DHA (docosahexaenoic acid), an unsaturated fatty acid which belongs to omega-3 family, is essential to human health.  
DHA is a major component of human brain and retina cells, in particular in human cerebral cortex
it is up to 20%, it is even the largest component in eye ritina, accounting for as much as 50%.

DHA is optional nutrient in infant formula according to China food regulations GB 10765 and GB 10767.