What is the tear film made of and what breaks down in it?
The surface of the eye is covered with a film several micrometers thick, and it is more complex than it seems. The inner, mucin layer is produced by special cells of the conjunctiva: it makes the surface of the cornea wet, otherwise water would simply roll off it in drops. The middle, aqueous layer is produced by the lacrimal glands - this is what is usually called a tear; it contains dissolved salts, proteins and substances that protect against microbes. The outer, lipid layer is secreted by the meibomian glands, located right in the thickness of the eyelids: their ducts open along the edge of the eyelid, at the very line of the eyelashes. This fat layer acts like a lid on a pan - it slows down evaporation. Once it becomes thin, the water leaves the surface of the eye in a matter of seconds.
- Deficiency of the aqueous layer - objectively little tears are produced; typical due to age, certain medications, and autoimmune diseases
- Evaporative form - there is enough tears, but it evaporates too quickly; it accounts for the majority of cases
- Dysfunction of the meibomian glands is the main cause of the evaporative form: the ducts become clogged, the secretion thickens and stops coming out
- Mixed form - over time, one form leads to another, and they reinforce each other
- Impaired eyelid closure, rare or incomplete blinking - the film simply is not renewed
The main paradox: dry eyes that run
A person comes with a complaint of constant lacrimation, the wind on the street causes streams of tears in his eyes, and at the same time there is a pain and a feeling of sand in his eyes. The diagnosis of “dry eye syndrome” sounds absurd to him. The mechanism, meanwhile, is simple. When the tear film breaks, the exposed nerve endings in the cornea send a signal of irritation to the brain. In response, reflex lacrimation is activated - the lacrimal gland releases a large volume of watery tears. But this tear is emergency: it contains little mucin and almost no lipids, it does not stay on the surface and rolls down over the edge of the eyelid. The surface of the eye remains the same dry, but it runs down the cheek.
This has a practical conclusion that saves months. Profuse lacrimation without purulent discharge, especially in the wind, in the cold, at the computer and in the evening, is a reason to check not the patency of the tear ducts, but the condition of the tear film and the edges of the eyelids. Rinsing the lacrimal canal in such a situation does not give anything, because the canal is initially passable. The diagnosis is made by examination at the slit lamp, and not by the patient’s sensations: the symptoms are too similar to allergies, conjunctivitis and “blown eye”.
- Feeling of sand, dryness, foreign body, more often towards the end of the day
- Stinging, burning, redness of the whites, heaviness of the eyelids
- Paradoxical lacrimation in the wind, cold and behind a screen
- Fluctuations in visual acuity: text becomes cloudy, clears up after a few blinks
- Intolerance to contact lenses that were previously worn comfortably
- Morning crusts on the eyelashes, redness and thickening of the edge of the eyelid
- Tired eyes, desire to close them and rub them
Screens, lenses and air conditioning
Three everyday factors explain most cases in young and able-bodied people, and all three are modifiable. The first and most powerful is the screen. When a person is focused on a monitor or phone, the blink rate drops from about 15-20 times per minute to 5-7. Worse, a significant portion of the remaining blinks become incomplete: the eyelid goes down, but does not close completely, and the lower third of the cornea does not actually receive a fresh film. Add to this a monitor standing above eye level - the palpebral fissure opens wider, and the area of evaporation increases.
- Screen: blinking is reduced by two to three times, some blinks are incomplete, the film is not updated
- Contact lenses: the lens divides the film into two thin layers and accelerates evaporation; In this case, dryness itself becomes the cause of lens intolerance
- Air conditioning and heater: Dry air and directional flow dramatically accelerate evaporation, especially in a car when the deflector blows in your face
- Dry air of the heating season: indoor humidity in winter often drops to 20-25 percent with a comfortable 40-60
- Smoking and tobacco smoke indoors - direct damage to the lipid layer
- Long flights: cabin air is very dry
It’s worth mentioning medications separately, because this connection is almost never thought about. Dry eyes can be aggravated by many medications that a person takes for other reasons: some allergy medications, some blood pressure medications, diuretics, antidepressants, hormonal contraceptives, isotretinoin for acne. A separate and very common situation is glaucoma drops with preservatives, which the patient is forced to instill for years. Under no circumstances should you cancel the prescribed treatment yourself, but you should definitely tell your ophthalmologist the full list of medications you are taking: sometimes it is enough to switch to a form without a preservative or shift the time of administration for the condition to noticeably improve.
Examination: what does an ophthalmologist look for?
- Опрос по стандартному опроснику сухости глаз — оценивает выраженность жалоб и позволяет потом сравнить результат лечения в цифрах.
- Осмотр за щелевой лампой: состояние края века, устьев мейбомиевых желёз, характер их секрета, наличие блефарита и демодекоза ресниц.
- Компрессионная проба — врач слегка надавливает на веко и смотрит, выходит ли секрет и какой он: прозрачный, мутный или пастообразный.
- Определение времени разрыва слёзной плёнки с окрашиванием флуоресцеином: в норме плёнка держится дольше 10 секунд, менее 10 секунд говорит об испарительной форме.
- Проба Ширмера — полоска фильтровальной бумаги за нижним веком на 5 минут; она оценивает объём выработки слезы.
- Окрашивание поверхности глаза красителями — показывает, есть ли уже повреждение эпителия роговицы и конъюнктивы.
- Оценка высоты слёзного мениска — полоски слезы вдоль края нижнего века.
- При подозрении на системное заболевание — анализы крови и консультация ревматолога.
Treatment: what works and what harms
Dry eye is a chronic condition, and the goal of treatment is not to “drink the course” and forget, but to restore the stability of the film and retain it. Therefore, therapy is almost always two-part: work with the eyelids and glands, plus replacement support with drops. One-time measures without eyelid care in the evaporative form provide only temporary relief.
- Warm compresses on the eyelids for 5-10 minutes: the heat softens the thick secretion in the ducts of the meibomian glands and allows it to come out
- Eyelid hygiene - cleansing the edge of the eyelid with special products or napkins after a compress, courses or constantly
- Massage the eyelids towards the edge after warming up - squeezes out the softened secretion from the ducts
- Tear substitutes: for mild forms - liquid drops several times a day, for severe forms - gels and ointments at night
- Forms without preservatives are essential if drops are needed more often than 4-6 times a day: the preservative itself, with frequent use, damages the epithelium
- Anti-inflammatory therapy as prescribed by a doctor for severe inflammation of the ocular surface
- Obturation of lacrimal openings with microscopic plugs - retains your own tears on the surface of the eye when there is a deficiency of production
- Hardware methods for the meibomian glands, including pulsed light procedures and heating with simultaneous massage
- Adequate fluid intake and fatty fish in the diet as an auxiliary measure
Now about the most harmful misconception. Vasoconstrictor “redness drops” are agents that constrict the vessels of the conjunctiva, and the eye turns white in just minutes. The problem is that they do not moisturize the surface and do not affect the cause, and after their action ends, the vessels dilate more than before. This is called recurrent redness: a person drips again, the effect is shorter each time, the dose is needed more often, and after a few weeks the eye turns red from the drops themselves. Additionally, these products usually contain a preservative, which, with frequent use, damages the corneal epithelium. The result is sad: the patient comes to the doctor with a much more severe picture than at the beginning, and some of the complaints are now caused by the treatment. The same applies to the idea of rinsing the eyes with tea, chamomile or boric acid: decoctions do not restore the lipid layer, but they wash away the remnants of their own film and often add allergies.
What to change in everyday life
- Правило зрительных пауз: примерно каждые 20 минут работы отводите взгляд вдаль на 20 секунд и сознательно сделайте несколько полных, плотных морганий.
- Опустите монитор ниже уровня глаз, чтобы взгляд был направлен слегка вниз: глазная щель сужается, площадь испарения уменьшается.
- Отверните дефлекторы кондиционера в машине и офисе от лица; не спите под прямым потоком воздуха.
- Поддерживайте влажность в помещении около 40-60 процентов, особенно в отопительный сезон.
- Сократите непрерывное время в линзах, чередуйте их с очками, при выраженной сухости обсудите смену типа линз или отказ от них.
- На ветру и на солнце носите очки, лучше с боковой защитой.
- Введите ежедневную гигиену век в привычную рутину, как чистку зубов, если у вас есть блефарит или дисфункция желёз.
- Не назначайте себе капли по совету аптеки и не пользуйтесь средствами от красноты дольше нескольких дней.
