1. Introduction
besity is a chronic metabolic disease that has become an epidemic. The World Health Organization identifies obesity as the most prominent chronic health problem in adults, even worse than malnutrition [1]. Recent changes in socioeconomic conditions, lifestyle, food consumption, and increasing urbanization have led to an increase in obesity. Obesity is a gateway for various diseases and has become one of the leading causes of disability and death, affecting not only adults but also children and adolescents around the world. It is associated with increased mortality and risks of cardiovascular disease, stroke, type 2 diabetes, and cancer [2, 3]. The World Health Organization defines obesity as an excessive or abnormal accumulation of fat associated with an increased risk of disease. Despite many studies on the effects of obesity on the body, few studies have investigated the impact of obesity on eye diseases.
2. Methods
This article is a review study. The search was performed using keywords of “obesity” and “eye diseases” in PubMed, Scopus, and Web of Science databases from 2000 to 2021. We investigated the relationships between dry eye, cataract, glaucoma, retinopathy, maculopathy, increased eye pressure, exophthalmos, and other eye diseases with obesity. 
3. Results
Obesity-related eye diseases are categorized as follows:
Floppy eyelid syndrome
Floppy eyelid syndrome is characterized by hyperelasticity of the upper eyelid. Many of the affected patients are obese, and it is believed that almost 100% of them suffer from obstructive sleep apnea [4].
Dry eye disease
Obesity may lead to dysfunction of the meibomian glands with secondary tear instability [5]. Obesity has been shown to double meibomian gland dysfunction and is associated with dry eye symptoms [6].
Cataract
Although the link between cataract and obesity has been confirmed, the exact cause-and-effect relationship between the two is not fully understood. High oxidative stress and increased inflammation are considered the most likely factors. Increased levels of inflammatory proteins and fibrinogen have been reported in the plasma of obese individuals [7, 8].
Glaucoma
Several studies provide evidence of a positive association between obesity and intraocular pressure as the strongest risk factor for glaucomatous visual neuropathy [9, 10]. Recent studies have reported a significant positive relationship between intraocular pressure and several factors, including body mass index [11].
Diabetic retinopathy
Obesity has been shown to impair vascular endothelial function and autonomic dysfunction, especially in people with diabetes [12, 13]. Most studies have documented an association between a higher body mass index and an increased risk of retinopathy [14, 15]. Recent data show that obesity is also associated with retinopathy symptoms in the general population and non-diabetics. In the Horn study in the Netherlands, the waist-to-hip ratio was also independently associated with several retinal symptoms, including retinal hemorrhage, microaneurysm, hard exudate, and soft exudate in the non-diabetic population [16].
Age-related maculopathy
The relationship between obesity and age-related macular degeneration has been investigated in several studies [17, 18]. Other studies, however, have reported different relationships between body mass index and different stages of age-related macular degeneration. Central obesity, defined by waist circumference, increases the risk of progressing to age-related macular degeneration [19].
Cerebral pseudotumor (idiopathic intracranial hypertension) 
It is a vision-threatening disorder that mostly affects obese women of childbearing age. Obesity is one of the factors that can increase the risk of cerebral pseudotumor. This risk is almost 20 times higher in obese women under 44 than in the general population. Children are also at risk [20].
Exophthalmos
Bilateral exophthalmos is found in many obese people, and it is important to distinguish it from Graves’ disease [21].
4. Discussion and Conclusion
This study shows that health systems should pay attention to eye diseases in obese people, much like screening for blood pressure, diabetes, and systemic diseases in obese people. Although the effectiveness of obesity treatment in reducing the risk of eye disease is not fully understood, studies in this area may provide a better insight into the potential use of eye disease screening strategies in obese individuals and subsequent weight loss to reduce potential burden.

Ethical Considerations
Compliance with ethical guidelines
This article is a review article with no human or animal experimentation.

Funding
This research did not receive any grant from funding agencies in the public, commercial, or non-profit sectors. 

Authors' contributions
All authors equally contributed to preparing this article. 

Conflicts of interest
The authors declared no conflict of interest.


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