All dry eyes are not created equal. The tear film is composed of three main ingredients: aqueous, mucin, and sebum. Much like a soufflé, your tear-film demands exact proportions of these main ingredients to remain stable and form a smooth surface over the cornea. Too much of one ingredient and not enough of another leads to premature break-up (instability) or drying up of the tear film, such that you may feel any one of the following uncomfortable sensations: burning, stabbing pain, itching, foreign body sensation (feeling of sand or eyelash in the eye), and blurry vision. A fourth important factor involved in regulating the tear film is the blink reflex. Most people blink between 6-8 times a minute. A good blink is a complete one (the upper and lower eyelids make contact) and spreads the tear film evenly across the cornea.
Two of the main ingredients in the tear recipe, sebum and aqueous, are released from your eyelid margin (from glands that sit behind your lashes). The third ingredient, mucin, is produced by marshmallow-shaped cells in the gooey skin of the eyeball, the conjunctiva. It then follows that eyelid inflammation will disrupt the production of sebum and aqueous and therefore affect the tear film. In a very common condition known as blepharitis (eyelid inflammation), dry eye syndrome results from faulty sebum or aqueous release. Reduced blinking rates or incomplete blinking also lead to drier eyes, because the tear film coats only those surfaces covered by the blink, leaving the remainder of the cornea high and dry. You may have noticed yourself that when you read a book/Kindle or work on the computer for a prolonged period of time, your eyes begin to burn and your vision blurs. Studies have shown that subjects focusing on these highly visual tasks blink less frequently. A reduced blink reflex means faster tear break-up and discomfort or pain. Why the blurry vision? Being a very powerful refractive surface (a surface that focuses light onto your retina), the tear film must be "just right" (think soufflé) in order to produce clear vision. As soon as it breaks up or dries up, the refractive surface is damaged and the image projected into your eye becomes unfocused and fuzzy.
My patients often ask me, with Nancy Kerriganian alarm and a dearth of tears in their eyes, "why me?!" The reasons for poor blinking and tear-film deficiency are multifactorial. First and foremost among these is aging. As sure as death, taxes, and cataracts, our aqueous tear production decreases with age. Another gender misfortune is female sex, especially as menopause nears and hormones involved in tear film regulation change. Drugs, such as anti-depressants, blood pressure, neurologic, and allergy medicines, contribute to dry eyes. Smoking (you heard it here first!) is bad for you, and interrupts proper tear-film production at its root and with second-hand smoke. Crack cocaine smoking is even worse and can lead to full-fledged corneal abrasions. Sorry to pull the race card, but white folks (you know who you are) with Rosacea, are more prone to blepharitis and, therefore, dry eyes. And, finally, disease states such as Lupus, Rheumatoid Arthritis, and Sjögren's Disease all contribute to dry eyes.
Now that we know the basics of tear production, lets talk about treatments. Depending on the underlying cause of dry eyes, I like to tailor therapy to target the specific problem. For example, if you have eyelid inflammation, I treat your ailing eyelids first, and if you have tear film deficiency I recommend lubricating the ocular surface or stimulating tear production with a prescription drop. If you sleep with your eye-lids slightly ajar (lagophthalmos), I recommend a drop that will keep your corneas moist at night. The corner-stone of dry eye treatment is artificial tears. By this I do not mean Visine, Naphcon-A, or any vasoconstricting drops. In fact, I would recommend you cease and desist use of the aforementioned, if you do. In the next few blog posts I will delve into therapies for different dry eye scenarios and talk about drops, gadgets, supplements, and routines that can help dry eyes feel better.
If you seem to have severe dry eye symptoms and have not found an answer to your predicament in this post, hold on to your seat-belt, I have only reached the tip of the iceberg. Please comment with your particular problem and I will address it in a future post.