How was the protective effect of lutein on the eyes discovered?

Basis of early research
Scientists have long studied the physiological structure and function of the eye. When studying the macula region of the retina, it was found that this region contains a yellow pigment. In the early 20th century, scientists became interested in this pigment and began to study its composition. With advances in chemical analysis techniques, in the mid-20th century, researchers determined that this pigment mainly contained lutein and zeaxanthin.
Early animal studies provided clues about the protective effects of lutein on the eyes. The researchers found that the level of lutein in the animals' retinas correlated with the health of the eyes. For example, in some animal models of retinopathy, lutein deficient animals have more severe symptoms. Retinopathy was improved in some animals by supplementing with lutein.
Research on macular degeneration of the retina
Age-related macular degeneration (AMD) is one of the leading causes of vision loss and blindness in the elderly. In the 1980s and 1990s, a large number of clinical observations and studies began to focus on the relationship between lutein and AMD. The researchers found that AMD patients had significantly lower concentrations of lutein and zeaxanthin in the macular region of the retina than the normal population.
A case-control study was used for further research. The researchers compared the dietary intake of AMD patients with healthy controls and found that those who ate more lutein-rich foods had a relatively low incidence of AMD. For example, in some long-term follow-up studies, people who ate a lot of leafy green vegetables (rich in lutein) had a significantly lower risk of developing AMD.
In order to verify the preventive and therapeutic effects of lutein on AMD, interventional studies have been carried out. In these studies, lutein and other related nutrients were given to AMD patients or people at high risk of developing AMD, and after observation over a period of time, the rate of vision loss was slowed in some patients and retinal function was improved. These findings suggest that lutein has an important role in preventing and improving AMD.
Research on other eye diseases
In studying diabetic retinopathy, scientists have found that lutein can reduce oxidative stress damage to the retina. The high sugar environment in people with diabetes leads to the production of large amounts of free radicals, which attack retinal cells. The antioxidant properties of lutein can scavenge free radicals and protect retinal cells from oxidative damage. Through animal experiments and small-scale human clinical trials, lutein supplementation has been found to help maintain the integrity of retinal microvessels in diabetic patients and reduce the occurrence of retinal bleeding and other diseases.
For the study of visual fatigue, scientists have found that supplementing lutein can improve blood circulation in the retina through the observation and experiment of people who use electronic devices for a long time. In some double-blind controlled trials, volunteers who were given lutein supplementation for a long period of time reported a reduction in visual fatigue symptoms (such as dry eyes, sore eyes, etc.) and an improvement in visual acuity. This suggests that lutein may alleviate eye fatigue by improving blood circulation and nutrient supply to the eyes.