Assessment of the Density of Suppression to Identify Risk of Intractable Diplopia in the United Kingdom

Opinions on Amblyopia Treatment in Microtropia - A Questionnaire Study of Orthoptists in Scandinavia

Background

Microtropia is a small angle strabismus of less than or equal to ten prism diopters. It often co-exists with anisometropia, and patients may require amblyopia treatment. Diplopia following amblyopia treatment is considered rare, but older literature can advise caution when treating amblyopia in microtropia. This study aimed to explore orthoptists' opinions on amblyopia treatment in microtropia.

Methods

Orthoptists working in Scandinavia were invited to complete an online questionnaire regarding their views on amblyopia treatment. They were presented with three different clinical scenarios: 1) patient with anisometropia; 2) patient with anisometropia and microtropia with identity; and 3) patient with anisometropia and microtropia without identity.

Results

The questionnaire received responses from 30 orthoptists, which were analysed. The results showed a significantly higher concern for diplopia in patients with microtropia undergoing amblyopia treatment than in patients with anisometropia. They responded that to prevent diplopia, it is more important to stop amblyopia treatment before equal visual acuity (VA) is reached in microtropia compared to anisometropia. Thus, amblyopia treatment was stopped more often in microtropia, even if VA was improving and diplopia was absent. Equal VA was perceived to be more difficult to achieve in microtropia, both with and without identity, compared to anisometropia.

Conclusion

Despite more recent evidence that diplopia following amblyopia treatment is extremely rare, orthoptists working in Scandinavia reported more concerns about diplopia when treating amblyopia in microtropia than in anisometropia. Stopping amblyopia treatment in microtropia before equal VA was achieved was considered somewhat important to prevent diplopia. Orthoptists also reported that equal VA was difficult to achieve in patients with microtropia, both with and without identity. Further research would help improve the evidence and inform clinical decisions about microtropia and amblyopia treatment in microtropia.

Feasibility of a new 'balanced binocular viewing' treatment for unilateral amblyopia in children aged 3-8 years (BALANCE): results of a phase 2a randomised controlled feasibility trial

OBJECTIVES

This study aimed to evaluate the safety of dichoptic balanced binocular viewing (BBV) for amblyopia in children, plus feasibility, adherence, acceptability, trial methodology and clinical measures of visual function.

DESIGN

We carried out an observer-masked parallel-group phase 2a feasibility randomised controlled trial.

SETTING

Two study sites, a secondary/tertiary and a community site.

PARTICIPANTS

We enrolled 32 children aged 3-8 years with unilateral amblyopia who had completed optical adaptation where indicated. 20 children attended the 16-week exit visit (retention 63%).

INTERVENTIONS

Children were randomised to BBV (movies customised to interocular acuity difference at baseline) for 1 hour a day (active intervention) or standard management as per parental choice (part-time occlusion or atropine blurring, control). All interventions were used at home, daily for 16 weeks.

PRIMARY OUTCOME MEASURE

'VacMan suppression test' of interocular balance at 16 weeks from randomisation.

SECONDARY OUTCOME MEASURES

feasibility outcomes (recruitment and retention ratios, adherence with the allocated intervention); safety outcomes at other time points (changes in prevalence of diplopia, manifest strabismus, suppression/interocular balance on a range of tests); efficacy outcomes (clinical measures of visual function, such as best-corrected visual acuity, BCVA). Outcome measures were identical to those planned in the protocol.

RESULTS

Primary outcome: At baseline, values for the interocular balance point were higher (indicating greater suppression of the amblyopic eye) in the occlusion group than in the BBV group. These values shifted downwards on average for the occlusion group, significantly decreasing from baseline to week 16 (t8=4.49, p=0.002). Balance values did not change between baseline and week 16 for the BBV group (t9=-0.82, p=0.435). At 16 weeks, there was no statistical difference in interocular balance/suppression change over time between the two arms. The difference at follow-up between the arms, adjusted for baseline, was -0.02 (95% CI -0.28 to 0.23, p=0.87).

FEASIBILITY

We prescreened 144 records of potentially eligible children. Between 28 October 2019 and 31 July 2021, including an interruption due to the COVID-19 pandemic, 32 children were screened and randomised (recruitment rate 22%), 16 to BBV and 16 to standard treatment. 20 children attended the 16-week exit visit (retention 63%). Mean adherence with BBV as proportion of viewing time prescribed was 56.1% (SD36) at 8 and 57.9% (SD 30.2) at 16 weeks. Mean adherence with prescribed occlusion time was 90.1% (SD 19.7) at 8 and 59.2% (SD 24.8) at 16 weeks.

SECONDARY SAFETY/EFFICACY OUTCOMES

One child in the BBV arm reported transient double vision, which resolved; two reported headaches, which led to withdrawal. BCVA improved from mean 0.47 (SD0.18) logMAR at randomisation to 0.26 (0.14) with standard treatment, and from 0.55 (0.28) to 0.32 (0.26) with BBV. Outcomes at 16 weeks did not differ between treatments.

PARTICIPANT EXPERIENCE

Families were generally positive about BBV, but families found both patching and BBV difficult to integrate into family routines.

CONCLUSIONS

Recruitment rates indicate that a future phase 3 trial will require multiple sites or a longer enrolment period. Retention and adherence rates were lower than anticipated, which will influence future study designs. Dichoptic treatment may be equal to occlusion treatment in safety and efficacy; headaches may lead to discontinuation. Integration into family routines may constitute a barrier to implementation.

TRIAL REGISTRATION NUMBER

NCT03754153.

Phase 2a randomised controlled feasibility trial of a new 'balanced binocular viewing' treatment for unilateral amblyopia in children age 3-8 years: trial protocol

INTRODUCTION

Treatments for amblyopia, the most common vision deficit in children, often have suboptimal results. Occlusion/atropine blurring are fraught with poor adherence, regression and recurrence. These interventions target only the amblyopic eye, failing to address imbalances of cortical input from the two eyes ('suppression'). Dichoptic treatments manipulate binocular visual experience to rebalance input. Poor adherence in early trials of dichoptic therapies inspired our development of balanced binocular viewing (BBV), using movies as child-friendly viewable content. Small observational studies indicate good adherence and efficacy. A feasibility trial is needed to further test safety and gather information to design a full trial.

METHODS/ANALYSIS

We will carry out an observer-masked parallel-group phase 2a feasibility randomised controlled trial at two sites, randomising 44 children aged 3-8 years with unilateral amblyopia to either BBV or standard occlusion/atropine blurring, with 1:1 allocation ratio. We will assess visual function at baseline, 8 and 16 weeks. The primary outcome is intervention safety at 16 weeks, measured as change in interocular suppression, considered to precede the onset of potential diplopia. Secondary outcomes include safety at other time points, eligibility, recruitment/retention rates, adherence, clinical outcomes. We will summarise baseline characteristics for each group and assess the treatment effect using analysis of covariance. We will compare continuous clinical secondary endpoints between arms using linear mixed effect models, and report feasibility endpoints using descriptive statistics.

ETHICS/DISSEMINATION

This trial has been approved by the London-Brighton & Sussex Research Ethics Committee (18/LO/1204), National Health Service Health Research Authority and Medicines and Healthcare products Regulatory Agency. A lay advisory group will be involved with advising on and disseminating the results to non-professional audiences, including on websites of funder/participating institutions and inputting on healthcare professional audience children would like us to reach. Reporting to clinicians and scientists will be via internal and external meetings/conferences and peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT03754153.

Effect of Viewing Conditions on Fixation Eye Movements and Eye Alignment in Amblyopia

Purpose

Patients with amblyopia are known to have fixation instability, which arises from alteration of physiologic fixation eye movements (FEMs) and nystagmus. We assessed the effects of monocular, binocular, and dichoptic viewing on FEMs and eye alignment in patients with and without fusion maldevelopment nystagmus (FMN).

Methods

Thirty-four patients with amblyopia and seven healthy controls were recruited for this study. Eye movements were recorded using infrared video-oculography during (1) fellow eye viewing (FEV), (2) amblyopic eye viewing (AEV), (3) both eye viewing (BEV), and (4) dichoptic viewing (DcV) at varying fellow eye (FE) contrasts. The patients were classified per the clinical type of amblyopia and FEM waveforms into those without nystagmus, those with nystagmus with and without FMN. Fixational saccades and intersaccadic drifts, quick and slow phases of nystagmus, and bivariate contour ellipse area were analyzed in the FE and amblyopic eye (AE).

Results

We found that FEMs are differentially affected with increased amplitude of quick phases of FMN observed during AEV than BEV and during DcV at lower FE contrasts. Increased fixation instability was seen in anisometropic patients at lower FE contrasts. Incomitance of eye misalignment was seen with the greatest increase during FEV. Strabismic/mixed amblyopia patients without FMN were more likely to demonstrate a fixation switch where the AE attends to the target during DcV than patients with FMN.

Conclusions

Our findings suggest that FEM abnormalities modulate with different viewing conditions as used in various amblyopia therapies. Increased FEM abnormalities could affect the visual function deficits and may have treatment implications.

The Role of Binocularity in Anisometropic Amblyopia

Anisometropic amblyopia is unilateral by definition and current treatment recommendations reflect that characteristic. However, recent research suggests a binocular component that deserves consideration. The aim of this review is to consider the levels of anisometropia deemed amblyogenic, and the cortical changes that occur in the presence of anisometropic amblyopia. Particular attention is given to cortical changes that impact the binocularity of these individuals. Knowledge of binocular deficits in anisometropic amblyopia has implications for current, accepted treatment regimens which are monocular in nature. Therefore, the integrity of binocular function in anisometropic amblyopia and its impact on the visual outcome will be evaluated. Given the rise in binocular treatments under clinical trial for amblyopia, this review also aims to evaluate the evidence of potentially enhanced benefits to anisometropic amblyopes from proposed new binocular therapies.

Bagolini filter bars: an analysis of light transmittance and their use in a pediatric population

Purpose: The purpose of this study is to determine whether the Sbisa bar (Sbisa Ophthalmic Instruments) (referred to in this article as the BF(Sbisa) bar) and Bagolini Filter bar (C.O.I. Vision) (referred to in this article as the BF(new) bar) are repeatable and comparable, for measuring density of suppression or strength of abnormal binocular single vision (BSV), in a pediatric population. Methods: Using a spot photometer, percentage light transmittance of filters on two BF(Sbisa) bars and two BF(new) bars was measured. Thirty-three participants aged 5-12 years with unilateral strabismus were recruited. Density of suppression or strength of abnormal BSV was measured with two of each bar, in addition to a repeated measure with one of each bar. Results: Light transmittance did not reduce consistently with increasing filter number (the number assigned to each filter by the manufacturer). Using data as filter numbers, a BF(Sbisa) bar was not comparable to a BF(new) bar (ᵶ = -3.936, p < 0.001, r = -0.28); different BF(Sbisa) bars were not comparable (ᵶ = -3.103, p = 0.005, r = -0.22) but different BF(new) bars were comparable (ᵶ = -1.165, p = 1.285, r = -0.08). Using light transmittance values, a BF(Sbisa) bar was comparable to a BF(new) bar (ᵶ = -0.385, p = 3.535, r = -0.03); different BF(Sbisa) bars were comparable (ᵶ = -1.476, p = 0.720, r = -0.10) but different BF(new) bars were not comparable (ᵶ = -3.354, p < 0.001, r = -0.24). The BF(Sbisa) and BF(new) bars were not repeatable using filter numbers (ᵶ = -3.648, p < 0.001, r = -0.26 and ᵶ = -3.099, p = 0.005, r = -0.22, respectively) or light transmittance values (ᵶ = -3.743, p < 0.001, r = -0.27 and ᵶ = -2.727, p = 0.025, r = -0.19, respectively). An order effect existed using filter numbers (ᵶ = -4.473, p < 0.001, r = -0.32) and light transmittance values (ᵶ = -4.525, p < 0.001, r = -0.32). Conclusion: There is a need for the production of bars with consistently reducing and comparable light transmittance of filters if measurement of density of suppression or strength of abnormal BSV with filter bars is to continue, because the current bars show inconsistencies, particularly at lower filter numbers. In the meantime, the bars are limited by their lack of comparability or repeatability. Using only BF(new) bars is preferable to using BF(Sbisa) bars or a mixture of the two types of bar because two different BF(new) bars may be comparable using filter number readings, but filter number readings from different BF(Sbisa) bars or from a BF(Sbisa) and BF(new) bar are not comparable. As the BF(Sbisa) and BF(new) bars are currently labeled, a second measure of density of suppression or strength of abnormal BSV is not recommended within 2 min of an initial measurement, because the measurement procedure seems to cause a reduction in suppression or abnormal BSV that does not recover with repeated measurements 2 min apart.

'It's too late'. Is it really? Considerations for amblyopia treatment in older children

In recent years, media coverage has demonstrated instances in which families of children aged 7 and older, newly diagnosed with strabismic and/or anisometropic amblyopia through community eyecare services, were told it was 'too late' for their child to effectively respond to conventional amblyopia treatment (occlusion or atropine penalisation). Formal guidance pertaining to binocular vision anomalies from eyecare professional bodies does not specifically make reference to a child's age, beyond stating the importance of early diagnosis and treatment of strabismus/amblyopia. However, there have been many changes in the way we view the recovery period for amblyopia, and it is well demonstrated both within literature and clinical practice that conventional treatment can improve amblyopic eye visual acuity in children beyond the age of 7 years. The occurrence of these media described cases within the community eyecare sphere would suggest it is worthwhile revisiting the literature on the subject of amblyopia treatment in older children (aged 7+ years), to address misconceptions and place in the spotlight current considerations facing clinicians when treating newly diagnosed amblyopia within this age group. This perspective review provides an evidence-based update covering the various considerations associated with treatment of amblyopia in older children, along with recent amblyopia treatment advances that could have an impact on treatment prospects for this patient group. Considerations include the risks, benefits and efficacy of treating newly diagnosed amblyopia in older children, monitoring density of suppression to mitigate intractable diplopia risk, and recent findings regarding binocular treatments for amblyopia.

Diplopia Following Short Treatment for Moderate Amblyopia

A case of an autistic child, aged 8 years, who reported binocular diplopia following just 2 hours total occlusion per day for 6 weeks for strabismic/anisometropic amblyopia is reported. There was a history of known long-standing reduced uniocular acuity without treatment. Pretreatment Sbisa bar assessment suggested moderate suppression. The diplopia was treated over 6 months including occluding the amblyopic eye and gradually reducing the density of the occluder until fixation with the nonamblyopic eye could be maintained and diplopia ignored. Possible contributing factors are discussed.

Incidence, risk factors and management of intractable diplopia

AIMS

There is a paucity of literature concerning intractable diplopia. The aims of this study were to determine the incidence of intractable diplopia in the UK, identify the causes and any associated risk factors, establish how cases are managed and if the treatment is successful and tolerated.

METHODS

A 1-year prospective observational study was undertaken via the British Ophthalmological Surveillance Unit (BOSU). This involved implementation of a reporting mechanism, which then triggered distribution of an incident questionnaire to explore clinical details concerning each case and a follow-up questionnaire 6 months later to explore how the case had been managed.

RESULTS

The incidence of intractable diplopia was 53 cases per year. The most common preceding events were strabismus surgery (32%), no known preceding event, that is,spontaneous (25%), severe head trauma (8%), cataract surgery (6%) and vitrectomy (6%). In the at-risk age group of 7 years and above, the incidence of intractable diplopia following strabismus surgery is 1 in 494 (95% CI; 1 in 296 to 790) cases. A total of nine different treatments were used in the management, with many patients receiving between two and four different methods. The overall success rate was poor, but most effective were opaque intraocular lenses (IOLs) (86%) and opaque contact lenses (50%).

CONCLUSION

Intractable diplopia is a relatively rare but important condition. The main risk factor is a pre-existing strabismus, and careful counselling is needed when planning surgical correction in patients with no demonstrable binocular function. Treatment success of intractable diplopia is high when using opaque IOLs, although with additional risk, but is often disappointing via other methods where it can be difficult to eradicate the diplopia successfully.