Convergence insufficiency

Question 1

What is it

Answer 1

Convergence Insufficiency (CI) is a syndrome characterized by a decreased ability to converge the eyes and maintain binocular fusion while focusing on a near target. CI is usually accompanied by a reduced near point of convergence (NPC), decreased convergence amplitudes or an exodeviation (usually > 10 prism diopters) at near. Patients often complain of eye strain, needing to close one eye when reading, or blurred vision after short periods of near work.

Question 2

Primary convergence insufficiency

Answer 2

Primary convergence insufficiency is present when other causes for convergence insufficiency have been excluded, including a significant degree of heterophoria. Features The main features are:
- frontal headaches and eyestrain associated with close work, caused by the effort needed to converge; blurred vision and intermittent diplopia for near fixation due to failure to maintain convergence.

Question 3

Investigations

Answer 3

• Cover test. This will show a slight exophoria for near fixation in most cases, with no significant heterophoria for distance fixation. The speed of recovery for near should be noted.
• Convergence. This should be assessed as described for heterophoria. Convergence insufficiency is present if the near point of convergence is less than 10 cm or if it can be maintained at this level only with effort and if it deteriorates on repeated testing.
• Accommodation. The near point of accommodation should be measured as already described and related to the patient’s age. Blurred vision for close work can result from convergence insufficiency or accommodative insufficiency. If uniocular accommodation appears significantly better than binocular accommodation, convergence insufficiency is the likely diagnosis. If accommodative insufficiency is present both uniocular and binocular accommodation is below normal for the patient’s age. The accommodative amplitude should also be measured for both near and distance.
• Fusional amplitude. This is measured at near using a horizontal prism bar. The positive fusion amplitude is deficient in convergence insufficiency but the negative amplitude should be normal. An accommodative target is preferable to a spotlight.

Question 4

Management

Answer 4

Any significant refractive error should be corrected if it is likely to account for the patient’s symptoms or result in compensation of the convergence defect. A cycloplegic refraction may be helpful in selected cases. Management should include:
- Correction of acquired myopia, which may compensate the condition by restoring a normal accommodative– convergence relationship.
- Correction of low degrees of astigmatism, which can cause symptoms similar to those of convergence insufficiency, especially if oblique.
- Correction of a low or moderate degree of hypermetropia, which does not necessarily make convergence more difficult.

Question 5

Orthoptic exercises

Answer 5

Patients are suitable for treatment if:

• The condition is symptom-producing and the symptoms are related to the use of the eyes for close work. There is sufficient cooperation and motivation.
• The patient is in good general health. Although it is an advantage if the patient can attend the clinic regularly, inability to do so is no bar to treatment since much of it can be carried out at home, providing that clear instructions are given. The stages in orthoptic treatment are:
  o Treatment to overcome suppression and obtain spontaneous recognition of diplopia on failure of convergence if this is not already present. This step is usually easily achieved by using coloured filters. Improvement of convergence and extension of the positive fusion amplitude. Simple convergence exercises can be given and the fusion amplitude extended using a prism bar base-out.

Question 6

Appreciation of Diplopia

Answer 6

• Appreciation of physiological diplopia, which can then be used in the uncrossed position to improve relative convergence and in the crossed position to ensure that relaxation of convergence is easy to obtain. The dot card and stereogram cards are useful methods based on physiological diplopia.
• Voluntary convergence. Not all patients can achieve this stage. The methods used in all stages of treatment. General guidelines
• The patient should be warned that the symptoms may become worse in the early stages of treatment and will only improve when convergence becomes easier to maintain.
• The patient must be able to recognise diplopia reliably before being given convergence exercises to practise at home
• . Detailed instruction on home exercises should be given, emphasising the time that should be spent on each. New skills should be added whenever possible to encourage the patient and maintain his or her interest.
• Relaxation exercises must be practised at the end of every clinic or home exercise session.