Many reagents have been developed recently to label living cells with substrates that will become fluorescent if an enzyme is active. The general principle is that the substrate will be taken up by living cells then detected only if the enzyme is active. These substrates work well with isolated individual cells, however, more difficulty can be encountered when studying whole tissues. Problems can range from substrate penetration into whole tissues to being able to detect the label effectively. We have used the chicken corneal epithelia for many studies, but the tissue is to thick to view with a conventional light microscope, therefore we have developed techniques using laser confocal microscopes to view this tissue in with a variety of techniques including in situ hybridization, immunohistochemistry, and vital dyes/stains.

Whole embryonic corneal epithelial sheets can be isolated without the basal lamina.