INTERMITTENT DISTANCE (+NON-SPECIFIC) EXOTROPIA Flashcards
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Management for non-specific xot?
Intermittent distance and nonspecific only differ in PCT – otherwise the same and investigation & management is the same
What is intermittent non-speicifc exotropia?
- Difference in PCT N & D <10∆
- XT may be intermittently manifest at any distance
o Usually distance fixation
What are characteristics of intermittent distance xot?
- Females > males
- Age of onset: >6 months
- Better control at near
- Suppression when manifest, sometimes panoramic vision
- Manipulation of accommodation and/or vergence to control
- Natural history variable
- Manifest – inattention (daydream), poor GH, fatigue, alcohol, bright lights
How does intermittent distance xot expected to progress from xop at dis?
- Xop at dis, NAD at nr
- Xot intermittent at dis, xop at nr
- Xot at dis, Xot intermittent at nr
- Xot at dis, xo tar nr
Investigations in intermittent distance xot? (in order!!!)
- Case History
- PFR (normal @ near (BO decreased) control good or not)
- Convergence (tells you about control)
- Bagolini (supress in the distance)
- Stereoacuity – N & D
- AC/A – measured in distance or near
- CBA – over accommodate to control so VA reduced
- PCT (far distance, distance, near)
- OM – lateral incomitance (sizegaze = adduction weakness) / A&V patterns (A = 10 ^ difference, V = 15^ difference)
- Diagnostic occlusion (patch, wait 30 mins, shut eyes and then open and do CT)
- Control score (newcastle)
- VA - equal
- CT (far distance) FD > D > N
What are subtypes of intermittent distance xot and how to determine them?
- Monoc occlusion for 1 hour (Gurlu & Erda 2008 = 1 hour)
a. No change in angle = measure with +3.00 DS
i. No change in dev angle = true intermittent distance xot
ii. Near angle now = distance angle = simulated due to accom distance xot c high AC:A
b. Near angle = distance angle = simulated due to fusion distance xot with normal AC:A
What is management for intermittent distance xot?
What is management for intermittent distance xot?
1. Correction of refractive error
* Generally no significant error
* <+3.00DS best left uncorrected
* >+3.00DS rare but may give improved control when issued
* >-0.50DS or significant aniso – correct
- VA restoration
* Amblyopia may improve with glasses alone
* Occlusion
O decompensation may occur
O generally increase in VA improves BSV and control
3: Observation
* Often variable control
* Several reviews prior to management decision
* Newcastle Control score particularly helpful = control questionnaire that grades seveity of int dis xt by using subj and obj qns to figure who needs sx (Score ≥3 unlikely to cure without surgery) also measures change overtime
What are we looking for when observing intermittent distance xot?
- Cover Test: Recovery speed and how readily the deviation decompensates
- Convergence = Deterioration = poor near control = leads to constant XT
- Angle of deviation- Increase in angle may indicate XT becoming more difficult to control combined with PFR result
- CBA = Watching for reduced distance CBA – using accommodation or vergence to control
- Uniocular VA = Amblyopia development implies manifest most of the time
What is distance stereoacuity test?
- FD2 – more sensitive in intermittent distance xot = reduced stereo in distance which improves after surgery (Adams et al. 2008)
When is treatment considered in intermittent distance xot?
- NCS - deviation manifest sufficiently often
- Cause concern
- Affecting BSV function and VA
What are Treatment Options in intermittent distance xot?
o Orthoptic exercises
o Optical
Concave lenses (OMLT)
Prisms
Tinted glasses
o Occlusion treatment
o Botulinium toxin
* Surgery
What are orthoptic exercises in intermittent distance xot used for?
- Generally of limited value as surgical alternative
- Cooperation and understanding required
o Unlikely in under 6 - Has been shown to enhance surgical result compared to surgery alone
- Role in postsurgical undercorrection
- Eliminate Suppression: Only if NRC demonstrable
- Strengthen BSV: Extension of positive fusion amplitude, Relative convergence
What is minus lens treatments in intermittent distance xot ?
- Optical Treatment – minus lenses
- Minimum strength that gives control (up to -3.00DS)
- Stimulates convergence by inducing accommodation
- Recent evidence that control of XT is disparity driven (Horwood & Riddell 2012)
o Minus lenses allow clear vision to compensate for convergence accommodation
o Would explain success in patients with or without high AC/A ratio - Those with high AC/A likely to have largest reduction in angle
o Still works in those with normal AC/A
Adverse effects of minus lens therapy in int distance xot?
O No evidence that prolonged use leads to long-term refraction changes- Kushner 1999
O Some evidence that those already myopic may have an increase in myopia during treatment - Chen et al. 2021
Method of using minus lens therapy in int distance xot?
- Minimum minus lens given (up to -3.00DS) that control deviation at near and distance without reducing VA
- Start at -1.00DS in a trial frame and increased by 0.50DS until deviation is controlled. If no improvement in control found then give -3.00DS.
- Issue for full time wear and review in 6 weeks
- If control isn’t maintained, reassess for an increase in concave lens. Leave for minimum of 6 months
- If control is not achieved or maintained then discard glasses
- If maintaining control then reduce in 0.50DS steps until able to discard of minus lenses. Increase strength again if control not maintained and wait a further 6 months
