Posterior Scleral Reinforcement as a means of myopia control

Paper Title: Treatment effect of posterior scleral reinforcement on controlling myopia progression: A systematic review and meta-analysis

Authors: Chih-An Chen (1), Pao-Yen Lin (2), Pie Chang Wu (1)

1. Department of Ophthalmology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan
2. Department of Psychiatry, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan

Date: May 2020

Reference: Plos One. 2020 [Link to open access paper]

Pathologic myopia is one of the major causes of blindness worldwide.¹ Degenerative changes associated with high myopia, including posterior staphyloma formation and scleral thinning, are caused by the progressive elongation of globe axial length and stretching of the sclera, choroid and retina.² The rapid axial length elongation associated with high myopia limits the efficacy of  traditional treatment options, including pharmacological intervention and contact lenses.³ There is currently no widely accepted medical or surgical intervention to prevent the fast progression of high myopia or limit the occurrence of myopic complications.^1,4 

Posterior scleral reinforcement (PSR) is currently the only existing surgical intervention for high/pathological myopia; however, previous reports of its benefits are conflicting.^{5 It was first described by Shevelev in 1930, and was modified as the Synder-Thompson method in 1972, which is the most common method performed currently. The surgery utilises biological or non-biological materials to strengthen the weakened sclera in the posterior pole and prevent  progressive elongation of axial length.5,6} The aim of this meta-analysis was to investigate and quantitatively define the efficacy of PSR in controlling axial elongation and refraction progression.

The study reported PSR may be an effective treatment option for patients with high myopia 

• In eyes treated with PSR versus control, there was a mean difference in: 
  • Myopia progression of 0.41D/year (95% CI 0.21 to 0.61; P<0.001)
  • Axial length change of -0.17mm/year (95% CI -0.22 to -0.11; P < 0.001)
• Consequently, this meta-analysis reports that PSR reduces axial length elongation and myopia progression in patients with high myopia
• Eye care practitioners may consider educating patients with high/pathological myopia on PSR as an option for treatment and discussing referral to an Ophthalmologist for evaluation

The efficacy of PSR differs depending on the surgical procedure

• Single strip surgical procedure is effective in reducing axial elongation and SER progression; however, X type operation is not
  • Subgroup analysis revealed significant subgroup difference (P < 0.001)
  • The X-type operation using a narrow strip was only able to reinforce macular type posterior staphylomas over a small supporting area of sclera. In contrast, the single wide strip operation not only supported a wider area, but extended from the superior-nasal to inferior-nasal quadrant, and the inferior staphyloma was thereby reinforced. 
  • Eye care practitioners should be aware of the limitations of the efficacy of PSR and advise patients that treatment outcomes are not comparable between surgical procedures 

PSR is associated with increased risk of sight-threatening complications

• The meta-analysis reported increased incidence of complications in eyes that underwent PSR vs control eyes
  • Myopia degeneration: 5.8% vs 2.7%
  • Macular haemorrhage: 2.3% vs 1.6%
  • Retinal detachment: 0.8% vs 0%
• While PSR may be effective in reducing progression of myopia, the associated risks are not negligible and the risk-benefit profile must be discussed with patients

Results from this meta-analysis must be interpreted with a level of caution, due to a number of limitations in design 

• A limited number of studies (11) were included
  • 10 of the 11 of these studies were cohort studies. Despite the cohort studies generally being of high quality (average NOS of 8/9), RCT's generate higher quality evidence
    • Majority of the cohort studies were retrospective and non-randomised, introducing potential bias
• High heterogeneity (greater than 75%) was observed when all studies were pooled. This heterogeneity was noted with both refraction progression (associated with different operation methods and age) and axial elongation
  • High heterogeneity indicates there is variability in the data and makes it difficult to reliably assess efficacy and complication rate. The observed heterogeneity may be due to different surgical technique, surgical skill and materials utilised 

Due to the lack of long term follow up studies for PSR operation, it is difficult to discuss efficacy and safety with confidence. The results of this meta-analysis indicate that further research is required.

• Further research should compare the outcomes of PSR undertaken with different surgical procedures and materials utilised in order to determine a superior methodology. 
  • Modified surgical variations of PSR have been reported in literature, including the biological material that is utilised. Previous studies have demonstrated that a homologous human scleral strip is superior.⁷
  • A recent study implemented a donor human sclera that had been cross-linked to augment tensile strength and prevent degradation.⁴
  • Further research in the form of RCT's and literature reviews are required, which will augment the confidence of Eye care practitioners in discussing risk benefit profile of PSR with patients
• A randomised clinical trial with 120 participants is currently being performed in Beijing that evaluates the safety and efficacy of PSR on controlling myopia progression. The results from this clinical trial are highly anticipated and will hopefully provide further insight.⁸ 

The meta-analysis did not include analysis of the change in BCVA of patients at baseline and follow up in either treatment or control group.

• Analysis or comment on potential improvement or reduction in BCVA following PSR surgery would have provided readers with further insight into robustness of the treatment as a means of myopia control 

This meta-analysis explored the treatment effect and complications of PSR in the treatment of high myopia.

This study is a systematic review and meta-analysis that utilised data from 11 articles and 320 patients. A broad and comprehensive literature search of Pubmed, EMBase and OVid was conducted. Search terms included "myopia", "scleral buckle", "posterior sclera* reinforce", "scleroplasty", "Synder Thompson", and "buckle reinforce". Two reviewers independently assessed the studies according to the inclusion criteria and exclusion criteria. 

Reviewers independently extracted data from the articles, including publication year, study design, country, patient ages, sample size, intervention and control methods, follow up duration, outcomes (change in SER and AXL, including 95% CI's) and number of adverse events.

11 articles were analysed, including 1 RCT and 10 cohort studies. The operation methods were single wide strip (n=9) and X-type PSR (n=2). 5 studies compared PSR versus a control group without PSR treatment, and 6 studies were self-control studies using the fellow eye as a control.

In two-arm meta-analysis comparing PSR and control groups, the weighted mean difference (MD) between cases and controls of myopia progression and axial elongation from baseline, corresponding 95% CIs and standard errors was calculated and presented in forest plots. In single-arm meta-analysis, outcomes of the change from baseline SER and AXL was obtained from PSR group, and the corresponding 95% CIs were calculated. The effect size was calculated using the Hedge's g to estimate the treatment effect for each outcome. Heterogeneity was assessed using I^2. Sensitivity analysis was performed by disregarding an individual study each time. Subgroup analysis was performed according to different operation methods and age groups to evaluate whether the observed effect size was different across subgroups. The pooled data was evaluated with a random-effects model and statistical significance was set at a two sided P < 0.05.

On estimating treatment effect, the mean differences of myopia progression and axial length changes between surgery and control groups were 0.41D/year (95% CI 0.21 to 0.61; P<0.001) and -0.17mm/year (95% CI -0.22 to -0.11; P < 0.001). Subgroup analysis showed significant treatment effects of the single wide strip operation; however, not with X-type operation. 

Single-arm meta-analysis showed less annual axial elongation in children subgroup. These results were robust by sensitivity analysis. The incidence of some major complications in the operation group were significantly greater, including myopic degeneration (5.8% vs 2.7%), macular haemorrhage (2.3% vs 1.6%) and retinal detachment (0.8% vs 0%).

It is interesting to note that despite two-arm meta-analysis subgroup analysis indicating no significant difference between children and adult groups, single-arm meta-analysis showed an axial elongation that was 2.7x faster in children vs adults in PSR operation group. Analysis demonstrated axial elongation stabilisation in children in only one study by Zhu et al.

PSR may be an effective surgical intervention for high myopia by preventing both refractive and axial length progression. However, frequent surgical complications should not be ignored. Further well-designed randomised control trials are needed to determine the long-term safety and efficacy of PSR, including the superior surgical procedure and material utilised. This information can then be used by Eye care professionals to advise highly myopic patients on their options for treatment.

Title: Treatment effect of posterior scleral reinforcement on controlling myopia progression: A systematic review and meta-analysis

Authors: Chen C, P Lin, P Wu.

Background: High myopia is a sight-threatening disease that causes axial length elongation and severe complications. Data on the benefits of posterior scleral reinforcement surgery in myopia control have been conflicting. The purpose of this study was to explore the treatment effect and complications of posterior scleral reinforcement in the treatment of myopia.

Methods: Articles were retrieved for relevant studies from inception to July 24, 2019, by PubMed, EMBASE, and Ovid. Analyses were conducted to compare the treatment effects of controlling spherical equivalent refraction and axial length elongation. The weighted mean difference and Hedges' adjusted g were used to evaluate the treatment effects, with a random-effects model. Heterogeneity was quantified using I² statistic and explored by subgroup analysis. Publication bias was addressed by funnel plots and Egger's test.

Results: A total of 11 articles were included in this meta-analysis. On estimating the treatment effect, the mean differences of myopia progression and axial length changes between surgery and control groups were 0.41 diopters per year (95% CI 0.21 to 0.61; P < .001) and −0.17 mm per year (95% CI −0.22 to −0.11; P < .001). Subgroup analysis showed significant treatment effects of the single wide strip operation. Single-arm meta-analysis showed less annual axial elongation in children subgroup. These results were robust by sensitivity analysis. The incidence of some major complications in the operation group were significantly greater (5.8% vs 2.7% for myopic degeneration; 2.3% vs 1.6% for macular hemorrhage; 0.8% vs 0 for retinal detachment).

Conclusion: 

Posterior scleral reinforcement may be an effective surgery on controlling myopia progression by slowing both refraction and axial length change. However, frequent surgical complications should be considered. Further well-designed studies are needed to determine the long-term safety and efficacy.