Before we understand the causes behind dry eyes, it is important to know how the process of tears works.
What are Tears?
Tears that our eyes produce are essentially a protective and cleansing layer on the surface of our eyes. Tears are a mixture of enzymes, proteins, peptides, fatty acids, water, and electrolytes, mostly salts. These tears can be divided into three layers, consisting of oil, water, and mucus. The oil is produced in the meibomian glands while the electrolyte water is produced by lacrimal glands. The presence of mucus helps in evenly spreading the oil and water on the surface of the eyes. The oil, water, and mucus come together to form a thin layer on the surface of the eye, known as tear film.
How are Tears Produced?
These tears are produced by tear ducts, scientifically known as meibomian glands and lacrimal glands. These small glands are located on the sides of both the eyes and produce tears which constantly protect and clean our eyes from foreign bodies and irritants as well as from bacterial, fungal and yeast infections.
What is Dry Eye Syndrome?
Any damage or disturbance to the delicate tear film of the eye causes a condition called dry eye syndrome. When deprived of tears, the eyes suffer a chronic lack of moisture due to damage to the tear gland. This results in persistent dryness, itchiness, and a burning sensation in the eye. Dry eyes are medically referred as keratoconjunctivitis sicca, which means a decrease in the quality/quantity of the tear supply. The eye depends on moisture for its proper functioning. The lesser the supply of tears, the worse the condition becomes.
According to the Optometric Clinical Practice Guidelines by the American Optometric Association, dry eyes have been categorized into:
- Aqueous deficient dry eye: This is a condition where lack of water in tears is the root cause.
- Mucin deficient dry eyes: In this condition, a lack of mucus in tears is the root cause.
- Surface abnormalities: These include an irregular epithelial surface on the eye surface.
Dry eyes can occur due to temporary issues or long-term health issues. Some of the common causes are explained below:
- Arrested tear production and evaporation: Dry eyes could result from arrested tear production and tear evaporation. Some common causes include advanced age, hormonal changes, decreased oil, water, or mucus production in the tear glands, damage to the tear glands, various autoimmune diseases, lupus, and rheumatoid arthritis.
- Inadequate blinking: Dryness in the eyes could happen due to inadequate blinking as well. Every time we blink, the tears lubricate our eyes and decrease strain. Often, when we are watching TV, working on the computer or working on something that requires a great deal of attention and concentration, we unconsciously cease blinking. This causes strain on the eyes. This strain adds up and causes dryness, irritation, and even damage in certain cases.
- Contact lenses: Use of contact lenses can also be attributed as a cause of dry eye syndrome. Wearing contact lenses is also attributed to bacterial keratitis. As the contact lens sits on the surface of the eye, it hinders the free circulation of tears on the surface, which leads to excessive evaporation of tears and dry eye syndrome.
- Medications: Certain types of medications such as antihistamines, antidepressants, beta-blockers, and oral contraceptives are known to decrease tear production.
- Diseases: Conditions such as strokes or Bell’s palsy make it difficult to close the eyes. This causes tear evaporation and leads to rapid drying out of the eyes.
- Aging: Dry eyes are also common among old people. Due to aging, the tear film begins to fade and thus gets damaged. Aging processes, such as menopause, may also be the cause of dry eyes.
- Vitamin A deficiency: A lack of vitamin A also leads to dry eyes. Vitamin A is one of the most important vitamins in regards to eyes. The carotenoids in vitamin A help in building up the tear glands. In the long run, a deficiency of vitamin A may lead to night blindness and cloud formation in front of the eyes.
Pain, irritation, scratchiness, burning sensation, and light sensitivity in the eyes are the primary symptoms of dry eyes. Other symptoms include:
- Blurred vision: Due to the lack of moisture, the eye fails to function ideally and vision might be blurred. When this happens, the patient should rest his eyes and not expose them to any form of strain.
- Foreign body sensation: The patient feels that there is something in their eye.
- Sjogren’s syndrome: In some cases, dry eyes, along with dry mouth and dry nose with minimal mucous secretion, is an indication of a disease called Sjogren’s syndrome, which is an autoimmune disease.
- Excessive tears: Rarely, dry eyes may cause excessive tear production. This works as a protective mechanism when dryness overstimulates the production of tears.