Dry eye is a broad term used to describe inadequacies of the eye to maintain healthy lubrication of the exposed surfaces. This causes the cornea and conjunctiva to become inflamed and irritated. The underlying causes of dry eyes are complex and numerous and need a thorough examination for your optometrist to determine the cause and most appropriate treatment.
There are many causes of dry eye. These fall into several broad categories that come with particular treatments. There can be some overlap between the types of dry eye, making the condition challenging for both the practitioner and patient to manage.
The majority of dry eye problems are due to evaporative dry eye. This is when the tears are produced at _normal _quantities but are quick to evaporate, leading to dryness. There are a number of factors which can lead to evaporative dry eye.
Evaporative Dry Eye is most commonly caused by Meibomian Gland Dysfunction (MGD). Also known as posterior blepharitis, in this condition the oil-producing glands in the lids become ineffective. The lipid/oil produced by the meibomian glands forms the outermost layer of the tear film, preventing evaporation of the watery aqueous component of the tears. It follows that when the lipid layer is compromised, the eye will become dry more quickly, leading to symptoms. It is important to note that treatment with drops designed for aqueous deficient dry eye will not be as effective for MGD caused evaporative dry eye, as the tears will still be unstable and quick to evaporate. For more information about MGD and its treatments visit our Meibomian Gland Dysfunction page here. The newest and most exciting treatment for MGD at Innovative Eye Care is the use of intense pulsed light (IPL) to improve your oil gland function. For more information about IPL treatment please click here.
CAPTION: The different layers of the tear film. Each serves an important role in keeping the cornea healthy and the vision clear.
Even patients with normal eyes can get evaporative dry eye if they spend time in heated, air-conditioned or low-humidity environments. The wind can also dry eyes out, much like clothes on a washing line. Prevention can be helpful here by using wrap-around glasses when outdoors, or using eye drops as recommended by your optometrist before and during situations that cause your eyes to dry out.
Some patients that do not blink fully or who keep their eyes open for long periods such as when staring at a computer screen may also have symptoms of dry eye. This is because the part of the eye's surface that is not regularly wiped with fresh tears by the lid will dry out and become irritated.
CAPTION: A typical irritated and dry eye. The green speckling shows the dry areas on the eye surface after instillation of a special eye drop.
This condition is less common than initially thought and in reality is the 'true' dry eye. The problem is due to decreased production of the watery compenent of the tears from the lacrimal glands in the eye. Aqueous deficiency is most frequently associated with auto-immune diseases (most notably Sjögrens Syndrome and rheumatoid arthritis). Other well-known causes are LASIK or other laser eye surgeries, where patients can experience dryness temporarily or even permanently due to severing of the corneal nerves. Medical treatments such a radiation or chemotherapy may have side effects which cause permanent damage to the lacrimal glands that produce most of your tears. Certain medications may cause aqueous deficiency including antihistamines, nasal decongestants, tranquilizers, certain blood pressure medicines, Parkinson's medications, birth control pills, hormone-replacement therapy and anti-depressants. The incidence of dry eye increases with age as we naturally produce less tears.
There are a variety of clinical signs that point towards a diagnosis of aqueous deficient dry eye (some will overlap with other conditions like meibomian gland dysfunction). These include:
CAPTION: Schirmer test to look for dry eyes. Less than 10mm of wetting in 5 minutes suggests dry eye.
Certain technologies are coming into use in optometry practices including machines that can measure tear osmolarity (which is elevated in dry eye), inflammatory markers (which are released into the tear film in dry, irritated eyes) and tear film properties. These should make the diagnosis of dry eye conditions easier in the future.
Each patient is different in terms of the severity of their dry eye. Management is tailored appropriately by your optometrist. These include (generally in order of dry eye severity):
CAPTION: A photo of a permanent punctal plug in the right punctum of a patient at Innovative Eye Care.