Convergence insufficiency is a common condition that is characterized by a patient 's inability to maintain proper binocular eye alignment on objects as they approach from distance to near. [1, 2] There is typically an exophoria or intermittent exotropia at near, a receded near point of convergence, reduced positive fusional convergence amplitudes, and a low accommodation convergence/accommodation (AC/A) ratio. The symptoms associated with convergence insufficiency vary from mild to severe, but they are often extremely troublesome for patients with this condition, especially when associated with a small angle exotropia at the near working distance causing binocular diplopia. 
The underlying etiology for convergence insufficiency is probably innervational.  The dramatic reduction of symptoms demonstrated by patients after undergoing appropriate therapy, which is accompanied by objective clinical findings of improved near point of convergence and fusional convergence amplitudes, strongly supports this hypothesis.
Some cases of convergence insufficiency also appear to have an etiologic connection to accommodative dysfunction. 
Convergence insufficiency is associated most commonly with an exophoric binocular posture at near, but patients with this disorder may demonstrate orthophoria or even mild esophoria at the time of their examination. The reasons for this variability are described within this article.
In the past, many ophthalmologists considered convergence insufficiency and its associated symptoms to be a neurotic manifestation of nonrelated psychological problems best dealt with by a psychiatrist.  However, it is now clear that convergence insufficiency is a legitimate, problematic binocular dysfunction. The clinician must consider whether the behavioral manifestations displayed by patients really result from the frustration caused by their inability to perform desired near vision tasks.
The prevalence of convergence insufficiency has been reported to be approximately 3-5% of the population. Incidence increases with additional near work demand. The disorder is reported to be rare in children younger than 10 years of age. However, the increased visual demands of schoolwork and prolonged periods of reading exacerbate symptoms in older children.  Indeed, many patients with this disorder have vocational and/or avocational visual demands that require prolonged close work. The most common presentation encountered by the clinician is that of a high school or college student who develops symptoms when excessive demands are placed on the visual system during extended periods of studying. Lack of sleep, illness, and anxiety are known to aggravate the problem.
The prevalence of this condition is the same in all industrial societies.
The morbidity of convergence insufficiency relates to the near point visual demands of the patient's activities. Headaches, fatigue, frequent loss of place when reading, as well as frank binocular diplopia associated with near point tasks are among the symptoms associated with this condition.
No racial predilection exists for convergence insufficiency.
No sexual predilection exists.
The frequency of symptoms may increase with age as patients' ability to compensate for their relative divergent binocular alignment decreases with time.
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