The goal of this clinical trial is to compare the efficacy of bilateral lateral rectus recession and bilateral primary medial rectus resection in basic type intermittent exotropia

Participants will be randomized into two groups: bilateral lateral rectus (BLR) recession and bilateral medial rectus (BMR) resection groups then followed up in the clinic for 6 months to compare motor alignment and sensory functions

Study location: Cairo university hospitals

Methodology:

Patients with basic type intermittent exotropia who are indicated to undergo surgical intervention will be grouped into two groups one group will undergo bilateral lateral rectus recession and the other will undergo bilateral medial rectus resection.

• Preoperatively, all patients will be subjected to:

  1. A detailed history taking including presence of asthenopia, monocular closure, disfigurement or diplopia. The previous use of glasses for optical correction, use of minus lenses, or prior part time occlusion will be documented.

  2. A detailed ophthalmological examination; including uncorrected and best corrected visual acuity whenever possible, cycloplegic refraction, anterior segment examination and dilated fundus examination.

  3. Motor Evaluation:

     • Ductions and versions will be done to assess the ocular motility in 9 positions of gaze.
     • The angle of deviation will be measured by the alternate prism cover test for both distance (6 meters) and near (33 cm) , with and without glasses.
     • The angles of misalignment will also be measured in side gazes and in straight up and down gaze whenever possible.
     • In patients with near-far disparity, the angle of deviation will be measured again after patching one eye for 30 minutes, as well as after putting +3 D lenses in front of each eye.

     Patients with near-far disparity >10 prism diopters (PD) will not be included

  4. Sensory Evaluation:

     Worth 4 dot test and stereopsis using Random dot test (when possible) The control of exotropia will be assessed using both the newcastle control score

     Patients will be randomly assigned to either surgery using simple randomization by random number generator

• Intervention:

  • One group will undergo bilateral lateral rectus recession and the other will undergo bilateral medial rectus resection according to the standard tables.
  • All cases will be done under general anaesthesia.
  • Both surgeries take about 30 minutes.
  • Postoperative treatment combined tobramycin 0.3% and dexamethasone 0.1% eye drops 3 times daily and the same combination eye ointment at night for 3 weeks.
  • Postoperative follow up will be 1 week, 6 weeks, 3 months and 6 months (minimum follow up)

• Postoperative assessment:

  • Extraocular movement in lateral gazes will be examined for comitance

  • Alignment in the primary position will be assessed and any deviation will be measured using alternate prism cover test

  • Palpebral fissure height will be measured

  • Worth 4 dot test and stereopsis will be assessed (when possible)

    • In cases of failure either over correction or under correction reoperation will be performed after 3 months of the initial surgery.

• Sample size

We are planning a study of the difference in the postoperative angle between the 2 surgical techniques. Assuming a mean difference of 5 PD with a standard deviation of 5 PD, an alpha error of 0.05 and a power of study of 0.8, a total of 17 subjects were found to be needed in each group. Assuming a drop-out rate of 20%, a sample of 20 subjects will be targeted in each group.

Inclusion Criteria:

• Patients with basic type intermittent exotropia
• Measurable angle 25-40 prism diopters

Exclusion Criteria:

• Restrictive or paralytic deviation or if forced duction test is positive on horizontal muscles
• Incomitant deviation, vertical or oblique muscles surgery and significant A or V pattern
• Previous strabismus, orbital or buckle surgery