Review articleAge-related eye disease and gender
Introduction
In the aging population, age-related cataract, age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy (DR) are prevalent in high numbers, with about 37%, 10%, 3%, and 2% of people 70–74 years old suffering from these conditions [1]. Even though the female to male ratio varies among these eye diseases, women are in majority among the blind and the visually impaired; about two of three blind people are women [2]. This gender difference may in part be explained by the longevity of women. Other causes however, such as differences in requirement for good vision in daily life activities, in the propensity to seek health care or gender inequity in access to health care, may also contribute to this discrepancy. In addition, life-style related factors, such as smoking and sun exposure, may differ between genders and thus influence the risk of eye diseases and its distribution between sexes. Lastly, there are sex-dependent biologic differences, which may affect the disease-causing pathogenic mechanisms.
In all parts of the world and at all time periods for which data exist, the longevity pattern is the same; women live longer than men. In average, life expectancy for women is 5 years longer than for men [3]. Even though this difference is smaller in countries with high pediatric mortality and more pronounced in countries with a high overall longevity, women outlive men everywhere regardless of educational, economic, political and health critera [3]. Men have higher mortality rates than women for all the common death causes, including accidents, cardio- and cerebrovascular disorders, cancers, infections and chronic pulmonary disease [4]. Possible biologic explanations for gender-related differences in mortality and morbidity basically fall into two categories; genetical or hormonal. Genetic factors that favor female longevity are 1. the heterogametic sex hypothesis; 2. telomere attrition; and 3. mitochondrial inheritance. The importance of sexual hormones in aging is central in the reproductive theory of aging, according to which a dysfunctional hypothalmic-pituitary-gonodal (HPG) axis is associated with increased mortality in both sexes [5]. The longer life-span in women, which is even more pronounced in those entering menopause at higher age, and the fact that castrated men have the same life expectancy as women suggest that estrogens are beneficial in the aging process [6]. It is known that the risk of cardiovascular disease increases with high androgen levels and low estrogen levels both in men and in postmenopausal women [7]. Compared to premenopausal women, men have a higher prevalence of hypertension and a higher risk of cardiovascular disease. However, after menopause there is no gender difference in risk of cardiovascular disease and women even have a higher prevalence of hypertension than men of the same age [8]. A summary of genetical and hormonal effects that may promote female longevity and health is shown in Table 1. For details on the listed mechanisms, see reviews by Austad and Zetterberg [4], [9].
This review will focus on the four most common eye diseases in elderly people; age-related cataract, age-related macular degeneration, glaucoma and diabetic retinopathy. Gender-specific prevalences and possible mechanisms for any gender differences, as well as the effect of endogenous and/or exogenous estrogen, will be presented. Knowledge on sex-related effects on pathogenic mechanisms is important to understand the basis of disease and thus provide means for new therapies. Also, finding socioeconomic explanations to gender differences in disease prevalence, such as gender inequity in access to cataract surgery, is crucial for equal allocation of health care resources (Table 2).
Section snippets
Methods
Data was identified through search in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) using the terms “age-related macular degeneration”, “aging”, “blindness”, “cataract”, “diabetic retinopathy”, “estrogen”, “eye disease”, “gender”, “glaucoma” and “visual impairment”. Bibliographies from identified articles were used to further augment the search. By design, both summaries of previous reviews, older original articles and newer studies were included. Only articles written in English were included.
Gender-based differences in visual impairment and blindness
The estimated number of people suffering from blindness globally is 32.4 millions [2]. For people with moderate and severe visual impairment (MSVI; decimal visual acuity of <0.3 but ≥0.05) the number is 191 millions [2]. The major cause of blindness globally is cataract, accounting for 51% of all blind people, whereas uncorrected refractive errors is the major cause of MSVI (43%) followed by cataract (33%) [10]. There are huge inequalities in the proportion of blind and visually impaired people
Lens opacities and cataract
When reporting the prevalence of cataract, a variety of definitions and study designs are used; either population-based studies on the presence of lens opacities with or without the requirement of visual impairment or studies on previous or current cataract extraction rates. Regardless of the criteria used, most studies report a higher prevalence of cataract in women than in men [12], [13], [14], [15]. Grading and classification of cataract is often done using photography-based grading scales,
Gender differences in access to health care
Several studies have demonstrated lower diagnostic and therapeutic efforts in women [91], [92]. Rius et al. demonstrated a higher disparity between diagnosis of cataract and rates of surgery among women than men, indicating that more women were waiting for cataract extraction, thus a lower therapeutic effort [93]. Since cataract is the leading cause of blindness worldwide, gender inequity in access to cataract surgery is a major cause of the higher prevalence of visual impairment and blindness
Conclusion and future perspectives
Women account for a majority of all blindness and this can be attributed to two main causes; 1. the relative longevity of women making a substantial number of them suffer from age-related eye diseases, and 2. the relative lack of information and financial resources for women compared to men. The latter is valid for treatable conditions like cataract, where gender inequity in access to surgery prevails in large parts of the world. Apart from age and socioeconomic factors, biologic factors may
Conflicts of interest
The author declare no conflict of interest.
Contributor
M.Z is the sole author and contributor for this article.
Acknowledgements
This work was supported by grants from the Sahlgrenska University Hospital (“Agreement concerning research and education of doctors”; ALFGBG-441721), Göteborg Medical Society, Marianne and Marcus Wallenberg Foundation, Dr Reinhard Marcuses Foundation, Konung Gustaf V:s och Drottning Victorias Frimurarestiftelse, Hjalmar Svensson Foundation, Greta Andersson Foundation, Herman Svensson Foundation, Ögonfonden, De Blindas Vänner and Kronprinsessan Margaretas Arbetsnämnd för Synskadade.
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