Cataract – A preventable cause of blindness
Cataract is the leading cause of preventable visual impairment and blindness worldwide, with a growing disease burden driven by population ageing. Numerous risk factors have been identified, among which smoking stands out as a modifiable factor that plays a significant role in promoting the early development and progression of cataract.
Keywords: Cataract, oxidative stress, smoking, vision loss, crystallin proteins
Overview
Cataract is characterized by a gradual loss of transparency of the crystalline lens, resulting in progressive visual impairment and potentially blindness if left untreated. It is one of the most common ocular diseases globally and represents the leading cause of preventable blindness. Visual impairment caused by cataract not only directly affects visual function but also reduces work capacity, increases the risk of falls, leads to loss of independence in older adults, and imposes a substantial burden on healthcare systems and society.
Cataracts significantly reduce the quality of life for those affected and can even cause blindness if left untreated.
Pathophysiology
The development of cataract is the result of structural and functional damage to the crystalline lens under the influence of multiple endogenous and exogenous factors, with oxidative stress playing a central role. Under normal conditions, lens transparency is maintained by the highly ordered arrangement of crystallin proteins and the effective activity of endogenous antioxidant systems. When the production of reactive oxygen species exceeds the body’s neutralizing capacity, crystallin proteins undergo oxidation, denaturation, and aggregation, leading to loss of light-transmitting ability and lens opacification. Concurrently, oxidative damage to membrane lipids and DNA of lens fibers impairs cellular repair mechanisms, accelerating ageing processes and resulting in irreversible lens opacification.
Etiology and pathogenesis
Role of smoking in disease progression
In addition to natural ageing and intrinsic metabolic disturbances, several environmental and behavioral factors contribute to the development and progression of cataract, among which smoking plays a prominent role due to its capacity to increase systemic oxidative stress and directly affect ocular tissues. Tobacco smoke contains numerous potent oxidants and toxic substances, including nicotine, aldehydes, and heavy metals, which enhance the production of reactive oxygen species within the lens and disrupt intracellular redox balance. As a result, crystallin proteins become more susceptible to oxidation, glycation, and denaturation, leading to protein aggregation and reduced light-transmitting capacity.
Beyond its direct effects on protein structure, smoking also depletes essential antioxidant reserves in the lens, including vitamin C, vitamin E, and carotenoids. This depletion renders the lens more vulnerable to damage induced by ultraviolet radiation and other oxidative stressors. These mechanisms help explain the strong association between smoking and the earlier onset and more rapid progression of cataract, particularly nuclear cataract, as well as the increased need for surgical intervention at a younger age compared with non-smokers.
Epidemiological burden and health inequities
Cataract remains the most prevalent cause of blindness worldwide, particularly in low- and middle-income countries. Population ageing continues to drive a rapid increase in the number of affected individuals, while access to high-quality ophthalmic care remains limited in many regions. Economic, geographical, and workforce-related barriers prevent timely surgical treatment for a large proportion of patients, resulting in prolonged visual impairment and serious public health consequences. Therefore, cataract represents not only an ophthalmic disorder but also a major global health equity issue.
Treatment and preventive strategies
Cataract surgery is currently the only effective treatment for restoring vision in patients with cataract. With advances in modern surgical techniques, this intervention is highly safe and provides long-term visual improvement. Nevertheless, prevention plays a crucial role in slowing disease progression and reducing healthcare burden. Measures such as smoking cessation, optimal control of chronic conditions such as diabetes mellitus, protection against ultraviolet radiation, and maintenance of an antioxidant-rich diet may contribute to reducing the risk of cataract development and progression.
References:
- World Health Organization. (2022, October 20). Smoking linked to early vision loss and cataracts.
https://www.who.int/news/item/20-10-2022-smoking-linked-to-early-vision-loss-and-cataracts - Cicinelli, M. V., Buchan, J. C., Nicholson, M., Varadaraj, V., & Khanna, R. C. (2023). Cataracts. The Lancet, 401(10374), 377–389.
https://doi.org/10.1016/S0140-6736(22)01839-6