ABSTRACT
The “ocular surface” is defined as the continuous sheet of tissue that extends from the grey line of the eyelid margin and includes the posterior lid surface, the fornix, the anterior surface of the globe and the cornea and is composed of the epithelium of the conjunctiva and cornea (Thoft and Friend, 1977). The normal corneal epithelium is a specialised, stratified squamous epithelium. It functions to provide an optically smooth, transparent anterior surface to the cornea, aids in the maintenance of relative stromal dehydration and provides a barrier against trauma and microbes. To ensure survival of the cornea and hence the animal there is usually a rapid healing response that does not impair
The ocular surface is a specialised structure that protects and maintains a smooth and transparent cornea and this ensures that light can be adequately refracted and focused on to the retina. To provide these unique functions, the corneal epithelium must be constantly moistened, desiccation can lead to damage within minutes. The tear film ensures that the epithelium remains transparent and healthy, smooths the ocular surface and provides protection against infection. Because of the nature of the tear film and its interaction with the cornea, in humans it is refreshed every few seconds with blinking. During sleep the lids are able to completely cover the ocular surface thereby providing further protection. To ensure that blinking and ocular movement can occur without corneal trauma, the inside of the lids and the surface of the globe is covered with mucous membrane, the conjunctiva, and this too is covered by the tear film. Adequate production of the tear film is assured by an intrinsic basal level of secretion and various reflexes that can increase tear production, increase the blink rate, close the eye or enact protective behavioural changes. This chapter will discuss the anatomy and physiology of the tear film and the ocular surface, outline the innervation and neural control mechanisms of the ocular surface and discuss the diseases and the management of tear film disorders.
