Adult-Onset Coats’ Disease: Systematic Review and Meta-analysis of Clinical Presentation, Imaging Characteristics, and Treatment Outcomes

1. Title Adult-Onset Coats’ Disease: Systematic Review and Meta-analysis of Clinical Presentation, Imaging Characteristics, and Treatment Outcomes 2. Background and Rationale Coats’ disease is a rare, idiopathic retinal vascular disorder characterized by telangiectatic vessels, exudation, and potential retinal detachment. While predominantly described in children, a subset of cases presents in adulthood, exhibiting distinct clinical features, slower progression, and differing response to treatment. Despite increasing recognition of adult-onset Coats’ disease as a separate clinical entity, the literature remains fragmented, consisting mainly of case reports and small case series. No prior systematic review or meta-analysis has comprehensively synthesized available evidence on clinical characteristics and outcomes in this population. Understanding treatment efficacy and prognostic factors in adult-onset Coats’ disease is critical to inform best practices and guide management. 3. Objectives To systematically evaluate the clinical presentation, imaging findings, treatment modalities, and outcomes of adult-onset Coats’ disease and to synthesize available data using descriptive and quantitative methods. Primary objectives: To estimate pooled anatomical success rates following treatment. To determine recurrence rates. To assess mean change in best-corrected visual acuity (BCVA) among adults. Secondary objectives: To describe the distribution of Shields stages at presentation. To compare outcomes by treatment modality (laser, anti-VEGF, corticosteroid implant, cryotherapy, vitrectomy, or combination therapy). 4. Eligibility Criteria Inclusion Criteria: Population: Adult patients aged ≥18 years diagnosed with idiopathic Coats’ disease. Study types: Case reports, case series (≥1 case), observational cohort studies (retrospective or prospective). Outcomes: Must report at least one of the following: anatomical resolution, recurrence, change in visual acuity, or imaging findings. Language: English, Portuguese, Spanish, or French. Study design: Human clinical studies. Exclusion Criteria: Pediatric-onset Coats’ disease without separate adult data. Secondary Coats-like vasculopathy (e.g., due to radiation, diabetic retinopathy, retinal vein occlusion, inflammation, or genetic syndromes). Reviews, editorials, conference abstracts without primary data. Animal studies or laboratory research. 5. Search Strategy Electronic databases (PubMed, Scopus, Web of Science, and Embase) will be searched from inception to the final search date using controlled vocabulary (e.g., MeSH terms) and keywords including “Coats disease”, “adult-onset Coats”, “retinal telangiectasia”, “exudative retinopathy”. Boolean operators (AND/OR) and filters for human subjects and age ≥18 will be applied where possible. References of included studies will be screened manually to identify additional eligible studies. A detailed search strategy will be provided in an appendix. 6. Study Selection Process All identified records will be imported into Rayyan software for duplicate removal and screening. Two independent reviewers will screen titles and abstracts according to inclusion criteria, followed by full-text assessment. Discrepancies will be resolved by consensus or consultation with a third reviewer. Reasons for exclusion at the full-text stage will be documented. The selection process will be reported using a PRISMA 2020 flow diagram. 7. Data Extraction Data will be extracted independently by two reviewers using a standardized form. Extracted variables include: Study characteristics (author, year, country, study design) Patient demographics (age, sex) Shields staging Clinical presentation and imaging features (fundoscopy, OCT, FA/OCTA) Treatment modalities and number of treatment sessions Follow-up duration Anatomical and visual outcomes Complications and recurrence Missing or unclear data will be requested from study authors when feasible. 8. Risk of Bias Assessment Methodological quality will be assessed independently by two reviewers using: JBI Critical Appraisal Checklists for case reports and case series. Newcastle–Ottawa Scale (NOS) for cohort studies. Disagreements will be resolved by consensus. Studies will not be excluded based solely on quality; however, risk of bias will be considered in the interpretation of results. 9. Outcomes Primary outcomes: Anatomical resolution of exudation or retinal detachment Recurrence rate of disease after treatment Change in BCVA (logMAR) Secondary outcomes: Number of treatment sessions Complications (e.g., neovascular glaucoma, vitreoretinal fibrosis) Predictors of poor visual or anatomical outcomes 10. Data Synthesis and Statistical Analysis A narrative synthesis will be conducted to summarize clinical and imaging characteristics. When ≥3 studies report comparable data, meta-analysis will be performed using a random-effects model (DerSimonian–Laird method). Continuous outcomes will be expressed as mean differences with 95% confidence intervals (CI), and dichotomous outcomes as pooled proportions. Statistical heterogeneity will be assessed with I² and τ² statistics. Prespecified subgroup analyses will be performed based on disease stage and treatment modality. Sensitivity analyses will evaluate the impact of excluding studies at high risk of bias. 11. Protocol Registration Statement This protocol will be prospectively registered in the Open Science Framework (OSF) registry. Any amendments made after registration will be documented with the date, rationale, and description of changes. 12. Conflicts of Interest The authors declare no conflicts of interest. 13. Funding No external funding was received for this work.

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