Observation Versus Occlusion Therapy for Intermittent Exotropia
Condition: Exotropia
MeSH terms: Exotropia
Study type: Interventional

Summary: 
      The present study is being conducted to assess the natural history of intermittent exotropia
      and to establish the effectiveness of occlusion in its treatment.

      Study Objectives:

        -  To determine the effectiveness of occlusion for the treatment of intermittent exotropia
           among patients aged 3 to < 11 years who have baseline near stereoacuity of 400 arcsec or
           better by Preschool Randot stereotest

        -  To determine the natural history of intermittent exotropia among patients aged 3 to < 11
           years who have baseline near stereoacuity of 400 arcsec or better by Preschool Randot
           stereotest
    

Detailed description: 
      Intermittent exotropia (IXT) is the most common form of childhood-onset exotropia with an
      incidence of 32.1 per 100,000 in children under 19 years of age. Intermittent exotropia is
      characterized by an exotropia that is not constant and is mainly present in the distance but
      may also be present at near. Many cases of IXT are treated using non-surgical interventions,
      such as part-time occlusion, fusional vergence exercises, and over-minus lenses. The
      rationale for such interventions is that they may improve the ability to control the IXT and
      preserve stereoacuity, thereby potentially addressing both visual function and social
      concerns, and may delay or eliminate the need for surgical correction of IXT. Nevertheless,
      the natural history of IXT is unknown and in many cases it is not known whether withholding
      treatment may in fact allow for spontaneous resolution or improvement in IXT, making
      non-surgical or surgical intervention unnecessary. Moreover, although non-surgical treatments
      for IXT are commonly prescribed, such treatments have not been subjected to rigorous study
      and their efficacy in improving visual function or social concerns remains unclear.

      One aim of the present study is to better understand the natural history of IXT. Available
      reports on the natural history of IXT disagree on the progression of the disease. A 1966
      study by von Noorden (cited in von Noorden and Campos) found that over an average of 3.5
      years of follow-up, 75% of 51 patients showed signs of IXT progression, 9% showed no change,
      and 16% improved without therapy. A 1968 retrospective study by Hiles et al found that after
      a minimum of 6 years follow up with observation and nonsurgical treatment, 81% of 48 patients
      showed no change in angle of deviation. The results of more recent retrospective studies show
      some reporting that the majority of cases improve over time, others reporting that most cases
      remain stable, and still others reporting that most cases deteriorate. It is therefore
      unclear what proportion of patients, if left untreated, is likely to deteriorate, improve, or
      remain stable over time. Natural history data acquired during this study will help determine
      not only what proportion of patients change over time, but whether there are associated
      prognostic indicators of deterioration or improvement. Such data will not only enable better
      identification of those patients with IXT likely to benefit from treatment and those for whom
      treatment is likely to be unnecessary, but will also improve the quality of medical advice to
      parents regarding the likely progression of the disease, thus alleviating anxiety.

      The aim of most forms of non-surgical treatments for IXT is to improve the strength and/or
      quality of binocular single vision by either eliminating suppression, increasing awareness of
      diplopia, and/or increasing positive fusional amplitudes. Commonly used non-surgical
      treatment methods include: occlusion, fusional vergence exercises (sometimes known as vision
      therapy or orthoptics), and over-minus lenses. When surveyed in 1990, members of the American
      Association for Pediatric Ophthalmology and Strabismus reported that occlusion was the most
      commonly used form of non-surgical treatment. More recently (2008), a poll of our
      investigator group revealed again that occlusion was the most widely prescribed non-surgical
      treatment for children affected by IXT.

      Occlusion is thought to work by interrupting the development of or eliminating already
      present suppression, an adaptation to avoid diplopia in IXT. Persistent or entrenched
      suppression prevents normal binocular vision and may lead to permanent loss of stereoacuity.
      If successful, occlusion may then result in improved binocular sensory fusion.

      As reported in recent reviews of treatment for IXT, previous studies of occlusion vary
      regarding the recommended occlusion dose (from 3 hours a day to full time), the optimum
      duration of occlusion treatment (from 6 weeks to 42 months), and which eye should be occluded
      (preferred/dominant eye or alternate eyes). For the majority of studies, part-time occlusion,
      rather than full-time occlusion was preferred. In the three occlusion studies conducted
      prospectively, the recommended dose was either 3 hours a day, 3 to 6 hours a day, or 4 to 6
      hours a day, and the duration of occlusion ranged from 3 months to 6 months to up to 42 (mean
      15) months. Nevertheless, these previous studies of occlusion for the treatment of IXT used a
      variety of outcome measures at a variety of non-standardized time points; therefore, no
      definite conclusions can be drawn from the existing literature.

      Although occlusion treatment for IXT treatment is widely used, there have been no randomized
      clinical trials evaluating its effectiveness. Understanding the degree of effectiveness of
      occlusion treatment for IXT and the natural history of IXT has important public health
      implications. Successful restoration of binocular alignment and normal binocular function
      with occlusion therapy, or spontaneous improvement, will reduce the proportion of children
      undergoing surgery. Defining the rate of success with either occlusion or observation is
      therefore important in planning treatment for children with IXT. Alternatively, evidence of
      low treatment effectiveness with occlusion will help avoid unnecessary treatment.

      The present study is being conducted to assess the natural history of IXT and to establish
      the effectiveness of occlusion in its treatment.
    

Intervention name(s): occlusion treatment
Intervention type(s): Device
Intervention description(s): Patients randomized to the occlusion treatment group will receive occlusion (patching) for 3 hours per day for at least 3 months. Choice of which eye to occlude, or whether to alternate daily, is at investigator's discretion.
Other intervention name(s): occlusion therapy; patching
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: intermittent exotropia; IXT; natural history; occlusion therapy; occlusion; patching; strabismus; strabismus treatment; stereoacuity; motor alignment