Decreased corneal sensitivity in patients with dry eye

To explore changes in corneal sensitivity that develop in patients with dry eye and the relationship between sensibility and severity of the dry eye disease.

Experiments were performed in 44 patients with dry eye and 42 healthy individuals. Corneal sensitivity was measured with the Belmonte noncontact gas esthesiometer. Mechanical (air jets at flow rates from 0 to 200 mL/min, reaching the corneal surface at 34 degrees C), thermal (cold or warm air at subthreshold flow rates changing corneal basal temperature +/-1 degrees C), and chemical stimuli (air containing 0% to 50% CO2 at subthreshold flow rate and temperature at the cornea of 34 degrees C) were applied to the center of the cornea to determine the sensitivity threshold for each stimulus modality. The clinical state of the ocular surface was also explored, measuring the fluorescein tear break-up time, the degree of corneal staining with fluorescein and Lissamine green, and tear production with the Schirmer test.

Both in control subjects and patients with dry eye, the corneal thresholds for mechanical, chemical, and thermal stimulation increased with age. Moreover, the thresholds for the three modalities of stimuli were significantly higher in patients with dry eye than in control subjects. In both groups, individual mechanical, chemical, and thermal thresholds correlated significantly. Also, high thresholds in patients with dry eye correlated with the intensity of fluorescein and Lissamine green corneal staining but not with the results of the Schirmer test.

Patients with dry eye exhibit corneal hypoesthesia after mechanical, thermal, and chemical stimulation that appears to be related to damage to the corneal sensory innervation.