A number of studies have identified various visual problems in children with ADHD. These include visuoperceptual problems, convergence insufficiency, impaired stereoacuity, more frequent refractive errors, an increased risk of strabismus and astigmatism, as well as deviations in eye movements and accommodation. ADHD is also associated with neurophysiological changes in the optic nerves, genetic correlations with the DRD4 dopamine receptor gene and asymmetrical pupil diameters. Visuomotor function, i.e. the coordination of visual perception and the locomotor system, correlates with cognitive abilities such as inhibition and cognitive flexibility.
ADHD is characterized by an impaired dopamine system with reduced extracellular dopamine.
Dopamine is also involved in the visual system.
Reduced visual performance was found in 76% of the children with ADHD examined. A meta-analysis of 35 studies with 3,250,905 participants found a 94% increased risk of unspecified visual problems in ADHD (OR = 1.94).
Young adults with ADHD showed more problems with depth perception, peripheral vision and color perception, especially in the blue spectrum, compared to non-affected individuals.
ADHD medication improved visual field abnormalities and visual acuity in children with ADHD. Another study found no significant improvements. In a small study, surgical treatment of strabismus improved ADHD symptoms in 7 out of 8 patients in the parent report.
A small study was able to distinguish ADHD sufferers from non-sufferers quite well using eye movement tracking.
It is therefore conceivable that eye problems can cause or exacerbate ADHD symptoms, just as ADHD can cause or exacerbate eye problems.
1. Visuoperceptive problems with ADHD (+ 1000 %)¶
One study found visuoperceptual problems in 21% of children with ADHD, compared with only 2% of those without the disorder.
2. Convergence and ADHD (+ 200 % to + 400 %)¶
One study found convergence insufficiency in 24% of children with ADHD, compared with only 6% of those without the disorder.
Several other studies found children with convergence insufficiency were 3 times more likely to have ADHD than unaffected children.
A meta-analysis of 35 studies with 3,250,905 participants found a fivefold risk of a reduced near-convergence point in ADHD (OR = 5.02).
3. Stereoacuity (stereotactic vision, depth perception) in ADHD (+ 333 %)¶
Stereoacuity is the ability of a person to recognize objects along different distances as separate entities.
Several studies report impaired stereoacuity in children with ADHD. Stereoacuity (depth perception) was impaired in 26% of children with ADHD, compared to 6% of those without.
4. Strabismus / heterophoria (strabismus / latent strabismus) in ADHD (+ 93 % to + 700 %)¶
One study found that children with ADHD
- More strabismus (squinting) (17% compared to 2% in non-affected people)
- More heterophoria (latent strabismus) (27 % compared to 10 % in non-affected people)
One cohort study found a 15% increased risk of ADHD with strabismus. Another cohort study found a doubled risk of ADHD with strabismus convergens (internal strabismus, esotropia) and a 44% increased risk of ADHD with strabismus divergens (external strabismus, exotropia).
A meta-analysis of 35 studies with 3,250,905 participants found a 93% increased risk of strabismus (OR = 1.93) and a 79% increased risk of hyperopia and hypermetropia (OR = 1.79) with ADHD.
An analysis of the KiGGS study (N = 13,488) found strabismus in 8.2% of children with ADHD compared to 4.2% of those without (OR 2.04).
ADHD and hyperopia, myopia, astigmatism and strabismus predicted each other.
5. Astigmatism in ADHD (+ 79 % to + 300 %)¶
One study found astigmatism in 24% of children with ADHD, compared to only 6% of children without the condition.
A meta-analysis of 35 studies with 3,250,905 participants found a 79% increased risk of astigmatism in ADHD (OR 1.79).
An analysis of the KiGGS study (N = 13,488) found strabismus in 10.9% of children with ADHD compared to 6.9% of those without (OR 1.84).
ADHD and hyperopia, myopia, astigmatism and strabismus predicted each other.
6. Eye movements (saccades) and ADHD¶
Various studies have found slower and more variable saccadic reaction times in children with ADHD using the gap/overlap test. One study was able to eliminate this biomarker using warning signals during the test.
An experimental study (n = 16) reported significant deviations of eye movements in ADHD measured by electrooculography (EOG).
Another study found that in children, visual field shifts moderated the relationship between hyperactivity/impulsivity on the one hand and problems focusing attention and taking in information on the other. Visual field shifts increased with a decrease in performance accuracy, although this correlation did not reflect the severity of the symptoms.
Another study found significant abnormalities in ADHD sufferers in the modulation of the eye vergence response (eye vergence = opposite / disjugate / disjunctive eye movements) during attention tasks. The diagnostic test accuracy was 79 %.
One large study found a correlation between premature anticipatory eye movements and inattention, but not between directional errors and ADHD symptoms.
A meta-study found evidence that children with ADHD
- made more directional errors in an antisaccade task
- were slower and performed worse in oculomotor tasks
- Performed eye movements less precisely
Saccadic eye movements (gaze jumps) are strongly influenced by factors such as attention and inhibition. Since attention and inhibition are impaired in ADHD, it seems plausible that saccadic eye movements are abnormal in ADHD.
Arbitrary eye movements are controlled by the dlPFC: The arbitrary control of eye movements is closely linked to attention control. The dlPFC also houses the working memory, which is typically impaired in ADHD.
One study found significantly higher pupillary velocity values in children with ADHD, which correlated positively with the RNFL measurements of their right eyes.
Faster visual orienting due to shorter saccadic reaction times (SRT) was found on baseline trials compared to overlap trials, on faces compared to non-face stimuli and, more clearly in children without ADHD and/or autism, on multimodal compared to unimodal stimuli. There was a linear negative correlation between presaccadic pupil size and SRTs in children with ASD without ADHD, and a quadratic correlation in children with ADHD without ASD, in whom SRTs were slower when intraindividual presaccadic pupil size was smallest or largest.
The deviations in saccadic eye movements in ADHD are said to be improved by computer training.
7. Macular thickness in ADHD¶
A small study hypothesizes that increased macular thickness in children with AD(H)D may represent the increased ratio of right frontal lobe to parietal cortex thickness in ADHD.
8. Accommodation for ADHD¶
Children with ADHD showed a reduced accommodation response that was not influenced by the accommodation stimulus. There was no clear effect of ADHD medication on accommodation accuracy. Accommodation refers to the ability of the eye to focus / focus on objects at different distances.
A meta-analysis of 35 studies with 3,250,905 participants found an increased risk for increased delay (Hedge’s g = 0.63 [CI: 0.30, 0.96]) and variability (Hedge’s g = 0.40 [CI: 0.17, 0.64]) of the accommodative response in ADHD.
9. Neurophysiological changes in the optic nerves in ADHD¶
One study found smaller optic nerves, smaller neuroretinal rim areas or reduced tortuosity of the retinal arteries in children with ADHD.
10. DRD4-7R and vision in ADHD¶
The D4 dopamine receptor gene, DRD4, is significantly involved in the conversion of light into electrical signals in the retina. The transcription of DRD4 shows a strong circadian pattern.
The DRD4 7R variant is one of the strongest single-gene risks for ADHD. See also ⇒ Candidate genes for ADHD In the chapter ⇒ Origin.
DRD4-7R correlates with a lower ability to reduce the light-sensitive second messenger cyclic adenosine monophosphate (cAMP) upon illumination.
In addition, DRD4-7R correlates with higher daytime sleepiness, which could be a consequence of the seesaw between dopamine and melatonin.
11. Pupil diameter and noradrenaline in ADHD¶
Tonic and phasic noradrenal infiring can be recognized by the pupil diameter.
The basal size of the pupil diameter corresponds to tonic noradrenal infiring and a change in pupil diameter corresponds to phasic noradrenergic activity. A phasic pupil dilation correlated with correct responses, a tonic pupil dilation with periods of low reward value. An increase in baseline pupil diameter correlated with a decrease in task utility and disengagement from the task (exploration); a decrease in baseline pupil diameter with an increase in task-induced dilation correlated with task engagement (exploitation)
Pupil dilation is a physiological index of increased arousal and noradrenergic activity of the locus coeruleus.
The pupil diameter in the resting state also reflects the connectivity between frontoparietal, striatal and thalamic brain regions.
Measurements of pupil diameter show deviations in the noradrenergic system in ADHD.
More on this at Tonic and phasic noradrenaline in ADHD In the article Noradrenaline.
12. Refractive errors and ADHD¶
One study found refractive errors in 83% of the children with ADHD examined. A meta-analysis of 35 studies with 3,250,905 participants found no accumulation of refractive errors in ADHD (Hedge’s g = 0.08 [CI: -0.26, 0.42]).
A dysfunction of retinal dopamine could influence the neurodevelopmental growth of the eye, leading to refractive errors. This could explain the frequency of refractive errors in ADHD.
There is growing evidence that the worldwide increase in myopia is dopaminergically mediated and linked to a lack of daylight.
Between 1981 and 2002, outdoor activities halved from 1 hour 40 minutes per week to 50 minutes per week.
12.1. Farsightedness (hyperopia) (+ 67 %)¶
An analysis of the KiGGS study (N = 13,488) found farsightedness in 13.0% of children with ADHD compared to 8.2% of those without (OR 1.67).
ADHD and hyperopia, myopia, astigmatism and strabismus predicted each other.
12.2. Short-sightedness (myopia) (+ 29 %)¶
An analysis of the KiGGS study (N = 13,488) found myopia in 16.2% of children with ADHD compared to 13.1% of those without (OR 1.29).
ADHD and hyperopia, myopia, astigmatism and strabismus predicted each other.
13. Retinal nerve fiber layer thickness unchanged¶
A meta-analysis of 35 studies with 3,250,905 participants found no change in the thickness of the retinal nerve fiber layer in ADHD (Hedge’s g = -0.19 [CI: -0.41, 0.02]).
14. Visuomotor skills correlate with inhibition and cognitive flexibility¶
Visuomotor skills are the coordination of visual perception and the musculoskeletal system and include eye-hand coordination.
A study reports:
Visuomotor fluency correlated significantly with cognitive inhibition. The ability to perform visually guided, continuous movements fluently correlates with the ability to inhibit the effects of distracting information.
Visuomotor flexibility correlated significantly with cognitive flexibility. The ability to spontaneously use visual information to flexibly change motor responses correlates with the ability to cognitively switch from one state of mind to another.
