Specialist Eyecare Centre
What is Convergence?
During a routine eye examination, near point of convergence will be measured (usually less than 10cm).
Convergence is where the eye muscles pull the eyes inwards towards the nose smoothly when looking at an object close up. This normally occurs without effort and allows comfortable use of both eyes “binocular vision”.
Weakness of these eye muscles may cause problems. This is called convergence insufficiency. There are many causes of convergence insufficiency for example, increased close work, worry, recent illness, and whiplash. Sometimes the reason is simply unknown.
Typical symptoms can be a headache at the front/forehead, around the eyes, eyestrain and difficulty in changing focus.
How to Treat Convergence
Treatment for convergence insufficiency usually involves convergence exercises that can be practised at home. Improvement is usually quite rapid if these exercises are carried out regularly.
Other visual stability tests exist such as Fixation Disparity test. A fixation disparity exists when there is a very small misalignment of the eyes when both eyes are used together (binocular vision).
This misalignment is much smaller than a squint which can cause a breakdown in binocular vision. Fixation disparity can however reduce a patient’s level of stereopsis.
To measure this, a Mallet Fixation Disparity test is generally used. This consists of a small central “X” letter surrounded by two “O” letters, one on each side of the “X”. These letters are viewed using both eyes (binocularly). Two coloured polarised bars are also viewed either side of the “X” (usually red for distance and green for near vision). These bars will be viewed separately. Any misalignment of the eyes will be indicated by the misalignment of the polarised bars in relation to the letter “X”. Special lenses called prisms can be used to realign the polarised bars and hence realign the eyes.
Anterior Eye Examination
It is also important to examine the front of the eye, which includes the eyelids, lashes, corneas and conjunctiva. For this, a slit lamp is used. The slit lamp is a table mounted microscope with special adjustable illumination with a stereoscopic view.
The illumination has a choice of filters for example cobalt blue. This gives an enhanced view especially when used alongside a yellow fluorescein die. There is also a red free (green) filter to give added definition.
The slit lamp can also be combined with specialised lenses which allow a stereoscopic view of the posterior eye including the vitreous and retina. Slit lamp and “Volk” lens is an important tool in the examination of those patient experiencing flashes and floaters.