DRY EYE:

The Human Tear Film

The tear film is a complex mixture of substances secreted from multiple sources on the ocular surface, including the lacrimal gland, the accessory lacrimal glands, the meibomian glands, and the goblet cells. It consists of an Inner Mucin layer, Middle Aqueous layer and an outer lipid layer.

With each blink of the eyelids, tears spread across the front surface of the eye, known as the cornea. Tears provide lubrication, reduce the risk of eye infection, wash away foreign matter in the eye and keep the surface of the eyes smooth and clear. Excess tears in the eyes flow into small drainage ducts in the inner corners of the eyelids, which drain into the back of the nose.

Dry Eye

Tears are necessary for maintaining the health of the front surface of the eye and for providing clear vision. Dry eye is a condition in which a person doesn't have enough quality tears to lubricate and nourish the eye.

People with dry eyes either do not produce enough tears or their tears are of a poor quality. However the DEWS II:

• Inadequate amount of tears. Tears are produced by several glands in and around the eyelids. Tear production tends to diminish with age, with various medical conditions or as a side effect of certain medicines. Environmental conditions, such as wind and dry climates, can also decrease tear volume due to increased tear evaporation. When the normal amount of tear production decreases or tears evaporate too quickly from the eyes, symptoms of dry eye can develop.
• Poor quality of tears. Tears are made up of three layers: oil, water and mucus. Each component protects and nourishes the front surface of the eye. A smooth oil layer helps prevent evaporation of the water layer, while the mucin layer spreads the tears evenly over the surface of the eye. If the tears evaporate too quickly or do not spread evenly over the cornea due to deficiencies with any of the three tear layers, dry eye symptoms can develop.

What causes dry eye?

Dry eye can occur when basal tear production decreases, tear evaporation increases, or tear composition is imbalanced. Factors that can contribute to dry eye include the following:

• Medications including antihistamines, decongestants, antidepressants, birth control pills, hormone replacement therapy to relieve symptoms of menopause, and medications for anxiety, Parkinson’s disease, and high blood pressure have been associated with dry eye.
• Advancing age is a risk factor for declines in tear production. Dry eye is more common in people age 50 years or older.
• Rosacea (an inflammatory skin disease) and blepharitis (an inflammatory eyelid disease) can disrupt the function of the Meibomian glands.
• Autoimmune disorders such as Sjögren’s syndrome, lupus, scleroderma, and rheumatoid arthritis and other disorders such as diabetes, thyroid disorders, and Vitamin A deficiency are associated with dry eye. 
• Women are more likely to develop dry eye. Hormonal changes during pregnancy and after menopause have been linked with dry eye. Women also have an increased risk for autoimmune disorders.
• Windy, smoky, or dry environments increase tear evaporation.
• Seasonal allergies can contribute to dry eye.
• Prolonged periods of screen time encourage insufficient blinking.
• Laser eye surgery may cause temporary dry eye symptoms.

How is dry eye diagnosed and treated?

People experiencing dry eye symptoms should consult an eye care professional to determine the cause, which guides treatment strategy.

Change medications. Consult a physician about switching medications to alternative ones that are not associated with dry eye. This may alleviate dry eye symptoms.

Over-the-counter (OTC) topical medications. Mild dry eye symptoms may be treated with over-the-counter medications such as artificial tears, gels, and ointments.

Environmental and lifestyle changes. Cutting back on screen time and taking periodic eye breaks may help. Closing the eyes for a few minutes, or blinking repeatedly for a few seconds, may replenish basal tears and spread them more evenly across the eye. Sunglasses that wrap around the face and have side shields that block wind and dry air can reduce symptoms in windy or dry conditions.

In cases of Meibomian gland dysfunction, warm lid compresses and scrubs may be helpful.

Smoking cessation and limiting exposure to secondhand smoke also may help.

Prescription dry eye medications. Cyclosporine and lifitegrast are the only prescription medications approved by the U.S. Food and Drug Administration for treating dry eye. Corticosteroid eye drops also may be prescribed short-term to reduce eye inflammation.

Devices. FDA-approved devices provide temporary relief from dry eye by stimulating glands and nerves associated with tear production.

Surgical options. Punctal plugs made of silicone or collagen may be inserted by an eye care professional to partially or completely plug the tear ducts at the inner corners of the eye to keep tears from draining from the eye. In severe cases, surgical closure of the drainage ducts by thermal punctal cautery may be recommended to close the tear ducts permanently.