DHA (docosahexaenoic acid, 22:6n-3) is now recognized as a physiologically-essential nutrient in the brainand  retina (of the eye) where it is required in high concentrations for providing optimal mental performance (neuronal  functioning) and visual acuity, respectively.

The highest body concentrations of DHA per unit tissue weight are found in the membrane phospholipid components of the photoreceptor outer segments of the retina. The unique biophysical and biochemical properties of DHA, including its imparting 'fluidity' to retinal membranes, render it an essential structural component thereby  mediating a faster response to stimulation. The optimal functioning of rhodopsin, the photopigment necessary for  initiating visual sensation, is considered to be supported by the presence of DHA in the retinal membranes.

DHA omega-3 deficiency is associated with both structural and functional abnormalities in the visual systems and  the resulting visual deficits have been related in part to a decreased efficiency of key visual signaling pathways due to the deprivation of DHA. A sufficient supply and accumulation of DHA appears necessaryor optimal  neurotransmission to support cognitive function in the brain and optimal visual transduction and functioning.