Phaffia rhodozyma is a species of red yeast that is notable for its production of astaxanthin, a potent antioxidant carotenoid. The association of Phaffia rhodozyma with eye health is primarily due to its astaxanthin content, not the yeast itself per se. Astaxanthin has been studied for its potential benefits in protecting eye tissues from oxidative stress, a key contributor to conditions such as age-related macular degeneration (AMD) and eye fatigue. Several clinical and preclinical studies have shown that astaxanthin supplementation can improve visual acuity, reduce eye fatigue, and protect retinal cells from damage induced by light and oxidative stress.

For example, human trials have reported improvements in subjective eye fatigue and accommodation (focusing ability) in people taking astaxanthin supplements. The mechanism is believed to involve astaxanthin's ability to cross the blood-retina barrier and neutralize reactive oxygen species in ocular tissues. However, the majority of studies utilize purified astaxanthin or extracts from other natural sources such as Haematococcus pluvialis. Research directly involving astaxanthin from Phaffia rhodozyma is more limited, but since the chemical structure of astaxanthin is consistent regardless of source, it is reasonable to extrapolate similar benefits.

Overall, the evidence base for astaxanthin’s role in supporting eye health is moderate, with several human and animal studies supporting its use, but more large-scale clinical trials would further substantiate these findings. Thus, the evidence rating is 3 out of 5.