Dr Ben Wild
Overview |
Our eye muscles are all interconnected in a complicated pathway with a common goal of delivering comfortable vision in any gaze and at any distance. To have comfortable near vision, the medial rectus muscles of each eye must pull the eyes inwards (converge the eyes), the pupils must shrink to help with depth of field, and the ciliary body, a muscle inside the eye, must constrict to change the shape of the lens inside the eye to focus the light from the near target on the retina.
Frontal view of a right eye with the extra-ocular muscles attached. The highlighted muscle represents the medial rectus muscle required to pull the eyes inwards (converge).
Convergence insufficiency is a condition whereby the medial rectus muscles of each eye are working well when looking at distant objects but have a hard time pulling the eyes inwards for near targets.
Signs and Symptoms |
Signs
Inability to converge (or cross) the eyes.
Symptoms
Eye strain after near work, double vision at near, loss of depth perception when looking at a near target, skipping words when reading, re-reading the same line in a book, headaches after near work, blurred vision, jumping words on a screen or a page.
Causes and Risk Factors |
Causes
The causes are unknown but there are many risk factors and correlated factors with convergence insufficiency.
Risk Factors
Concussion, traumatic brain injury, convergence fatigue (can converge well but, after a while, the muscles tire out), Grave’s disease (thyroid related), Myasthenia Gravis, Parkinson’s, Alzheimer’s, accommodative insufficiency.
Prevention and Treatment |
Prevention
Allow children to crawl and develop their near vision, avoid head trauma, apply the 20-20-20 rule (after 20 minutes of near work look at a target at least 20 feet away for 20 seconds).
Treatments
· Vision therapy including eye exercises that stimulate gradual convergence (pencil push ups, Brock string, etc.), jump convergence (Brock string, Hart Chart, etc.), prism training to simulate change in focal distance, computer-based training, in office-based training, and many more.
· Seek out an optometrist who specializes in vision therapy.
· Surgery as last resort.
Prognosis |
When not associated with a systemic health condition or traumatic brain injury, convergence insufficiency exercises have an 80% success rate at eliminating all signs and symptoms. When associated with a traumatic brain injury, exercises may still help but take much longer and require more dedication. When associated with systemic diseases, exercises will actually tire out the muscles and make the symptoms worse without providing any future benefit.