Learning disabilities and visual difficulties

Children and young people with learning disabilities often have co-existing impairments, such as hearing or visual impairment, which impact on communication skills (Cockerill 2002).

Studies carried out in Denmark concluded that the prevalence of visual impairment, refractive errors and strabismus among children with

Nielsen, Skov et al. 2007b). The terms developmental delay (DD) or intellectual disability (ID) are synonymous with learning disability.

In one of the Danish studies, 923 children, aged 4 to 15, all with IQs equal to or less than 80, underwent an eye examination (Nielsen, Skov et al. 2007a). The results of the study included:

 10.5% (n=97) of the 923 children had visual impairment.

 The children with visual impairment were predominantly among the children with low IQ; 22.4% of children with IQ less than 50 had visual impairment.

 Most commonly, visual impairment among the 97 children with visual impairment was due to prenatal causes (55.7%, n=54) such as genetic or chromosomal.

 Overall, the main cause of visual impairment among the 97 children were sequelae to brain disorders (64.9%, n=63), comprising cerebral visual impairment (49.5%, n=48), secondary optic atrophy (13.4%, n=13) and hemianopia (2.1%, n=2).

 Congenital cataracts caused visual impairment in 7 (7.2%) of the 97 children.

 Overall, the prevalence of blindness was 3.8%.

 Children with developmental delay had a highly increased risk of visual impairment.

Nielson, Skov and Jensen also examined refractive errors, strabismus and contrast sensitivity among the same population (Nielsen, Skov et al. 2007b):

 53.0% (n=470) of the children had hyperopia greater than +1D in the right eye.

 15.3% (n=136) of the children had hyperopia equal to or greater than +3D in the right eye.

 10.8% (n=96) of the children had myopia equal to or less than -0.5D.  1.8% (n=16) of the children had excessive myopia equal to or less

than - 6.0D.

 Astigmatism was more frequent and more pronounced in children with low IQ.

 26.8% (n=244) of the children had manifest strabismus (squint).

 The prevalence of strabismus was highest among children with low IQ.  Contrast sensitivity was evaluated in 40.0% (n=365) of the children.

Reduced contrast sensitivity was associated with low IQ and low visual acuity.

Similar results have been found in other studies. For example:

a) Another study carried out in Denmark (Nielsen, Jensen et al. 2008), involving 719 children aged 4 to 15, found that visual impairment was diagnosed in

12.9% of the children, significant refractive errors in 44.8% and strabismus in 31.1%. The study also found that if a child has cerebral dysfunctions or a known genetic syndrome, the risk of ophthalmic disorders increased significantly. In addition, the study proposed that children suspected of having developmental delay should be referred (early) for an ophthalmological examination.

b) An usually high prevalence of severe visual impairment (25%), refractive errors (24%) and squint (8%) were found among 260 residents in a specialist unit (Kwok, Ho et al. 1996).

c) A study involving 73 children, aged 5 to 19, showed that ophthalmologic abnormalities were present in 60.2%. The most common disorder was optic atrophy (16.4%) followed by refractive errors (15%). The results of visual acuity testing of 60 children showed that 25 (41.6%) had visual impairment (Mwanza, Nkidiaka et al. 2000).

d) Another study in Denmark, involving 7722 children aged under 21 years, with IQ equal to or less than 70, found that 3.9% (300) were blind (acuity equal to or less than 6/60), compared with the prevalence among all Danish children of 0.0019% (Warburg 1979).

The prevalence of visual impairment, refractive errors and ocular disorders among children with learning disabilities are higher than among children without learning disabilities. The American Academy of Neurology recognises this and

1. Children with global developmental delay may undergo appropriate vision and audiometric assessment at the time of their diagnoses.

2. Vision assessment can include vision screening and a full ophthalmologic examination (visual acuity, extra-ocolor-movements, funduscopic).

(Shevell, Ashwal et al. 2003)

In addition to studies involving children and young people, studies with adult cohorts have shown that visual impairment is more prevalent among individuals with learning disabilities than among those without (Kiani and Miller 2010).

One study found that 92% of adults (n=76) with severe and profound multiple disabilities (SPMD) had a visual impairment (van den Broek, Janssen et al. 2006). Prior to the study, only 30% were known to have visual problems. None of the participants had 'normal' acuity and the severity of visual impairment correlated positively with the severity of the learning disability. Impaired visual fields, contrast sensitivity and binocular functioning were also found among the study cohort.

A literature review was carried out by Warburg to compare the results of studies of the prevalence of visual impairment among individuals with intellectual

disabilities (Warburg 2001). One study, presented in the literature review, found the prevalence of visual impairment to be 40% (Sacks, Goren et al. 1991). Another study found a prevalence of 28% (Haire, Vernon et al. 1991). Every study described a high prevalence of visual impairment among individuals with learning disability. In addition, the studies showed that the severity of visual impairment increased significantly with the severity of the intellectual disability and with age.

In another study, involving 1358 individuals, the prevalence of visual impairment ranged from 2.2% (young people with mild learning disability due to causes other than Down's Syndrome) to 66.7% (people aged 50 or over with Down's Syndrome and profound intellectual disabilities) (van Splunder, Stilma et al. 2006).

In a study of 269 individuals (aged 17-79) with intellectual disabilities, 107 (52%) were found to be visually impaired or blind, based on WHO definitions (Evenhuis, Sjoukes et al. 2009).

A study of 166 individuals (aged 9 to 50) found that refractive error was the principle ocular diagnosis (33.8%). Strabismus was found in 31 of the 166 individuals (18.7%) (Karadag, Yagci et al. 2007).

As the prevalence rates of visual impairment, refractive errors and ocular

disorders are high among adults with learning disabilities, it has been proposed that adults with severe or profound learning disabilities should be considered visually impaired until proven otherwise (van Splunder, Stilma et al. 2006).