Factors predicting the ocular surface response to desiccating environmental stress

Abstract

Purpose: To identify factors predicting the ocular surface response to experimental desiccating stress.

Methods: The ocular surfaces of both eyes of 15 normal and 10 dry eye subjects wearing goggles were exposed to a controlled desiccating environment (15%-25% relative humidity and 2-5 L/min airflow) for 90 minutes. Eye irritation symptoms, blink rate, tear meniscus dimensions, noninvasive (RBUT) and invasive tear break-up time, and corneal fluorescein and conjunctival lissamine green-dye staining were recorded before and after desiccating stress. Pre- and postexposure measurements were compared, and Pearson correlations between clinical parameters before and after desiccating stress were calculated.

Results: Corneal and conjunctival dye staining significantly increased in all subjects following 90-minute exposure to desiccating environment, and the magnitude of change was similar in normal and dry eye subjects; except superior cornea staining was greater in dry eye. Irritation severity in the desiccating environment was associated with baseline dye staining, baseline tear meniscus height, and blink rate after 45 minutes. Desiccation-induced change in corneal fluorescein staining was inversely correlated to baseline tear meniscus width, whereas change in total ocular surface dye staining was inversely correlated to baseline dye staining, RBUT, and tear meniscus height and width. Blink rate from 30 to 90 minutes in desiccating environment was higher in the dry eye than normal group. Blink rate significantly correlated to baseline corneal fluorescein staining and environmental-induced change in corneal fluorescein staining.

Conclusions: Ocular surface dye staining increases in response to desiccating stress. Baseline ocular surface dye staining, tear meniscus height, and blink rate predict severity of ocular surface dye staining following exposure to a desiccating environment.

Keywords: cornea; dry eye; tears.

Figures

Figure 1.

Rendition of modified laboratory goggles used to create a drafty low humidity environment around the eye. Ambient air was pumped continuously at a flow rate of 3 L/min through a conditioning system and into the goggles such that the air surrounding the eye and adnexa maintained a relative humidity of 15% to 25% (mean, 21%). Small vents on the top surface of the goggles prevented pressure buildup. Relative humidity (humidity sensor), temperature (thermistor), and airflow were measured by sensors in the goggles and recorded in real time in an electronic database.

Figure 2.

Graph of percentage relative humidity and airflow (L/min) measurements taken every 10 seconds over the 90-minute test period from a representative subject.

Figure 3.

Percentage change from baseline in severity of fluorescein staining in five zones on the cornea and lissamine green staining in nasal and temporal bulbar conjunctiva.

Figure 4.

Blink rate. Lines show the mean ± SD of blink rate in the normal control and dry eye groups. Asterisks indicate significant differences between the groups (P < 0.05).