What are dry eyes?
Tears keep the corneal surface moist and lubricated. They are produced by the tear glands and reach the eye surface through the tear ducts. A decrease in the production of tears or increased evaporation leads to a condition called dry eyes.
What causes dry eyes?
Normally tears form a continuous film on the corneal surface. Less tears resulting from increased evaporation or decreased production causes instability of the tear film which leads to dry patches on the corneal surface. Moreover, tears are mostly made up of water and salts. Decreased tear production and increased evaporation increases the salt content of the tears i.e. their osmolality, which further pulls water from the corneal surface. This causes discomfort and abrasion on the surface of the cornea further leading to inflammation.
Decreased tear production can occur due to:
- Sjogren’s syndrome: This is an autoimmune disease where antibodies are made by the body against its various tissues. Inflammation can occur in the tear glands and salivary glands leading to decreased secretion from these glands resulting in symptoms of dry eyes and dry mouth (primary Sjogren’s syndrome). Sjogren’s syndrome may occur with other autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, scleroderma, polymyositis (secondary Sjogren’s syndrome).
- Other factors that lead to reduced production of tears include sarcoidosis, vitamin A deficiency, trachoma, trauma, previous eye surgery involving corneal incision, long term contact lens wear, working on a computer for long hours, past herpes infection, diabetes and aging.
Increased evaporation of tears can occur due to:
- Environmental factors such as dry weather, wind, air pollution, hair dryer use, air-conditioned environments
- Inflammation of the eyelid as in cases of blepharitis, rosacea and Meibomian gland dysfunction
- Certain medicines such as birth control pills and allergy medications
- Thyroid disorder that can result in retraction of the upper eye lid
What are the symptoms of dry eyes?
Patients suffering from dry eyes usually complain of:
- A stinging, burning or scratching sensation
- Discomfort in wearing lenses
- Eye irritation in air-conditioned places and in wind
- Tired eyes
- Blurring of vision
- Discomfort from glaring light
- Increased tear production due to eye irritation
How are dry eyes diagnosed?
Although dry eyes can be diagnosed based on the symptoms, your doctor may perform certain simple tests to assess your condition.
- Schirmer’s eye test: A very small filter paper strip is placed touching the lower eye lid for a specific time. A wetting value of less than 5mm of the filter paper strip in 5 minutes indicates dry eyes.
- Phenol red thread test: This test uses a cotton thread coated with phenol red dye. It is kept for 15 seconds in the lower conjunctival fornix. A wetting length of 9- 20mm is considered normal while less than 9mm wetting length suggests dry eyes.
- Tear break up time: A strip of fluorescein will be applied to the lower eyelid and removed. Then, you will be told to blink your eyes three times and look forward without blinking. The tear film formed is observed under a slit lamp microscope and the breakup time of the film is recorded. A break up time of 10 seconds or less indicates dry eyes.
- Another more accurate and patient friendly test measures tear break up time using a tearscope. In this test, values of less than 15 seconds indicate dry eyes.
What if dry eyes remain untreated?
If untreated, severe dry eyes can lead to ocular surface damage, ulceration of the cornea, infection and visual impairment. Thus, proper diagnosis of the cause of dry eyes and its timely treatment is very important.
What are the treatment options for dry eyes?
There is no cure for dry eyes. Treatment strategies depend on whether the problem is temporary or chronic.
The two main strategies include:
- Replacing natural tears with artificial tears by using eye drops
- Letting the tears stay in the eye longer rather than being drained by the lacrimal duct into the nose.
Natural tears contain water, mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin, immunoglobulins, glucose, urea, sodium, and potassium.
No artificial tears can replace natural tears however, they can increase the volume of the tear film when they are in contact with the eye surface. Thus, hydrogels are added to artificial tears to increase their viscosity so that they can remain in the eye longer. Artificial tears contain preservatives to increase their shelf life. Tears with preservatives are more gentle on the eye and are preferred. Some artificial tears also contain other substances that confer additional surface healing and surface protective properties.
Anti-inflammatory eye drops
Topical corticosteroids may be given as a short-term therapy for quick relief (2-4 weeks). Corticosteroid drops may cause cataracts and glaucoma if given for long periods so Cyclosporin drops are given simultaneously. Cyclosporin drops require several weeks and sometimes even 6 months for clinical effect.
To conserve tears the opening of the tear ducts may be plugged with punctal plugs. There is one tear duct in the lower eyelid and another in the upper eye lid. One or both can be plugged. Temporary punctal plugs may be collagen or silicone based.
Windless sun glasses
These protect from wind, dust and pollen by sealing the eye space from the outside environment much like swimming goggles.
Treatment for Meibomian gland dysfunction
This condition results in changes in the lipids secreted by the tear glands which leads to increased evaporation of the tears. It is treated by prescribing oral antibiotics, lipid containing eye drops and warm compresses to provide symptomatic relief.
Other strategies to manage dry eyes:
- Decrease or avoid caffeine and alcohol and drink more water.
- Increase omega-3 fatty acids through foods such as fish and flaxseed oil or with oral supplements.
- Keep environmental factors promoting dryness under control.
- Use humidifiers in dry weather conditions.
- Avoid use of room heaters.
- Take breaks while working on a computer for a long time. Keep the screen low or use a laptop as the upper eye lid covers half of the eye while looking down at the laptop screen.
- Avoid smoke and dust.
What is the prognosis of dry eyes?
Prognosis depends on the severity of the condition. Dry eyes do not cause any permanent vision loss. Symptoms are usually well managed with treatment. Rarely, a corneal ulcer or eye infection may develop which can be treated.