DoctorSpeak: Why unchecked dry eye disease can affect vision
As the use of digital devices rises, cases of dry eye disease are increasing rapidly even among children
Ever wondered why most fish don’t blink? They don’t have eyelids as they don’t need them. Living in water, their eyes stay constantly lubricated and moist. When vertebrates moved from the ocean to land, they faced a major challenge of their eye surfaces drying out, that affected their vision. From forming a simple mucoid layer on the eyes of tetrapods as in frogs, evolution more than 350 million years ago created a tiny ocean around the surface of the eyes, known as tears.
Tears provide an extremely smooth surface at the air-cornea interface for high-quality image formation. These also keep the surface of the eye moist, and form the first line of defence by washing away dust, debris, or microbes that otherwise would settle on the eye surface.
Tears form a very thin layer (3-5 µm) on the surface of the eye, held in place between the upper and lower eyelids. Every time we blink, the upper eyelid acts like a windscreen wiper, spreading tears evenly and helping them drain through two tiny channels near the lid margins, close to the root of the nose. Between blinks, the tear film can stay stable for more than 10 seconds; afterwards, it begins to break up, causing dry patches on the ocular surface.
These dry patches result in gritty sensations that can worsen with eye rubbing. The normal blink rate is about 12-20 times a minute, higher in women than in men. Like breathing and swallowing, blinking is a hybrid of both involuntary and voluntary action. We can hold the blink. When we focus on a screen or a book, or when we stare, blinking is greatly reduced, thereby breaking up the tear film.
Dry eye disease (DED) is one of the most common chronic eye conditions among older adults, especially postmenopausal women, and a frequent reason for visits to ophthalmologists. A gritty sensation, as if dust particles have fallen in the eye, is a common complaint that often worsens with air-conditioning in summer; in dry, windy conditions; and in winter with the use of room heaters, as tears evaporate quickly. It can be highly disabling at its worst. As the use of digital devices rises, symptoms of DED are increasing rapidly, sometimes even among children.
The tear film is a dynamic muco-aqueous layer secreted by the main and accessory lacrimal glands, covered by a superficial lipid layer (0.1µm thick) produced by the meibomian glands. Most of these glands are located in the tarsal plate within the upper eyelid. The oily (lipid) layer prevents evaporation of the aqueous layer and helps stabilise it.
Dysfunction of the meibomian glands, leading to evaporative dry eye, accounts for the majority (around 60–70 per cent) of cases. Androgen hormones regulate the secretion of the meibomian glands. Women have lower androgen levels; tear film breaks down more quickly, and corneal nerves are more sensitive. Consequently, post-menopausal women face a higher risk of developing DED.
Using eye drops with preservatives more than four times a day may worsen the existing DED. Digital device use, thyroid eye disease, environmental factors, and medications such as antihistamines, antidepressants, and antianxiety drugs can cause reversible DED.
Blepharitis, an inflammation of the eyelid margins, blocks the secretion of oils from the meibomian glands, leading to a rapid evaporation of tears. Warm, wet compresses on the lids, gentle lid massage, and omega-3 fatty acid supplements aid in resolution.
Common multi-organ inflammatory diseases like sarcoidosis and some autoimmune diseases such as rheumatoid arthritis, lupus and primary Sjogren Syndrome and chemical burns can permanently destroy the lacrimal glands that secrete the aqueous (water) component of tears, leading to severe, blinding DED. Nearly 10 per cent cases of DED may have primary Sjogren’s syndrome and also have dry mouth. If left untreated early, it may lead to corneal melting.
The gritty sensations in the eyes warrant a visit to the ophthalmologist, who can easily identify the cause of DED. Tear film break-up time and tear production are straightforward to measure. An increase in tear osmolarity, the thickness of the oily layer, and the morphology and density of the lipid-secreting Meibomian glands can be evaluated at advanced facilities.
Managing mild-to-moderate DED involves avoiding the risk factors listed above and using tear substitutes. For more severe cases, several additional strategies are available and will be recommended by your ophthalmologist based on individual needs. DED begins as a minor irritation and, if left untreated, can lead to vision loss over time.
— The writer is Emeritus Professor, PGI, Chandigarh
Factcheck: Dry Eye Disease (DED) is rising rapidly in India, driven by high urban pollution, environmental factors, allergens, excessive screen time, and air-conditioned environments, with prevalence rates over 60 pc in some regions. While it's common in older adults (60% prevalence in >50 years), there's a significant rise in young, working-age, and students due to excess screen time. Children are increasingly affected, with a prevalence of around 7.6 pc to 11 pc in the paediatric population (7-18 years), often causing red, itchy and tired eyes.
