Children with certain neurodevelopmental disorders show altered ocular movements and a more reduced amplitude of accommodation, however, vision problems are not always present in these children and so cannot be considered an aetiological factor.
Neurodevelopmental disorders (NDD) are characterised by early-onset deficits of variable severity in personal, social, academic or occupational functioning, as defined in the Diagnostic and Statistical Manual of Mental Disorders 5th Edition (DSM-5).1 Developmental deficits may vary from very specific limitations of learning or control of executive functions to global impairments of social skills or intelligence.2
Alterations in ocular movements and a large variety of visual problems have been associated with certain types of NDDs in children, which has lent support to the idea that the NDDs represent an aetiological factor.3-12 Specifically, different types of accommodative, binocular and oculomotor alterations have been reported in dyslexia, attention deficit/hyperactivity disorder (ADHD) and developmental coordination disorder (DCD).
Investigations carried out to date only suggest the potential for visual problems to be a comorbidity in these conditions and so it cannot be concluded that these alterations are causal factors. Indeed, one hypothesis proposes that the concept of dorsal stream vulnerability can be used to explain a cluster of problems that are common to many NDDs, including poor motion sensitivity, visuomotor spatial integration for planning actions, attention and number skills.13,14
To attempt to shed more light on the link between visual problems and NDDs, we recently conducted a clinical study to analyse the distribution of oculomotor and visual alterations, defined according to standard clinical tests in children with dyslexia, ADHD and DCD (three of the more common NDDs that can be examined easily in clinical practice), and to compare the distribution with that obtained in healthy children without ocular pathology but with and without oculomotor anomalies.15,16
A total of 69 children (6 to 13 years old) were evaluated in the prospective, non-randomised comparative study, which was conducted at the Child Development Unit of the Alto Aragon Polyclinic, Huesca, Spain. All children were evaluated by an optometrist, an ophthalmologist, a speech therapist, a psychologist and a neuropaediatrician.
Among children recruited for the study, three groups were clearly differentiated:
A complete visual examination was conducted, including measurement of uncorrected and corrected distance visual acuity; manifest and cycloplegic refraction; cover test; Maddox rod test; measurement of near point of convergence (NPC); distance and near stereopsis; four-dot Worth test; fusional vergence measurement; monocular and binocular accommodative facility; amplitude of accommodation; accommodative response at 40 cm (monocular estimation method); and subjective evaluation of oculomotricity with Northeastern State University College of Optometry’s Oculomotor (NSUCO) and developmental eye movement (DEM) test.
An objective evaluation of oculomotricity was carried out with the Eye Tracker Tobii Eye X (Tobii) and the Clinical Eye Tracker software (Thomson Software Solutions) in a subsample of 15 healthy children and 17 children with NDDs.
Significantly worse near stereopsis was found in children with NDDs compared with healthy children (60.1±71.2” vs 30.7±23.9”, P <0.001) and those with oculomotor abnormalities but without NDDs (60.1±71.2” vs 30.8±18.9”, P = 0.001). Likewise, a significantly lower amplitude of accommodation was found in children with NDDs compared with healthy children in both the right (11.4±2.8 vs. 9.0±2.0 D, P = 0.001) and left eyes (10.1±2.8 vs. 9.2±1.9 D, P <0.001).
No statistically significant differences between groups were found in the measurement of near and distance phoria (P ≥0.557), NPC (P = 0.700) and fusional vergences (P ≥0.059). According to standard criteria, no statistically significant differences were present among groups in the number of cases with binocular or accommodative disorders (P ≥0.471).
The comparison between the three types of neurodevelopmental disorders included revealed the presence of a significantly lower amplitude of accommodation in children with DCD compared with dyslexics. Furthermore, less exophoria at near was present in children with dyslexia compared with children with ADHD (P = 0.018) and DCD (P = 0.054).
Concerning oculomotricity, significantly impaired scores were found with the subjective test (NSUCO and DEM tests) in children with NDDs compared with healthy children (P <0.001), with no significant differences between children with oculomotor abnormalities but without NDD and children with NDDs (P ≥0.063). Regarding eye tracking analyses, we found a significantly higher number of hypometric saccades in children with NDDs compared to healthy children (P ≤0.044).
Likewise, we found a significantly higher percentage of regressions in the group of children with NDDs when a time interval of presentation between stimuli of 1 second was used (P = 0.012). Significant correlations were found between different NSUCO scores and percentage of regressions, number of saccades completed and number of hypometric saccades.
Children with dyslexia, ADHD and DCD show an altered oculomotor pattern and a more reduced amplitude of accommodation, however, this is not always compatible with the diagnostic criteria of an accommodative insufficiency. Accommodative and binocular vision problems are not always present in these children and so cannot be considered an aetiological factor.
Likewise, hypometric saccades and regressions are commonly present in children with NDDs. However, oculomotor anomalies can be present in children with and without NDDs, and therefore they do not seem to be a good diagnostic criterion of these complex types of disorders.
Future research should be focused on the analysis of the impact of oculomotor alterations associated with NDDs and how complementary binocular and accommodative anomalies impact on the child’s development. This is critical since it will help define a standardised scientific-based approach for the management of the visual and oculomotor problems in children with NDDs. This, in turn, will help prevent exposure to pseudotherapies and treatments based on visual approaches that are not useful.