Figure 4  .

Hypothetical scheme of the pathophysiology of delayed tear clearance. Delayed tear clearance can be induced by ineffective or decreased blinking (functional block) or mucosal inflammation and oedema in the nasolacrimal drainage system (partial anatomical block). The former is contributed by such risk factors as old age, female sex, decreased corneal sensitivity, and lid laxity including floppy lids. The latter can intrinsically be generated by allergy, atopy, rosacea, and meibomian gland dysfunction, or extrinsically caused by medication toxicity. A vicious cycle can form between delayed tear clearance and mucosal inflammation and oedema leading to ocular irritation, medicamentosa, drug induced pseudopemphigoid, and steroid induced ocular hypertension.