Dry eye is a complex disease of the tears and the ocular surface and often presents with symptoms including irritation, foreign body sensation, and fluctuating vision. Dryness of the ocular surface is often accompanied with an increase in the saltiness of the tear film which causes corneal inflammation and pain. A normal healthy tear film is made up of three layers, an inner mucin layer, a middle watery aqueous layer and an outer oily lipid layer. Maintaining a perfect balance of these three layers is vital to prevent dry eye disease.
THE TWO TYPES OF DRY EYE
There are two types of dry eye commonly found in individuals. The most common form is known as evaporative dry eye and is caused by the increased evaporation of the tear film. This form accounts for almost 90% of dry eyes. Evaporative dry eye is caused by low humidity, warm dry air, wind and reduced blinking associated with visual concentration. Eyelid disease associated with blepharitis and meibomian gland dysfunction is also a common cause of evaporative dry eye.
The second form of dry eye is known as aqueous deficient dry eye and is caused by the decreased production of the watery component of the tear layer. Aqueous defecient dry eye is caused by aging, thyroid disease, sjogrens syndrome, and certain medications including antihistamines, anti-depressants, oral contraceptives and following laser and cataract surgery.
DRY EYE ASSESSMENT TOOLS AT THIS PRACTICE
DRY EYE QUESTIONNAIRE: We use two different questionnaires that assesses dry eye symptoms and the effect it has on vision. These questionnaires are considered the gold standard for dry eye assessment and can be used for accurate monitoring of dry eye symptoms following dry eye treatment.
CORNEAL HEALTH EXAMINATION: Various dyes and stains are used with special coloured filters at an illuminated microscope to provide an accurate assessment of corneal tissue health. At a microscopic level it is possible to visualise defects in the corneal epithelium that would not otherwise be observable to the naked eye. These small defects or 'abrasions' contribute to a significant amount of the discomfort associated with dry eye disease. This practice has a microscope that records images of the cornea which can then be compared in the future following dry eye treatments.
TEAR FILM SURFACE QUALITY: This practice uses sophisticated software combined with Placido disc videokeratography which non-invasively analyses changes in tear film stability. The instrument captures four photokeratoscopic images per second whilst blinking is supressed and this video is analysed to determine the length of time the tear film is stable between each blink. The software automatically saves the information so that future comparisons can be made after dry eye treatment has been commenced.
MEIBOMIAN GLAND ASSESSMENT: Meibomian glands are meibum or 'lipid' producing glands located in our upper and lower lid margins. The oily meibum produced by these glands coats the surface of the eye preventing the evaporation of the eye's watery or 'aqueous' tear fluid. If meibum quality or quantity is low then the tear fluid on the eye will quickly evaporate leaving the surface of the eye feeling dry. Using an infrared camera, the health of the meibomian glands can be assessed which provides a more accurate management plan for the treatment of dry eye disease.
LID MARGIN ASSESSMENT: The eyelid margin is examined using a high powered microscope which can help determine the exact cause of dry eye symptoms. Each eyelid margin contains approximately 25 meibomian glands, each producing 'oil' to protect our tear film from drying out. The general health of these glands and the quantity and consistency of 'oil' is assessed during this examination. Also, the base of the eyelashes is carefully checked for the presence of debris as this directs where attention should be focussed for dry eye treatment.