8. Heterophoria & Convergence Insufficiency

Question 1

Heterophoria meaning?

Answer 1

This is the term used to describe a condition whereby both visual axis are directed towards the fixation target, however upon dissociation, the axis deviates (latent squint).

Question 2

Esophoria meaning?

Answer 2

Latent deviation of the visual axis inwards.

Question 3

Classification of Esophoria?

Answer 3

• Convergence Excess Type: Angle greater for near.
• Divergence Weakness Type: Angle greater for distance.
• Non-specific Type: No significant difference between near and distance angles.

Question 4

Exophoria meaning?

Answer 4

Latent deviation of the visual axis outwards.

Question 5

Classification of Exophoria?

Answer 5

• Convergence weakness type: Angles is greater for near.
• Divergence excess type: Angle is greater for distance.
• Non-Specific type: No significant difference between near and distance angle.

Question 6

Hyperphoria/ Hypophoria meaning?
Common aetiologies?

Answer 6

• A latent vertical deviation is present on dissociation.
• One eye moves upwards to fix and the other downwards.
  –Common aetiologies including congenital vertical muscle palsies and thyroid eye disease (TED).

Question 7

Compensated control of phoria?

Answer 7

The patient has sufficient fusional reserves to maintain BSV without undue effort. People with longstanding large ‘phoria adapt and develop increased fusional range.

Question 8

Decompensating control of phoria?

Answer 8

• The patient must make a considerable effort in order to maintain BSV.
• Excessive effort results in asthenopia.
• When fusion breaks a ‘tropia’ results and the patient may complain of blurred vision or diplopia.

Question 9

3 causes of decompensation?

Answer 9

1. Optical- Uncorrected/ inaccurate correction of refractive error, ill fitting glasses, aniseikonia.
2. Medical- Poor GH, head trauma, drugs. (fatigue or generally feeling unwell reduces fusional reserves).
3. Others- change in visual demands. - change in occupation that requires more close work.

Question 10

Aims when investigating the phoria?

Answer 10

Classify the deviation.
Measure the ‘phoria’.
Assess compensation
Identify symptoms
Identify cause of decompensation
Manage appropriately

Question 11

2 types of management for phoria?

Answer 11

1. Conservative (Correct refractive error, orthoptic exercises- not used often, prims)
2. Invasive (Botulinum Toxin, Convergence insufficiency)

Question 12

How are different Rx refractive errors corrected?

Answer 12

Fully correct hyperopic corrections in cases of esophoria to ensure deviation is as small as possible and controlled can be achieved without undue effort.

Can consider under-correcting hyperopia in case of exophoria to induce accommodation and therefore convergence in order to reduce exophoria and encourage fusion.

It is not really possible to under-correct myopia in cases of esophoria as VA will be compromised but in case of exophoria it may be possible to undertake minus lens therapy and increase myopic Rx to induce more accommodative convergence and therefore reduce the size of the exophoria.

Question 13

Orthoptic exercises tend to be useful when?

Answer 13

Small ‘phorias where only a small increase in fusional reserves is required.

Question 14

Stereograms are performed in the near position to help control ?

Answer 14

To help control exophorias by exercising positive relative convergence.

Question 15

Stereograms are performed in the distance position to help control?

Answer 15

To help control esophorias by exercising negative relative convergence

Question 16

Which type of phoria is prescribed with prism?

Answer 16

Only prescribe prisms if the patient has symptoms related to decompensation.

Question 17

Botulinum Toxin is offered to pxs?

Answer 17

To patients whose angle is too small for surgical correction but who want more than a prism.
Deviations can be over-corrected initially then as the effect of the toxin reduces the eye are aligned. Injections will be repeated probably on a 4-6 monthly basis.

Question 18

Convergence insufficiency meaning?

Answer 18

• The inability to obtain and maintain adequate binocular convergence without undue effort.
• Near point of convergence is greater than 10cm.

Question 19

What is primary convergence insufficiency?

Answer 19

CI is the primary defect
* Pre-disposing factors include wide IPD, occupations/hobbies involving excessive uniocular work, little or no close work.
* Precipitating causes include illness, fatigue, prolonged close work and poor lighting, toxins, age, and pregnancy.
* There is not always a reason for why some people have a CI.

Question 20

Secondary CI is as a result of?

Answer 20

• Squint (latent or manifest)
• Refractive error
• Systemic disorders (Parkinson’s, TED, INO)
• Accommodative anomalies

Question 21

Management of convergence insufficiency?
Treatment options?

Answer 21

• Aims is to relieve symptoms, improve convergence, and improve fusional reserves.
• Treat underlying cause (Secondary CI)

Treatment options:
* Convergence insufficiency exercises.
* Surgery/ prisms in extreme cases.

Question 22

What is a requirement for orthoptic exercises?

Answer 22

A patient has to be aware of diplopia in order to undertake exercises.

Question 23

Aim of orthoptic exercises?

Answer 23

• Improve convergence
• Improve fusional reserves
• Achieve voluntary convergence

Question 24

Orthoptic exercise for convergence insufficiency?

Answer 24

• Instruct patient to fix on approaching target.
• Encourage patient to maintain fusion and single vision.
• When diplopia is noticed patient must move target back until single vision is restored.
• Procedure is then repeated, and the patient encouraged to maintain single vision as target is moved closer and closer.
• This process is to be undertaken for approx. 5 mins 3-4 times per day.
• Encourage the patient to ‘relax eyes’ following each period of exercise.

Question 25

What is jump convergnce?

Answer 25

When near point of convergence has improved, jump convergence is introduced.

Question 26

How is jump convergence done?

Answer 26

Patient instructed to fix on each point individually and encouraged to maintain single vision, px fixing on distance target then converges onto a spot on the jump card.