The Tear Film and Dry Eye

Key points

• • The tear film has three layers: an outer oily layer, a middle watery layer, and an inner mucus layer that sticks it to the eye.
• • The oily layer slows evaporation, the watery layer nourishes and cleans, and the mucus layer spreads the tears evenly.
• • The tear film keeps the cornea smooth for clear vision, washes away dirt, and contains substances that fight germs.
• • Dry eye occurs when too few tears are made or they evaporate too fast, causing grittiness, burning and, oddly, reflex watering.
• • It is common with age, in some autoimmune diseases such as Sjogren's, and with long screen use that reduces blinking.