III. Corneal epithelial cell collection (left eye only) Corneal epithelial cells can be collected non-invasively in vivo using a custom-made ocular irrigation chamber specific for these types of studies. The corneal irrigation chamber collects corneal epithelial cells into a 15 ml test tube. The patient is seated with forehead resting against a headrest; a fixation target is placed to orient the eye to be irrigated downwards; and the irrigating tip is positioned 2 mm below the corneal apex. Irrigation involves the delivery of 9 ml of sterile saline to the central cornea for a period of 1 minute via a tubing pump.