|To reach a diagnosis of convergence insufficiency the eye doctor must evaluate eye alignment at distance and at near and the ability of the patient to converge as an object is slowly moved towards the eyes. A minimum of three tests are required to reach this diagnosis. They include the:
- Cover test
- Near point of convergence
- Convergence amplitude
The doctor used a plastic cover paddle and moves it back and forth from the right to the left eye several times while the patient maintains fixation on a distance and then a near object. The test generally requires less than a minute and allows the doctor to determine if the eyes have a tendency to drift outward (exophoria).
Near Point of Convergence
The doctor asks the patient to look at a small letter on a stick that looks like a tongue depressor and instructs the patient to keep the letter single as it moves closer and closer to the bridge of the nose. Studies have shown that both children and adults should be able to maintain single vision until the object reaches about 6 cm (2 inches) from the bridge of the nose. People with convergence insufficiency may report double vision when the letter is significantly further away.
This simple test also requires less than a minute to perform.
A measuring device (prism bar) with a series of increasingly stronger prism is held before one eye while the patient tries to keep a small letter single and clear. The doctor slowly increases the magnitude of the prism until the patient reports blurry vision or double vision. This yields a measurement of the patients' ability to converge the eyes. The patient's performance can then be compared to well-established expected findings. This test also requires very little time to complete.
Thus, the diagnosis of convergence insufficiency requires simple equipment, a very short period of time and the procedures are well-established and accepted by eye care professionals. It is also important to note that these tests can be performed even with young children who may not be able to accurately report their experiences. The doctor is able to objectively watch the eyes and determine the test results.