Wednesday, 26 March 2014

Vision impairment and ADHD?

Science often has the ability to surprise.

So it was when I first read the paper by Dawn Decarlo and colleagues* (open-access here) which suggested that: "children with vision impairment may be more likely to be diagnosed with ADHD [attention deficit hyperactivity disorder] than children in the general population". I should point out that this observation should not be totally unexpected given some media for other studies by the authors (see here).
Lady in a green jacket @ Wikipedia  

The Decarlo study was based on a question of "whether the prevalence of parent-reported ADHD diagnosis in a cohort of pediatric low vision subjects was similar to that reported for the general population". It seems researchers were a little bit worried that there may be some mixing up of the signs and symptoms of possible ADHD as a consequence of a child's visual impairment and sought to further look into the issue.

So, bearing in mind the paper is open-access, a few study details:

  • Alabama, USA was the study setting, and the medical records of participants (N=245) with low vision were drawn from two sites. Researchers garnered various details about participants covering basic demographic information and that relevant to vision including "primary ocular diagnosis, presence or absence of nystagmus, and best-corrected visual acuity in each eye". They also asked participants' parents whether or not their child had ever received a diagnosis of ADHD and had state and national ADHD prevalence estimates to hand.
  • Results: the Alabama state ADHD prevalence estimate (based on 2007 data) was 14.3% and the US national prevalence 9.5%. The parent-reported prevalence rate of study children ever having a diagnosis of ADHD was 22.9% (56.245). Examination of an additional cohort of 19 children with almost total vision loss for a diagnosis of ADHD was 10%.
  • Albinism - a condition concerned with the production of melanin - was the most frequently reported eye problem among participants (16%) and similar to the issue of optic nerve hypoplasia (ONH), saw a prevalence of ADHD diagnosis at 20% of these cases. Indeed, ONH has previously been linked with 'behavioural problems' in other research** and indeed, some of the features of autism***.
  • Researchers concluded: "the prevalence of parent-reported ADHD among children with vision impairment in the present study is considerably higher than that reported by the Centers for Disease Control and Prevention".

There is obviously more to do in this area insofar as ascertaining whether these results are more widely applicable to cases of paediatric vision impairment or just a statistical blip. Noting for example, that the State of Alabama has an ADHD prevalence estimate some way above the US national estimate, might imply that ADHD is more generally apparent as a diagnosis there, so children were more likely to receive a diagnosis as a result of better screening facilities for example. Indeed, in my review of some of the [worldwide] prevalence rates of pediatric ADHD rates (see here), the figures coming back were nearer the US national average than the Alabama state estimate although potentially rising.

The lack of an external control group looking both at asymptomatic controls or even those children with something like hearing impairment in the Decarlo study, means that some caution must be exercised before leaning too far into the suggestion of any relationship.

The question of what mechanism might be behind any association is also important. I could suggest that the quite recent report of a link between solar intensity and ADHD (see here) might potentially offer some clues if one is to assume that vision is a common denominator across these areas of research. That being said, it is quite a tentative link and as yet, I can offer no further support for this suggestion.

Perhaps more relevant are the discussions about shared genetic/environmental influences which affect vision and potentially, risk of ADHD, as being linked to any association. Taking you back to the paper by Antoine and colleagues**** which was discussed in another post (see here) on inner ear conditions being linked to hyperactivity, one might assume similar mechanisms to be plausible. That also the paper by Kim and colleagues***** reported issues with vision function and colour vision to be linked with cases of adult ADHD is something else to throw into the mix.

Whatever the reason(s) for such a correlation, I am intrigued by the Decarlo findings and wait attentively for any further movement in this area of investigation.

Music to close, and having recently heard the song Purple Rain on the radio, I have a rekindled respect for Prince...

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* Decarlo DK. et al. Prevalence of attention-deficit/hyperactivity disorder among children with vision impairment. J AAPOS. 2014 Feb;18(1):10-4.

** Teär Fahnehjelm K. et al. Optic nerve hypoplasia in children and adolescents; prevalence, ocular characteristics and behavioural problems. Acta Ophthalmol. 2013 Oct 7.

*** Parr JR. et al. Social communication difficulties and autism spectrum disorder in young children with optic nerve hypoplasia and/or septo-optic dysplasia. Dev Med Child Neurol. 2010 Oct;52(10):917-21.

**** Antione MW. et al. A Causative Link Between Inner Ear Defects and Long-Term Striatal Dysfunction. Science. 2013; 341: 1120-1123.

***** Kim S. et al. Visual function and color vision in adults with Attention-Deficit/Hyperactivity Disorder. J Optom. 2014 Jan-Mar;7(1):22-36.

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ResearchBlogging.org Decarlo DK, Bowman E, Monroe C, Kline R, McGwin G Jr, & Owsley C (2014). Prevalence of attention-deficit/hyperactivity disorder among children with vision impairment. Journal of AAPOS : the official publication of the American Association for Pediatric Ophthalmology and Strabismus / American Association for Pediatric Ophthalmology and Strabismus, 18 (1), 10-4 PMID: 24568975