Convergence insufficiency and Brock string exercises
15 October, 2026 | 2:00 PMConvergence insufficiency means your eyes find it hard to turn inwards together for close work. Brock string exercises are a simple home practice your optometrist may give you to help the eyes work as a team. Do them only as prescribed, and stop if they cause pain or dizziness.
What convergence insufficiency is
To read or look at a phone, both eyes turn slightly inwards. This is called convergence. With convergence insufficiency (CI), that teaming takes extra effort.
Common signs include:
- Tired or sore eyes after reading
- Headaches with close work
- Words that seem to move or blur
- Double vision up close
- Losing your place, or rereading lines
CI affects children and adults. Your plan may include home exercises, therapy sessions in the clinic, or both. Some people also need glasses for close work.
What you need
A Brock string: a cord about 1.5 to 3 metres long, with three coloured beads.
How to do the exercise
- Tie one end of the string to a doorknob or chair at eye height.
- Hold the other end against the tip of your nose and pull the string straight.
- Place the first bead a short distance from your nose, the second about halfway along, and the third near the far end.
- Look at the nearest bead. You should see one bead, with two strings crossing at it in an X.
- Hold your focus on that bead for 5 to 10 seconds.
- Move your focus to the middle bead. The X should move there too. Hold for 5 to 10 seconds.
- Move your focus to the far bead. The two strings should meet there in a V.
- Move slowly back and forth between the beads.
- As it gets easier, slide the near bead a little closer to your nose.
What you see tells you what your eyes are doing.
- Strings cross at the bead: your eyes are working together.
- Strings cross in front of or behind the bead: your eyes are turning in too much or too little. Keep your focus and try to bring the X back to the bead.
- Only one string: one eye may be switching off. Tell your optometrist at your next visit.
How often
Practise once or twice a day, for as long as your optometrist prescribes. Short, regular sessions are easier to keep up. Bring the string to your review so we can check your technique.
Do and don't
Do
- Practise in good light
- Take breaks between rounds
- Wear your glasses if prescribed for close work
Don’t
- Practise when very tired
- Push through pain
- Change the routine without asking
When to stop and call us on (03) 9702 9118
- Headache or eye pain during or after exercises
- Dizziness or nausea
- Double vision that stays after you stop
- Symptoms getting worse over a week or two
Call 000 straight away if
double vision starts suddenly, especially with a headache, weakness, numbness, slurred speech or a drooping eyelid. These can be signs of a stroke.
To book a binocular vision assessment, book online or call us on (03) 9702 9118.
FAQs
What is a Brock string used for?
A Brock string helps train both eyes to point at the same spot together. It also shows you how well your eyes are teaming.
How long until Brock string exercises help?
It varies from person to person. Many therapy programmes run for around 12 weeks. Your optometrist will review your progress.
Is it normal to see two strings?
Yes. Two strings crossing in an X at the bead you are looking at is the expected result.
Can children do Brock string exercises?
Yes, with an adult helping. Your optometrist will advise whether they suit your child.
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