What is dry eye syndrome?
Dry eye syndrome is one of the most common problems treated by eye specialists in the UK. Despite its name, it often causes excessive watering of the eyes, but it is usually caused by a problem with the quality rather than the quantity of the tear film that lubricates the eyes.
The tear film can be simply thought of as being comprised of 3 layers. The innermost layer is described as a mucin layer which coats the cornea (the eye's outer clear window) and forms a foundation to keep the tear film in place across the surface of the eye.
The middle layer is called the aqueous* layer and this provides moisture, nutrients and oxygen to the cornea, together with antibodies to fight infection. This aqueous layer consists of 98% water and is made increasingly viscous (sticky) in the deeper parts by the presence of soluble mucins.
The outermost layer is known as the lipid layer and is an oily film that seals the tear film onto the eye and helps to prevent evaporation of the underlying aqueous layer.
The three layers of tears are made in a number of different glands around the eye. The aqueous (watery) layer is produced in the lacrimal gland, located under the upper eyelid. Several smaller glands in the lids make the lipid and mucin layers.
With each blink, the eyelids spread the tears over the eye. Excess tears flow into two tiny drainage ducts in the corner of the eye by the nose (the tear ducts). These ducts lead to tiny canals that connect to the nasal passage. The connection between the tear ducts and the nasal passage is the reason that crying causes a runny nose.
In addition to lubricating the eye, tears can also be produced as a response to outside stimulus such as an injury or emotion. However, these 'reflex tears' do little to soothe a dry eye, which is why someone with watery eyes may still complain of irritation.
Many factors, such as hot, dry or windy climates, high altitudes, air-conditioning and cigarette smoke can add to the problem and some people also find their eyes become irritated when reading or working on a computer. Stopping periodically to rest and blink helps to keep the eyes more comfortable. Contact lens wearers may suffer from dryness, because the contact lenses absorb the tear film, causing proteins to deposit on their surface.
Causes of dry eye syndrome
One of the most common reasons for the syndrome is simply the normal ageing process. As we grow older, our bodies produce less oil, about 60% less at age 65 than at age 18. This is more pronounced in women, who tend to have drier skin than men. The oil deficiency also affects the lipid layer of the tear film. With less oil available within the overall bodily system there is less oil to make the lipid layer which seals in the watery layer, the tear film therefore evaporates much faster, leaving dry areas on the cornea, which then become uncomfortable leading to dry eye syndrome.
Dryness can also be caused by medications such as antihistamines, nasal decongestants, birth control pills, some medications for high blood pressure, antidepressants and isotretinoin tablets for acne. Thyroid disorders, vitamin A deficiency and Parkinson's disease (due to decreased blinking) may also cause dryness. Dry eye syndrome can also be a symptom of inflammatory disorders such as rheumatoid arthritis and systemic lupus erythematosus. In these cases referral to an ophthalmologist must be sought, as it can be associated with dryness of the mouth and other mucous membranes; this manifestation is known as Sjogren's syndrome. Women also frequently experience problems with dry eyes due to hormonal changes as they enter the menopause.
The symptoms of dry eye syndrome can include one or more of the following problems:
• Redness (underlying systemic connective tissue disorders)
• Blurred vision that improves with blinking
• Excessive tearing
• Increased discomfort after periods of reading, watching TV, or working on a computer
• Foreign body sensation
Detection and Diagnosis
There are several ways to test for dry eyes. The doctor will try to identify the underlying cause by measuring the production, evaporation rate and quality of the tear film.
How is dry eye syndrome treated?
The treatment of dry eye syndrome is a very individual subject because everyone is, of course, different and what works well for one person may be unsatisfactory for another. Many people find considerable relief simply by using 'artificial tears' on a regular basis. Some of these products are watery and alleviate the symptoms temporarily; others are thicker and adhere to the eye longer. There are also preservative-free formulations which are recommended for those who have an allergic reaction to the preservatives used in the standard artificial tear drops.
If artificial tears are not successful in making life comfortable, another option is for the eye specialist to close the opening of the tear duct in the eyelid with special inserts called punctal plugs. This works like closing a sink drain with a plug. These special plugs trap the tears on the eye, keeping it moist. This may be done on a temporary basis with a dissolvable collagen plug, or permanently with a silicone plug.
Antibiotics such as tetracyclines can be useful when the lipid tear film layer is problematic. When there is insufficient aqueous component production, as in Sjogren's syndrome, oral pilocarpine can be useful.
There are simple changes that you can make to your lifestyle to reduce your symptoms. When outdoors, you should wear sunglasses to reduce exposure to sun, wind and dust; those with a foam or seal at the sides are preferred to completely protect the eye.
Indoors, an air cleaner can filter out dust and other particles from the air, while a humidifier adds moisture. Dietary modifications can also improve dry eye, specifically through increasing omega-3 fatty acids, which can be found in fish oils and flaxseed oil.
You can enhance this with supplements or through the increased consumption of coldwater fish such as salmon, sardines and herring or with flaxseed and walnuts. Make an effort to blink frequently and try to avoid rubbing the eyes as this only makes the irritation worse.
Treating dry eye can be challenging but is usually successful in the hands of an expert ophthalmologist.