Vitamin A Deficiency (Xerophthalmia)
A recent analysis of data indicates that vitamin A deficiency is the leading cause of childhood blindness. It was estimated that 70% of the 500,000 children who become blind annually do so because of xerophthalmia. This corresponds to a prevalence of roughly 1 million in view of the high mortality among affected children. (Thylefors, et al., 1995).
Causes of Childhood Blindness: U.S Only
Amblyopia and Strabismus
It is estimated that between 1 and 4% of the childhood population is affected by strabismus, and 1 to 2% suffer from amblyopia (National Eye Institute, 1993).
Among children under 5 years of age, prenatal cataract is the leading cause of legal blindness, accounting for 16% of all cases (National Society to Prevent Blindness, 1980). However, in the developed world, congenital cataract, when appropriately managed, is the only cause of visual impairment to have recently shown a decrease in prevalence (Taylor, 1994).
Cortical Visual Impairment (CVI)
Cortical visual impairment is defined as a temporary or permanent visual loss caused by disturbances of the posterior visual pathways and/or occipital lobes. The vast majority of children with CVI have residual vision (Jan & Wong, 1991).
In developed countries, CVI has become more frequent (Johnson-Kuhn, 1995) and can be considered one of the major causes of visual handicap in children of developed regions (Good, et al., 1994).
Infantile glaucoma occurs in 1 out of 10,000 live births (Teplin, 1995).
Optic Nerve Atrophy
Optic nerve atrophy accounts for 12% of all cases of legal blindness in children (National Society to Prevent Blindness, 1980).
Retinopathy of Prematurity (ROP)
Retinopathy of prematurity (ROP) is characterized by the abnormal growth of blood vessels in the retina of premature infants. Infants in whom ROP is diagnosed during the perinatal period are at risk for ocular abnormalities and for deficits in visual function.
The following data are from The Multicenter Cryotherapy for Retinopathy of Prematurity (CRYO-ROP) study reported according to international classification based on the severity of ROP. The data were collected from 4,099 infants born between January 1986 and November 1987 with birth weights of less than 1251 grams.
Of 4,099 infants in the CRYO-ROP study:
2,699 (65.8%) developed some degree of ROP, with no effect
on visual acuity.
730 (17.8%) were classified as prethreshold, with little effect on visual acuity. 246 (6%) were classified as threshold in one or both eyes. Within this group of 246 infants, 123 (50%) were blind and 123 (50%) had visual acuity that was significantly below normal. For the group of 123 infants with visual acuity significantly below normal, cryotherapy improved 49 (40%) of the cases. For each 100-gram decrease in birth weight, there was a 27% higher risk that an infant would develop threshold ROP (Dobson & Quinn, 1996).
According to "Registry of Early Childhood Visual Impairments in Central and Northern California," a report by The Blind Babies Foundation, of 971 children born with visual impairments in the years 1980 to 1995, 572 (59%) have multiple impairments (Johnson-Kuhn, 1995).
According to the preliminary report Educational Outcomes for Colorado Students with Visual Disabilities, based on 98 randomly selected students with visual impairments (from those registered with the Colorado Instructional Materials Center as receiving vision or orientation and mobility services), 43 (43.9%) were identified with a primary disability of multiply handicapped (Ferrell & Suvak, 1993).
The PRISM Project: A National Longitudinal Study of Developmental Patterns of Children Who Are Visually Impaired, conducted by the University of Northern Colorado, reported that at the end of the 5 year study, 59.9% of PRISM subjects (birth to five years) had been diagnosed with additional disabilities. Over one-third of the children with additional disabilities had conditions considered to be mild, while two-thirds were considered to be severe (Ferrell, Shaw, & Dietz, 1998). (See Appendix C for discussion on this data.)
The Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP) was established by the Center for Disease Control in 1991 to monitor the occurrence of selected developmental disabilities including visual impairment. The Metropolitan Atlanta Developmental Disabilities Study is the first U.S., population-based epidemiological study of the prevalence of mental retardation, cerebral palsy, hearing impairment, and visual impairment among school-age children (Yeargin-Allsop, Murphy, Oakley, Sikes, & Metropolitan Atlanta Developmental Disabilities Study Staff, 1992). Data from this study were used to describe the underlying causes of visual impairment (visual acuity in the better eye of 20/70 or worse) in children 3 to 10 years old in metropolitan Atlanta in 1991-1993. The review of multiple educational and medical sources revealed 228 children that fit the MADDSP definition. The 228 children were categorized as having isolated visual impairment or multiple disabilities (mental retardation, cerebral palsy, hearing impairments, epilepsy). Causes were assigned to one of three developmental time periods: prenatal (before the onset of labor), perinatal (labor to first month), or postnatal (after one month) or unknown timing.
Of the 228 children who met the MADDSP definition of visual impairment:
74 (32%) had isolated visual impairment, and 154 (68%) had multiple developmental disabilities.
Of the 185 for whom severity of visual impairment could be determined:
120 (65%) had low vision (visual acuity of 20/70 -20/400), and 65 (35%) were blind (visual acuity worse than 20/400).
Prenatal conditions were the most commonly identified etiologies in both children with isolated visual impairment and those with multiple disabilities. Prenatal conditions occurred twice as often in those with isolated visual impairment (62% vs. 34%). Albinism was the single most common prenatal condition among children with isolated visual impairment.
Perinatal etiologies were found nearly twice as often in multiple disabilities group as in the isolated visual impairment group (32% vs. 18%). Retinopathy of Prematurity (ROP) was the single most common perinatal etiology for both groups of children. The only perinatal etiology found in the isolated visual impairment group was ROP.
Postnatal etiologies were nearly four times as prevalent among children with multiple disabilities as among children with isolated visual impairments (10% vs. 3%). In addition, etiologies that occurred later in a childs development tended to be associated with more severe visual impairment.
(Mervis, Yeargin-Allsopp, Winter, & Boyle, 2000).
Low Birth Weight: U.S. Only
Blindness occurs mainly among children with birth weights below 1,000 grams (2 lbs. 3 oz) at rates of 5 to 6% (Hack, Klein, & Taylor, 1995).
Cerebral palsy, hydrocephalus, microcephaly, blindness, deafness, and seizure disorders each occur at the following rates:
20% of infants with birth weight below 1,000 grams.
14 to 17% of infants with birth weight of 1,000 to 1,500 grams.
6 to 8% of infants with birth weight of 1,500 to 2,499 grams (Hack, et al., 1995).
The following estimates are based on data collected for children from birth to 36 months of age, from the PRISM Project Registry of Early Childhood Visual Impairment Collaborative Group (PRISM Project Newsletter, 1996). It should be noted that these figures include only those individuals registered with this project.
The following presents the most frequently reported visual impairments among PRISM children (N=165):
Optic nerve hypoplasia
Cortical visual impairment
Leber's Congenital Amaurosis
Bilateral detached retina glaucoma
Cytomegalo virus (CMV)
Septic optic hypoplasia