Figure 2. Fluorescent labeling of corneal nerve fibers. A–C, Nerve fibers were loaded with tetramethylrhodamine dextran (10 kDa) 24 hr before confocal microscopy. A, Subepithelial nerve plexus lying within the stromal layer. B, Superficial nerve terminals 5 µm below corneal surface. C, Nerve terminals lying deeper within the corneal epithelium. Scale bars: (in A) A, B, 25 µm; C, 50 µm. D, E, Nerve terminals loaded with Oregon Green 488 BAPTA-1 dextran (10 kDa) 24 hr before imaging with a cooled CCD camera. D, Nerve terminals imaged immediately before electrical stimulation. E, Same nerve terminals as in D imaged 1 sec after the start of a train of 10 field stimuli (10 Hz). F, F/F₀ trace for a section (marked by arrowheads) of the middle nerve terminal seen in D and E; arrow indicates the start of electrical stimulation. Scale bar: (in E) D, E, 35 µm. For Ca²⁺ imaging in D—F, 500 msec exposures were collected at 1.67 Hz.