Vital staining properties of neutral red. Vital staining of cornea and conjunctiva.

Vital staining by instillation in the conjunctival sac of 1% neutral red in 54 normal and 153 differently affected eyes was studied by slit lamp examination. Of these, 134 eyes were after-stained by a mixture of 1% tetrazolium and 1/4% alcian blue and 73 eyes were after-stained by a mixture of 1% rose bengal and 1% fluorescein. Microscopy of a further 10 conjunctival scrapings and 40 mucous conjunctival threads disclosed neutral-red-stained inclusion bodies in the cytoplasm of the epithelial cells and the granulocytes. In the slit lamp the cornea and the conjunctiva were seen to be stained only rarely and, if so, poorly by neutral red, both in normal and affected eyes. Better staining was obtained with tetrazolium, and the best with rose bengal. The plica semilunaris, Marx' line, and the mucous thread were stained by neutral red, more intensely by rose bengal, and the least by tetrazolium. The inferior fornix and the tarsus were rarely stained by any of the three dyes. Neutral red seems to offer no diagnostic advantages over the vital stains with which the dye has been compared in the present study. More particularly we found no pathological processes that were stained more intensely by neutral red than by the other vital stains.