Convergence insufficiency prevalence in attention deficit and hyperactivity disorder children depends on the diagnosis criteria

Abstract

Purpose

Attention deficit and hyperactivity disorder (ADHD) is a neurodevelopmental condition commonly seen in children and adolescents, characterised by an increase in distractibility or inattention. Several studies have noted a higher rate of visual problems in this group, especially convergence insufficiency (CI), but when using different diagnostic criteria. The aim of this study was to evaluate visual function in ADHD children and non‐ADHD controls to compare the different signs for diagnosis of CI.

Method

In this prospective case‐control study, a group of children aged 7–17 years, diagnosed with ADHD before the start of pharmacological treatment and matched for age and gender with non‐ADHD controls were examined. Visual acuity (VA), objective and subjective refraction, accommodative amplitude and facility, heterophoria, positive and negative fusional vergences (PFV and NFV) and stereopsis were assessed.

Results

Sixty participants (30 ADHD and 30 non‐ADHD controls) were evaluated. There was no significant difference between the two groups for VA, refraction and accommodative abilities. There were significant differences in PFV and NFV: PFV break/recovery values for the ADHD and control groups were 18.9/16.2∆ and 26.9/22.1∆, respectively. Respective values for NFV were 15.7/13∆ and 19.3/15.9∆. Using the three signs of receded near point of convergence (NPC), decreased PFV and exophoria 4∆ greater at near than distance, the prevalence of CI was equivalent for the ADHD and controls (p = 0.34) If only two signs were considered for the CI diagnosis, (i.e., receded NPC and decreased PFV), then prevalence was significantly greater for the ADHD group (p < 0.01).

Conclusions

These results show a higher prevalence of binocular vision problems in the ADHD group. This suggests a relationship between vergence problems and ADHD, but the direction of this link remains unclear. Further studies with specific samples may be needed to understand fully the association between binocular vision disorders and ADHD.

Key points.

• The established relationship between convergence insufficiency and attention deficit and hyperactivity disorder found in the literature depends on the diagnostic criterion used to diagnose convergence insufficiency.

• Whether considering three parameters for the diagnosis of convergence insufficiency (i.e., near point of convergence, positive fusional vergence and exophoria at near) or considering the near point of convergence only, it was not possible to establish a higher prevalence of convergence insufficiency in attention deficit and hyperactivity disorder. When two parameters were considered (near point of convergence and positive fusional vergence), a higher prevalence of convergence insufficiency was found in the attention deficit and hyperactivity disorder group.

• Low scores were obtained in binocular tests that required sustained effort. These results led us to hypothesise that decreased performance was due to inattention rather than a primary dysfunction of binocular vision.

INTRODUCTION

Attention deficit hyperactivity disorder (ADHD) is one of the most prevalent neurodevelopmental disorders in school age. ¹ This condition can affect the proper development and functioning of the child and often persists into adolescence and adulthood. Characteristic symptoms are attention deficit, hyperactivity and over aroused behaviours. For ADHD to be diagnosed, symptoms should be evident before 7 years of age and be pervasive in at least two domains, either family, school or social. ²

The high prevalence of this disorder, namely, 5.28% in populations younger than 18 years of age, ³ has motivated a growing interest in scientific, scholarly and social circles. However, it remains controversial, with attitudes ranging from scepticism and denial to excessive medicalisation of the disorder. ⁴ , ⁵ The clinical diagnosis based on the observance of specific behaviours according to the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DMSV) ¹ , ⁶ criteria, has remained the most successful method for diagnosing the condition. ⁷ Even though the brain maturation theory delay has been supported with image findings, ⁸ they are not diagnostically specific. Differences in brain structure volume (striatal, accumbens, hippocampal and amygdala) found in ADHD groups cannot be used as a parameter for individual diagnosis, but these neuroimaging findings may lead to the association with other clinical manifestations, such as ocular anomalies. The ocular system is a part of the central nervous system; therefore, evaluation of visual function, in particular saccades ⁹ , ¹⁰ and vergences, ¹¹ , ¹² , ¹³ , ¹⁴ has been shown to be sensitive for CNS anomalies.

Convergence insufficiency (CI) is a binocular vision disorder characterised by three signs: (1) exophoria that is 4Δ greater at near than distance, (2) a near point of convergence (NPC) > 6 cm and (3) decreased positive fusional vergence (PFV) at near (<15Δ). ¹⁵ , ¹⁶ , ¹⁷ Symptoms such as asthenopia, headache or diplopia are often associated with this condition. ¹⁸ , ¹⁹

Numerous investigators and eye care practitioners have used different criteria for the diagnosis of CI. Some have simply used a receded NPC while others considered that CI could be diagnosed if at least two of the three signs listed above were present. ²⁰ Grönlund et al. found significant differences in several visual variables between ADHD and a control group. Twenty‐nine percent of the ADHD participants had heterophoria (exophoria ≥ 4Δ or esophoria ≥ 2Δ at near and/or at distance) compared with only 10% of the control group. The NPC was impaired in 24% of the former group and in 6% in the control group. ¹⁴

Granet et al. ¹³ found a threefold higher prevalence of CI in subjects with ADHD compared with a non‐ADHD sample. The presence of a receded NPC (>6 cm) and reduced positive fusional amplitudes (≤15Δ at near) was required for CI diagnosis. A systematic review ²¹ found that ADHD was indeed associated with a reduced NPC, but other anomalies related to CI diagnoses, such as vergence ranges, heterophoria or symptoms, were not analysed. Other investigations have not found higher rates of convergence abnormalities in an ADHD group. For example, Mezer and Wygnanski‐Jaffe did not find higher rates of convergence abnormalities but rather found higher values of ametropia in individuals with ADHD. ²²

Without consistent CI diagnostic criteria, the association between CI and ADHD is unclear and shows high variability depending on the visual signs being considered. This case‐control study evaluated the prevalence of one, two or three signs of CI in both an ADHD group and a neurotypical age‐matched control group. Results were compared with prevalences reported in published studies considering their diagnosis criteria. For further analysis, the study was extended by performing other tests analysing visual function, with the differences between the ADHD and the control group being evaluated.

Participants and method

In this prospective study, ADHD subjects were recruited through the Maresme Child and Adolescent Mental Health Centre. The diagnosis was made by two specialist psychiatrists. The diagnostic criteria of the DMS V were followed, in addition to a mental health assessment and an analysis of psychopathology and comorbidities with the Kiddie‐Schedule for Affective Disorders and Schizophrenia, Present and Lifetime Version 22; ²³ developmental, medical, academic and social history information was obtained, the ADHD‐DSM V Conners scale test(mhs.com) was performed and IQ was calculated using the Wechsler Intelligence Scale for Children (WISC) test. ²⁴ Persistence of clinical dysfunction in at least two settings (school and home) were used as criteria. Medication or behavioural intervention, if needed, was deferred until the visual function tests were performed. The exclusion criteria were previous diagnosis of strabismus or amblyopia (visual acuity [VA] with correction worse than 0.15 logMAR), diminished intellectual capacity (IQ < 70) and neurological or medical illnesses that by their nature or treatment affected cognition, attention or other functions related to ADHD.

After the diagnosis and before starting pharmacological or behavioural treatment, participants were referred to the optometrist for examination. Thirty‐eight naive ADHD subjects were referred from the mental health centre but eight were unable to complete testing.

The age‐matched non‐ADHD controls were randomly selected from a primary care centre in Mataró (primary care centre Cirera‐Molins). Non‐ADHD participants were obtained after finding the ADHD sample. A list of boys and girls from 7 to 17 years of age from a referral area (250.000 inhabitants) was obtained. Then, for each ADHD participant, a non‐ADHD participant was selected (the selection was randomised using a Microsoft Excel [Microsoft.com] tool). When the matched participant was selected, a short telephone interview was conducted with his/her parents to explain the study and to rule out any neurodevelopmental or learning disorders. When the answer was not very accurate or uncertain, the participant was rejected and a new participant was obtained. This process was repeated until the number of matched controls was reached.

Sixty participants between 7 and 17 years of age participated in this study. Thirty ADHD subjects (23 boys and 7 girls, mean age ± SD, 10.17 ± 2.55 years) along with 30 age and gender‐matched controls. The sample size was selected based on the prevalence of CI signs previously observed in an ADHD population. ¹³ , ¹⁴ , ²⁵

The study was approved by the ethics committee of the Consorci Sanitari del Maresme following the standards of good clinical practice in accordance with the principles of the Declaration of Helsinki. Written informed consent was obtained from the parents on behalf of their children enrolled in the study.

In both groups, the examination was performed under the same distances and lighting conditions by a single optometrist (LC). Distance vision tests were performed at 4.80 m with a 22″ LED optotype screen (CC‐100 Topcon, topconhealthcare.com) and near vision tests at 40 cm using a chin rest to ensure the correct distance. Distance VA and subjective monocular static refractive error were assessed in both eyes using the tumbling E chart. The obtained refractive correction was used in all the subsequent tests. For the binocular vision and accommodation assessment, all measurements were performed three times and averaged. Detection of strabismus or heterophoria was performed using the alternating cover test, measurement of lateral far and near heterophoria with the Von Graefe test and prism bars, near PFV and negative fusional vergence (NFV) with prism bars, NPC with an accommodative stimulus (break and recovery), binocular accommodation amplitude using the Donders method, binocular accommodation facility with ±2.00 D flipper lenses at near distance and stereopsis with the random‐dot TNO stereo test (TNO, tno.nl) (See Appendix 1 for a full description of testing procedures). The complete examination was attempted in a single session. When a subject was not able to complete all of the tests due to tiredness or distractibility, the examination was carried out in two or three different visits. In both groups, about half of the subjects were able to complete all the tests in one visit (14/30 and 16/30 in the ADHD and control groups, respectively). The remaining subjects required two or more visits to complete the testing. Participants who were unable to complete all of the tests in three sessions were excluded from the study.

Statistical analysis

Statistical analysis was performed using SPSS software version 13.0 (ibm.com). Descriptive statistics (mean [standard deviation {SD}]) were used to characterise the sample. For comparison of the main study factors (visual function) between cases and controls, a bivariate analysis was performed. The Chi‐square test for categorical variables and Student's two‐tailed t‐test for normally distributed data were applied with the corresponding post‐‐hoc analysis. The level of significance was set at p < 0.05.

RESULTS

Visual function parameters of a sample of 60 children (30 ADHD and 30 control) were obtained from two different optometric offices. There were no statistically significant differences between the two groups regarding age (t‐test for equality of means, p = 0.95) and sex (Pearson's Chi‐square p = 0.20).

In relation to distance VA and refraction, no statistically significant differences were found between the ADHD and control groups (Table 1). No significant amounts of ametropia were found in the sample.

TABLE 1.

Visual acuity (VA) and subjective refraction.

	ADHD (n = 30); mean (SD)	Control (n = 30); mean (SD)	p‐Value a
RE VA (logMAR)	0.02 (0.01)	0.01 (0.01)	0.13
LE VA (logMAR)	0.02 (0.01)	0.00 (0.00)	0.06
RE Sph (D)	+0.35 (0.51)	+0.35 (1.01)	0.36
LE Sph (D)	+0.36 (0.57)	+0.35 (1.10)	0.82
RE Cyl (D)	−0.25 (0.28)	−0.21 (0.39)	0.84
LE Cyl (D)	−0.18 (0.28)	−0.25 (0.39)	0.56

Abbreviations: ADHD, attention deficit and hyperactivity disorder; Cyl, cylinder; D, dioptre; LE, left eye; RE, right eye; Sph, sphere.

^a t‐Test.

Binocular vision analysis showed statistically significant differences in some parameters between subjects and controls. Mean break and recovery values of PFV and NFV were significantly lower in the ADHD group than the control group (Table 2) especially the PFV finding (break 18.9 ± 6.8∆ vs. 26.9 ± 5.5∆ p < 0.01; recovery: 16.2 ± 6.1∆ vs. 22.1 ± 5.1∆ p < 0.01). No significant differences were observed for the remaining parameters.

TABLE 2.

Convergence and accommodation evaluation results for both groups.

	ADHD (n = 30); mean (SD)	Control (n = 30); mean (SD)	p‐Value a
Lateral distance heterophoria (∆)	0.07 Esophoria (0.61)	0.27 Esophoria (0.9)	0.13
Lateral near heterophoria (∆)	0.9 Exophoria (2)	0.83 Exophoria (2)	0.91
PFV break (∆)	18.9 (6.8)	26.9 (5.5)	<0.01*
PFV recovery (∆)	16.2 (6.1)	22.1 (5.1)	<0.01*
NFV break (∆)	15.7 (3.9)	19.3 (4)	<0.01*
NFV recovery (∆)	13 (4.3)	15.9 (3.1)	<0.01*
Binocular AA (D)	14.28 (3.2)	14.42 (3.2)	0.88
Acomm. facility (cpm)	8.34 (2.7)	9.23 (2.2)	0.27
NPC (cm)	4.23 (2.47)	4.58 (2.9)	0.70
Stereopsis (TNO) (″)	63.6 (11.8)	61.3 (7.03)	0.30

Abbreviations: AA, amplitude of accommodation; ADHD, attention deficit and hyperactivity disorder; NFV, negative fusional vergence; NPC, near point of convergence; PFV, positive fusional vergence.

^a t‐Test.

^* p‐Values denote significant differences.

Table 3 shows the prevalence of abnormal values for the three clinical signs used for the diagnosis of CI. There were no significant differences in the NPC between the two groups. In contrast, if the CI criterion used by Granet et al. ¹³ were adopted, (i.e., NPC > 6 cm and PFV < 15∆) there would be six cases (20%) in the ADHD group and none in the control group. Considering the three clinical signs as diagnostic criteria for CI (NPC > 6 cm, PFV < 15∆ and near exophoria > 4∆ distance heterophoria), then two cases were found in the ADHD group and none in the control group. PFV break was the only isolated clinical CI sign that showed statistically significant differences between cases and controls.

TABLE 3.

Data of the three signs of convergence insufficiency for the two groups.

Signs	ADHD (%)	Control (%)	p‐Value a
NPC > 6 cm	6 (20)	4 (13)	0.32
Near Exo 4∆ > Far	2 (6.6)	2 (6.6)	>0.99
PFV < 15∆	11 (36)	0	<0.01*
NPC > 6 cm + PFV < 15∆	6 (20)	0	<0.01*
NPC > 6 cm + Near Exo 4∆ > Far	2 (6.6)	1 (3.3)	>0.99
PFV < 15∆ + Near Exo 4∆ > Far	2 (6.6)	0	0.34
NPC > 6 cm + PFV < 15∆ + Near Exo 4∆ > Far	2 (6.6)	0	0.34

Abbreviations: ADHD, attention deficit hyperactivity disorder; Exo, exophoria; NFV, negative fusional vergence; NPC, near point of convergence; PFV, positive fusional vergence.

^a t‐Test.

^* p‐Values denote significant differences.

DISCUSSION

The association between visual function disorders and ADHD cannot be overlooked. Many studies support links between the two entities regarding accommodation, ²⁶ saccadic dysfunction, ²⁷ refractive error ²² and binocular vision diagnoses. ¹³ , ²⁵ A recent meta‐analysis established links with a higher prevalence of reduced colour discrimination and contrast sensitivity, atypical accommodative responses and poor convergence in individuals with ADHD. ²¹

The present work focuses on the association between CI and ADHD. No distinction was made between the different subtypes of attention disorders, while visual testing was performed prior to any pharmacological treatment that could distort the results.

Spherical equivalent refractive error and distance VA were similar in both groups. These results are in agreement with Fabian et al., ²⁸ who also found no significant differences found between ADHD and non‐ADHD controls. While Grönlund and Mezer ¹⁴ , ²² found a higher prevalence of refractive errors in ADHD participants, they included amblyopic and strabismic subjects who were excluded from the present investigation.

Heterophoria values observed here also differed from previous studies. Grönlund et al. ¹⁴ reported that 29% of the ADHD group had exophoria (near or far) > 4∆ or esophoria (near or far) > 2∆, while in the control group, only 10% of participants showed such values of heterophoria. Following this criterion, in the present study, 10% of the subjects in each group demonstrated heterophoria within this range.

Regarding binocular vision abnormalities, only PFV and NFV showed a significant difference between the groups, with lower values being observed in the ADHD group. However, significant differences in NPC or near heterophoria were not found here, so we could not conclude that participants with ADHD had higher rates of CI than a non‐ADHD population. Table 4 shows results obtained in both former and current works. Granet et al. ¹³ associated ADHD and CI by studying the prevalence of both entities through a retrospective analysis of medical records. The diagnostic criteria for CI included: proximal convergence point > 6 cm, PFV < 15∆ and the presence of associated symptomatology (headache, asthenopia). According to the criteria of Granet et al., excluding associated symptomatology, 20% of the current ADHD participants would be identified as having a CI. However, Fabian et al. ²⁸ did not find a higher prevalence of CI using these three diagnostic criteria. The NPC was the only sign measured in the works of Ababneh et al. and Gronlund et al. ¹⁴ , ²⁵ Both studies found higher rates of receded NPC in the ADHD group. In the current work, as well as Ababneh et al. and Gronlund et al., NPC was measured with an accommodative target whereas other investigations ¹³ , ²⁸ do not specify the type of target used. Target selection can affect NPC values, especially in people with convergence problems. An accommodative target is less sensitive to detect subtle CI and may result in better convergence values. ²⁹ This may explain why we did not find a difference in NPC between the two groups. Karaca et al. ³⁰ measured only PFV and NFV, and found no significant differences between cases and controls in terms of the mean values, but they did not analyse the rates of abnormality found in each group.

TABLE 4.

Data of convergence abnormalities extracted from different studies.

Study ref.	n	Study design	ADHD subtipes treatment	Diagnostic criteria	Findings
Granet et al. 13	266 ADHD	Retrospective	All subtypes. Either not or on medication	NPC, positive fusional vergence	Greater incidence
Fabian et al. 28	56 ADHD 66 controls	Prospective case‐control	All subtypes. Either not or on medication	NPC, positive fusional vergence and heterophoria	No greater incidence
Ababneh et al. 25	55 ADHD 55 controls	Prospective case‐control	All subtypes. On medication	NPC	Greater incidence
Gronlund et al. 14	42 ADHD 50 controls	Prospective case‐control	All subtypes. Either not or on medication	NPC	Greater incidence
Karaca et al. 30	23 ADHD 48 controls	Prospective case‐control	All subtypes. Not on medication	Positive and negative fusional vergence	No greater incidence
Clavé et al.	30 ADHD 30 controls	Prospective case‐control	All subtypes. Not or on medication	NPC, positive fusional vergence and heterophoria	No greater incidence for the three signs. Greater incidence of NPC and PFV

Abbreviations: ADHD, attention deficit hyperactivity disorder; NPC, near point of convergence.

In a meta‐analysis, Bellato et al. ²¹ observed a higher prevalence of CI in ADHD subjects, but using a very limited definition of CI (simply a receded NPC).

Outcomes obtained in this study, along with other works ¹³ , ¹⁴ , ²⁵ suggest a relationship between vergence abnormalities and ADHD, but the bidirectional relationship in which this link is established remains unclear. Several authors have found that treatment with stimulants could lead to changes in some visual skills. ¹⁴ , ³¹ On the other hand, Lee et al. ³² found that improving vergence skills through vision therapy decreased scores on ADHD symptom questionnaires.

The finding that both convergence and divergence skills were reduced in ADHD is new, to the best of our knowledge. We hypothesise that there could be two reasons for this finding. First, the accommodative‐vergence mismatch during vergence testing may result in poor attention to the vergence task. During the examination, we noticed a lack of attention due to the intrinsic nature of ADHD and hypothesise that the loss of concentration may cause an early break of fusion during the measurement of fusional reserves. This led us to wonder whether the attentional problem could be leading to lower values. For the heterophoria measurement, where binocular vision is suspended and no additional effort is required, we found no statistically significant differences between the two groups. Poltavski et al. ³³ showed that sustained attention can be influenced by accommodative‐vergence stress, such as the convergence and accommodation mismatch that occurs during fusional reserves measurement. They suggested that a bottom‐up processes could exacerbate attentional problems in ADHD individuals. This hypothesis could be supported by recent research linking attention problems to poor binocular control ³⁴ and the relationship between ocular dynamics and attentional control. ³⁵ Second, the brain areas affected by ADHD may contribute to both convergence and divergence. Oculomotor signals are distributed across several brain areas, the parietal and frontal cortex, the basal ganglia, thalamus and brainstem reticular formation among others. ⁸ , ³⁶ Recent neuroimaging findings evidence differences in some brain structures in ADHD subjects. ⁸ , ³⁷ For instance, Hoogman et al. ⁷ confirmed a delay of brain maturation in ADHD subjects with reduced volume of accumbens, amygdala and the basal ganglia. Further, Johnston et al. ³⁷ reported brainstem reticular formation abnormalities in ADHD participants, which receives input from the frontal cortex. ³⁸ These findings lead us to hypothesise that the abnormalities in ADHD brain structures may be responsible for the impaired vergence observed in the present study.

It should be pointed out that in general, studies involving ADHD participants and vision testing do not take into account all the variables that could play confounding factors (such as ADHD subtypes, interaction with pharmacological treatments, high refractive error or strabismus) In the present study, only non‐medicated participants were included, thereby removing one variable in the analysis of the results. Further investigations with specific samples and involving multidisciplinary collaborations (e.g., ocular dynamics, psychiatric and neuroimaging assessment), may be needed to understand fully the association between binocular vision disorders and ADHD.

This study did have some limitations. The sample size may be acknowledged as a possible limitation. The examiner was not blinded regarding the group to which participants belonged. The ADHD group was obtained from a single hospital, although its referral area was around 250,000 inhabitants. The IQ test was part of the psychiatrist protocol for the diagnosis of ADHD, but it was not applied to the control group. Therefore, the two groups may have differed in mean IQ. However, both groups were able to understand all instructions adequately; for that reason, we do not believe that this possible difference would interfere with the results. Finally, during the ADHD group recruitment, uncooperative participants were found in whom visual function testing was not possible. There was no distinction made regarding the severity of ADHD. It is possible that the most severe cases were the uncooperative participants for whom visual function testing could not be performed. This may have resulted in a sample of children with only mild ADHD, and thus fewer convergence problems than in the general ADHD population.

AUTHOR CONTRIBUTIONS

Laura Clavé: Conceptualization (equal); data curation (lead); formal analysis (lead); investigation (lead); methodology (lead); writing – original draft (lead). Aurora Torrents: Conceptualization (equal); data curation (supporting); formal analysis (supporting); investigation (equal); methodology (equal); supervision (equal); writing – review and editing (supporting).

FUNDING INFORMATION

Public, from the Agencia Estatal de Investigación of the Spanish Government, under project Ref. PID2020‐114582RB‐I00/AEI/10.13039/501100011033.

CONFLICT OF INTEREST STATEMENT

None.

APPENDIX 1.

All tests were performed with full distance correction. All examinations were conducted three times and averaged.

Tests:

Distance visual acuity: 22′ CC‐100 LED optotype screen (Topcon) tumbling E chart in logMAR progression.

Cover test: 0.20 logMAR VA isolated E Snellen stimulus.

Far and near heterophoria by Von Graeffe with prism bars: 0.20 logMAR VA vertical chart line.

Near positive and negative fusional vergence with prism bars: 0.20 logMAR VA horizontal chart line.

Near point of convergence (NPC): 0.20 logMAR VA i∆solated stimulus.

Binocular accommodation amplitude using the Donders method: 0.20 logMAR VA horizontal chart line.

Binocular accommodation facility with ±2.00 D flipper lenses at near distance: 0.20 logMAR VA horizontal chart line.

Stereopsis: Random‐dot TNO test.

Procedures and instructions for participants

Far and near heterophoria by Von Graeffe with prism bars

Far: With the placement of a fixed dissociating prism 6∆ b∆ase‐up into the trial frame in front of the left eye and 20∆ base‐in from the prism bar in front of the right eye while the participant is observing the accommodative target. The participant was instructed to fixate the lower image and to keep the chart clear. Then, the b∆ase‐in prism from the prism bar is gradually decreased and the participant is instructed to report the point at which the upper and lower stimulus are aligned.

Near: For the measurements at near (40 cm), a 9∆‐prism b∆ase‐up prism was placed in front of the left eye and a 20∆ base‐in prism was placed in front of the right using the same procedure as far.

Near positive and negative fusional vergence (PFV, NFV)

Fusional convergence and divergence amplitudes at a distance (4.8 m) and at near (40 cm) were measured with the placement of the horizontal prism bar (1–40∆ in front of an eye, while the participant was fixating on an accommodative target. The base‐out prism power was gradually increased for convergence and the base‐in prism bar was gradually increased for divergence and the participant was asked to identify the point at which the target image appeared to be doubled; this prism power was designated as “the break point”. Then, the base‐out prism power was gradually decreased for convergence and the base‐in prism bar was gradually decreased for divergence and the participant was asked to identify the point at which the participant reported fusion (recovery point).

Near point of convergence (NPC)

The accommodative stimulus was located 50 cm from theparticipant and moved slowly in the mid‐sagittal plane closer to the participant's nose. The participant's subjective response to diplopia or the examiner's observation of when fixation was lost was used to determine the NPC break point. The NPC was measured from the bridge of the nose to the target in centimetres.

Binocular accommodation amplitude

The test was performed using the Donders method. The accommodative target was moved slowly in the mid‐sagittal plane closer to the participant's nose. The participant was asked to report the first sustained blur and this point was measured from the bridge of nose in centimetres. The inverse of the distance in metres between the bridge of nose and the target was recorded as the amplitude of accommodation in dioptres.

Binocular accommodation facility

The accommodative stimulus was located 40 cm from the participant. A manual ±2.00 D flipper was placed in the spectacle plane. Then the participant was asked to clear the negative power, then, the flipper was switched to the plus side and the participant was asked again to clear the target. This was recorded as one cycle. The number of cycles per minute that the participant could complete was recorded as binocular accommodation facility.

Clavé L, Torrents A. Convergence insufficiency prevalence in attention deficit and hyperactivity disorder children depends on the diagnosis criteria. Ophthalmic Physiol Opt. 2025;45:23–30. 10.1111/opo.13411