6. Exotropia Flashcards
What is exotropia?
A manifest deviation where there is misalignment of the visual axis resulting in an outward turning of one eye.
- X
- XT
- X(T)
Meanings
- X = exophoria
- XT = exotropia
- X(T) = intermittent exotropia
Is lateral incomitance common in exo deviation?
And what is it?
YES
This is where the deviation is smaller on lateral gaze.
What is primary constant exotropia?
2 types?
Exotropia in all conditions. Squint is the initial problem.
1. Early onset
2. Decompensated exotropia or intermittent exotropia that will become constant
What is early onset primary constant esotropia? Surgery useful?
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.
What is Decompensated exophoria or an intermittent exotropia that has become constant.
When is the patient likely to be symptomatic?
BSV possible after surgery?
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.
How to differentiate between early onset and decompensated exophoria?
Through H&S.
How to differentiate between early onset and decompensated exophoria, through diplopia?
Diplopia suggests no suppression and therefore not early onset exotropia.
If an early onset XT and not alternating of constant exotropia, px likely to?
To be amblyopic
CT of decompensated exophoria?
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.
How does checking for BSV, help determine if early onset or decompensating constant exotropia?
use that BI prism and check for stereopsis using any test available. If yes, potential for BSV hence, decompensated exophoria.
Early onset or decompensated exophoria: Adult px + unilateral squint
Decompensated exophoria, Suggesting that during the plastic period they were binocular.
Test to differentiate: Early onset vs decompensated exophoria
When deviation corrected on prism cover test, px can pass stereopsis test- suggests px have BSV= Decompensated exophoria
Management of primary constant exotropia?
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.
Classification of primary intermittent exotropia?
Exotropia is the only problem and present sometimes only.
1. Distance exotropia (true & simulated)
2. Near exotropia
What is distance exotropia?
Exotropia at distance, exophoria at near.
Suppression for distance + BSV when controlled for near fixation.
Older onset
True vs Simulated distance exotropia?
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.
What do parents notice with primary intermittent exotropia?
Parents often complain of children closing one eye especially in bright sunlight.
Minus lens therapy for exotropia?
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.
What is near exotropia?
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.
Secondary exotropia?
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.
Management of secondary exotropia?
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.
What is consecutive exotropia?
*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.
Management of consecutive exotropia?
- Observe: If cosmetically good with no diplopia. -nothing done. Keep observing.
- Botulinum toxin: Useful if angle is considered too small for surgery or to ascertain best post op deviation that will render patient asymptomatic.
- Prisms can be used to place patient back in suppression scotoma if diplopia is present.
- 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.
