Asthenopia (2002-2006 Studies) Reducing with Astaxanthin
A couple of randomized double blind placebo controlled pilot studies demonstrated the positive effects of astaxanthin supplementation on visual function. For example, a study by Nagaki et al., (2002), demonstrated that subjects (n=13) who received 5 mg astaxanthin per day for one month showed a 54% reduction of eye fatigue complaints. In a sports vision study led by Sawaki et al., they demonstrated that depth perception and critical flicker fusion had improved by 46% and 5% respectively on a daily dose of 6 mg (n=9). The effect of astaxanthin on visual performance prompted a number of other clinical studies to evaluate the optimum dose and identify the mechanism of action.
A study by Nakamura (2004), demonstrated significant improvements in reducing asthenopia and positive accommodation for the 4 mg (p<0.05) and 12 mg (p<0.01) groups. However, it was not until Nitta et al., (2005), who established the optimum daily dose at 6 mg (n=10) for a period of 4 weeks by comparing eye fatigue using a visual analogue scale (VAS) based questionnaire and accommodation values. Overall, the 6 mg group improved significantly better at week 2 and 4 of the test period. Furthermore, questionnaire results obtained by Shiratori et al., (2005) and Nagaki et al., (2006), also confirmed the previous findings that astaxanthin supplementation at 6 mg for 4 weeks improved symptoms associated with tiredness, soreness, dryness and blurry vision. Another study by Takahashi & Kajita (2005), also demonstrated that astaxanthin attenuates induced-eye fatigue, as opposed to treating eye fatigue, which suggests prevention rather than treatment. Astaxanthin treated groups (asthenopia negative) were able to recover quicker than the control group after heavy visual stimulus. Later, Iwasaki & Tawara (2006) also confirmed the same tendencies of subjective eye fatigue complaints in a randomized double-blind placebo controlled double-crossover study.