Chronic Dry Eye Information:

Clinical Definition of Chronic Dry Eye

Chronic Dry Eye can be defined as a condition involving abnormalities and deficiencies in the tear film, initiated by a variety of causes. Chronic Dry Eye is also known as keratoconjunctivitis sicca (KCS) or is referred to as Dry Eye Disease.

Chronic Dry Eye has a complex pathology. It is mostly known as a condition of tear deficiency, but it is just as much a condition of altered tear composition. To see why, let’s review the process by which tears are made.

Secretion of natural tears is controlled by the lacrimal functional unit, which
consists of1

• The main lacrimal gland, accessory lacrimal glands
• The ocular surface – including the cornea, conjunctiva, goblet cells, and meibomian glands
• The interconnecting innervation

The lacrimal functional unit is responsible for both tear quantity and tear quality. It ensures that the 3 major tear film components – mucin, aqueous, and lipid – are secreted to the ocular surface in a controlled and coordinated fashion.1

Production of normal tears by the lacrimal functional unit depends on a neuronal feedback loop involving neural stimulation from the ocular surface of the eye, causing secretomotor nerve impulses from the brain to the lacrimal glands, which in response produce an appropriate quantity and quality of tears for the ocular surface.

Click on the headings for "Normal Tear Production" and "Chronic Dry Eye Tear Production" to see how the neural loop is affected by Chronic Dry Eye.

In Chronic Dry Eye there is a malfunction in the neural feedback loop that controls both tear production and tear composition. Chronic irritation causes excessive firing of the neural loop. In the compromised lacrimal functional unit, inflammation ensues in the lacrimal glands which cause secretion of altered tears. Untreated, the dysfunctional tear-producing cycle will continue and potentially get worse over time.

Reference:
1. Stern ME, Gao T, Siemasko KF, et al. The role of the lacrimal functional unit in the pathophysiology of dry eye. Ex Eye Res. 2004; 78:409-416.