Dr Carmen Bilbao

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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).

 Developmental deficits may vary from very specific limitations of learning or control of executive functions to global impairments of social skills or intelligence.

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.

 Specifically, different types of accommodative, binocular and oculomotor alterations have been reported in dyslexia, attention deficit/hyperactivity disorder (ADHD) and developmental coordination disorder (DCD).

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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.

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.

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.

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Among children recruited for the study, three groups were clearly differentiated:

Healthy children with oculomotor abnormalities; and

Children diagnosed with an NDD. No comorbidity of NDD was present in any case.

Characteristics of each group of children enrolled in the study.

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”, 

 <0.001) and those with oculomotor abnormalities but without NDDs (60.1±71.2” vs 30.8±18.9”, 

= 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, 

= 0.001) and left eyes (10.1±2.8 vs. 9.2±1.9 D, 

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No statistically significant differences between groups were found in the measurement of near and distance phoria (

 ≥0.059). According to standard criteria, no statistically significant differences were present among groups in the number of cases with binocular or accommodative disorders (

Distribution of binocular and accommodative problems detected in the three groups of children evaluated. 

(Figure courtesy of Dr Carmen Bilbao and Dr David P. Piñero)

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 (

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Concerning oculomotricity, significantly impaired scores were found with the subjective test (NSUCO and DEM tests) in children with NDDs compared with healthy children (

<0.001), with no significant differences between children with oculomotor abnormalities but without NDD and children with NDDs (

 ≥0.063). Regarding eye tracking analyses, we found a significantly higher number of hypometric saccades in children with NDDs compared to healthy children (

Eye tracking registry of saccades in a child with dyslexia from our sample in which the presence of hypometric saccades and regressions can be clearly distinguished. 

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 (

= 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.

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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.

Mrs Bilbao is based at the Department of Optometry, Policlínica Alto Aragón, Huesca, Spain.

Dr Piñero (*corresponding author) is part of the Group of Optics and Visual Perception, Department of Optics, Pharmacology and Anatomy, University of Alicante, Spain, and is based at theDepartment of Ophtalmology, Vithas Medimar International Hospital, Alicante.

The authors declare no conflict of interest.

1. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-5), 5th ed.; American Psychiatric Association: Washington, DC, USA, 2013.

2. Posar A, Visconti P. Neurodevelopmental disorders between past and future. 

3. Bilbao C, Piñero DP. Diagnosis of oculomotor anomalies in children with learning disorders. 

4. Bilbao C, Piñero DP. Clinical characterization of oculomotricity in children with and without specific learning disorders. 

5. Molina R, Redondo B, Vera J, García JA, Muñoz-Hoyos A, Jiménez R. Children with attention-deficit/hyperactivity disorder show an altered eye movement pattern during reading. 

6. Hussaindeen JR, Shah P, Ramani KK, Ramanujan L. Efficacy of vision therapy in children with learning disability and associated binocular vision anomalies. 

7. Falkenberg HK, Langaas T, Svarverud E. Vision status of children aged 7–15 years referred from school vision screening in Norway during 2003–2013: A retrospective study. 

8. Mahone EM, Mostofsky SH, Lasker AG, Zee D, Denckla MB. Oculomotor anomalies in attention-deficit/hyperactivity disorder: Evidence for deficits in response preparation and inhibition. 

9. Loe IM, Feldman HM, Yasui E, Luna B. Oculomotor performance identifies underlying cognitive deficits in attention-deficit/hyperactivity disorder. 

10. Bucci MP, Brémond-Gignac D, Kapoula Z. Poor binocular coordination of saccades in dyslexic children. 

11. Grisham D, Powers M, Riles P. Visual skills of poor readers in high school. 

12. Kapoula Z, Bucci MP, Jurion F, et al. Evidence for frequent divergence impairment in French dyslexic children: Deficit of convergence relaxation or of divergence per se? 

13. Atkinson, J. The Davida Teller Award Lecture, 2016: Visual brain development: A review of “dorsal stream vulnerability” – motion, mathematics, amblyopia, actions, and attention

14. Braddick O, Atkinson J, Akshoomoff N, et al. Individual differences in children’s global motion sensitivity correlate with TBSS-based measures of the superior longitudinal fasciculus. 

15. Bilbao C, Piñero DP. Objective and subjective evaluation of saccadic eye movements in healthy children and children with neurodevelopmental disorders: a pilot study. Vision 2021.

16. Bilbao C, Piñero DP. Distribution of visual and oculomotor alterations in a clinical population of children with and without neurodevelopmental disorders. 

Articles

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.

Author | Dr Carmen Bilbao

Articles

Examining the link between neurodevelopmental disorders and visual problems