Top 3 Causes of Dry Eyes

There are many causes of dry eyes in our world. Some are obvious, such as a windy day. Some are insidious side effects of medications and some are hard to pin down.

Symptoms of dry eyes
Dry Eye Treatment

Dry eye results from one of two beginnings - either a decrease in the secretion of the tears, or an increase in the rate of evaporation.

Normal Tears

First, let's understand what it takes to have a 'normal' tear film.

Your eyes are kept moist throughout the day by a layer of fluid called the tear film. This fluid is itself made up of three layers that each have an important part to play. Imbalances in these three layers are frequently the underlying causes of dry eyes and dry eye symptoms.

Layer 1 - Lipid

The outermost layer of the tears is composed of oily substances called lipids. This helps to prevent your tear film from evaporating. A deficiency in this layer can lead to dry feeling eyes due to the tears evaporating quickly in normal circumstances and even faster in adverse conditions like air conditioning and windy environments.

This layer is secreted by glands along the edge of your eyelid, just inside the lashes (Meibomian glands). Meibomian Gland Dysfunction leads to these glands getting clogged and not secreting normally, leading to deficiency in the lipid layer.

Layer 2 - Water

The middle layer is the thickest. It is made up of water, salts and nutrients to nourish the cornea. This is why your tears taste salty when you cry. These tears are the crying tears; produced by the lacrimal glands, located above the eyeball. The tears are used to rinse away debris and foreign bodies (like dust, pollen and eyelashes).

When this layer is deficient it reduces the volume of tears available to cover the eye. Loss of the water results in 'saltier' tears when the salts are left behind (higher osmolarity). This then pulls water out of the corneal cells to try to equalise and you end up with dry eyes, not just thin tears.

Layer 3 - Mucous

The innermost layer of the tear film is made up of mucous that sticks the tears to the top layer of the cornea and fills in the gaps in the cells of the cornea to give a smooth surface. Dry spots in the cornea easily form where the mucous is deficient. The higher osmolarity produced by the loss of water layer can damage the "goblet cells" in the conjunctiva that are responsible for secreting this mucous.

So, what causes dry eyes?

Dry eye results from one of two beginnings - either a decrease in the secretion of the tears, or an increase in the rate of evaporation.

Decreased tear secretion may occur due to conditions that damage the lacrimal glands. Autoimmune diseases (such as Sjogrens, Lupus, Rheumatoid Arthritis) with inflammation of the tear gland are the most common.

Tear secretion also may be reduced by any condition that affects corneal sensation, including diabetes, herpes zoster, long-term contact lens wear and some corneal surgery.

Reduced Tear Secretion:

Age - as we age our whole body gets drier and wrinklier. The eye is no exception. Decreased production of tears secreted by the glands is responsible for these causes of dry eyes. Most people over the age of 40 will have drier eyes than a 20 year old. Though not everyone will be dry enough to cause them dry eye symptoms.

Hormones - our hormones control the levels of secretions in the body so fluctuations can cause dry eye. The most common is Menopause in women. Other hormonal problems such as Thyroid problems can also dry out the eyes.

Auto immune disease - dry eye is common in arthritic conditions such as rheumatoid arthritis, Sjogrens syndrome and Lupus.

Medications - Many common medications can be causes of dry eyes through interfering with normal secretions, including:

• Contraceptives
• Antihistamines and decongestants (to dry up that running nose)
• Sleeping pills
• Many blood pressure medications
• Certain antidepressants
• Some drugs for treatment of acne
• Opiate-based pain relievers, such as morphine

Evaporation:

Exposure

Sleeping with your eyes partially open or staring at a computer screen without blinking very often gives evaporation a long run.

The environment

The drier the air, the easier it is for your tears to evaporate. This is why we have a high rate of dry eye in Australia. Add to that our love of air conditioning and it's a wonder we don't all have symptoms!