Posterior segment eye diseases and the benefits of polyphenols
The most common causes of blindness in Ghana are cataract (54.5%), Glaucoma (19.4%), Posterior Segment Disease including Diabetic Retinopathy (12.9%) and corneal-related causes (11.2%) (Ghana Blindness and Visual Impairment Study, 2015).
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The latest estimates of global visual impairment (VI), or Posterior Segment Eye Diseases (PSED) show that Glaucoma; Age-Related Macular Degeneration (ARMD) and Diabetic Retinopathy (DR) are now recognised as major causes of VI world-wide and are more prevalent than infectious causes of VI such as trachoma and corneal ulcers.
In 2010, the WHO listed posterior segment eye diseases as the leading causes of visual impairment (VI) and blindness. Posterior segment eye disease is a Non-Communicable Disease (NCD).
Posterior segment eye disease (i.e. affecting the back of the eye), epidemiologically is commonly defined as diseases of the retina, choroid and optic nerve and primarily includes glaucoma, age-related macular degeneration (AMD) and diabetic retinopathy (DR).
Visual impairment and blindness
About 285 million people are visually impaired (VI) world-wide, About 90 per cent of persons world-wide with VI live in low-income countries. NCDs are the leading causes of VI, in part due to the successful control of infectious diseases. The VI is ranked sixth in the top ten causes of burden of disease in terms of disability-adjusted life-years (DALYs) in low-income, middle-income and high-income countries.
The number of people visually impaired in the WHO African region is estimated to be 26 million of whom almost six million are blind. Despite Africa having one of the highest prevalence of blindness, it is the most underserved continent in terms of human resources available to treat and manage eye disease, with the greatest gap between existing need and provision.
Initiative
VISION2020 is the global initiative for the elimination of avoidable blindness, launched in 1999 jointly by WHO and the International Agency for the Prevention of Blindness (IAPB) and provides technical support and advocacy for the prevention of blindness activities worldwide.
It aims over two decades to prevent 100 million people from becoming blind. VISION2020 has largely focused on the elimination of anterior segment diseases, primarily cataract, as it alone causes almost half of blindness and is amenable to cure through surgery.
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VISION2020 has not focused on PSED to date mostly due to a lack of data on the magnitude of these conditions and lack of cost-effective treatment options. The posterior segment of the eye is represented by all-optical structures behind the lens, including the vitreous, retina, choroid and optic nerve.
The retina is a complex structure, rich in blood vessels and a dense network of neurons that capture and process light by the visual pigments. It is a highly energy-consuming tissue that relies on abundant mitochondrial oxidative phosphorylation and aerobic glycolysis to sustain the energy demand.
Indeed, the retina has the highest oxygen consumption rate (per gram of tissue) in the body, which can produce a considerable amount of reactive oxygen species (ROS) in addition to that generated by exposure to visible and UV light. The retina has significant defence strategies against ROS.
The vitreous is a viscoelastic gel in the eye’s posterior chamber, with a high water content (99 per cent) and few resident cells. It occupies about 80 per cent of the eye globe volume.
It presents a vast array of both an enzymatic cell and non-enzymatic antioxidant profile, including ascorbic acid, riboflavin and trace metals (zinc, and selenium). When antioxidant patrolling is inadequate and/or ROS production is excessive, the delicate balance between ROS generation and ROS scavenging executed by antioxidants leads to “oxidative stress”, a chronic condition in which ROS overwhelm antioxidant shield activity.
In this scenario, progressive cell dysfunctionality follows the uncontrolled reaction of ROS with cellular proteins, lipids, and other cellular molecules (Rodelia et al. Antioxidant Nutraceutical Strategies in the Prevention of Oxidative Stress Related Eye Diseases.
1,2 Nutrients 2023, 15(10), 2283; https://doi.org/10.3390/nu15102283
I have earlier referred to the VISION2020 intervention which focused essentially on diseases of the anterior aspect of the eye. The inability to tackle posterior segment eye diseases was ascribed to resource constraints.
The reinforcement of the endogenous antioxidant system of ocular tissues can be achieved through nutrition and food supplementation. To this end, the consumption of polyphenol-rich foods with proven high antioxidant capacity should be adopted by all.
Posterior segment eye disease (PSED) is a major cause of visual impairment world-wide. The PSED can lead to partial or complete blindness. The formation of pathological blood vessels, known as angiogenesis, epithelial-mesenchymal transition and associated with invasion and migration of cells belong to the mechanisms responsible for the development of these eye disorders.
Polyphenol-rich foods have pro-life properties including anti-inflammatory and anti-oxidative activity. Polyphenols can inhibit epithelial-mesenchymal transition to PSED.
Polyphenols are effective and safe components of the human diet with the capacity to limit the development and progression of PSED (Caban et al. Polyphenols and Posterior Segment Eye Diseases:
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Effect on Angiogenesis Invasion, Migration and Epithelial-Mesenchymal Transition. Food Reviews International. Dec. 2021). Cocoa is an excellent source of polyphenols.
The writer is a
Chief Pharmacist,
Cocoa Clinic