The activity of the enzyme glutamine synthetase was found to be high in the normal human retina. Comparable levels of enzyme were observed when pieces of retina were maintained in tissue culture for 24 hours. Addition of hydrocortisone to such cultures did not increase levels of the enzyme as has been observed in other systems with native retinal tissue.
Chader GJ, Saunders L, Reif-Lehrer L. Glutamine Synthetase in the Normal Human Retina. Arch Ophthalmol. 1971;85(3):286-287. doi:10.1001/archopht.1971.00990050288007