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A large-scale randomized clinical trial known as the Convergence Insufficiency Treatment Trial (CITT) found that office-based vision therapy combined with at-home therapy was more effective than placebo therapy (in-office placebo treatments) for improving symptoms and clinical signs of convergence insufficiency in children and adults.
In studies that used standardized definitions of convergence insufficiency, investigators have reported a prevalence of 4.2–6% in school and clinic settings. The standard definition of convergence insufficiency is exophoria greater at near than at distance, a receded near point of convergence, and reduced convergence amplitudes at near. [5]
Accommodative excess may occur secondary to convergence insufficiency also. In convergence insufficiency near point of convergence will recede, and positive fusional vergence (PFV) will reduce. So, the patient uses excessive accommodation to stimulate accommodative convergence to overcome reduced PFV. [5]
Fusional amplitude and relative fusional amplitude training are designed to alleviate convergence insufficiency. The CITT study (Convergence Insufficiency Treatment Trial) was a randomized, double-blind multi-center trial (high level of reliability) indicating that orthoptic vision therapy is an effective method of treatment of convergence ...
Accommodative insufficiency (AI) involves the inability of the eye to focus properly on an object. Accommodation is the adjustment of the curvature of the lens to focus on objects near and far. In this condition, amplitude of accommodation of a person is lesser compared to physiological limits for his age. [ 1 ]
Near (1/3m): 15Δ BI → 35-40Δ BO; Distance (6m): 5-7Δ BI → 15Δ BO; Vertical: 3Δ BU → 3Δ BD; If patient results do not reflect the normal values, they may have the following issues: Convergence insufficiency - usually associated with accommodative difficulties, the fusional convergence range of these patients is reduced.
When humans accommodate to a near object, they also converge their eyes and constrict their pupils. The combination of these three movements (accommodation, convergence and miosis) is under the control of the Edinger-Westphal nucleus and is referred to as the near triad, or accommodation reflex. [47]
Negative relative accommodation (NRA) was proposed by Joseph Kearney of Oxford University in 1967 as a measure of the maximum ability to relax accommodation while maintaining clear, single binocular vision.