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Strabismus -  Accurate measurements of esotropia without a prism test Lecture 17 of 54  NEXT»

"How can accurate measurements be obtained in a child with partially accommodative esotropia to determine the appropriate amount of surgery without a prism adaptation test when a Fresnel prism isn't available?"

One example is a child wearing + 9.00 diopter glasses with a deviation that is the same at distance and near with no A or V patterns and no muscle overactions.

The first point is to make sure that this child has had a repeat cycloplegic refraction with cyclogel or atropine after the child has been wearing the +9.00 glasses for 30 days or more.  If the repeat refraction detects +.75 diopters of hyperopia or more, then new spectacle lenses need to be prescribed and worn for 30 days and then the deviation re-measured.

The first goal is to make sure that the total accommodative element has been detected and controlled with glasses.

The amount of esotropia measured through +9.00 glasses with prism and alternate cover test will probably be a few diopters less than the actual total amount of esotropia present.  With the eyes turned nasally from the center of the spectacle lenses, the eyes are looking though base-out prisms created by the nasal part of the convex hyperopic lenses. These “base-out prisms” are like additional base-out prism on top of the prism you are holding in front of the glasses when you do the prism and alternate cover test and help to compensate for the amount of esotropia present.  There are rules to determine this, but for this clinician, I add ˝ additional millimeter to the surgical recession number for each medial rectus when the amount of hyperopic spectacle correction is +5.00 or more.  I am assuming that the actual amount of esotropia is 5 – 10 prism diopters more than that measured by normal alternate prism and cover test when the child is wearing significant hyperopic spectacles.  

For this child with 25 prism diopters of esotropia measured by alternate prism and cover test, I would recess each medial rectus 4.5 mm which is ˝ mm. more that the surgical numbers listed in the American Academy of Ophthalmology Section Six Manual.

For years, people have added additional amounts of surgery for partly accommodative esotropia.  Some would add up to a full mm. and if the near deviation was greater than the distance, would operate for the near deviation.

Preoperative prism adaptation can be very useful in all of these cases of acquired esotropia and especially those of partly accommodative etiology.  This is a required part of the pre-operative workup for all of these type patients under my care.  I understand that you do not have Fresnel prisms available, but I would encourage you to try and obtain them as prism adaptation can be very useful in determining how much surgery to do in these cases.

 

- Jack Baker, M.D.
  Pediatric Ophthalmology/Strabismus
  Children's Hospital of Michigan
  Detroit, Michigan

 

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