Causes of Dry Eye


Tears have very important functions.  As well as washing out dust and debris and keeping eyes moist, tears contain enzymes, which neutralise the eye and keep the eye healthy.  The cause of dry eye may be attributed to a lack of tear production.  Also, tears have many components including oil, water and mucus.  An in-balance in these may cause dry eyes. 

The meibomian glands produce oil known as lipids.  These smooth the tear surface and prevent the water in tears from evaporating too fast.  Problems with lipids cause evaporation to speed up and eyes begin to feel dry.  The meibomian gland may become clogged and people with blepharitis and certain other skin disorders may be more at risk of this.  The middle part of the tear film is made mainly of water and functions to cleanse the eye and remove particles or irritants from the eye.  If the water layer is too shallow, the tear film may become unstable because the other two layers of oil and mucus can touch each other and the eye may produce a discharge.  If the layer of mucus over the eye is patchy, a dry area can be found because tears will not be spread evenly over the eye surface.

An in-balance in oil, water and mucus may be caused by environmental factors, certain medical conditions and certain medications, as well as certain eye procedures, eyelid problems and eye injury. 

Medical Conditions

Medical conditions, which may have an affect, include diabetes, a dry mouth, arthritis, lupus and Sjogren's syndrome.  A deficiency in vitamin A, may also have an affect.  If eyes become inflamed along the edge of the eyelids in a condition known as blepharitis, dry eyes are often a symptom.  If eyes do not close properly, they can also become dry.  This may be a side effect of blepharoplasty, which is the cosmetic surgery for droopy eyelids.

Medications

There are many medications, which can cause a reduction in tear secretion and cause eyes to become dry.  These may include sleeping pills, antidepressants diuretics, betablockers, antihistamines, pain relievers and even alcohol.   Some none prescriptive medications can also pose a problem.  If you are taking any medications and are experiencing dry eye symptoms, check the side effects listed on the information leaflet with the medication.  It may also be an idea to speak with your GP or pharmacist and seek their advice.  They may be able to suggest alternative medication

Eye Procedures

LASIK eye surgery can cause dry eye as well as other laser eye procedures but this is usually only a temporary side effect as the eye heals over.  LASIK induced dry eye may be due to cutting of a flap on the cornea in order to access underneath it.  This may be why dry eye is reported more with LASIK surgery compared with other types of laser eye surgery such as PRK and LASEK, which apply the laser directly to the eye.  Laser eye surgery may damage or disrupt the tear system and so it may not function properly following surgery. 

Age

With age, tear production lessens and eyes become dry, this is known as keratoconjunctivitis sicca and is more common in women than men, particularly after menopause.  This may be due in part to hormonal changes.  With age, blinking may change and tears may not spread over the eye surface evenly, causing eyes to become dry.  Poor blinking may be due to out-turning of the lids (ectropion) or an in turning of the lids (entropion).

Contact Lenses

Long-term use of contact lenses can cause eyes to become dry.

Environmental Conditions

Eyes can become dry with sun exposure, excessively windy conditions, high altitudes, very dry conditions and from air conditioning.  People who excessively concentrate on a computer screen or intense visual concentration from reading or driving can reduce blink rate and cause eyes to become dry.

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