Anatomy & Physiology

Anatomy & Physiology Study Guide

©2018 Achieve Page 190 , are a continuation of the skin. Their continual blinking keeps the surface of the eye lubricated, and they act like windshield wipers, removing dust and debris. The eyelids can also close firmly to protect the delicate surface of the eye. The eyelashes, located along the margins of the eyelids, are hairs that aid to prevent foreign matter (including insects) from touching the eye. Unusually large sebaceous glands are associated with eyelashes. Along the inner margin of the lid, modified sebaceous glands, called tarsal glands or Meibomian glands, secrete a lipid-rich product that helps keep the eyelids from sticking together. The skin covering the observable surface of the eyelid is fine. Deep in the skin lie the muscle fibers of the orbicularis oculi and levator palpebrae superioris muscles; they are responsible for closing the eyelids and raising the upper eyelid, respectively. The epithelium covering the inner surfaces of the eyelids and the outer surface of the eye is called the conjunctiva . It is a mucous membrane protected by a specialized stratified squamous epithelium. The ocular conjunctiva extends to the edges of the cornea, a transparent part of the outer fibrous layer of the eye. The cornea is covered by a very delicate squamous corneal epithelium, five to seven cells thick. A continuous supply of fluid flows over the surface of the eyeball, keeping the ocular conjunctiva and cornea moist and clean. Conjunctivitis, or pinkeye, results from damage to and irritation of the conjunctival surface. The Lacrimal Apparatus The lacrimal apparatus produces, secretes, and removes tears. This apparatus of each eye consists of a lacrimal gland and ducts, lacrimal sac, paired lacrimal canaliculi, and a nasolacrimal duct. The pocket created where the palpebral conjunctiva becomes continuous with the ocular conjunctiva is known as the fornix of the eye. The lateral part of the superior fornix receives 10–12 ducts from the of 368 Accessory Structures of the Eye The accessory structures of the eye contain the superficial epithelium of the eye, the eyelids, and the lacrimal structures associated with the production, secretion, and removal of tears. Eyelids and Superficial Epithelium of the Eye The eyelids, or palpebrae