Convergence insufficiency: symptoms, causes and eye exercises

When you look at something close, such as a page or a phone, both eyes turn slightly inwards so that the object lands on the same spot of each retina and the brain sees a single image. This inward turning is called convergence. United Lincolnshire Hospitals explains that convergence insufficiency is a weakness in the mechanism that holds the eyes in this slightly inward position for reading and other near tasks.

If the mechanism is weak, the trust says, the eyes either strain to stay in position or cannot be held there. Dudley Group NHS Foundation Trust describes it as difficulty focusing both eyes together on a target as it moves closer to the nose, causing symptoms such as double vision, blurred vision for close work, headaches and eye strain. It is also called convergence weakness.

It is a problem of eye coordination and muscle control, not of eye health. The eyes themselves are normal, and it does not damage vision, but it can make reading, study and screen work uncomfortable enough to affect school and work.

The symptoms occur mainly with near tasks and usually get worse the longer someone reads or looks at a screen. They are not specific to this condition, so an eye examination is needed to find out what is causing them.

• Eyestrain or tired, aching eyes during or after reading or screen work.

• Headaches in or around the eyes or forehead, often after reading.

• Blurred vision when reading or looking at something close.

• Double vision, particularly as an object comes closer to the nose.

• Difficulty concentrating on close work, or losing your place on the page.

The NHS leaflets say there are many possible causes. United Lincolnshire and Leeds list a change of occupation involving more close work, an intensive period of close work such as studying for exams, overwork, worry, recent illness or whiplash. Sometimes no reason is found.

Because the cause is often a change in the amount or intensity of near work, the symptoms can start quite suddenly in a student or office worker who has never had eye problems before. It can affect children and adults.

Convergence problems can also occur after head injury or alongside other conditions affecting eye movement or the nervous system. If the double vision is new and not tied to close work, or comes with other symptoms such as weakness, speech change or severe headache, it needs prompt medical assessment rather than exercises.

A routine eye test with an optometrist is a sensible first step if reading regularly causes headaches, blurred or double vision. They can check whether glasses are needed and can refer to an orthoptist or hospital eye service if the eyes are not working together properly.

Sudden double vision, double vision that is present in the distance, a drooping eyelid, a sudden severe headache, or double vision after a head injury needs urgent assessment through NHS 111, an urgent eye service or A&E, and call 999 if there are stroke symptoms such as facial droop, arm weakness or slurred speech.

An orthoptist, who specialises in eye movements and binocular vision, measures how close an object can be brought towards the nose before one eye drifts outwards or the image doubles, and how easily the eyes can recover. They test the way the eyes align at near and distance, and the ability to focus, and they check for other causes of symptoms.

The United Lincolnshire leaflet advises bringing up-to-date reading and distance glasses to every appointment. The same orthoptist will usually decide which form of treatment is most suitable.

United Lincolnshire lists the options as glasses, a course of convergence exercises, prisms on or in glasses and, in extreme cases, covering one eye. The orthoptist decides which suits the individual. Exercise is the mainstay.

Leeds Teaching Hospitals describes four types: smooth convergence, in which a target is slowly brought towards the nose while keeping it single and clear; jump convergence, looking between a distant and a near target; a dot card that is held from the nose while moving the gaze along the dots; and stereograms. It suggests doing them several times a day, for example five or six times per day for 2 to 3 minutes. Dudley says do them four or five times every day for a few minutes at a time.

After each session, both trusts advise relaxing the eyes by closing them or looking at the horizon or into the distance for a minute or two. Both warn that symptoms may increase slightly at the start and that this is normal and should not deter you. The treatment can only be successful if the exercises are done regularly at home as shown by the orthoptist; attending appointments alone will not improve symptoms.

Leeds says that people who carry out the exercises as instructed should recover within four weeks, sometimes sooner. Some people take longer, and symptoms can return at times of heavy near work, so keeping a few exercises in reserve can help.

Practical steps include good lighting, regular breaks from screens and reading, holding reading material at a comfortable distance, and wearing your usual reading glasses during exercises if you have them. Children who are struggling with reading should have their eyes checked as part of any assessment of learning difficulties.