6. Exotropia

Question 1

What is exotropia?

Answer 1

A manifest deviation where there is misalignment of the visual axis resulting in an outward turning of one eye.

Question 2

• X
• XT
• X(T)
  Meanings

Answer 2

• X = exophoria
• XT = exotropia
• X(T) = intermittent exotropia

Question 3

Is lateral incomitance common in exo deviation?
And what is it?

Answer 3

YES
This is where the deviation is smaller on lateral gaze.

Question 4

What is primary constant exotropia?
2 types?

Answer 4

Exotropia in all conditions. Squint is the initial problem.
1. Early onset
2. Decompensated exotropia or intermittent exotropia that will become constant

Question 5

What is early onset primary constant esotropia? Surgery useful?

Answer 5

Early onset of esotropia (early childhood), hence early onset of suppression. Px has very little experience being binocular, poor prognosis of BSV after surgery.
Surgery only used for cosmesis, poor prognosis of BSV after surgery.

Question 6

What is Decompensated exophoria or an intermittent exotropia that has become constant.
When is the patient likely to be symptomatic?
BSV possible after surgery?

Answer 6

Exophoria previously, they have decompensated so they are no more an intermittent but a CONSTANT Exophoria.
Px symptomatic and complains of diplopia if onset after plastic period, because suppression not developed.
BSV possible after surgery.

Question 7

How to differentiate between early onset and decompensated exophoria?

Answer 7

Through H&S.

Question 8

How to differentiate between early onset and decompensated exophoria, through diplopia?

Answer 8

Diplopia suggests no suppression and therefore not early onset exotropia.

Question 9

If an early onset XT and not alternating of constant exotropia, px likely to?

Answer 9

To be amblyopic

Question 10

CT of decompensated exophoria?

Answer 10

Look for any sign of intermittent control even if it appears constant on observation. E.g. exo in distance but accommodate and convergence on near.

Question 11

How does checking for BSV, help determine if early onset or decompensating constant exotropia?

Answer 11

use that BI prism and check for stereopsis using any test available. If yes, potential for BSV hence, decompensated exophoria.

Question 12

Early onset or decompensated exophoria: Adult px + unilateral squint

Answer 12

Decompensated exophoria, Suggesting that during the plastic period they were binocular.

Question 13

Test to differentiate: Early onset vs decompensated exophoria

Answer 13

When deviation corrected on prism cover test, px can pass stereopsis test- suggests px have BSV= Decompensated exophoria

Question 14

Management of primary constant exotropia?

Answer 14

Treat any amblyopia, if concerned about post-op diplopia: Bot-tox injection used prior to surgery- does the px get double vision?
Adjustable surgery is done -allows alteration after surgery.
Decompensated exophoria- complain of constant double vision –> fresnel prism used. If px doesn’t want surgery or if in the waiting list.

Question 15

Classification of primary intermittent exotropia?

Answer 15

Exotropia is the only problem and present sometimes only.
1. Distance exotropia (true & simulated)
2. Near exotropia

Question 16

What is distance exotropia?

Answer 16

Exotropia at distance, exophoria at near.
Suppression for distance + BSV when controlled for near fixation.
Older onset

Question 17

True vs Simulated distance exotropia?

Answer 17

1.TRUE: Distance angle is greater than near angle. Exotropia at distance, esophoria at near.
2.SIMULATED: Near angle appears smaller because patient uses either FUSION or ACCOMMODATION to control near angle. Present as a distance exo, use excessive fusion or accommodation to hold that.

To differentiate: Initiate one hour of uniocular occlusion whilst in the clinic to disrupt fusion, then re-measure near angle. Angle of deviation measured using +3.0s at near fixation to eliminate accommodation. If angle has increased in either case then the distance exotropia is stimulated.

Question 18

What do parents notice with primary intermittent exotropia?

Answer 18

Parents often complain of children closing one eye especially in bright sunlight.

Question 19

Minus lens therapy for exotropia?

Answer 19

It works on the principle that minus lenses induce accommodation and therefore convergence. This extra convergence may reduce the size of the exo deviation, hopefully to a size where control can occur and BSV is restored.
Glasses are prescribed with extra -2, full time wear for 3 months, then reduced in 0.5D steps.
Child will learn how to control accommodation.

Question 20

What is near exotropia?

Answer 20

Exotropia at near fixation and orthophoria or exophoria at distance fixation can either be a primary near exotropia with suppression at near and BSV at distance fixation.

Question 21

Secondary exotropia?

Answer 21

It is secondary to a pathological condition (congenital or acquired) giving rise to poor/ poorer vision e.g. cataract, optic atrophy etc. in one eye.

Question 22

Management of secondary exotropia?

Answer 22

1.Usually requires surgery though results may be more unpredictable due to poor VA. Again aim for slight ET post-op.
2.Botulinum toxin
3.Occlusion therapy may be undertaken if it is thought there is strabismic amblyopia superimposed on the reduction in VA as a result of the pathology.

Question 23

What is consecutive exotropia?

Answer 23

*This is exotropia that exists in a patient that previously had esotropia.
*Can occur spontaneously: eyes that are not binocular commonly diverge with time, or it can occur post operatively.
*Patients may complain of diplopia if out of initial suppression scotoma.

Question 24

Management of consecutive exotropia?

Answer 24

1. Observe: If cosmetically good with no diplopia. -nothing done. Keep observing.
2. Botulinum toxin: Useful if angle is considered too small for surgery or to ascertain best post op deviation that will render patient asymptomatic.
3. Prisms can be used to place patient back in suppression scotoma if diplopia is present.
4. Surgery: Undertaken if cosmesis poor or constant diplopia due to drifting out of the suppression scotoma (in a deviation considered large enough for surgery). The aim of surgery if possible, would be to place eyes in a slightly esotropic position post- operative. This allows the eyes to re-diverge with time but remain cosmetically good.