Reviewed by Desiree Vanderstar, OD Resident, Southern College of Optometry
In India, the prevalence of learning disabilities is approximately 15% in 8-11 year olds, with reading as the primary area of concern. It is logical that this should raise concerns about the efficacy of the visual system in this group of children. Literature supports that about 80% of the children who have been identified to have a learning disability have also been shown to have accommodative and vergence difficulties. This includes convergence insufficiency (CI), poor accommodative and vergence facility, reduced fusional ranges, and reduced amplitudes of accommodation. These difficulties can lead to reduced reading speed, poor accuracy and overall lower reading efficiency.
The authors propose that it is essential to assess the binocular system in children with learning disabilities but that there is a lack of randomized controlled trials testing the efficacy of vision therapy in this subset of the population. This article defines a learning disability as “a generic term that refers to a heterogeneous group of disorders manifested by significant difficulties in the acquisition and use of listening, speaking, reading, writing, resonating or mathematical skills”.
Their aim was to establish the frequency of binocular vision (BV) issues in children diagnosed with specific learning disabilities (SLD), such as poor reading or writing and to assess efficacy of vision therapy (VT) in improving their oculomotor, accommodative and vergence parameters. They also compared visual efficiency parameters between children with normal binocular vision and non-strabismic binocular vision anomalies (NSBVA’s).
The study was carried out at a school for children with learning disabilities. All 96 children, aged 10-21, underwent a comprehensive eye exam and binocular vision testing. A single student with Down’s syndrome and a single student with a pervasive disorder were excluded. The remaining 94 students had been previously diagnosed with a specific learning disability and all had documented problems with reading, writing and spelling. All children had normal IQ levels for their age and had no reported neurological issues. Eleven had a comorbid diagnosis of attention deficient disorder.
Of those 94 students, 46 were diagnosed with a NSBVA and were enrolled in a pre and post-experimental study design. This included 22 patients who received no intervention and 24 patients who were enrolled in 10 session of vision therapy.
Binocular vision testing included: Randot stereo plates, extraocular motility testing, cover test at distance and near, push up amplitudes, monocular and binocular accommodative facility, monocular estimate method of retinoscopy, near point of convergence (NPC), step vergences at distance and near with negative fusional ranges tested prior positive fusional vergence (PFV) ranges and the developmental eye movements (DEM) test. Vision related quality of life assessment (VR-QOL) was assessed using the modified COVD VR QOL questionnaire and symptomology was assessed verbally by asking about eyestrain, headaches, eye pain, or other visual discomfort associated with near work. Reading rate was assessed by asking each child to read a given paragraph for 3 minutes. Errors were subtracted and the reading rate was calculated for 1 minute of time.
Vision therapy was completed on the school premises for 45 min during regular class hours. The procedures used were adopted from Scheiman and Wick protocol for NSBVA and were carried out by an optometrist who would modify the technique whenever necessary according to the child’s responses. The activities focused on training vergence and accommodation through utilization of computer based therapies, tranaglyphs and vectograms. Teachers were blinded to which students received treatment and for ethical reasons, the control group was also administered vision therapy after the study brought to completion.
Of the 46 patients diagnosed with a NSBVA, 31 had accommodative infacility, 11 had convergence insufficiency, 1 had divergence excess, 1 had fusional vergence dysfunction and 2 had convergence insufficiency comorbid with accommodative infacilty. Mann – Whitney U statistical testing a revealed significant difference between NPC break and recovery, near PFV break and recovery, monocular and binocular accommodative facility in children with normal BV compared to the NSBVA group.
After 10 sessions, BV parameters and reading rate were reassessed in all test subjects. This helped examiners evaluate the true effect of vision therapy, negating placebo, learning and test retest effects. All parameters, except negative fusional vergence showed statistically and clinically significant difference post VT, when compared to baseline. In contrast, none of the control/non-intervention group showed statistically significant changes. The largest effects were seen on accommodative facility and PFV, followed by accommodative facility and NPC.
The average VR QOL score prior to therapy was 8 in the NSBVA and 3 in the normal BV group, with a higher number indicating a reduced quality of life. These scores did not show statistically significant improvements. However, the administration is often limited by bias on the part of the teacher or caregiver. This is an area that will require more study and exploration
The DEM results showed that all children diagnosed with a learning disability had a longer than expected horizontal time, whether they were diagnosed with a NSBVA or not. This supports that patients with specific reading related learning disabilities have poor saccadic eye movements. The median reading rate was also slower in the NSBVA group and faster in patients who had a faster time on the horizontal component of the DEM. As is logically expected from these results, the DEM results were negatively correlated with reading rate. This is in agreement with other literature. DEM horizontal and vertical times did not differ post VT. This result was expected, as the bulk of the therapy worked on accommodative and vergence activities. A regime dedicated to improving oculomotor skills would likely yield similar statistically significant improvement, as were seen in vergence and accommodative abilities.
Overall, the study confirms that children with specific learning disabilities have higher frequency of NSBVA when compared to age matched controls. These anomalies are an added hindrance to their pre existing reading difficulties.
The majority of the studies’ patients were identified as having convergence insufficiency or accommodative infacilty, and thus, the results are especially applicable to these two diagnoses. Since the differences in BV parameters were not present in the control group, the effects can be attributed to VT alone, without placebo, test re-test or learning effects factored in.
Also, because 5 of the 9 criteria for ADHD in DSM IV overlap with symptoms of CI (loss of concentration when reading, reading slowly, failure to complete assignments and trouble concentrating in class), it is extremely important to screen all of these patients for BV anomalies. In order to provide the best care, a comprehensive binocular vision assessment should be a part of the treatment plan for all children with LD’s and vision therapy should subsequently be recommended, especially to those with NSBVA’s.