Dry Eyes by David R. Jordan, M.D., F.A.C.S., F.R.C.S.(C)
The term dry eye, refers to a group of disorders of the tear film with a reduced tear production or excessive tear evaporation that are associated with symptoms of ocular discomfort and that may cause damage to the ocular surface. The cornea is kept moist by the lubricating effect of tears which are exchanged regularly with each eyelid blink. Tears are produced by 2 methods.
One method (basic tear secretion) produces tears at a slow, steady rate and is responsible for normal eye lubrication. The other method (reflex tear secretion) produces large quantities of tears in response to eye irritation (foreign body) or emotions such as crying. The tears themselves are made up of a delicate balance of oil, water, and mucous; produced by various glands in the eyelid and conjunctival area. Dry eyes may be caused by changes in the quantity and/or quality of the natural tears produced by the various tear forming glands (lacrimal gland, meibomian glands, goblet cells, glands of Krause, and glands of Wolfring).
What are the symptoms of a dry eye?
The usual symptoms and signs include:
- redness
- foreign body sensation on the eye surface (gravel, sand feeling, grittiness)
- burning, stinging, scratchiness sensation
- photophobia (light sensitivity)
- mucous discharge on the lids
- eye irritation from smoke or wind
- difficulty wearing contact lens
- excess tearing
What exactly is the tear film?
A film of tears is spread over the surface of the cornea each time the eyelids open and close (Figure 1). Tears are much different then water and are made of an oil layer, a water layer, and a mucous layer (Figure2).
Each component is important for a stable tear film. If one of the components is deficient, the tear film will be unstable resulting in ocular irritation. The oil layer is produced by the meibomian glands of the eyelid and not only smoothes the tear surface but reduces evaporation of tears. The middle layer is a watery layer produced by the main lacrimal gland and accessory lacrimal glands (glands of Wolfring and Krause) located in the conjunctival fornices. This layer cleanses the eye surface and rinses away foreign particles. The inner most tear layer consists of mucous produced by the goblet cells of the conjunctiva. Mucous allows the watery layer to spread evenly over the surface of the eye and help the team to remain wet. Without mucous, tears would not adhere to the eye.
What are some of the causes of a dry eye?
Tear production normally decreases as we age. Although a dry eye can occur in both men and women at any age, women are most often affected (especially after menopause). A dry eye can also be associated with arthritis and accompanied by a dry mouth. People with dry eyes, dry mouth and arthritis are said to have a condition called Sjogrens Syndrome. This entity is characterized by infiltration of the lacrimal glands and salivary glands with lymphocytes causing secondary compromise of the gland function. Women are more commonly involved then men. Patients with primary Sjogrens have non-classifiable systemic disease and symptoms that may include anthralgia, myalgia, or fatigue. Patients with secondary Sjogrens have a distinct autoimmune disease such as Rheumatoid Arthritis, Scleroderma, or Systemic Lupus Erythematosus. Diagnosis and treatment of underlying systemic immune disorders may decrease morbidity and may even be life saving
Rosacea is a disease of the skin and eyelid that is seen more frequently in fair skinned individuals, but can be found in all races. Characteristic facial skin changes include erythema, telangiectasia, pustules, prominent sebaceous glands, and rhinophyma. Meibomian gland dysfunction develops in the majority of patients with rosacea.
Stevens Johnson Syndrome, Ocular Cicatricial Pemphigoid, chemical injuries, Herpes Simplex conjunctivitis, and other cicatrizing processes involving the conjunctiva may lead to scarring of the conjunctiva and resultant dry eyes secondary to an unstable tear film (goblet cells affected).
Blepharitis (inflammation of the meibomian glands) is extremely common and associated with small bits of debris along the lash roots. With inflammation of the meibomian glands, the oil component of the tear film is affected. With a disruption of the oil component of the tears, an unstable tear film may result. Blepharitis may cause symptoms of irritation on its own but also is commonly associated with another disruption of the tear film (i.e. decreased production of the water component from the lacrimal gland). Patients that have both blepharitis and decreased lacrimal gland production are always worse than those with just one or the other.
A variety of common medications (prescription and over the counter) can cause a reduction in tear formation and as a result, dry eyes. Examples include diuretics, betablockers, antihistamines, anticholinergics, psychotropics, some sleeping pills, and some pain killers. Since these medications are generally required, some level of dry eye may have to be tolerated by the patient.
Eyelid Spasm Cont'd
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