Dry Eye Causes: Why the Tear Film Fails

There is no single cause of dry eye. StatPearls sorts nearly every case into two overlapping mechanisms: evaporative, where tears are made but do not last, and aqueous-deficient, where the glands do not produce enough in the first place. Most patients have some of both, and the mix decides which treatment is worth trying.

Evaporation: the oil layer fails

The outermost layer of the tear film is oil, secreted by the meibomian glands along the lid margin. Its job is to slow evaporation. When those glands thicken, clog or atrophy — meibomian gland dysfunction is the most common single contributor — the watery layer beneath is left uncovered and boils off between blinks. Lid inflammation, rosacea and eczema around the lids feed the same problem, and MedlinePlus notes that meibomianitis alone can create or worsen the syndrome.

Deficiency: the lacrimal gland underdelivers

The aqueous middle layer comes from the lacrimal glands. Output falls with age, with certain systemic diseases, and after damage from radiation, graft-versus-host disease or surgery. When the deficiency is severe and paired with a dry mouth, Sjögren syndrome is the diagnosis being ruled in or out.

The medication list is longer than most people expect

Drugs are the most reversible cause and the least often suspected. StatPearls lists systemic antihistamines, antihypertensives, diuretics, anxiolytics and benzodiazepines, antidepressants, systemic hormones, corticosteroids, anticholinergics and isotretinoin, which causes meibomian gland atrophy outright. Topical drugs count too: glaucoma medication, and preservative toxicity from any drop used several times a day for months.

Hormones and age

Prevalence climbs with age and is consistently higher in women. The mechanism is the fall in androgen levels around menopause, since those hormones support both the lacrimal and the meibomian glands. The American Optometric Association adds pregnancy and oral contraceptives to the list, which explains why the difference between men and women shows up decades before 65.

Systemic disease

Rheumatoid arthritis, lupus, thyroid disease, diabetes and multiple sclerosis all appear on the StatPearls list. So does severe vitamin A deficiency, which produces xerophthalmia. The National Eye Institute puts autoimmune conditions such as lupus and Sjögren syndrome among its five main risk factors, alongside age over 50, female sex, contact lens wear and low intake of vitamin A or omega-3 fatty acids.

Environment, surgery and habits

Wind, heat, low humidity, altitude, pollution and smoke all accelerate evaporation. Refractive surgery, cataract surgery, keratoplasty and lid surgery can cut corneal nerve feedback and reduce tear production for months. Smoking, alcohol, poor sleep and long stretches of screen work all appear on the same list — and screens deserve their own treatment, in dry eyes from screen time.

Why the vision goes soft

The tear film is the first refractive surface light meets, before the cornea. When it breaks up early, the image degrades until the next blink rebuilds it. That is why blurring from dry eye comes and goes with blinking rather than staying put, and why it is worst during the tasks that suppress blinking. The full symptom picture is in dry eye symptoms.

This content is informational and does not replace medical consultation, diagnosis, or treatment. See also itchy eyes causes and dry eyes at night.