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The symptoms and signs associated with convergence insufficiency are related to prolonged, visually demanding, near-centered tasks. They may include, but are not limited to, diplopia (double vision), asthenopia (eye strain), transient blurred vision, difficulty sustaining near-visual function, abnormal fatigue, headache, and abnormal postural adaptation, among others.
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]
Vision therapy is a broad concept that encompasses a wide range of treatment types. [3] These include those aimed at convergence insufficiency – where it is often termed "vergence therapy" or "orthoptic therapy" – and at a variety of neurological, educational and spatial difficulties. [3]
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 ]
In a small-scale study, adults whose reading difficulties due to convergence insufficiency had been unsuccessfully addressed by convergence exercises, base-in prism glasses or strabismus surgery showed improved reading after botulinum toxin therapy, maintaining improved reading remaining also after six months. [5]
Clinically, accommodative convergence is measured as a ratio of convergence, measured in prism diopters, to accommodation, measured in diopters of near demand. The patient is instructed to make a near target perfectly clear and their phoria is measured as the focusing demand on the eye is changed with lenses.
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.
The topic of multifocal displays has been generously researched for at least several decades, [25] [26] nevertheless, there is only a limited offering of commercially available multifocal near-eye displays. Light field displays are one of the best ways to solve the vergence-accommodation conflict. [22] They share features with integral imaging ...