Role of excessive weight in intraocular pressure: A systematic review and meta-analysis

Author: Waspodo N, Giffari MMA, Nislawati R, Ismail A, Taufik FZ A, Lolok GB.

Geographical coverage: Israel, South Korea, Turkey, Thailand, and United States of Ameria (USA).

Sector: Risk factor

Sub-sector: Excess body weight

Equity focus: Not explicitly stated

Study population: Patients with glaucoma

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background:

Glaucoma is the second leading cause of permanent vision loss globally, with intraocular pressure (IOP) being a key modifiable risk factor. IOP results from the balance between aqueous humour production and outflow; an imbalance can lead to increased pressure, optic nerve damage, and visual field loss. Obesity affects 1.9 billion adults worldwide and is linked to diseases such as type 2 diabetes and hypertension. Recent studies suggest a potential link between obesity and increased IOP, with some reporting higher IOP in overweight individuals, though findings are inconsistent.

Objectives

To analyse the effect of excess body weight on intraocular pressure (IOP) values.

Main findings

Overall, the authors found that excessive body weight tends to lead to higher IOP, which is a major risk factor for glaucoma.

The authors’ review encompassed nine studies involving a total of 22,920 participants for both qualitative and quantitative analyses. The research was carried out across six different countries. Among the studies, four were cross-sectional, two were case-control, and three were cohort studies. The overall quality of the studies was deemed good: one study was rated poor, another fair, and the remaining seven were generally of good quality.

The findings revealed a mean difference of 0.93 (95% confidence interval (CI): 0.67 to 1.18, p<0.00001) in intraocular pressure (IOP) between individuals with excessive body weight and those with normal weight, indicating that people with excess body weight tend to have higher IOP values. Subgroup analyses further demonstrated a mean difference of 0.60 (95% CI: 0.48 to 0.72, p<0.00001) in the overweight subgroup, 1.02 (95% CI: 0.60 to 1.44, p<0.00001) in the obese subgroup, and 1.25 (95% CI: 0.96 to 1.54, p<0.00001) in the morbidly obese subgroup.

Methodology

The authors included observational studies, including cohort, case-control, and cross-sectional designs, that compared intraocular pressure (IOP) between individuals with excess body weight and those with normal weight. They focused on studies published in English within the last 15 years.

They searched different databases, including PubMed, Medline, and ScienceDirect, on May 18, 2023. Two reviewers independently screened the potentially relevant articles against the eligibility criteria, resolving any disagreements through discussion.

The quality of the included studies was assessed using the Newcastle-Ottawa Scale. Data extraction was conducted by one reviewer and verified by a second reviewer for accuracy. When necessary, the investigators contacted study authors to obtain missing data.

Meta-analysis was performed, and heterogeneity was assessed using I2 statistics. If I2 was less than 50%, a fixed-effects model meta-analysis was used; if I2 exceeded 50%, a random-effects model was applied. For cases of high heterogeneity (I2≥80%), Duval and Tweedie’s trim-and-fill analysis was performed to recalculate effect sizes, removing studies that could cause publication bias. Publication bias was evaluated using a funnel plot test.

Applicability/external validity

The authors identify several limitations, including variations in body mass index (BMI) classifications, differences in IOP measurement techniques, and the exclusion of factors such as genetic predisposition, inflammatory markers, and corneal thickness. These factors could affect the applicability and external validity of the review findings. Additionally, most studies were observational, which restricts the ability to draw causal inferences.

Geographic focus

Included studies were conducted in Israel, South Korea, Turkey, Thailand, and USA.

Summary of quality assessment

Overall, there is medium confidence in the conclusions about the effects of this study as this review is prone to language and publication bias.