Vergence dysfunction involves disjunctive eye movements in which the visual axes either move toward each other (convergence) or away from each other (divergence), resulting in the inability of the eyes to accurately fixate and stabilize a retinal image.In simpler words, vergence dysfunction is the inability of the two eyes to accurately point in the same position at any particular time at any particular distance.
Causes of Vergence Dysfunction
It may occur due to
- Disturbances in binocular eye movements
- Alteration in visual environment
- Head trauma
- Certain systemic disorders like Graves’s disease, Parkinson disease, Alzheimer disease etc.
- Genetic predisposition
Types of Vergence Dysfunction:
- Convergence Insufficiency
- Divergence Excess
- Basic Exophoria
- Convergence Excess
- Divergence Insufficiency
- Basic Esophoria
- Fusional Vergence Dysfunction
- Vertical Heterophorias
Out of these, convergence insufficiency (CI) is the most common binocular vision disorder in which eyes do not work together for near work.
Symptoms of patients with Vergence anomalies:
Most of the persons with vergence anomalies remain asymptomatic until the time visual environment is altered specifically in the situation of increased near work. Usually following symptoms are found in a person with vergence anomalies:
- Blurred vision
- Double vision (Diplopia)
- Heavy eyelids
- Ocular discomfort
- Eye fatigue
- Lack of concentration
- Avoidance of eye contact
- One shoulder higher
- Short attention span
- Movement of print while reading
- Frequent loss of place while reading
- Squinting of eye
- Excessive rubbing of eyes
- Cover or close one eye while reading
- Motion sickness and/or vertigo
Early detection and prevention of Vergence Dysfunction
Early detection of vergence dysfunction is required to prevent the conversion of this anomaly to squint. The most important age to detect any vergence dysfunction is before 2 years as this is the developmental age of normal binocularity. In children, it is all the more important to diagnose the condition as early as possible to provide best academic success opportunities.
Diagnosis of Vergence dysfunction
Careful examination of the patient holds key for proper diagnosis of vergence dysfunction. It may include the following:
- Complete patient history
- Thorough eye examination including:
- Visual Acuity
- Ocular Motility and Alignment
- Near Point of Convergence
- Near Fusional Vergence Amplitudes
- Relative Accommodation Measurements
- Accommodative Amplitude and Facility
- Ocular Health Assessment
- Systemic Health Screening
Management of Vergence Dysfunction
After thorough interpretation and analysis of the examination results, a strategy to manage the condition is drafted that may include:
- Correction of any refractive error like far-sightedness, near-sightedness, astigmatism etc.
- Prism lenses
- Training Spectacle lenses for all close work to improve focusing stamina
Vision Therapy for Vergence Dysfunction:
The main aim of vision therapy in Vergence dysfunction patients is to eliminate the signs and symptoms and improve the quality of life of the patient. VT works in following three phases:
- First phase normalize accommodative and vergence amplitudes by using large targets and encouraging patient to maximize his efforts to increase vergence amplitudes.
- Second phase increase the speed of response to accommodative and vergence stimuli by using targets and different stimuli.
- Third phase is called jump or step vergence stimuli in which patient is required to make large-jump accommodative and vergence movements instead of incrementally increasing stimuli. This phase automate both accommodative and vergence reflexes.
Advantages of vision Therapy:
- Improves reflex-fast fusional vergence
- Expands slow vergence responses
- Restores accommodative flexibility
- Enhances the flexibility between accommodation and vergence
- Re-establishes automated, effortless accommodative and vergence responses under any stimulus condition.