Ultraestructural changes in human corneal nerves with Herpetic Keratitis

Abstract

Abstract: : Purpose: Pain serves as a warning sign which prevents our organism from real or potential damage. There are viral diseases that affect corneal sensitivity like the ones produced by herpes simplex virus (HSV). This pathology affects the cornea producing focal anesthesia which later on spreads to the entire cornea exposing it to suffer damage. Since HSV has been reported as a neurotropic virus, its important to investigate if there is damage in nerve structures in charge of nociceptive transmition (Fibers A–δ y C) due to the virus. Methods: Corneal buttons from patients with herpetic keratitis were used as cases, controls were obtained from patients with mechanical injuries without corneal pathology that underwent penetrating keratoplasty. Tissue was fixed for electron microscopy with glutharaldehyde 1.25% and paraformaldehyde 1% in a cacodylate buffer. Later on the tissue was posfixed in 1% OsO₄. The pieces were flat embedded on epon–araldite resin. Sagital and frontal sections were cutted at 90nm thickness. Ultrathin sections were stained with uranyl acetate and led citrate and inspected using Philips EM 208s electron mycroscope. Results: In section analysis we found nerves corresponding to C fibers in the basal membrane of the epithelium of control corneas. The diameter range was 0.46 to 1.2 microns which is the normal size of oligomyelinic fibers. The structures in these fibers were well preserved showing microtubules, microfilaments and defined myelin layers. In the herpetic corneas we found similar elements with severe structural changes characterized by axon liquefaction, loss of microtubules, microfilaments and ill–defined mitochondrial membranes, delamination of the myelin in these fibers was also observed. Conclusions: These findings support that the structural changes described in herpetic corneas could be responsible for the interrupted action potential of the high threshold fibers that conduct nociceptive information.

Keywords: herpes simplex virus • microscopy: electron microscopy • innervation: sensation