Purpose: Cataracts are often considered to be an unavoidable consequence of aging. Oxidative damage is a major cause or consequence of cortical and nuclear cataracts, the most common types of age-related cataracts. Methods: In this review, we consider the different risk factors, natural history and etiology of each of the 3 major types of age-related cataract, as well as the potential sources of oxidative injury to the lens and the mechanisms that protect against these insults. The evidence linking different oxidative stresses to the different types of cataracts is critically evaluated. Results: We conclude from this analysis that the evidence for a causal role of oxidation is strong for nuclear, but substantially lower for cortical and posterior subcapsular cataracts. The preponderance of evidence suggests that exposure to increased levels of molecular oxygen accelerates the agerelated opacification of the lens nucleus, leading to nuclear cataract. Factors in the eye that maintain low oxygen partial pressure around the lens are, therefore, important in protecting the lens from nuclear cataract. Conclusions: Maintaining or restoring the low oxygen partial pressure around that lens should decrease or prevent nuclear cataracts.

/pdf/oxidative-damage-and-the-prevention-of-age-related-cataracts-3mq065r6xa.pdf

Oxidative Damage and the Prevention of Age-Related Cataracts

Vitreous Substitutes: A Comprehensive Review

Retinal oxygen: from animals to humans

This literature review is aimed at the evaluation of the potential for cataract prevention in Europe. It was performed using PubMed with Mesh and free-text terms. Studies included were (i) performed on a population of Caucasian origin at an age range of 40-95 years, (ii) cataract was clinically verified, (iii) drug record of prescriptions, their indication, a record of every diagnosis, dosage and quantity of prescribed medicine were available, (iv) sample size >300 and (v) published between 1990 and 2009. The results of 29 articles were reviewed. Former [3.75 (2.26-6.21)] or current smoking [2.34 (1.07-5.15)], diabetes of duration >10 years [2.72 (1.72-4.28)], asthma or chronic bronchitis [2.04 (1.04-3.81)], and cardiovascular disease [1.96 (1.22-3.14)] increased the risk of cataract. Cataract was more common in patients taking chlorpromazine during ≥90 days with a dosage ≥300 mg [8.8 (3.1-25.1)] and corticosteroids >5 years [3.25 (1.39-7.58)] in a daily dose >1600 mg [1.69 (1.17-2.43)]. Intake of a multivitamin/mineral formulation [2.00 (1.35-2.98)] or corticosteroids [2.12 (1.93-2.33)] also increased the risk of cataract. Corticosteroids applied orally [3.25 (1.39-7.58)], parenteral [1.56 (1.34-1.82)] or inhalational [1.58 (1.46-1.71)] lead to cataract more frequently than those applied topically: nasal [1.33 (1.21-1.45)], ear [1.31 (1.19-1.45)] or skin [1.43 (1.36-1.50)]. Outpatient cataract surgery was negatively associated with total cataract surgery costs, and chlorpromazine, corticosteroids and multivitamin/mineral formation increase the risk of posterior subcapsular cataract dependent on dose, treatment application and duration. This review presented a comprehensive overview of specific and general cataract risk factors and an update on most recent experimental studies and randomized control trials directed at cataract prevention.

/pdf/cataract-prevalence-and-prevention-in-europe-a-literature-hn3s6h8slr.pdf

Cataract prevalence and prevention in Europe: a literature review

Metabolic physiology in age related macular degeneration.

Objective To investigate the rate and mechanism of oxygen consumption by the vitreous. Methods Oxygen consumption was measured with a microrespirometer. Vitreous ascorbate was measured spectrophotometrically and by gas chromatography–mass spectrometry. Vitreous degeneration was related to the rate of oxygen consumption and ascorbate concentration in samples obtained during vitrectomy. Results Prolonged exposure to oxygen or treatment with ascorbate oxidase eliminated oxygen consumption by the vitreous. Adding ascorbate restored oxygen consumption. Oxygen consumption persisted after boiling or treating the vitreous with the chelating agents EDTA and deferoxamine. In patients undergoing retinal surgery, liquefaction of the vitreous and previous vitrectomy were associated with decreased ascorbate concentration and lower oxygen consumption. Conclusions Ascorbate in the vitreous decreases exposure of the lens to oxygen. The catalyst for this reaction is not known, although free iron may contribute. The gel state of the vitreous preserves ascorbate levels, thereby sustaining oxygen consumption. Vitrectomy or advanced vitreous degeneration may increase exposure of the lens to oxygen, promoting the progression of nuclear cataracts. Clinical Relevance Determining how the eye is protected from nuclear cataracts should suggest treatments to reduce their incidence.

https://jamanetwork.com/journals/jamaophthalmology/articlepdf/422840/els80015_475_482.pdf

Paula E. Malone

Papers

The gel state of the vitreous and ascorbate-dependent oxygen consumption: relationship to the etiology of nuclear cataracts.