Dry eye is a general term used to describe a heterogeneous group of diseases resulting from inadequate wetting of the cornea and conjunctiva by the pre-corneal tear film (PCTF). Millions of people worldwide suffer from dry eye.

Despite its high prevalence, dry eye is not always easy to diagnose. The vast majority of patients have symptoms that are mild to moderate in severity. Although these patients are genuinely suffering discomfort, objective signs of dry eye may be missed, and without proper diagnosis, patients may not receive the attention and treatment that this condition warrants.

The signs and symptoms of dry eye can be misinterpreted as evidence of other conditions such as infectious, allergic, or irritative conjunctivitis.

What causes Dry Eye?

Pathophysiology of Dry Eye Syndrome

Dry eye conditions are classified as various types of abnormalities that can lead to insufficient wetting of the corneal surface. These classifications are:

• Abnormalities of the aqueous layer
• Abnormalities of the mucin layer
• Abnormalities of the lipid layer
• Abnormalities of the corneal epithelium
• Abnormalities of the lids

Insufficient production of the aqueous component of the tear film is the most common cause of dry eye. The resulting condition, known as keratoconjunctivitis sicca (KCS), is usually due to decreased tear production by the accessory lacrimal glands. Inflammation of the lacrimal glands, a common cause of dry eye, may also be accompanied by inflammation and drying of other mucous membranes, particularly those in the mouth, vagina, and/or respiratory tract.

Abnormalities of the mucin layer Deficient production of mucin interferes with the even distribution (spreading) of the tear film across the corneal surface, resulting in a very unstable and uneven tear film with a rapid break-up time (BUT). Abnormalities in the mucin layer of the PCTF nearly always occur as a result of damage to the goblet cells of the conjunctival epithelium.

Abnormalities of the lipid layer

Abnormalities in the lipid layer of the PCTF are relatively uncommon. When they do occur, deficiencies in the lipid layer result in excessive evaporation of the aqueous component of the tear film, which in turn leads to drying of the ocular surface.

Abnormalities of the corneal epithelium

Alterations in the normal morphology of the corneal epithelium that can adversely affect tear film stability are called epithelial cell defects. Infections and trauma resulting in corneal scars and ulcerations can damage the microvilli, causing permanent dry spots. Damage to the corneal surface can also result from exposure to certain drugs, including many types of general anesthesia.

Abnormalities of the lids

Because the eyelids play such an important role in distributing the tear film, normal blinking is essential to maintaining a healthy corneal and conjunctival surface. Thus, anything that interferes with normal blinking, or anatomic abnormalities, which interfere with the complete closure of the eyelids during blinking, can result in drying of the ocular surface.

Signs and Symptoms of Dry Eye

The symptoms of dry eye vary considerably from one individual to another, most patients complain of a foreign body sensation, burning and general ocular discomfort. The discomfort is typically described as a scratchy, dry, sore, gritty, smarting or burning feeling. Discomfort is the hallmark of dry eye because the cornea is richly supplied with sensory nerve fibers.

A significant percentage of patients also experience photophobia and intermittent blurring or other problems with visual acuity.

Individuals with dry eye commonly remark that their eyes tire easily, making it difficult for them to read or watch television. The reason for this difficulty is that the frequency of blinking typically decreases during tasks that require concentration. As blink frequency decreases, there is more time for the tear film to evaporate. If blinking is infrequent enough, the duration of exposure will exceed the BUT, resulting in the formation of one or more dry spots on the corneal surface.

Contact lens intolerance can also be a symptom of dry eye. Sometimes, a patient with mild to moderate dry eye may not experience symptoms until contact lenses are fitted. The placement of a contact lens can upset the delicate balance of tear film production and distribution, leading to lens intolerance.

What can you do about Dry Eye?

There is no known “cure” for dry eye. However, in most cases, dry eye can be treated with an artificial tear solution. Designed to replace your eye’s missing moisture, these lubricating drops reduce signs and symptoms of dry eye and increase eye comfort. There are many types of artificial tear solutions that are available without a prescription.

Preventing the evaporation of tears can also help in the fight against dry eye. When conditions are especially dry, the use of a humidifier in your home can add moisture to the air. Other helpful tips include drinking plenty of water, avoiding drafts from radiators or air conditioners, and protecting your eyes on hot, windy days.