Most developmental optometrists have stories of patients whose academic behaviours and performance have improved following vision therapy treatment of their binocular vision problems. Research studies have shown the same results.
General binocular dysfunction is the inability to move your eyes together in an effective manner. Each eye has six extraocular muscles that move the eyes in a coordinated manner. this movement is controlled by the brain. In a pediatric population, the prevalence of binocular disorders have been found to be 9.7 times greater than the prevalence of any other ocular disease. Subcategories of binocular dysfunction include:
- Accomodatedive disorders: the inability of the eyes to focus. The eyes must be able to sustain focus for long periods of time when doing near work. Also, the eyes must be able to quickly and accurately change focus from distant to near objects.
- Convergence disorders: the inability to use both eyes as a team when looking at something up close. When looking at near objects, both eyes should turn inwards and maintain single vision.
- Divergence disorders: the inability to use both eyes as a team when looking at something in the distance. When looking at far away objects, both eyes should turn outwards and maintain single vision.
- Oculomotor disorders: the inability to quickly and accurately move our eyes. These are sensory motor skills that allow us to move our eyes so that we can fixate on objects (fixation), move our eyes smoothly from point to point as in reading (saccades) and to track a moving object (pursuits).
Studies on the connection between binocular vision disorders and academic performance
A 2010 study published in the journal BMC Ophthalmology by Dusek at al. investigated the visual functioning of two groups of school-aged children in Austria - one group that was diagnosed with reading and writing difficulties and the other which was a clinical age-matched control group. The study found that the group of children with reading difficulties was statistically more likely to have visual problems such as poorer distance visual acuity, an binocular problems such as exophoric deviation at near, a lower amplitude of accommodation, reduced accommodative facility, reduced vergence facility, a reduced near point of convergence, a lower AC/A ratio and a slower reading speed. The study confirmed the importance of a full assessment of binocular visual status in order to detect and remedy these deficits in order to prevent the visual problems continuing to impact upon educational development.
Similar results come from a 2007 American study by Grisham et al. published in the Journal Optometry that measured visual skills and visual acuity in 461 students with an average age of 15.4 years in four California high schools within the same school district. Participating students had been identified by their schools as poor readers. In the studied sample, 80% of the students were found to be inadequate or weak in one or more of the following binocular visual skills: binocular fusion ranges at near, accommodative facility, and convergence near point. In contrast, only 17% had deficient visual acuity—20/40 or worse in one eye— which is the standard model of deficiency for school vision screenings. This demonstrates not only the inadequacy of school vision screenings but also that academic deficits are correlated much more strongly with binocular vision problems (which can’t be fixed with corrective lenses) rather than with acuity (which can be fixed with corrective lenses).
How prevalent is binocular dysfunction among students?
A 1997 study by Porcar and Martinez-Polomero published in the journal Optometry and Vision Science concluded that acommodative and nonstrabismic binocular vision problems are prevalent in the university population. Accommodative excess is the most common condition. Because these dysfunctions have a negative effect on performance, appropriate vision evaluation for this population is important. The researchers concluded that among university students, 32.3% showed general binocular dysfunctions. In 10.8% of the cases, accommodative excess was present. 7.7% had convergence insufficiency with accommodative excess. 6.2% showed accommodative insufficiency. 3.1% had basic exophoria.
More recently, a longitudinal study was published by Jorge et al. in 2008 in Optometry and Vision Science the purpose of which was to investigate the changes in accommodation and binocular vision parameters during a 3-year period. The research team found significant changes in near heterophoria, fusional vergences, and positive relative accommodation.
These two studies indicate that binocular dysfunction is not rare in university students and that the demands of university appear to worsen binocular vision over time.
No post on binocular vision disorders would be complete without mentioning convergence insufficiency, which is the most common binocular vision disorder with a prevalence of around 15% according to some studies.