Macular degeneration associated with age and drusen is the leading cause of severe visual acuity loss in the United States and Western Europe in persons aged 55 years old or older. Age-related macular degeneration (AMD) is a collection of clinically recognizable ocular findings that can lead to blindness. The findings include drusen, retinal pigment epithelial (RPE) disturbance—including pigment clumping and/or dropout, RPE detachment, geographic atrophy, subretinal neovascularization and disciform scar. Not all these manifestations are needed for AMD to be considered present. The prevalence of persons with ophthalmoscopically or photographically identifiable drusen increases with age, and most definitions of AMD include drusen as a requisite. However, drusen alone do not seem to be directly associated with vision loss. It is rather, the association of drusen with the vision-threatening lesions of AMD, i.e., geographic atrophy, RPE detachment and subretinal neovascularization, that has led to their inclusion in the definition of AMD. Although recent studies have demonstrated the benefit of laser photocoagulation in those individuals with macular degeneration who develop acute, extrafoveal choroidal neovascularization, no treatment has been shown to be of benefit to the majority of people who have AMD. The cause of macular degeneration is unknown.
Recently, attention has been focused on the possible involvement of various minerals in retinal disease. Zinc has received particular notice in this regard due to the observation of high concentrations of zinc in ocular tissues, particularly the retina, pigment epithelium and choroid. Zinc is an important micronutrient that plays an essential role in human growth and function. Zinc is necessary for the activity of over a hundred enzymes, including carbonic anhydrase, superoxide dismutase and alkaline phosphatase. Zinc acts as a cofactor for numerous metalloenzymes, including retinol dehydrogenase and catalase. Zinc also is a cofactor in the synthesis of extracellular matrix molecules, is essential for cell membrane stability, is needed for normal immune function, is associated with melanin and is taken up in a facilitated manner by the retinal pigment epithelium. Despite the evidence supporting the notion that zinc must be essential to the metabolism of the retinochoroidal complex, relatively little is known of its role in the maintenance of normal eye function.
Toxicity from free radicals and oxidizers has also generated significant interest with regard to macular degeneration and the progression thereof. Circumstantial evidence indicates that protection against phototoxicity and oxidizers, such as would be provided by antioxidants, could slow the onset and progression of age-related macular degeneration as well as cataracts. If a treatment modality could slow down the progression of macular degeneration and/or cataracts, it would have a tremendous impact on the number of individuals who suffer from such problems due to the fact that such problems generally occur at significantly more advanced ages.
Accordingly, a need still exists in the art to provide methods and compositions for the treatment of macular degeneration and/or cataracts in the absence of surgery.