Managing Amblyopia: Approaches for Effective Intervention

Amblyopia, the most common cause of monocular sight loss in children, is thought to be a developmental disorder with no obvious organic abnormality in the eye or brain. Decreased visual acuity, in one or both eyes, is associated with strabismus, anisometropia and sensory deprivation that occurs in early infancy through to childhood.

Robust public health awareness campaigns are key to ensure no child misses out on screening

Table 1. Visual acuity testing in children.

In addition to deterioration of visual acuity, the overall visual perception of a child through to adulthood can be affected. This includes abnormal contour interactions, reduced contrast sensitivity, positional uncertainty, spatial distortion, impaired accommodation, abnormal eye movements and suppression.⁴

SCREENING

Early access to screening for amblyopia is critical, as this is the time when visual development has maximal plasticity and early intervention can be most effective.³ Nationwide coordinated programs ensure the majority of children are captured, however, this can be challenging in developing nations and areas of social depravation.¹ 

In the United Kingdom, all children are screened in the first year of entering primary school with visual acuity assessment and referral through the national health system. The age of screening ranges from four to five years, as all children must enter reception (kindergarten) by the time they turn five in August of the school year. This is one of the gold standard models of screening as the early discovery of amblyopia ensures the ability to treat for a number of years before expected visual maturation.⁴ Screening and treatment at the age of four to five years is cost efficient and clinically effective for the duration of the child’s life into adulthood.

In Australia, the current model is to screen new-borns and at six-weeks, for sensory deprivation for lens opacities or masses which are amblyogenic.⁵ Guidelines for amblyopia screening are developed through state government initiatives such as the NSW run StEPS program (State-wide Eyesight Pre-schooler Screening). This offers free vision screening through local health district preschools and childcare centres for all four-year-old children before school starts. Opt-in consent forms are needed to participate, and alternative options for vision assessment are possible at a NSW Health Child and Family Health service/GP practice. While this program is highly successful, limiting screening to preschools means children who are not in childcare can miss out.

School screening has been discussed and considered, given the limitation of preschool programs, however the challenge is to balance capturing the highest numbers of children with early enough intervention. This is because screening at the school level is complicated by the age of the child in the first year of primary. Unlike the United Kingdom model, the parents of children in NSW have some choice over when they start their children at school. Some choose to hold their children back from starting kindergarten until they are six. This may be too late for the initiation of amblyopia treatment, as the window is missed for maximal plasticity of the visual development system. While the exact age of this period is undefined, the generally held view is that the optimal time to initiate intervention is from ages three months to seven years.

Perhaps a two-model approach would be ideal, with both preschool screening and a safety net primary school screening for those who have missed out on the earlier program. Funding for this model would be a key consideration in regards to implementation.

Children are often asymptomatic. History of an intermittent turning of the eye, frustration with vision and objection to occlusion can be subtle. Hence the need for successful and robust screening programs.

CLINICAL ASSESSMENT AND TREATMENT

The types of amblyopia that we see in the majority of cases include anisometropia (one or both eyes) or strabismus, with some children having both.

Unilateral amblyopia is conventionally defined clinically as a difference in best-corrected visual acuity (BCVA) between the two eyes of 0.20 logMAR.⁴ Refractive errors – hypermetropia and myopia – are corrected with full time glasses wear from the moment a child wakes until their sleep time.

Table 2. When to give glasses in very young children under three years-of-age at presentation.

Children with amblyopia can have problems with eccentric fixation where the object of view falls on the parafoveal region. This is a monocular phenomenon, unlike abnormal retinal correspondence. The crowding phenomenon is particularly important when accessing children with amblyopia as this cohort performed better with single optotypes and thus can mask the severity of amblyopia. When presented a line of consecutive optotypes, children can typically read one to two lines less than single optotypes, so it is important to try and use these types of visual acuity charts despite the challenges. Amblyopic patients should have an assessment with neutral density filters, which reduce luminance without colour change. A neutral density filter can show a deterioration in the better eye and highlight the amblyopia.²

Age-appropriate visual acuity charts should be used (Table 1) with, in some cases, both the easier and harder test (e.g. kays picture and logMar) to ensure comparisons can be made with the progressive chart at follow-up.

Cycloplegic retinoscopy with cyclopentolate or atropine should be obtained, and the full glasses prescription given. Refractive correction with glasses alone can correct amblyopia in one third of cases, and in these patients, patching will not be required.³

Hyperopia should be fully corrected. To aid treatment compliance, the prescription can be reduced by 1.5 diopters or less for some patients. This is particularly the case in young children, with the premise being that full correction will be established once the child is used to the glasses. This needs careful discussion with parents and compliance of glasses is important in the early stages of treatment.³ 

Myopic patients should not have any myopia progression treatment until amblyopia has been treated and excellent symmetrical vision is obtained in both eyes. Prism cover tests should be performed, as well as the vertical prism test, with a 15 or 20 prism block.²

Ideally, glasses are given and the patient is followed-up at 12 weeks for visual adaptation and compliance. Residual monocular amblyopia is then treated with patching/atropine. In certain circumstances – be it a dense amblyopia, issues with follow-up, or parental wishes – both patching and glasses can be started. In theory this may prove practical for some, especially older children identified with less time to adapt during their critical period. It may also be appropriate in resource-poor settings, where access to ophthalmic services is limited; however wherever possible, single introduction of interventions will be more effective in achieving compliance.⁶ A graduated approach demonstrates to parents the benefit of treating refractive errors, and gently introduces children to treatment plans. Inevitably, the clinician is best placed to decide treatment courses with early dual intervention.⁵

PEDIG STUDIES: PATCHING AND ATROPINE

One must acknowledge the Paediatric Disease Investigator Group (PEDIG) for their landmark studies on amblyopia treatment regimens. These can be reviewed at pedig.jaeb.org/Studies.aspx and abcdvision.org/amblyopia/ats-pedig.html.

Patching and its compliance are still the hallmark of treatment, once refractive errors are corrected. Duration and timing of patching can vary, depending on severity of amblyopia and the age of the child. Compliance is the single biggest reason for failure to achieve an improvement, and patching can be very challenging for parents and their children. Careful counselling, empathy and understanding of both the parents and child is important in the clinical consult.^5,7 

PEDIG studies have highlighted that two hours of quality patching was just as effective as six hours of patching in mild-to-moderate amblyopia. Additionally, six hours of patching was non-inferior to full-time patching in severe amblyopia.⁸ Children who have passed the critical neuroplasticity age of seven or eight years could still benefit from amblyopia treatment, especially glasses and patching if they had never patched before. Atropine penalisation (1%) was effective in treating amblyopia and was non-inferior to patching.^9,10,11,12 Atropine 1% is instilled in the better eye, which encourages the weaker eye to be used.

Ideally, children should be followed-up every eight weeks until improvement is seen in the weaker eye, and dual therapy with patching and atropine should be commenced if no benefit is seen with single treatment.⁵

ADJUNCT TREATMENTS

Binocular therapies have been studied with improvement in visual acuity believed to be the result of reduced interocular suppression. A home-based binocular treatment system, using gameplay and viewing of dichoptic movies to increase compliance, was studied. This treatment was reported to elicit “high levels of compliance (on average, 89.4% +/- 24.2% of daily dose in 68.23% +/- 12.2% of days on treatment)”. Additionally, it led to a mean improvement in acuity of 0.27 logMAR (SD 0.22) for the amblyopic eye. Importantly, acuity gains were not correlated with a reduction in suppression.^4,13 

Oral levodopa with patching two hours a day, studied in children aged seven to 12 years with residual amblyopia, did not produce a clinically or statistically meaningful improvement in visual acuity compared with placebo and patching.¹⁴ 

EDUCATION AND SUPPORT

Robust public health awareness campaigns are key to ensure no child misses out on screening. Once children are identified with amblyopia, it is important for parents and children to have a clear understanding of treatment goals to increase compliance. Treatments can be challenging and aids such as educational books, school support, parents’ forums and reducing stigma of patching all assist in reducing this disease burden. Working closely with optometry, orthoptists and paediatric ophthalmologists can help tackle amblyopia.

Dr Rushmia Karim BSc MBBS MMed (Ophthsc) MMed (Clinical Epidemiology) Hons Genomics (PG Cert) FRCOphth is a UK-trained ophthalmologist with over 10 years of experience. She specialises in children’s eye health and is a skilled surgeon, performing cataract, lens and strabismus surgery in both adults and children. She also has a special interest in neuro-ophthalmology. Dr Karim has an extensive research portfolio. She has performed and published systematic reviews including Cochrane reviews, randomised controlled studies and observational studies. Dr Karim consults at Vision Eye Institute in Chatswood, Drummoyne and Tuggerah Lakes (Central Coast) in New South Wales. 

References 

1. Chen AM, Cotter SA. The Amblyopia Treatment Studies: Implications for Clinical Practice. Vol. 1, Advances in Ophthalmology and Optometry. Elsevier Inc; 2016. p. 287–305. 
2. Chowdhury P, Shah B. Summary of Amblyopia- easy to Understand. Ophthalmology Research: An International Journal. 2018 Mar 16;8(4):1–4. 
3. The Clinical Profile of Moderate Amblyopia in Children Younger Than 7 Years. Archives of Ophthalmology. 2002 Mar 1;120(3):281. 
4. Tailor V, Bossi M, Greenwood JA, Dahlmann-Noor A. Childhood amblyopia: Current management and new trends. Vol. 119, British Medical Bulletin. Oxford University Press; 2016. p. 75–86. 
5. Repka MX. Amblyopia Outcomes Through Clinical Trials and Practice Measurement: Room for Improvement: The LXXVII Edward Jackson Memorial Lecture. American Journal of Ophthalmology. 2020 Nov;219:A1–26. 
6. Cotter SA. Treatment of Anisometropic Amblyopia in Children with Refractive Correction. Ophthalmology. 2006 Jun;113(6):895–903. 
7. Holmes JM, Melia M, Bradfield YS, Cruz OA, Forbes B. Factors Associated with Recurrence of Amblyopia on Cessation of Patching. Vol. 114, Ophthalmology. 2007. 
8. Beck RW. A Randomized Trial of Prescribed Patching Regimens for Treatment of Severe Amblyopia in Children. Ophthalmology. 2003;110(11):2075–87. 
9. A comparison of atropine and patching treatments for moderate amblyopia by patient age, cause of amblyopia, depth of amblyopia, and other factors. Ophthalmology. 2003 Aug;110(8):1632–7. 
10. A Randomized Trial of Patching Regimens for Treatment of Moderate Amblyopia in Children. 
11. Stewart CE, Stephens DA, Fielder AR, Moseley MJ. Objectively monitored patching regimens for treatment of amblyopia: Randomised trial. British Medical Journal. 2007 Oct 6;335(7622):707–11. 
12. Repka MX, Kraker RT, Beck RW, Birch E, Cotter SA, Holmes JM, et al. Treatment of severe amblyopia with weekend atropine: Results from 2 randomized clinical trials. Journal of AAPOS. 2009 Jun;13(3):258–63. 
13. Bossi M, Tailor VK, Anderson EJ, Bex PJ, Greenwood JA, Dahlmann-Noor A, et al. Binocular therapy for childhood amblyopia improves vision without breaking interocular suppression. Investigative Ophthalmology and Visual Science. 2017 Jun 1;58(7):3031–43. 
14. Repka MX, Kraker RT, Dean TW, Beck RW, Siatkowski RM, Holmes JM, et al. A randomized trial of levodopa as treatment for residual amblyopia in older children. Ophthalmology. 2015 May 1;122(5):874–81.