Microbiology, 2021

858 21 • Skin and Eye Infections
Figure 21.4 (a) Acne is a bacterial infection of the skin that manifests as a rash of inflamed hair follicles (folliculitis). The large whitehead
near the center of the cheek is an infected hair follicle that has become purulent (or suppurative), leading to the formation of a furuncle. (b)
An abscess is a pus-filled lesion. (credit b: modification of work by Bruce Blaus)
Figure 21.5 Numerous causes can lead to skin lesions of various types, some of which are very similar in appearance. (credit:
modification of work by Bruce Blaus)
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Anatomy and Microbiota of the Eye
Although the eye and skin have distinct anatomy, they are both in direct contact with the external
environment. An important component of the eye is the nasolacrimal drainage system, which serves as a
conduit for the fluid of the eye, called tears. Tears flow from the external eye to the nasal cavity by the lacrimal
apparatus, which is composed of the structures involved in tear production (Figure 21.6). The lacrimal gland,
above the eye, secretes tears to keep the eye moist. There are two small openings, one on the inside edge of the
upper eyelid and one on the inside edge of the lower eyelid, near the nose. Each of these openings is called a
lacrimal punctum. Together, these lacrimal puncta collect tears from the eye that are then conveyed through
lacrimal ducts to a reservoir for tears called the lacrimal sac, also known as the dacrocyst or tear sac.
From the sac, tear fluid flows via a nasolacrimal duct to the inner nose. Each nasolacrimal duct is located
underneath the skin and passes through the bones of the face into the nose. Chemicals in tears, such as
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