The purpose of this study is to determine the therapeutic effect of the chronic application of eye-drops on tear evaporation rate in dry eye and normal subjects exposed to a condition of environmental stress. The effect will be studied in terms of changes in tear physiology and the inflammatory biomarkers on the ocular surface.
Environmentally induced dry eye is a condition which occurs in otherwise asymptomatic individuals in certain situations, for example with the use of computers, in overheated or air conditioned workplaces and in conditions of low humidity. The most common ocular complaints associated with these environments are burning, dryness, stinging, and grittiness. Although the exact cause of these symptoms is unknown, it is thought that increased tear evaporation rate due to low humidity plays a vital role. The changes in tear film physiology, which occurs in these environments, have traditionally been dealt with by the use of eye drops (particularly the highly viscous variety), which have been shown to be an effective therapeutic option in the treatment of environmental dry eye disease. Previous studies of the use of eye-drops of various formulations has shown improvements in tear physiology in mild to moderate dry eye patients with their use in both acute and chronic application protocols. In this study, an attempt was made to relate the effects on tear physiology induced by variations in environmental conditions to the beneficial effect produced by the use of eye-drops.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
SINGLE
Enrollment
38
One drop both eyes 4 times daily for two weeks
One drop both eyes four times daily for two weeks
One drop both eyes four times daily for two weeks
Glasgow Caledonian University
Glasgow, United Kingdom
Tear Film Evaporation
Tear film evaporation will be determined with a 'Servo-Med EP-Evaporimeter'. This measures the relative humidity and temperature at two sensors separated by a known distance, above the evaporative surface. The ocular surface evaporation will be calculated from measurements of fluid loss with the eyes open and closed while the subject sits with the eye covered by a modified goggle.
Time frame: Each subject will be followed for the duration of the study, an expected average of 8-9 weeks
Interferometry
The structure and quality of the tear film will be assessed by observing the interference fringes of the lipid layer. Interferometry facilitated with a miniature slow motion video will be used. The grading system developed previously in our laboratory will be utilised to grade the tear film distribution. This grading system classifies the tear film structure on the basis of the distribution of tears after a blink. Measurements are made while the subject sits quietly and looks into the lens of the device.
Time frame: Each subject will be followed for the duration of the study, an expected average of 8-9 weeks
Tear Film Osmolarity
Tear film osmolarity was measured using an 'OcuSense TearLab Osmometer'. This employs a single use, disposable test card mounted to a collection pen, to obtain a small sample of tear fluid by passive capillary action from the inferior-temporal tear meniscus. The measurement of the electrical impedance is carried out within the pen. The pen is then docked into the reader, which calculates and displays the osmolarity result.
Time frame: Each subject will be followed for the duration of the study, an expected average of 8-9 weeks
Non-invasive tear break up time
The 'HIR-CAL Grid' system based on a modified Bausch and Lomb keratometer will be used. The 'HIR-CAL Grid'will be focused on the pre-corneal tear film and the time before first distortion of the grid image will be recorded. This will indicate the non-invasive tear break up time. Three measurements will be taken while the subject is instructed to blink and then to hold the eye open while the examiner watches the reflection from the tear film, and the mean calculated.
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Time frame: Each subject will be followed for the duration of the study, an expected average of 8-9 weeks
Tear sampling and bio-marker analysis
Approximately 1 μl of tears will be collected from the subject's eye using a sterile micropipette. It will then be diluted in cytokine assay buffer and simultaneously analysed for biomarkers of ocular surface disease (cytokines) using the Luminex Beadlyte assay system. The bio-markers to be studied are included in the Human high sensitivity cytokine/chemokine kit (Millipore). These markers are associated with pro-inflammatory activation and have been previously studied in dry eye and other inflammatory conditions.
Time frame: Each subject will be followed for the duration of the study, an expected average of 8-9 weeks