Dry Eye Syndrome (Keratoconjunctivitis Sicca)

Dry eye disease (DED) is the most common chronic ocular condition, affecting 5-50% of adults globally with rising prevalence due to aging populations, screen use, and environmental factors. The 2017 TFOS DEWS II definition emphasizes 'multifactorial disease of the ocular surface characterized by a loss of homeostasis of the tear film, accompanied by ocular symptoms, in which tear film instability, hyperosmolarity, ocular surface inflammation and damage, and neurosensory abnormalities play etiological roles.' Subtype classification: aqueous-deficient (lacrimal gland dysfunction in Sjögren or non-Sjögren) and evaporative (meibomian gland dysfunction—MGD—the most common form, ~85%); most patients have mixed disease.

Pathophysiology involves a vicious cycle: tear film instability and hyperosmolarity activate ocular surface inflammation (MMP-9, IL-1, IL-6, TNF-alpha) damaging epithelium and goblet cells; lacrimal gland and meibomian gland dysfunction reduce tear production and lipid layer integrity; neurosensory abnormalities alter blink dynamics and tear secretion; corneal nerve damage causes neuropathic pain disproportionate to objective findings. Risk factors include age, female sex, autoimmune disease (Sjögren, rheumatoid arthritis, lupus), medications (antihistamines, antidepressants, isotretinoin, hormone therapy), screen use with reduced blink rate, contact lenses, dry/windy environments, refractive surgery, and Demodex/blepharitis.

Diagnosis combines symptom questionnaires (OSDI, SPEED), tear film tests (TBUT—tear break-up time <10 seconds suggests instability, Schirmer test <10 mm/5 min suggests aqueous deficiency, tear osmolarity >308 mOsm/L), ocular surface staining (fluorescein, lissamine green—corneal/conjunctival staining indicates damage), meibography (gland atrophy in MGD), and matrix metalloproteinase-9 (MMP-9, InflammaDry) for inflammation. Treatment is stepwise (TFOS DEWS II): step 1—patient education, lifestyle modifications, environmental adjustments, lubricants (artificial tears, gels, ointments); step 2—non-preserved drops, anti-inflammatory drops (cyclosporine 0.05% Restasis, 0.09% Cequa, lifitegrast 5% Xiidra), tear conservation (punctal plugs/cautery), MGD treatments (warm compress, lid hygiene, oral doxycycline, omega-3, LipiFlow, IPL); step 3—autologous serum tears, scleral lenses, surgical interventions; step 4—long-term immunomodulators, amniotic membrane, surgical eyelid procedures. Treatment must address ocular surface inflammation and root causes (Sjögren, MGD, medications).