Intermittent Esotropia

Question 1

What is Primary Intermittent Esotropia?

Answer 1

The esotropia is the initial defect and is intermittently present under certain circumstances (accommodative effort, fixation distance, time/day)

Question 2

How might primary intermittent esotropia be split?

Answer 2

Accommodative (either Convergence Excess ET or Fully Accommodative ET)

Time (Cyclic ET)

Distance (Near ET or Distance ET)

Non-Specific

Question 3

What’s the difference between Near ET and Convergence Excess ET?

Answer 3

Near ET have a normal or low AC/A ratio whereas Convergence Excess ET have a high AC/A ratio

Question 4

What’s an Intermittent fully accommodative ET? Definition:

Answer 4

Corrected at both near and distance with refractive correction.

The ET is driven by clarity without glasses and when asked to relax accommodation (make the world blurry) the ET disappears to straight eyes.

A fully accommodative esotropia is a condition in which binocular single vision (BSV) is present for all distances when the hypermetropia is corrected, but in which an esotropia develops without the hypermetropic correction, as accommodation is exerted (and thus accommodative convergence) to overcome the uncorrected hypermetropia.

Question 5

What are the features of an Accommodative ET?

Answer 5

May result from:
Uncorrected refractive error
High AC/A ratio

Horwood and Riddel (2013, 2014) have shown that accommodative esotropia is sensitive to blur and excessive accommodation is exerted to see clearly.

Hypermetropia (+2.00 to +7.00DS)

Onset around 2-5 years

Presentation typically an intermittent
esotropia noticed when perform near tasks

BSV is present when hypermetropia is corrected

Child may rub/ close one eye (uncomfortable to have to do additional accommodation all of the time)

Intermittent diplopia (rarely volunteer; brain will often have suppressed also)

May have family history of hypermetropia/ strabismus

Question 6

Why is ET associated with hypermetropia?

Answer 6

• Blurred image on the retina triggers an accommodative response
• Accommodative mechanisms are related to convergence mechanisms so there is increased accommodative effort leading to over-convergence and then in the absence of adequate divergent fusion reserves, an accommodative ET presents

Question 7

In an intermittent ET that has a low degree of refractive correction (<+3.00DS) what causes the ET?

Answer 7

To see clearly, the child has to exert increased accommodation to overcome uncorrected hypermetropia which causes an increased amount of accommodative convergence, however, if there’s sufficient negative fusional reserves then BSV is maintained.

They may be able to control it some of the time to overcome the hypermetropia but in times of fatigue for example this may breakdown

Question 8

If someone has an intermittent ET with a moderate refractive error (+3.00DS - +6.00DS), how does this present?

Answer 8

Usually occurs between 2-5yo due to increased visual demands and accommodation required at this age.

They must accommodate to overcome the hypermetropia, if they have sufficient negative fusional reserves to control the AC then BSV is maintained, but if they do not this breakdown leads to the ET.
If they can accept a blurred single image however, BSV continues to be maintained.

Once hypermetropia is corrected and deviation controlled with glasses they become a fully accommodative ET

Question 9

If someone has an intermittent ET with a high degree of refractive error (>+6.00DS), how does this present?

Answer 9

This degree of uncorrected hypermetropia exceeds that possible to control with the accommodative system which is known as ‘insuperable hypermetropia’ so there is no benefit of accommodating and thus a persist blurred image is appreciated. The eyes therefore remain straight or diverge.

Question 10

What is ‘Insuperable Hypermetropia’?

Answer 10

A high degree (>+6.00DS) of uncorrected hypermetropia that exceeds that possible to control with the accommodative system which is known as ‘insuperable hypermetropia’.

Question 11

Should we give a child full hypermetropic correction?

Answer 11

Cycloplegic drugs used to test. Research says if they’re hypermetropic, give them the full prescription as there is little fluctuation between the ages of 1 - 8yo but after this age decreases slightly (previously there was some debate between giving full prescription or lesser prescription). If 4D or larger then at 6yo we start to see this decrease.

Question 12

What are the long-term treatment results of accommodative ET?

Answer 12

Mohan & Sharma (2014) -

At the first examination performed 10 years after spectacle correction (mean, 10.2 years), 85 patients (79%) had orthophoria or esotropia ≤10(Δ) at both near and distance fixation, 14 (13%) had consecutive exotropia, 5 (5%) had decompensation and 3 (3%) had esotropia with a high ratio of accommodative convergence to accommodation (AC/A). The mean time interval between presentation and prescription of full hyperopic correction, initial cycloplegic refraction, and presence of amblyopia was not associated with consecutive exotropia, decompensation, or a high AC/A ratio esotropia.

Question 13

What’s the definition of a convergence excess ET?

Answer 13

Convergence excess accommodative esotropia describes an esotropia on accommodation at near fixation, which persists with refractive correction, and is controlled to an esophoria/orthophoria at distance fixation with binocular single vision.

Bifocals – Near is more +ve convex lens
Give bifocals so that the prescription is higher in the near compared to their “near” prescription in order to give them straight eyes when looking at near.

Question 14

What are the features of Convergence Excess ET?

Answer 14

Onset around 2-5 years

Main aetiological factor is high AC/A ratio.

AC/A ratio may be 5 or 6 times the normal amount, resulting in a manifest convergent deviation for near whenever accommodation is exerted

Persistent esotropia on accommodation at near despite refractive correction

BSV is present in the distance when hypermetropia corrected

Question 15

What is Hypo-Accommodative, Convergence Excess ET?

Answer 15

Arnoldi KA (1999)

A much less common aetiological factor is thought to be a remote near point of accommodation. Excessive effort to accommodate resulting in excessive convergence and a manifest convergent squint on accommodation

BUT
This is where 1% of convergence excess patients present with low AC/A ratio (making them hypo-accommodative) so defective accommodation meaning they cannot accommodate effectively and so in constantly trying to make something clear it causes the eyes to drive in.

Question 16

What is Hypo Accommodative, convergence excess ET also known as?

Answer 16

Hyperkinetic ET

Question 17

What is the definition of Near ET?

Answer 17

A concomitant esotropia which presents at near and BSV is demonstrated in the distance, when accommodation is relieved and without the presence of a high AC/A ratio.

Only difference between near eso and convergence excess is that convergence excess have a high AC/A ratio whereas a near eso don’t have this.

= Low or normal AC/A ratio
No accommodative element or component

Question 18

What is another way of saying Distance ET?

Answer 18

Divergence Insufficiency ET

Question 19

What’s another way of saying Divergence Insufficiency ET?

Answer 19

Distance ET

Question 20

What’s a definition of distance ET?

Answer 20

A concomitant esotropia that presents on distance fixation and BSV is demonstrated at near with normal ductions.

Question 21

What are the features of distance ET?

Answer 21

Differential diagnosis:

• Mild lateral rectus palsy
• Decompensated divergence weakness esophoria
• Divergence paralysis
• Accommodative and/or convergence spasm

Question 22

What did Herlihy et al (2013) find about Distance ET in children?

Answer 22

Children:
More likely to have mild LR palsy with central nervous system (CNS) disorders opposed to a distance ET
Expect sudden onset
93% had underlying CNS disorder

Question 23

What did Herlihy et al (2013) find about Distance ET in adults?

Answer 23

Adults:
24% had associated CNS disorders
35% accommodative spasms or drug-induced reduction of accommodation,
remaining distance ET
Usually gradual onset

Question 24

How does Age-Related Distance ET present (Godts & Mathysen, 2013)?

Answer 24

Age-related distance esotropia

• Acquired, small concomitant distance esotropia (<20∆)
• Observed in elderly patients >60 years
• Gradual onset
• Slow increase in angle of deviation observed over 6-12 year period
• May initially complain of blurred vision followed by complaint of diplopia on distance fixation only
• Full OM’s

Question 25

What is the definition of Cyclical ET?

Answer 25

A rare condition in which an esotropia presents at near and distance at regular intervals, and BSV is demonstrated at other times.

• Rare disorder 1:5000 cases of strabismus
• Spontaneous onset, 2-6 years
• Associated with diurnal (day/night) clock mechanism so often an alternate day cycle
• Abnormality in superior colliculi, oculomotor nuclei or other nuclei

Question 26

What are the types of Intermittent ET?

Answer 26

• Fully Accommodative ET
• Convergence Excess ET
• Near ET
• Distance ET
• Cyclical ET

Question 27

What types of strabismus are association with IO overactions?

Answer 27

Accommodative ET’s
Distance XT
Infantile ET

Question 28

What differences would we see in our investigations between a convergence-excess esotropia and a near esotropia?

Answer 28

Conv XS ET management option is related to the accommodation at near. In Near ET accom is not a factor, just the fixation distance.
Conv XS ET typically try conservative management options. Near ET less likely to be managed conservatively.

Near ET could have prisms at near to help regain BSV at near. Prisms less likely to be effective in convergence XS ET as the deviation is driven by accommodation.

In Conv XS ET bifocals commonly prescribed - use minimal amount of + lens at near that allows ET to be controlled to E and BSV to be achieved. Typically try bifocals. Can use exercises with bifocals to help consolidate BSV and help reduce bifocal strength. Bar reading and negative relative convergence exercises.

In Near ET bifocals and additional + lens at near will not change deviation and will not allow BSV to be regained. Near ET likely to need surgery to align the eyes at near. Could use prism adpatation test to investigate correction of near deviation and effect on distance deviation. Useful if there is a large near/distance disparity in deviation size.

Question 29

What can a convergence excess be broken down into?

Answer 29

True
Simulated (by fusion) via monocular occlusion or by PAT

Those with simulated convergence excess have a comparable near deviation to those with true convergence excess but can be shown to have a distance deviation that approaches the size of the near strabismus once the normal fusional mechanisms are disrupted by a period of prism adaptation.