In addition to their important sensory function, the corneal nerves provide protective and trophic functions and also regulate corneal epithelial integrity, proliferation, and wound healing.
2 Consequently, the anatomy of corneal nerves has been studied for many years by a large variety of methods including light and electron microscopy and, since the mid-1990s, by in vivo confocal microscopy (IVCM).
1,3 IVCM is a noninvasive imaging technique that provides high-resolution images of corneal structures in the living human eye. Although IVCM can visualize the subbasal nerve fibers, the subepithelial plexus as well as the stromal nerves, because of the particular distribution of nerve fibers within the cornea,
4 the majority of IVCM studies on corneal nerves have so far evaluated only the subbasal nerves in the central part of cornea.
3 Subbasal nerve fibers form a plexus between Bowman's membrane and basal epithelial cells easily visible using IVCM as hyper-reflective, well-defined linear structures with dichotomous branches and thin connecting fibers. Several morphologic parameters have been developed,
2 and IVCM has already been used to evaluate corneal subbasal nerves in healthy subjects
2 and in different pathological conditions,
3 such as diabetes mellitus, dry eyes, keratoconus, contact lens wear, glaucoma patients,
5,6 and after penetrating keratoplasty or refractive surgery. Nevertheless, the relationship between the corneal nerve structures evaluated in vivo with IVCM and corneal nerve function remains unclear in ocular surface diseases. In dry-eye patients, corneal sensation has been correlated with subbasal nerve density and number,
7 whereas Martone et al.
6 observed a significant correlation between corneal sensitivity and nerve tortuosity in patients under topical antiglaucoma therapy. Considering the variations in the methods used to evaluate subbasal nerve parameters and the different types and generations of the in vivo confocal microscopes used, it is difficult to compare different studies or different pathologies.
3