Corneal Sensitivity and Tear Meniscus Area after Instillation of Artificial Tears Containing Sodium Hyaluronan

Abstract

 

Purpose:

 

To measure corneal sensitivity and tear meniscus area after the application of artificial tears containing different concentrations of sodium hyaluronan (NaHA).

 

Methods:

 

In young healthy volunteers of both sexes (19-35 years), corneal sensitivity to mechanical (air at 0-200 ml/min flow), chemical (0-60%CO₂ in air) and cold stimuli (air at 25º to -10ºC) was measured using a gas esthesiometer before and after NaHA application. Intensity and other psychophysical attributes of the evoked sensation were scored at the end of the stimulus, using separate 10 cm visual analogue scales. Images of the anterior segment were taken using Visante OCT (Zeiss) before and 5-30 min after the instillation of NaHA solutions (0.1, 0.18 and 0.3%, in different sessions).The area, height and angle of the superior and inferior tear meniscus were measured using Image J software. Data were compared using ANOVA.

 

Results:

 

Topical NaHA solutions reduced the irritative components of the sensation evoked by mechanical and chemical stimulation of the cornea, having stronger effects with higher NaHA concentrations, while the intensity parameter was only weakly reduced by higher NaHA concentrations. Cold sensations evoked by cooling were not modified significantly by NaHA treatment. The meniscus area was slightly increased after instillation of low NaHA concentrations while it decreased after high NaHA concentrations (Table 1).

 

Conclusions:

 

NaHA solutions decrease the irritation components of the sensation evoked by high intensity mechanical and chemical stimuli while the discrimination of stimulus intensity was only slightly affected. Compared with low concentration NaHA solutions, high concentration NaHA decreased the tear meniscus area, probably reflecting a more homogeneous distribution throughout the ocular surface. This difference may explain the efficacy of high concentration NaHA solutions in reducing corneal irritation.  

 

Keywords: innervation: sensation • cornea: tears/tear film/dry eye • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)