Biological markers for ADHD in children have been supported by brain imaging studies. The retina has been considered to represent the brain status, and a relationship between retinal pathology (retinal nerve fibre layer thickness) and ADHD has been reported (Herguner et al. 2016). This study aimed to find biomarkers of ADHD in the retina and assess the relationship between macular thickness of the retina and cortical thickness of the brain in children with ADHD.
Children were recruited from the Department of Psychiatry of Chung-Ang University Hospital in Seoul, Korea and completed a variety of assessments.* Macular thickness was obtained according to the Early Treatment Diabetic Retinopathy Study (ETDRS). All children underwent full ophthalmologic examinations and brain magnetic resonance imaging. Children with a history of an axis I psychiatric disorder other than ADHD were excluded from the study, as were those taking psychiatric medications and children with any ocular condition that could affect vision.
In total, 12 children with ADHD (mean [standard deviation (SD)] age 10.6 [1.9] years) and 13 children without ADHD (mean [SD] age 9.8 [2.1] years) were included in the study. Children without ADHD had a higher mean (SD) IQ score than children with ADHD (102.8 [9.4] vs 91.0 [16.4], respectively; p = 0.04); the mean (SD) Korean ADHD Rating Scale (K-ARS) score was higher in the ADHD group compared with the control group (18.5 [15.9] vs 5.7 [3.8], respectively; p = 0.04). Children’s Depression Inventory scores did not differ between groups (ADHD: 10.6 [9.4] vs control: 9.8 [10.2]; p = 0.69).
The rest of the study results were as follows:
- Mean (SD) inner ETDRS ring thickness was thinner in controls (left eye: 308.8 [11.4] µm; right eye: 305.6 [9.5] µm) compared with children with ADHD (left eye: 319.1 [11.9] µm; right eye: 315.0 [12.4] µm; p = 0.04).
- For outer ETDRS ring thickness, children with ADHD also had higher values compared with controls for the left eye (277.8 [17.0] µm vs 266.6 [9.5] µm, respectively; p = 0.02) and the right eye (275.6 [10.3] µm vs 265.4 [9.5] µm, respectively; p = 0.02).
- In children with ADHD, only the right ETDRS ring thickness had a positive correlation with the K-ARS scores (r = 0.66; p = 0.036). There was no correlation between ETDRS ring thickness and K-ARS scores with the left inner (r = 0.46; p = 0.183), right outer (r = 0.24; p = 0.500) or left outer (r = –0.01; p = 0.977).
- There was no significant difference between mean (SD) cortical thickness of the frontal, parietal, temporal or occipital cortex between children with and without ADHD. However, children with ADHD had an increased ratio of right frontal to parietal cortical thickness (114.7 [3.3]) compared with the control group (112.2 [2.2]; p = 0.04).
- There were no differences (95% confidence interval [CI]) in thickness of the frontal and parietal cortices (left hemisphere: –0.12 [–3.74 to 3.50]; p = 0.94), and between the left (–1.32 [–3.65 to 1.01]; p = 0.25) and right (–2.09 [–4.37 to 0.19]; p = 0.07) frontal and temporal cortices between groups.
Relationship between macular and cortical thickness
- The mean of the inner right ETDRS ring thickness was positively correlated with thickness of the left paracentral thickness (r = 0.81; p = 0.0008) and the right isthmus cingulate (r = 0.80; p = 0.001) in children without ADHD.
- For children with ADHD, the mean of the inner right ETDRS ring thickness was negatively associated with left frontal pole (r = –0.82; p = 0.0009) and right pars triangularis (r= –0.82; p = 0.0011) thickness.
This study had several limitations. The sample size was small, meaning that the findings could not be generalised to the general population, and the relationship between clinical measures and cortical or macular thickness could not be considered. In addition, some of these results did not survive after Bonferroni correction.
The authors concluded that the different patterns in macular thickness may represent the immature cortical thickness of the brains of children with ADHD. These results may highlight the importance of macular thickness abnormalities as a marker in children with ADHD and identify an association between the retina and the brain.
*Assessments included the Korean Kiddie Schedule for Affective Disorders and Schizophrenia–Present and Lifetime version, the Children’s Depression Inventory and the Korean Wechsler Intelligence Scale for Children. Parents completed the Korean ADHD Rating Scale for participants
Bae S, Kim JT, Han JM, et al. Pilot study: an ocular biomarker for diagnosis of attention deficit hyperactivity disorder. Psychiatry Investig 2019; 16: 370-378.
Hergüner A, Alpfidan İ, Yar A, et al. Retinal nerve fiber layer thickness in children with ADHD. J Atten Disord 2018; 22: 619-626.