Oxidative photodegradation of ocular tissues: Beneficial effects of filtering and exogenous antioxidants

Abstract

The fact that light is necessary for life is generally accepted as an axiom. The extent to which light interacts and influences human biology, however, is often not fully appreciated. Exposure to sunlight, for instance, can both promote and degrade human health. There is now general scientific consensus that, although the eye evolved to respond to light, it is also damaged by excessive exposure. Light-mediated ocular damage is involved in the pathophysiology of many common forms of blindness. The type of ocular tissue damage induced by light exposure depends on the extent of exposure and wavelength. The tissues of the lens, cornea, and retina contain specific chemical moieties that have been proven to exhibit light-mediated oxidative degradation. Proteins and lipids present in the cornea, lens, and retina, meet all of the physical requirements known to initiate the process of oxidative photodegradation upon exposure to solar radiation. As such, different mechanisms have evolved in the lens, cornea, and retina to ameliorate such light-mediated oxidative damage. It appears, however, that such mechanisms are ill-matched to handle modern conditions: namely, poor diet and longer life-spans (and the degenerative diseases that accompany them). Hence, steps must be taken to protect the eye from the damaging effects of light. Preventative measures include minimizing actinic light exposure, providing exogenous filtering (e.g., through the use of protective lenses), and enhancing antioxidant defenses (e.g., through increased dietary intake of antioxidants). These strategies may yield long-term benefits in terms of reducing oxidative photodegradation of the ocular tissues.

A Double-Blind, Placebo-Controlled Study on the Effects of Lutein and Zeaxanthin on Photostress Recovery, Glare Disability, and Chromatic Contrast

“…Thus, as shown in Figure 1 of Hammond et al, 20 we used a xenon source that closely matched the spectral distribution of sunlight (an even better match can be made to the solar spectrum provided in Fig. 1 of Hammond et al 23 ). For the GD measurement, subjects adjusted the intensity of an annulus (centered at 11.58 eccentricity) until it veiled a 18 circular grating (4 cyc/deg) target.…”

A contra-lateral comparison of the visual effects of a photochromic vs. non-photochromic contact lens

“…Not surprisingly, most organisms have evolved mechanisms for dealing with the bright light of the sun [4]. For example, humans have brow ridges and intraocular filters such as melanin and retinal macular pigments [5]. Contact lenses, in contrast, are generally transparent to visible light and hence generally do not influence visual function in bright light conditions; although they may, in some cases, increase scatter and worsen vision in such circumstances [6].…”

Photopigment self-screening and the determination of macular pigment absorbance using heterochromatic flicker photometry

“…Although trace amounts are found across the retina, MP is heavily deposited in and around the fovea where fine spatial and color vision are most highly developed. MP absorbs primarily short-wave (SW) light which is potentially degrading to visual performance (e.g., Wooten and Hammond, 2002) and damaging to retinal cells (e.g., Hammond et al, 2014). There is significant variability between individuals in the amount of MP found in the retina: some have none or very little, while others may have as much as 1.5 OD (Hammond et al, 1997).…”