What is convergence excess?
Convergence excess describes a condition where the eyes do not exactly aim together; rather, they aim too close or in front of the object. As a consequence, blur, confusion or fatigue may result.
Convergence excess will effect near work tasks, especially reading and writing. Symptoms of convergence excess include eyestrain, headaches, blurred vision, double vision, sleepiness and (if reading) trouble remembering what was read.
Rapid changes in convergence demands such as copying from the blackboard are often very difficult for children with convergence excess. Some children may move their book closer or forward to ‘see better’, when in fact what they are doing is trying to relieve their convergence excess difficulties. When they get close enough to the page they may be using their ‘stronger eye’, thereby reducing the confusion and strain of trying to use both eyes together.
This excess of vergence is commonly associated with an accommodative insufficiency. The eyes are aimed closer in than desired in an attempt to compensate for reduced focus stamina or focus ability. This leads to a mismatch between vergence and focus, thus affecting binocular vision accuracy.
Management of convergence excess requires therapeutic prescription lenses to enhance the focus efficiency thus reducing the need to pull the eyes closer in. The lenses are typically worn for close work tasks such as reading, writing, computer work and copying from the blackboard. This is a therapeutic treatment that requires monitoring over time to ensure the excessive demand is reduced to within a normal range of focus and convergence.
Usually over time prescriptions can be reduced and wearing time reduced. In some cases, vision therapy may be required in addition to the glasses. Visual therapy on its own does not work well to alleviate these problems. Therapy teaches better control but does not relieve the fatigue component.
If vision therapy is required it usually consists of six in-office visits spaced one week apart, along with home based therapy between these visits. Treatment duration will depend on the particular patient’s condition.