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Trial registered on ANZCTR

Registration number
Ethics application status
Date submitted
Date registered
Date last updated
Date data sharing statement initially provided
Type of registration
Prospectively registered

Titles & IDs
Public title
Use of customised minus lens in the treatment of intermittent outward deviation of eyes
Scientific title
Efficacy of Optimised Minus Lens in the Treatment of Intermittent Exotropia: A Randomised Clinical Trial
Secondary ID [1] 297605 0
Universal Trial Number (UTN)
Trial acronym
Linked study record

Health condition
Health condition(s) or problem(s) studied:
Intermittent Exotropia 311817 0
Strabismus 311820 0
Bitemporal hemiretinal suppression 311884 0
Condition category
Condition code
Eye 310425 310425 0 0
Diseases / disorders of the eye

Study type
Description of intervention(s) / exposure
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.
Intervention code [1] 313801 0
Treatment: Devices
Comparator / control treatment
In this randomized clinical trial, there will be control and treatment groups. While the subjects in the treatment group will receive optimized minus lens overcorrection, subjects in the control group will get no minus lens overcorrection . However, the control group will be corrected for their normal refractive error, if any.
Control group

Primary outcome [1] 319291 0
Control score: An office based control score, Mahoney & Holmes, system will be used in determining the control of tropia. The control score system has been used previously in similar studies. Success will be defined as at least one control score improvement after use of minus lens overcorrection for 3 and 6 months post treatment.
Timepoint [1] 319291 0
6 months following the commencement of the treatment
Secondary outcome [1] 367586 0
Angle of deviation of IXT (secondary outcome) will be assessed 3 months and 6 months post treatment. using prism alternate cover test (PACT). Success will be defined as improvement of at least 10 prism diopter compared to the baseline angle of deviation.
Timepoint [1] 367586 0
6 months following the commencement of the treatment
Secondary outcome [2] 367587 0
Suppression: suppression will be assessed using Worth-4-dot test and amblyoscope at study each visit.
Timepoint [2] 367587 0
3 and 6 months after the commencement of treatment
Secondary outcome [3] 367588 0
Myopia progression: Refraction and ocular biometry will be performed at baseline (pre-treatment) and final (post treatment) visits. Changes in anatomical parameters, with special attention in axial length of the eye, will be assessed and compared to monitor progression of myopia.
Timepoint [3] 367588 0
6 months following the commencement of the treatment
Secondary outcome [4] 367773 0
Stereopsis. Near and distance stereopsis will be assessed and monitored pre and post treatment conditions using random dot stereo tests for near and distance.
Timepoint [4] 367773 0
6 months following the commencement of the treatment
Secondary outcome [5] 367830 0
Fusional Vergence: Fusional vergence amplitude for near and distance will be compared between the groups and also between pretreatment and post treatment for each subject in the treatment group. Major amblyoscope will be used to measure the fusional vergence.
Timepoint [5] 367830 0
6 months following the commencement of the treatment

Key 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
Minimum age
4 Years
Maximum age
15 Years
Both males and females
Can healthy volunteers participate?
Key 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

Study design
Purpose of the study
Allocation to intervention
Randomised controlled trial
Procedure for enrolling a subject and allocating the treatment (allocation concealment procedures)
Methods used to generate the sequence in which subjects will be randomised (sequence generation)
Masking / blinding
Blinded (masking used)
Who is / are masked / blinded?
The people receiving the treatment/s

Intervention assignment
Other design features
Not Applicable
Type of endpoint(s)
Statistical methods / analysis
The primary analysis of the results will involve comparison of proportion of success rates in controlling IXT between treatment and control groups (where improvement is defined as greater than 1 point better control score in their distance deviation among the treatment group) using a Chi-square test at each time point or over time using a Generalized linear mixed model analysis with time, group and interaction time by groups as fixed effect and patient as random effect. Mean distance control will also be compared between the groups and time points (baseline, 3 months and 6 months post treatment) using a linear mixed model approach with time, group and time by group interaction as fixed effects and patient as random effect. When a significant interaction is identified, multiple comparisons with adjustment for multiple testing using Bonferroni correction will be performed.
The comparisons provide a statistically powerful interpretation of the benefit of optimised minus lens over-correction. To evaluate the hypothesised superior response of optimised minus lens over-correction compared to traditional fixed over-correction, results from the current study will be compared with the results from other studies applying similar research methodologies published in literature.
The secondary analysis will involve a comparison of the secondary outcomes such as angle of deviation, fusional vergence, suppression, distance stereopsis and myopia progression between two groups and across time using a linear mixed model for Gaussian outcomes or generalized linear mixed model analysis when the outcome is binary.
Non-linear results of questionnaire relating to compliance and comfort of prescribed spectacles will be analysed using Rasch model.

Recruitment status
Not yet recruiting
Date of first participant enrolment
Date of last participant enrolment
Date of last data collection
Sample size
Accrual to date
Recruitment in Australia
Recruitment state(s)
Recruitment hospital [1] 13281 0
Queensland Children's Hospital - South Brisbane
Recruitment postcode(s) [1] 25847 0
4101 - South Brisbane

Funding & Sponsors
Funding source category [1] 302119 0
Name [1] 302119 0
Queensland Children's Hospital
Address [1] 302119 0
Study, Education and Research Trust Account (SERTA)
Queensland Children's Hospital
501 Stanley Street
South Brisbane
Queensland 4101
Country [1] 302119 0
Primary sponsor type
Children's Health Queensland
Queensland Children's Hospital
501 Stanley Street
South Brisbane
Queensland 4101
Secondary sponsor category [1] 301956 0
Name [1] 301956 0
Address [1] 301956 0
Country [1] 301956 0

Ethics approval
Ethics application status
Ethics committee name [1] 302800 0
Children's Health Queensland Hospital and Health Services Human Research Ethics Committee
Ethics committee address [1] 302800 0
501 Stanley Street
South Brisbane
Queensland 4101
Ethics committee country [1] 302800 0
Date submitted for ethics approval [1] 302800 0
Approval date [1] 302800 0
Ethics approval number [1] 302800 0

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.
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.
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.

Trial website
Trial related presentations / publications
Public notes

Principal investigator
Name 91442 0
Dr Jit B Ale Magar
Address 91442 0
Level 2, Queensland Children's Hospital
501 Stanley Street
South Brisbane
QLD 4101
Country 91442 0
Phone 91442 0
+61 7 3068 2626
Fax 91442 0
Email 91442 0
Contact person for public queries
Name 91443 0
Dr Jit B Ale Magar
Address 91443 0
Level 2, Queensland Children's Hospital
501 Stanley Street
South Brisbane
QLD 4101
Country 91443 0
Phone 91443 0
+61 7 3068 2626
Fax 91443 0
Email 91443 0
Contact person for scientific queries
Name 91444 0
Dr Jit B Ale Magar
Address 91444 0
Level 2, Queensland Children's Hospital
501 Stanley Street
South Brisbane
QLD 4101
Country 91444 0
Phone 91444 0
+61 7 3068 2626
Fax 91444 0
Email 91444 0

Data sharing statement
Will individual participant data (IPD) for this trial be available (including data dictionaries)?
No/undecided IPD sharing reason/comment
For privacy purpose as instructed by HREC
What supporting documents are/will be available?
No other documents available
Summary results
No Results