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 rhodobsin, the photopigment necessary for initiating visual sensation, is considered to be supported by the presence of DHA in the retinal membranes.