CONSTANT ESOTROPIA WITH AN ACCOMMODATIVE ELEMENT (PARTIALLY ACCOM SOT)

Question 1

Characteristics of a constant SOT with an Accom element?

Answer 1

• Onset 1-3 years, gradual
• Hypermetropia
• Anisometropia/astigmatism
• Angle reduces with correction (10∆) but doesn’t correct fully
• Strabismic/ Aniso Amblyopia
• Poor BSV potential – likely suppression, possible ARC (small angle)
• o/a of IO muscles

Question 2

Aetiology of constant sot c accom element

Answer 2

Decomp fully accom or convergence excess = non accom element develops
* Small angle costant ET that develops accom element = increase deviation size probably due to lack of bsv

Question 3

Investigations in constant sot with accom element?

Answer 3

• Hx
• Rx + adaptation = give full plus
• VA
• CT (light, target, c glss, s glss)
• OM

Question 4

Investigation for BSV potential in Constant SOT with an accom element:

Answer 4

• Prism adaptation Test (To assess potential for BSV & appropriate sx target angle)
• Synoptopher (older children)
• Post-op diplopia test (children > 5 y/o, those who don’t show evidence of BSV, unlikely if sot left uncorrected)

Question 5

How to conduct a prism adaptation test?

Answer 5

• To assess potential for BSV & appropriate sx target angle
• Correction of non-accommodative component with prisms
• Should be attempted in all patients over 3 yrs
• All those with 0.3 or better in worse eye
• Those with <40∆ deviation
• If angle greater for near than distance

O Correct larger angle
O Divide strength of prism between 2 eyes
O If VA unequal, higher prism before better eye
leave for 1 week?

• 4 possible responses

1. Visual axes become straight & BSV confirmed or
2. Residual microtropia with BSV = Prism responder - ∆ gradually increased to assess maximum angle. When stable <8∆ Sx to correct max angle.
3. Visual axes reconverge – ‘eating up’ prism – possible ARC or
4. Remain convergent – lack of binocular cooperation = Nonresponder – BSV cannot be demonstrated

• Sx on angle measured initially (before PAT). Will have Suppression or Possible diplopia (rare)
  = If ET >8∆ & no BSV after 1/52, increase ∆, see weekly until stable angle <8∆ or ET greater than able to correct with ∆

Question 6

Management Aims of constant SOT with an Accom Element?

Answer 6

• Obtain optimum or equal VA
• Restore normal BSV if possible
  O Early identification of these patients to expedite their treatment for good prognosis
• Improve cosmetic appearance if no potential for BSV

Question 7

Management of constant SOT with an Accom Element non surgical

Answer 7

Correct any refractive error
* Fully correct – MAXIMUM PLUS
* Refractive adaptation
* Long-term use likely
* If <+3.00DS without cyl & no sign of + increasing, gls could be discarded
O VA and angle reassessed
O Surgery to correct angle without glasses

Treat any amblyopia
* Strabismic amblyopia common
* May also have Anisometropic / Meridional
* Treat amblyopia before attempting to correct deviation

Question 8

Management of constant SOT with an Accom Element - Treatment to restore BSV?

Answer 8

• Identify patient with potential for BSV from investigation
• Prism Adaptation Test, BSV test with correcting prism or synoptopher or will have negative sensory / stereo tests
• These patients have NRC
• Aim
  o Achieve BSV for near and distance with glasses
  o Consider PAT to identify true angle of deviation
• Used to restore or promote development of BSV
• Temporary or incorporated
• Nonaccommodative component up to 20∆ most suitable
• Prisms:
  o Used to restore or promote development of BSV
  o Temporary or incorporated
  o Nonaccommodative component up to 20∆ most suitable
• Botulinium Toxin A
  o MR of deviating eye
  o Causes paralysis of MR for 3/12
  o Temporary reduction or correction of angle
  o Allows investigation of sensory status over vide range of angles
  o Can cause incomitance/vertical deviation/ptosis
  o If gives them BSV, may remain straight
• Surgery:
  o Type of surgery depends on
   Size of deviation
   Difference between near and distance angle
   Previous surgery
  o Procedure
   Unilateral MR recess / LR resect – deviation N=D
   Bilateral MR recess – deviation N>D
   3-4 procedures if large angle, IO o/a & V-pattern

Question 9

Management of constant SOT with an Accom Element - Treatment to improve cosmetic appearance – no BSV potential?

Answer 9

• Good cosmesis = Observation:
  o Small deviation – cosmetically acceptable
  o Treat amblyopia
  o Observe until 7-8 years
  o Patient with ARC – no need for surgery, eyes revert back to original angle
• Poor cosmesis = Make deviation less noticeable
• Slightly undercorrect angle – aim for 5-8∆ (residual ET) – PODT
  o Botulinum Toxin A
  o High risk diplopia / unsuitable for surgery
  o Controversial in young due to repeat injections

O Surgery:
O 15-35∆ - 1 muscle surgery = Unilateral MR recess / LR resect – deviation N=D
O 50-70∆ - 2 muscle surgery = Bilateral MR recess – deviation N>D
O >70∆ - 3 muscle surgery = Bilateral MR recession / LR resection, IO o/a & V-pattern

Question 10

Prognosis of long term surgical outcome of constant SOT with accom element?

Answer 10

• 19% residual ET (Deteriorated refractive ET, Moderate – severe amblyopia, Increasing + with age)
• 37% surgical success
• 44% developed consecutive XT (Distance-near disparity, Low + Rx, Anisometropia, Poor BV, Undercorrection of + prior to Sx)