scenario, children present in infancy with nystagmus, sluggish pupils, and visual inattention. Ophthalmological findings reveal anterior segment or optic nerve disorders such as cataract, corneal opacities, glaucoma, and microphthalmia. The posterior segment abnormalities include colobomas of the optic nerve or retina, optic nerve hypoplasia or atrophy, retinal dystrophy, retinopathy of prematurity, or retinoblastoma.
3. In the third scenario, infants show visual inattention, nystagmus, and variable pupillary responses. Ophthalmological evaluation reveals a normal globe and intact red reflex. Strabismus may be present. Electoretinogram (ERG) testing is most helpful in revealing the nature of these disorders. The most common is Leber’s congenital amaurosis, a recessively inherited retinal dystrophy with an extinguished ERG. This disorder currently accounts for 10% of childhood blindness with a range of visual function from legal blindness to no light perception. Associated findings may include renal and skeletal anomalies and cataracts, strabismus, and keratoconus. Additional differential diagnoses in this scenario are rod monochromatism, an autosomal recessive disorder with missing cone photoreceptors, congenital stationery night blindness, and retinitis pigmentosa.
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