Eye Disorders: Dry Eye Syndrome
When the eyes don't produce enough tears to keep them lubricated and healthy, it is called dry eye syndrome. The tear film of the eye has three layers. A disorder of any of the layers can cause dry eyes. The three layers are:
1. the mucous layer on the bottom, produced by the goblet cells on the conjunctival surface of the eye;
2. the middle aqueous (salt water) layer, produced by the lacrimal and other glands; and
3. the outer lipid (fat) layer, responsible for preventing evaporation of the tears, produced by the meibomian glands along the eye lid margin.
Mucous layer disorders are rare. Examples of disorders of the goblet cells include an inflammatory condition called Stevens-Johnson syndrome, and a deficiency of vitamin A.
Aqueous layer disorders are common. The primary problem that occurs with the middle aqueous layer is simple deficiency related to age. The rate of production of aqueous can be measured with a simple office test called the Schirmer's test. Certain systemic diseases, notable Sjogren's syndrome and Rheumatoid arthritis, can damage the lacrimal gland leading to decreased aqueous production. Many medications can decrease aqueous production as well. Examples include diuretics, beta-blockers, antihistamines, and certain antidepressants. Environment, like a dry Minnesota winter, may play an important role. Contact lenses may cause a borderline dry eye to become symptomatic. Another common issue is menopause -- sometimes hormone replacement therapy will help a dry eye.
Meibomian glands can sometimes produce an oil that is too thin, too thick, or too soapy, which doesn't cover the aqueous layer well. This leads to increased evaporation of the aqueous layer and dry eye. The abnormal oils themselves can cause inflammation on the eye surface. The most common example of meibomian gland disease is facial rocasea. Rosacea is a disorder of the sebaceous glands of the face, of which meibomian glands are close cousins. Recurrent chalazia and styes are related to meibomian gland dysfunction. An overgrowth of bacteria on the lid margin, or eczema of the lid margin, often cause oil gland dysfunction. Disorders of the meibomian glands are termed "blepharitis."
What are the symptoms of dry eye?
Common symptoms of dry eye include burning, foreign body sensation, and intermittent blurry vision that clears with repetitive blinking. Other symptoms include itchy lids, mucous discharge, red eyes, difficulty wearing contact lens, and difficulty performing sustained visual tasks like reading. A common (and counterintuitive) symptom is excess tearing. When the eye senses that it is dry or irritated, the lacrimal gland reflexively produces a large amount of tears that overwhelm the normal drainage pathways, leading to tearing. Sustained visual tasks, like reading, or going outdoors into a dry environment, like a Minnesota winter, can cause tearing for this reason.
How is dry eye treated?
There are many approaches to the treatment of dry eye. The eye examination will determine which factors are contributing to a person's dry eye. Depending on the findings, the following may be recommended.
1. The rare goblet cell disorder, if identified, requires specific therapy
2. Aqueous insufficiency
- Add moisture with artificial tears, especially preservative free, or lacricerts
- Thicker tears, like liquigels, gels, or ointments may help if dry eye is severe
- Conserve tears by temporarily or permanently plugging the tear drains out of the eye.
- Change the environment by using a humidifier indoors or occlusive glasses outdoors.
- Increase tear production by using Cyclosporin eyedrops (Restasis)
- Consider medications, systemic diseases, contact lens use, hormone status, etc.
3. Meibomian gland disorders, often termed "blepharitis"
- Warm compresses with a clean washcloth, 5 minutes a day
- Followed by baby shampoo eyelash scrubs
- Doxycycline if Rosacea is identified
- Topical antibiotic and steroid may be used.
4. Treat any possible contributing conditions, such as allergy.
More information on Dry Eye can be found at the National Eye Institute's website, under the corneal section.