Convergence is the inward movement that both eyes make when, for example, we are approaching an object close to the eyes. Both eyes should be looking at the same location in space.
Convergence insufficiency is a difficulty for the eyes to move more and more near the nose. When convergence is insufficient, the child may suffer from eyestrain or even double vision, depending on the extent of the problem.
In fact, the convergence test is rather simple to administer. Ask the child to look at a target (small penlight or a pencil, for example) which is located at eye level. Approach the target to the eyes, which will be converging until either 1) the child reports double vision or 2) you can observe that one eye loses fixation and moves outwards. Note the distance at which this occurs. This portion of the test is called the “break point of convergence.” The normal distance is about 5 cm (2 inches). Closer still, the eyes can not converge anymore.
The second part of the test is to measure the “recovery point” of convergence. Once the break point is reached, you simply move the target slowly away from the eyes until you see that both eyes are now fixating the target. The normal distance from the point of recovery is about 10 cm (4 inches) (see figure below). Of course, doing the test requires some practice.
We note the test as follows:
Convergence test: 8 cm / 20 cm (break point / recovery point)
Possible link between convergence and ADHD
An article published in the scientific literature in 2005 has created a stir that still persists. We know that the diagnosis of ADD or ADHD is mainly done by questionnaire and that there are no objective tests to make this diagnosis. But in 2005, a research has shown a possible link between convergence insufficiency and attention deficit hyperactivity disorder (ADHD). The beginning of a new era?
A potential relationship between convergence insufficiency and attention deficit hyperactivity disorder (ADHD) has been uncovered by researchers at the University of California, San Diego. “This is the first report on the potential connection of these two disorders,” Dr. David B. Granet, ophthalmologist [UCSD Shiley Eye Center].
The study “showed that children with convergence insufficiency are three times more likely to be diagnosed with ADHD than children without the disorder.” We will come back to this study and others…
Now back to the study by Dr. Granet and his team. This study argues that children being evaluated for attention deficit hyperactivity disorder (ADHD) often have an eye exam as part of their evaluation. The symptoms of convergence insufficiency (CI) can make it difficult for a student to concentrate on extended reading and overlap with those of ADHD. Surprising statement from an ophthalmologist when we know that these doctors are rarely concerned with such problems.
A retrospective review of 266 patients with CI presenting to an academic pediatric ophthalmology practice was performed. All patients included were diagnosed with CI by one author and then evaluated for ADHD diagnosis. A computerized review was also performed looking at the converse incidence of CI in patients carrying the diagnosis of ADHD.
Twenty-six patients (9.8%) were diagnosed with ADHD at some time in their clinical course. Of the patients with ADHD and convergence insufficiency, the review of computer records showed a 15.9% incidence of CI in the ADHD population. It would therefore seem to be a three-fold greater incidence of ADHD in patients with convergence insufficiency when compared with the incidence of ADHD in the general US population (1.8-3.3%). The authors also noted a three-fold greater incidence for this convergence problem in the population with ADHD. This may simply represent an association and not be a causal link.
But just before Dr. Granet’s article, a team of optometrists (Borsting et coll., 2005) publihed a research on the same subject a a few months before.
Borsting et al. identified accommodative (focusing) and convergence insufficiency problems in relation to other learning difficulties such as attention deficit hyperactivity disorder (ADHD). The purpose of this study was to evaluate the frequency of ADHD behaviors in school-aged children with symptomatic accommodative dysfunction or convergence insufficiency.
24 children from 8 to 15 years of age with symptomatic accommodative dysfunction or convergence insufficiency were included in this study. One parent of each child completed the Conners Parent Rating Scale-Revised Short Form (CPRS-R:S). The children’s scores on the CPRS-R:S were compared with the normative sample.
Regarding the Conners questionnaire, and more specifically the S, cognitive problem/inattention, hyperactivity, and ADHD indexes were significantly different from normative values (p < or = .001 for all tests).
The results from this preliminary study suggest that school-aged children with symptomatic accommodative dysfunction or convergence insufficiency have a higher frequency of behaviors related to school performance and attention as measured by the Conners questionnaire.
Gronlund et al. in 2007 studied various aspects of visual function in children with attention deficit hyperactivity disorder (ADD / ADHD) and establish whether treatment with stimulants is reflected in functioning of the visual system.
In all, 83% of children had normal visual acuity without treatment, and 90% with the use of stimulants. A problem with eye alignment (phoria) was found in 29% without treatment, and 27% with stimulants. A stereoscopic vision problem (three-dimensional vision) was found in 26% without stimulants, and 27% with stimulants. Abnormal convergence (> 6 cm or no convergence) was noted in 24% without treatment and 17% with treatment. Signs of visual-perceptual problems were found in 21% of all children. Children with AD/HD had a high frequency of visual findings, which were not significantly improved with stimulants.