- How it Works
October 24, 2017
Dry eye is caused by a reduction in natural tears and is fairly common in older adults. About 3.2 million women and 1.68 million men age 50 and older are impacted by dry eye syndrome. In normal circumstances, tears spread across the eye’s surface when a person blinks. To better understand dry eye, it helps to have basic knowledge about how tears form and the specific functions of each of the three layers that comprise tears.
Oily layer: Produced by the meibomian glands, this is the outer layer of the tear film. Meibomian glands are tiny oil glands lining the margin of the eyelids (the edges which touch when the eyelids are closed). Every human eye has 45-70 meibomian glands, counting the upper and lower eyelids. The oil content helps keep the tear surface smooth and prevents them from drying up too quickly.
Dysfunction of the meibomian glands is thought to be the leading global cause of dry eye disease. Inflammation along the eyelid edges (blepharitis), rosacea, and other skin disorders can cause the meibomian glands to become blocked, increasing the risk of dry eye. Like dry eye, meibomian gland dysfunction tends to impact older adults more commonly. In a study on 233 older adults, 59% had at least one sign of meibomian gland dysfunction.
Watery layer: This is the middle layer of the tear film and is produced by the lacrimal glands. This is the visible component of tears and is composed of proteins, electrolytes, and water. The primary function of this layer is to clean the eyes and wash away particles that don’t belong such as sand or grit. A decrease or lack of lacrimal gland secretion is the leading cause of a type of dry eye called aqueous tear deficient dry eye syndrome (DES). Inflammation of these glands can result from autoimmune diseases like Sjögren’s syndrome, organ transplantation, or simply be a result of aging.
Mucin layer: The inner layer of the tear film is produced by the conjunctiva, the clear tissue covering the white of the eye and inside of the eyelids. This layer helps spread the watery layer over the eye’s surface, keeping it moist. Mucus helps the tears spread over the front surface of the eye (cornea), so when a malfunction occurs, dry patches can form on the cornea.
In addition to autoimmune diseases, aging and some skin conditions, many over-the-counter and prescription drugs can cause dry eye. As many as 95% of patients experience dry eye symptoms after LASIK surgery, but this is usually temporary. Dry eye is more common in women than men, likely due to hormonal changes during pregnancy and after menopause. Furthermore, women have an increased risk of autoimmune disorders, which already mentioned, is a dry eye risk factor.
Dry eye symptoms caused primarily by insufficient tears tend to worsen throughout the day and be more noticeable at night. Whereas symptoms of dry eye associated with blepharitis are typically worse in the morning.
A stinging or burning sensation
Feeling of dryness, grittiness (like sand), and soreness
Stringy mucus in or around eyes
Eye sensitivity to smoke or wind
Difficulty keeping eyes open
Eye fatigue after reading, even for a short period
Blurred vision, especially at night
Sensitivity to light
Discomfort when wearing contact lenses
Eyelids sticking together when waking up
Many people wonder if reduced moisture in the eyes can harm their eyesight. The front surface of the eye is the most powerful focusing surface of the eye, therefore a dry ocular surface can affect eyesight. A decrease or fluctuation in visual acuity, in which objects appear blurry or less defined is not uncommon. A sensitivity to light (photophobia) can occur because a dry ocular surface has more irregularities, scattering light entering the eye. Last, difficulty seeing at night, especially when driving, is quite common. Light hitting the dry ocular surface and scattering can produce halos and glares from oncoming headlights. These are all aggravating side effects, but the question is whether dry eye can impart permanent refractive changes?
For years, eye doctors did not believe dry eye impacted visual acuity because these symptoms were subtle. Moreover, many patients were able to pass vision tests with 20/20 vision because they blinked enough to produce adequate tears during the exam. Now, it is known that a small number of patients with more severe dry eye have highly irregular corneas, resulting in a reduction in vision.
The Interval Visual Acuity Decay (IVAD) can detect whether people with dry eye experience vision changes throughout a blinking cycle. For example, a person with dry eye who keeps their eyes open may have 20/20 vision for four seconds, then 20/40 for another second, 20/50 for two more, 20/60 for a second or two, and then perhaps as bad as 20/80 before having to blink again. An IVAD study on 18 dry-eye patients and 17 age-matched controls provided further evidence of this phenomenon. Dry-eye patients could only maintain their best-corrected visual acuity for 8.75 ±6.6 seconds before it started to degrade, whereas normal patients maintained it for a statistically significant longer period of 19.46 ±15.97 seconds.
Treatment for dry eye includes artificial tears, prescription eye drops, and tiny punctal plugs which are inserted into the tear ducts. Drinking adequate water throughout the day and maintaining proper humidity in the house can also help. You can also explore this blog for 5 easy ways to relieve dry eye.
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