Reactive oxygen species (ROS) are produced easily in the retina and evoke photoreceptor degeneration. Astaxanthin, a carotenoid and powerful antioxidant, was shown to have a protective effect against light-induced retinal degeneration in a mice model.

Otsuka et al.¹ studied the protective effect of astaxanthin on light-induced retinal degeneration in mice exposed to white light at 8000-lux for 3 hours. It was found that oral administration of 100 mg/kg astaxanthin reduced oxidative stress caused by light irradiation. In vitro study also showed that light exposure to the mouse retinal cone-cell line 661W induced the production of ROS, and it was partly prevented by astaxanthin treatment.

Astaxanthin (100 mg/kg, p.o.) significantly prevented retinal damage induced by light irradiation. The researchers proposed that the protective effect of astaxanthin against light-induced retinal damage via reduced oxidative stress was not limited to DNA damage or apoptotic degeneration, but also included lipid peroxidation, inflammation and other effects. The study also suggests that astaxanthin does not interact with endogenous antioxidants. Furthermore, this study is consistent with previous studies that found astaxanthin supplementation to be safe in animals as well as in humans.

Retinal light toxicity and effect of antioxidants

Eyes are constantly exposed to light due to their role in visual perception. Compared to other organs, the eye is particularly susceptible to oxidative damage due to its exposure to light and high metabolism rate of their tissue cells². Excessive light exposures, especially blue light, have been known to cause retinal injury³ and cause vision problems like age-related macular degeneration (AMD). AMD is one of the leading causes of progressive vision loss and blindness in the aging population⁴.

Carotenoids, particularly lutein and zeaxanthin, are two antioxidants that have strong singlet oxygen quenching and free radical scavenging activity. They are found abundantly in the macular region of the retina and their role in the prevention of photic damage to the retina has been well documented in literature⁴.

In recent times, the overlooked antioxidant, astaxanthin, which is a dark-red colored carotenoid found abundantly in algae, salmon, trout, shrimp and lobsters has gained substantial interest and promoted several research studies on visual benefits after the groundbreaking research by Tso et al.⁴ who proved its ability to cross blood-brain barrier and blood-retinal barrier. They found its effectiveness against light-induced eye damage, photoreceptor cell damage, ganglion cell damage, inner retina neuronal damage and inflammatory damage in murine models. Miki W.⁵ also found it to be 10 times more potent anti-oxidant than other carotenoids, namely, zeaxanthin, lutein, canthaxanthin and beta-carotene, and 100 times stronger antioxidant than alpha-tocopherol.

Iwamoto et al.⁶ found a dose-dependent increase in oxidation lag time with 1.8, 3.6, 14.4 and 21.6 mg doses while studying the in vitro and ex vivo inhibitory effects of astaxanthin on LDL oxidation. In another study, Ohgami et al.⁷ suggested the dose-dependent anti-inflammatory effect of astaxanthin on suppressing the development of endotoxin-induced uveitis in rats.

These studies led Nakamura et al.⁸ to hypothesize that astaxanthin might have a dose-dependent improvement in accommodation time in humans. The group evaluated the effect of astaxanthin supplementation on visual functions of 49 healthy subjects aged 40 years and above. When the visual functions were compared before and after 4-week supplementation of 4 mg and 12 mg of astaxanthin, the result showed a statistically significant improvement in uncorrected far visual acuity and shortened positive accommodation time.

In conclusion, studies have shown that astaxanthin improves visual functions in humans and protects against light-induced retinal degeneration in mice. Future research could be done to study the role of astaxanthin in the prevention of AMD in humans.