Corneal Sensitivity in Patients With History of Herpes Keratitis

Abstract

Purpose: : To determine corneal sensitivity to selective mechanical, chemical and thermal (heat and cold) stimulation of subjects with history of herpes simplex virus (HSV) keratitis.

Methods: : Corneal sensitivity to different modalities of stimulus was determined in sixteen patients diagnosed with unilateral HSV keratitis 1-12 months prior to the study by the presence of dendritic corneal ulceration or by microbiological confirmation (viral culture or antigen detection). On slit-lamp examination 13 HSV eyes showed corneal scarring or opacities and 3 HSV eyes presented non-specific signs of previous episodes of keratitis. Corneal sensitivity was determined using the Belmonte non-contact gas esthesiometer. Mechanical (3s-air jets at flow rate from 0 to 300 ml/min), chemical (air containing 0 to 80% CO₂ at subthreshold flow rate), heat (subthreshold flow air pulses at temperatures between +50º and +80°C) and cold stimuli (air at temperatures between +50º and -10ºC) were applied to the center of the cornea of both eyes. Sensitivity threshold was determined for each stimulus modality. Data from HSV eyes were compared with their contralateral eyes and with those from 10 age-matched healthy individuals (control eyes).

Results: : In all control and contralateral eyes selective mechanical, chemical, heat and cold stimulation of the central cornea evoked sensations whose subjective intensity was proportional to the magnitude of the applied stimulus. Some HSV eyes showed no sensitivity to mechanical (40%), heat (25%), cold (6%) or chemical (6%) stimulation. Also, mechanical (p<0.005) and heat (p<0.05) thresholds were significantly higher in HSV eyes than in healthy eyes. No differences were found for CO₂ and cold sensitivity thresholds. Unless chemical stimuli were perceived in HSV eyes, subjects were not able to identify the intensity of the stimulus. Sensitivity to cold stimuli was unaffected in HSV eyes.

Conclusions: : Corneal sensitivity to mechanical, chemical and heat stimulation is reduced in eyes previously affected by HSV keratitis. This could be explained by partial loss of corneal polymodal nociceptive nerve endings consecutive to HSV infection.

Keywords: innervation: sensation • herpes simplex virus • cornea: epithelium