Astaxanthin is a carotenoid antioxidant, often derived from microalgae, that's drawn research interest specifically because of its ability to cross the blood-retinal barrier — giving it more direct access to retinal tissue than many other antioxidants.
Several small, placebo-controlled trials have examined astaxanthin's effect on eye fatigue (asthenopia) and accommodation — the eye's ability to shift focus. In one double-blind, placebo-controlled study, subjects extensively exposed to screens received either 5mg/day astaxanthin or placebo for 4 weeks; 50% of the astaxanthin group reported no eye strain by the end of the study, compared to 7% in the placebo group [1]. Other trials using doses between 4–12mg/day over 4–12 weeks found improvements in accommodative function and reduced subjective fatigue scores [2].
Astaxanthin is thought to work partly through improving blood flow — research has linked it to increased retinal capillary blood flow near the optic nerve head and support for ciliary body circulation, which may explain improvements in accommodative function specifically [3].