CONVERGENCE EXCESS ESOTROPIA Flashcards
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What is a convergence excess SOT?
Esotropia at near, Esophoria in the distance
* Esophoria at near with +3.00D
* High AC:A ratio (normal 3-5:1) causing SOT at near
Characteristics of convergence excess?
Onset : 2-5 years old
* Characteristics: Hypermetropia (+1.50 to +5.00 DS), int ET to an accommodative target, SOT on near fixation even with full +, BSV in distance when corrected, ET N>D s gls, High AC:A ratio often 8:1 or more, monocular eye closure seen, equal VA generally, supp’n at near when ET.
Differential diagnosis of convergence excess sot?
- Near SOT (normal AC:A), Fully Acoom SOT (undercorected +, fully cyclo + atropine/tropicamide), Constant SOT c accom element (ET in distance for constant – no BSV), V SOT (OM height noticed, CT in depression, PCT in different positions)
Investigation in convergence excess?
- Cyclo Refraction and adaptation period (16-18 wks) – give full +
- VA
- CT; light, accom, target, with and without glasses
- AC/A Ratio
- Prism adaptation test
O Pre-operative use – beneficial to surgical outcome
oMedian increase in angle of 20∆ seen at 1/3m and 6m following PAT (Garretty (2018))
What are the types of treatment in convergence excess SOT?
Orthoptic treatment
* Optical treatment – bifocal spectacles or contact lenses
* Pharmacological
* Botox - Not found to be effective or a useful long-term Mx
* Surgery
Management for convergence excess sot depends on?
- Size of deviation
O Large near angle more likely long-term bifocal or Sx
O Small near angle short-term bifocal and orthoptic exercises - AC/A ratio
O Larger than 8:1 likely require Sx - Level of BSV
O ABSV or little motor fusion – post-op consecutive XT risk
What happens next if bifocals are tolerated well and compensated well in convergence excess sot?
- Gradual reduction in bifocals rx to wean off + add rx, decrease by +0.50 and check CT, Bag Gls, PFR and Stereo + can combine with orthoptic exercises e.g. negative relative convergence in bar reading
O If works then eventually bifocals discarded and px remains compensated, no further treatment!
O If there is recurrence of SOT at near then long-term bifocals needed (young adults not able to accommodate so generally not recommended) or surgical treatment!
What happens next if bifocals are poorly tolerated or not well compensated well in convergence excess sot?
- Surgical treatment – prev. bifocal use = no detrimental influence of surgical outcome (Lueder & Norman (2006))
Assessing for bifocals in convergence excess sot?
1: Establish minimal reading correction
* Print comparable with size used at school
* Start with +1.00DS
* Increase by +0.50DS until BSV and clear print
2: Post- 1 month trail
* If control not maintained can increase lens strength
* If control, continue with review
* Or BSV is not maintained, discard with bifocals
* Minimum 18 months wear
3: If maintaining control
* Attempt to reduce by 0.50DS steps until discarded
* Wait until child is 6 years old before attempting to reduce +
What type of segment for bifocals in convergence excess sot?
D-35 or D-40 segment
* Fitted so top of reading segment passes just below middle of pupil when eye in PP
What are advantages and disadvantages of bifocals in convergence excess sot?
Bifocals Advantages:
* Short-term use an effective method of treatment – maintain BSV
* Medium and long-term an alternative to surgery
Bifocals Problems:
* Poorly fitted reading segment
* Keeping lenses centred
* Blurred vision – reading difficulties
Surgery in convergence excess sot?
- ET >20∆ at near
- AC/A >8:1
- Poor or no response to nonsurgical treatment
- Decision based on PAT (prism adaptation test) at near
O Remain E then success likely (Group 1 – E <8∆ N& D = Bilateral MR recession (maximum post-prism angle)
O If become XT at D more difficult to manage – risk of surgical overcorrection (Group 2 – E <8∆ N, XT in D = Bilateral MR recession + posterior fixation suture – 2/3 of final prism angle to leave E at D)
- Bi-medial recession +/- hangback suture
- Warning of crossed diplopia on versions postoperatively
