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Intraday Variability of Control in Intermittent Exotropia

Sarah R. Hatt, Brian G. Mohney, David A. Leske, Jonathan M.

Holmes

Mayo Clinic, Rochester, MN, USA

Intermittent Exotropia - Control• Poor control:

> 50% of waking hours

• Deterioration – consecutive visits: indicator for surgery

• Type and degree of variability of control within 1 day is not known

Implications for: • defining severity• interpreting change in control over time

Purpose

To assess the variability of control over one day

in children with intermittent exotropia

using control scale to quantify control

Methods – Control AssessmentControl Score Control Score Description

5 Constant exotropia during a 30-second observation period (before dissociation)

4 Exotropia >50% of the time during a 30-second observation period (before dissociation)

3 Exotropia <50% of the time during a 30-second observation period (before dissociation)

2 No exotropia unless dissociated (10 seconds): recovery in > 5 seconds

1 No exotropia unless dissociated (10 seconds): recovery in 1-5 seconds

0 Pure phoria: < 1 second recovery after 10-second dissociation

Mohney BG, Holmes JM. An office-based scale for assessing control in intermittent exotropia. Strabismus 2006;14:147-50.

Control scale reliability near control k=0.95 distance control k=0.94

Inve

stig

ato

r 2

Investigator 1

0

1

2

3

4

5

0 1 2 3 4 5In

vest

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2Investigator 1

0

1

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0 1 2 3 4 5

Scores differed by no more than one level on the control scale:

Real change in control defined as change of 2 or more levels on scale.

Methods – Intraday variability

• 13 children with intermittent exotropia (median age 8 years; range 1 to 13) No convergence insufficiency type exotropia

• No co-existing ocular pathology

• No amblyopia

Methods – Intraday variability

Examined 3 or 4 times over one day

(minimum 2 hours apart)

Control assessed using control scale

Variable = change in control 2 or more levels on control scale over day (distance or near)

Stable = no change in control over day

10:31-13:008:00 -10:30 13:01-15:30 15:31-18:00

Results – Intraday variability of control

Median angle - near

30^26^Median angle - distance

11Median control - near

20^25^

1*2.75Median control - distance

7.2 years7.3 yearsMean age

Stable control

7/13 (54%)

Variable control

6/13 (46%)N=13

* p=0.04

Patient 1

Patient 10

Patient 13

Results – Variable distance control

Assessment time

Con

trol

sca

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atin

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0

1

2

3

4

5

8:00 -10:30 10:31-13:00 13:01-15:30 15:31-18:00

Tro

pic

Ph

oric

0

1

2

3

4

5

8:00 -10:30 10:31-13:00 13:01-15:30 15:31-18:00

Patient 3

Patient 5

Patient 11

Patient 13

Results – Variable near control

Assessment time

Con

trol

sca

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Ph

oric

Tro

pic

Results – Summary

• Control varies over one day in some patients with intermittent exotropia.

• Change occurs between spontaneous tropia and well controlled phoria.

• Worst control not always at the end of the clinical day.

Change in distance control

0

1

2

3

4

5

January April August

Assessment time

Con

trol

sca

le r

atin

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Tro

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Ph

oric

10:30

12:45 14:49

Conclusions• An isolated measure of control may be insufficient

to represent: baseline severity change over time.

• If control has a role in evaluating severity, multiple measures will be needed.

• Change in isolated measures of control should not be used for surgical decision making.

Thank You

Supported by:

EY015799 (JMH)

Research to Prevent Blindness, Inc.