None listed
Conditions
Brief summary
Intermittent exotropia (IXT), characterised by periodic divergence of visual axes and exacerbated when tired or sick, is the most common subtype of ocular misalignment among children affecting about 25% of the total strabismic population. Minus lens over-correction is one of the most common non-surgical method used in the treatment of IXT. Although improved control has been reported, no clear clinical guideline exists in determining the over-correcting minus lens strength; some adopted ‘one-for-all’ approach prescribing a constant power (-2.0D or -2.5D) while others used a ‘trial and error’ method. In this study, a novel method of customising minus lens over-correction based on angle of deviation, AC/A ratio and amplitude of accommodation will be used. Primary outcome is the IXT control after using customised minus lens where the success defined as the improvement of greater than 1 control score from the pre-treatment (baseline) score. Additional outcomes include measurement of angle of deviation, range of fusional vergence, suppression, distance stereopsis, and progression of myopia. This is a single site, prospective, randomised clinical trial. Subjects will be block-randomised depending on severity of IXT among children aged between four and fifteen years old. The treatment group will receive custom minus lens overcorrection whereas the control group will receive only their refractive correction, if any. The study will be conducted at ophthalmology department of Queensland Children’s Hospital under strict ethical guideline subject to approval from the relevant ethical committee. 2. OBJECTIVE The major objective of the study is to investigate efficacy of uniquely customised minus lens over-correction in the treatment of IXT. Additional objectives are to compare effectiveness in controlling distance deviation and to assess improvements in distance stereopsis, fusional vergence and suppression. 3. HYPOTHESIS Maximum tolerable minus lens overcorrection without compromising visual acuity and comfort is governed by available accommodative amplitude. Similarly, minimum strength of minus lens required to control IXT is governed by angle of deviation and fusional vergence in reserves. Having knowledge of these factors, a clinician can determine an individualised optimum over minus prescription. Therefore, we hypothesise that custom optimised minus lens based on angle of deviation, AC/A ratio and accommodative amplitude produces improved control of the IXT without compromising visual acuity and comfort.
Interventions
Minus Lens overcorrection in Intermittent Exotropia
Use of minus lens overcorrection in the treatment of intermittent exotropia is described for over a century which has gained more attention in recent times. Recently, plethora of reports have been published demonstrating variable success rate of minus lens over correction. However, majority of the studies are poorly designed, have limited sample size or lack clarity on minus lens prescription method.
In the current study, a novel approach of
Minus Lens overcorrection in Intermittent Exotropia Use of minus lens overcorrection in the treatment of intermittent exotropia is described for over a century which has gained more attention in recent times. Recently, plethora of reports have been published demonstrating variable success rate of minus lens over correction. However, majority of the studies are poorly designed, have limited sample size or lack clarity on minus lens prescription method. In the current study, a novel approach of prescribing minus lens, called 'optimized minus lens' will be used. The optimm minus lens will be determined based on the angle of deviation, amplitude of accommodation and AC/A ratio. Patients with intermittent exotropia will be assessed by experienced orthoptist and ophthalmologist at the Ophthalmology department of Queensland Children's Hospital, Brisbane. The entire study related examinations takes about 45 minutes. Subjects in the treatment group will be prescribed with individually customized minus lens to wear over the study period of six months. The participants will be examined at two follow up visits in three months interval following commencement of the treatment. At each follow up visits, subjects will be assessed for outcome variables outlined in the relevant section. Parents will need to answer a set of spectacle related compliance and comfort questionnaire. This information will be analysed separately to relate compliance versus success of the treatment.
Sponsors
Children's Health Queensland
Study design
Allocation
Randomised controlled trial
Intervention model
Parallel
Primary purpose
Treatment
Masking
Blinded (masking used) (Subject)
Eligibility
Sex/Gender
All
Age
4 Years to 15 Years
Healthy volunteers
No
Inclusion criteria
- Age between 4 and 15 years - Patient with IXT measuring >10pd of distance IXT and mean distance control score of 2 points or worse - Best corrected visual acuity 6/9 or better in each eye - Near stereopsis of 100” arc or better - No ocular pathology that might affect ocular motility and visual acuity - Parents willing to and able to provide signed informed consent
Exclusion criteria
- Constant strabismus/exotropia - IXT of convergence insufficiency type - near deviation not exceeding the distance deviation by >10pd - IXT treated with minus lens, prism or surgery within the last 6 months. Patients receiving alternate pathing will be eligible for the study. - Any previous strabismus and/or intraocular surgery - Interocular difference of visual acuity by 2 or more lines - Cycloplegic spherical equivalent refraction exceeding -6.0D myopia or +2.0D hyperopia on cycloplegic refraction. Ametropic criteria are selected with the assumptions that: myopia over 6.0D for the target age group is likely to be pathological in nature; and hyperopia over 2D is likely to be symptomatic manifest hyperopia which normally should be fully corrected. - Inability to determine accurate visual acuity and strabismus assessment due to poor cooperation and/or intellectual impairment - Conditions potentially affecting vergence and accommodation - Developmental delay or general debility interfering study purpose
Outcome results
None listed