What are some potential causes of Dry Eye symptoms?

Dry eye symptoms may be caused by:

• Age - Healthy tear production often diminishes with age. Dry eyes are more common in people over the age of 50

• Gender – Females tend to produce fewer tears, often associated with hormonal changes (pregnancy, menopause, use of birth control pills)

• Environmental conditions (wind, dry climate, air conditioning, heat, smoke, sun exposure, or chemical fumes)

• Contact lens wear for long periods of time or inappropriate contact lens usage

• Vitamin A deficiency

• Low Omega-3 fatty acid intake (from diet or supplements)

• Rheumatoid Arthritis, Sjogren’s syndrome, lupus, and other autoimmune conditions

• Thyroid disease

• Medications (prescription and non-prescription) such as beta-blockers, antihistamines, diuretics and anxiety medications

• Eye surgery - Refractive surgery (LASIK), cataract surgery

• Tear gland damage (inflammation or radiation)

• Eyelid disorders such as ectropion (outturning of the eyelid), or entropion (inturning of the eyelids)

Many people that have dry eye symptoms that persist for a long period of time (chronic dry eye) have inflammation and irritation of their lacrimal glands (glands where tears are produced), their eyelids, and their conjunctiva (the front surface of the eye). Ongoing inflammation of these structures can potentially lead to permanent damage and more serious eye problems.

What are tears made of?

Every time we blink, we spread tears across the front surface of the eye, also known as the cornea. Tears act as an important barrier between our eyes and the outside world. They provide lubrication, maintain moisture, and wash away any particles and microorganisms that might come into contact with the eye. Tears are produced by tiny glands above our eyes, called tear glands, or lacrimal glands. Excess tears drain into the small ducts in the corners of our eyelids and eventually flow into the back of the nose.

The tear film is composed of three layers, lipids (oil), aqueous (water) and mucus. The aqeuous layer is produced by lacrimal glands located behind the outer edge of the upper eyelids. The lipid layer helps to prevent the water layer from evaporating, ensuring that the moisture stays on the surface of the eye. The lipid layer is produced by meibomian glands located along the edge of the eyelids. The mucus layer spreads the tears evenly across the surface of the eye and anchors them there. The mucus is produced by goblet cells in the conjunctiva -- the clear, thin membrane that covers the white part of the eye (sclera). Any imbalance or deficiency in any of the three layers can lead to dry eye symptoms.

 

Are there different types of Dry Eye with different causes?

When determining the cause of someone’s dry eye symptoms, it is helpful to identify the type of dry eye disease they may have. There are two common types of dry eye disease:

1. aqueous deficient dry eye (eye do not produce enough tears)

2. evaporative dry eye (poor quality tears that evaporate from the eye surface too quickly)

Determining which type of dry eye someone has can help to find the best treatment to use. People may have a combination of both types of dry eye, meaning that they produce too few tears and these tears evaporate too quickly.   

Aqueous Deficient Dry Eye

Aqueous deficient means that the eye is not naturally producing enough tears (medical term: keratoconjunctivitis sicca - KCS). The inability to produce enough tears is relatively uncommon, it is more likely that the tears produced are not the best quality and evaporate from the eye surface too quickly.

Evaporative Dry Eye

Evaporative refers to evaporation of the tears that are naturally produced, often because these tears do not have the right balance of lipids (oils) that help to protect and lubricate the eye and keep the tears on the eye surface longer. Some people experience excessive tear production, their eye’s response to dryness or irritation, but because of the inadequate amount of lipids, the tears run out of the eye, rather than staying to protect its surface.

The meibomian glands are a series of small glands on the rims of the upper and lower eyelids that secrete the lubricating lipids that help to prevent tears from evaporating from the eye surface. There are approximately 25 to 40 glands on the upper eyelid and 20 to 30 on the lower. When these glands are not functioning properly or are blocked, it is referred to as Meibomian Gland Dysfunction (MGD), which is one of the most common forms of dry eye disease. Blocked meibomian glands are more common in people with inflammation along the edge of their eyelids (blepharitis), rosacea or other skin disorders.

Can screen time cause dry eye?

Yes, digital screen time (phone, tablet, computer, television) reduces the frequency of blinking. Blinking is what activates the meibomian glands to continue to produce lipids and spread them across the surface of the eye. People tend to concentrate with their eyes open wide and blink less often. Excessive screen time over long periods of time and decreased blink frequency can reduce the healthy long-term ability of the glands to produce lipids and their overall functionality can decline over time.

Similar to screen time, driving for long periods of time can also reduce the amount of blinking and cause dry eye symptoms.  

Blinking can help with Dry eye

A resting blink rate is estimated at 8-21 blinks per minute, but when having a conversation, it can increase to 10.5-32.5 blinks per minute. [2] When we focus on a specific visual task, such as reading or working on the computer, blink rates have been shown to drop by 60%, or to 4.5 blinks per minute. [1] However, it can be hard for someone to change their blinking rate as it can require a significant amount of concentration to do this.

Diseases, Disorders and Medications that cause dry eye symptoms

Various diseases, medications or medical procedures can cause dry eye symptoms and if these symptoms persist, it is important to discuss them with a physician to determine if treatment might be a helpful option.

Some diseases, disorders and medications can alter blink rate. Diseases associated with abnormal dopamine levels have been found to alter blink rate.  Dopamine is a chemical in the central nervous system that is associated with motor movements, including blinking. People with Parkinson’s disease, caused by declining levels of dopamine, have shown decreased blink rates, while those with schizophrenia, associated with dopamine abnormalities, have increased rates. [3]

Medications can also affect blink rate. As an example, women taking hormonal birth control pills have been shown to blink 32% more frequently than women not taking this medication. [7] As well, it has been speculated that estrogen may negatively affect the meibomian glands that produce the lipid layer of healthy tears.

Common medications like antihistamines, which can be effective for relief of runny nose, sneezing, and itchy eyes, can also dry out the watery layer of tear film. Antihistamines may cause fewer tears to be produced and those tears to evaporate more quickly.

Beta blockers are used to treat people with high blood pressure and abnormal heart rhythms by blocking the effects of adrenaline, a hormone produced when the body feels it is under high stress. These drugs slow the heart rate and among their side effects, include dry eye symptoms.  

Diuretics (also known as “water pills”) are also used to lower blood pressure by having the kidneys increase the amount of salt and water pass through the body in the form of urine. The reduction in bodily fluid, reduces the overall fluid going through the blood vessels, lowing blood pressure. This reduction in overall fluid in the body can result in reduced tear production.

Antidepressant, antipsychotic, and Parkinson’s medications block the transmission of nerve impulses. This can block the nerve sensations that communicate the signal of dry eye to the brain, that would normally stimulate tear production.

Medications used to treat severe acne are very powerful and have a drying effect on oil glands, including the meibomian glands. These medications are also known to cause eye irritation and decrease mucus production, a key component to healthy tears.

Eye surgery can cause dry eye symptoms

Laser refractive surgery (laser-assisted in situ keratomileusis (LASIK)) is a frequently performed procedure used to correct refractive error and allow people to rely less on glasses or contact lenses.  

The most common complication of refractive laser surgery is dry eye, occurring in up to 95% of patients immediately after surgery, up to 60% of patients 1 month after surgery, and up to 40% experience symptoms for at least 6 months.[4, 6] Since dry eye is such a common side effect, physicians provide treatment options for dry eye after corneal refractive surgery as a standard of care.

Why does refractive surgery cause dry eye?

There are several reasons that dry eye symptoms may occur after laser refractive surgery. The surgery may cause some damage to the corneal nerve and the suction devices used may cause conjunctival goblet cell loss. The corneal nerves are important because they provide sensation and send signals to the brain that more tears need to be produced. Goblet cells produce an inner mucus layer of normal tear film which allows the tears to spread evenly over the eye surface. After surgery, any inflammation that occurs may aggravate any pre-existing causes of dry eye and sometimes tear distribution that would normally occur during blinking is disrupted because of changes that are made to the corneal surface. [4]

Someone who is considering refractive surgery such as LASIK should consider obtaining formal dry eye testing by their eye care provider before having the procedure performed.  

Cataract Surgery and Dry Eye

Cataract surgery commonly leads to dry eye symptoms for many of the same reasons as laser refractive surgery. The corneal nerves are damaged and typically take a few months to regenerate before the dry eye symptoms subside. Cataract surgery also causes inflammation in the eye, which may adversely affect the production and quality of tears produced. Recent studies have also shown that low goblet cells after cataract surgery contribute to dry eye symptoms in these patients.[5]

Can Dry Eye be Prevented?

Treatment for dry eye symptoms is available but it is also possible to prevent or lessen exposure to certain situations that may cause or aggravate symptoms.

• Reduce eye exposure to direct air such as fans, hair dryers, heaters or air conditioners. Also try to shield your eyes from outside wind.

• Glasses, sunglasses or other protective eyewear can help to shield the eye from wind and dust particles that can dry and irritate the surface.  

• Increase the amount of moisture in your environment. Using a humidifier indoors in dry regions or in winter can increase the amount of moisture in the indoor air.  
  High altitudes, cold weather, desert regions and airplanes can be especially environments and irritating to eyes.  

• Limit screen time or take frequent breaks from reading computer work or driving. Concentrating on a visual task can decrease the frequency of blinking and prevent tears from being adequately distributed over the eye surface. Positioning computer screens below eye level has been shown to be helpful because the eyes are not required to open as wide, reducing the surface area of tear evaporation.  

• Stop smoking and avoid smoky environments. Smoke can irritate and dry the eye surface.  

• Artificial tears may be an option to help alleviate temporary dry eye symptoms by keeping the eye moist and lubricated.

• Take a dietary supplement to support healthy tears. Dietary supplements with omega-3 fatty acids may help support the lipid layer on the surface of the eye, which can help the eye stay lubricated and tears evaporate more slowly.

 

References:

[1] Blehm C, Vishnu S, Khattak A, Mitra S, Yee RW. Computer vision syndrome: A review. Surv Ophthalmol 2005;50:3: 253-262.  https://www.ncbi.nlm.nih.gov/pubmed/15850814

[2] Doughty MJ. Consideration of three types of spontaneous eyeblink activity in normal humans: During reading and video display terminal use, in primary gaze, and while in conversation. Optom Vis Sci 2001;78:10:712-725.  https://www.ncbi.nlm.nih.gov/pubmed/11700965

[3] Karson CN. Spontaneous eye-blink rates and dopaminergic systems. Brain 1983;106 (Pt 3):643-653  https://www.ncbi.nlm.nih.gov/pubmed/6640274

[4] Raoof D, Pineda R. Dry eye after laser in-situ keratomileusis. Semin Ophthalmol. 2014 Sep-Nov; 29(5-6):358-62.  https://www.ncbi.nlm.nih.gov/pubmed/25325861

[5] Ryan DS, Bower KS, Sia RK, Shatos MA, Howard RS, Mines MJ, Stutzman RD, Dartt DA. Goblet cell response after photorefractive keratectomy and laser in situ keratomileusis.  J Cataract Refract Surg. 2016 Aug;42(8):1181-9.  https://www.ncbi.nlm.nih.gov/pubmed/27531295

[6] Wallerstein A, Jackson WB, Chambers J, Moezzi AM, Lin H, Simmons PA.  Management of post-LASIK dry eye: a multicenter randomized comparison of a new multi-ingredient artificial tear to carboxymethylcellulose.  Clin Ophthalmol. 2018 May 7;12:839-848.  https://www.ncbi.nlm.nih.gov/pubmed/29765198

[7] Yolton DP, Yolton RL, Lopez R, Bogner B, Stevens R, Rao D. The effects of gender and birth control pill use on spontaneous blink rates. J Am Optom Assoc 1994;65:11:763-770.  https://www.ncbi.nlm.nih.gov/pubmed/7822673