Lacrimal Functional Unit
The lacrimal functional unit (LFU; Fig 1-2) is a highly complex apparatus comprising the lacrimal glands, ocular surface, and eyelids, as well as the sensory and motor nerves that connect these components. The LFU is responsible for the regulation, production, and health of the tear film. The LFU responds to environmental, endocrinologic, and cortical influences. Its overall functions are to preserve the following:
Figure 1-2 The sensory and motor nerves connecting the components of the lacrimal functional unit. CN = cranial nerve.
(Modified with permission from Pflugfelder SC, Beuerman RW, Stern ME, eds. Dry Eye and Ocular Surface Disorders. New York: Marcel Dekker; 2004.)
integrity of the tear film (by carrying out lubricating, antimicrobial, and nutritional roles)
health of the ocular surface (by maintaining corneal transparency and the surface stem cell population)
the quality of the image projected onto the retina
The afferent component of the LFU is mediated through ocular surface and trigeminal nociceptors, which synapse in the brainstem with autonomic and motor (efferent) nerves. The autonomic nerve fibers innervate the meibomian glands, conjunctival goblet cells, and lacrimal glands. The motor nerve fibers innervate the orbicularis muscle to initiate blinking. During blinking, the meibomian glands express lipid, and the tears are replenished from the inferior tear meniscus and spread across the cornea while excess tears are directed into the lacrimal puncta.
Pflugfelder SC, Beuerman RW, Stern ME, eds. Dry Eye and Ocular Surface Disorders. Boca Raton, FL: CRC Press/Taylor & Francis; 2004.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.