Preface

Many studies have been performed to describe and to understand the correlations between the structures of the eye, also known as the "ocular surface." This book focuses on the preocular tear film, a thin layer of tears covering the cornea of the eye. It presents research on tear film physiology, its changes in various disturbances and diseases, and the influence of those changes on the ocular surface. It also presents up-to-date information on keratoconus, a condition affecting both the preocular tear film and the ocular surface in which the cornea thins and bulges outward.

This book was made possible thanks to the collaboration of many researchers in the field of ophthalmology. I wish to thank them as well as the staff at IntechOpen for their invaluable contributions. I hope ophthalmologists, practitioners, and students will find this book interesting and useful for understanding the role of preocular tear film in ocular surface integrity and stability.

> **Dr. Dorota Kopacz** Medical University of Warsaw, Warsaw, Poland

Department of Ophthalmology, Infant Jesus Teaching Hospital, Warsaw, Poland

**1**

**Chapter 1**

**Abstract**

those diseases.

**1. Introduction**

of various diseases and conditions on it.

and Disorders

Tear Film – Physiology and

*Dorota Kopacz, Łucja Niezgoda, Ewa Fudalej,* 

*Anna Nowak and Piotr Maciejewicz*

Disturbances in Various Diseases

The tear film is a thin fluid layer covering the ocular surface. It is responsible for ocular surface comfort, mechanical, environmental and immune protection, epithelial health and it forms smooth refractive surface for vision. The traditional description of the tear film divides it into three layers: lipid, aqueous and mucin. The role of each layer depends on the composition of it. Tear production, evaporation, absorption and drainage concur to dynamic balance of the tear film and leads to its integrity and stability. Nonetheless, this stability can be disturb in tear film layers deficiencies, defective spreading of the tear film, in some general diseases and during application of some general and/or topical medications. Dry eye disease is the result of it. In this review not only physiology of the tear film is presented. Moreover, we would like to discuss the influence of various diseases and conditions on the tear film and contrarily, spotlight tear film disorders as a manifestation of

**Keywords:** tear film, dry eye, mucins, lipid layer, aqueous layer, ocular surface

The tear film is a thin fluid layer covering the ocular surface; it is the interface of the ocular surface with the environment. It is responsible for ocular surface comfort, mechanical, environmental and immune protection, epithelial (both corneal and conjunctival) health and it forms smooth, refracting surface for vision [1, 2]. Tear production (about 1,2 microliters per minute, total volume 6 microliters, 16% turnover per minute), evaporation, absorption and drainage are responsible for dynamic balance of the preocular tear film [1, 3–5]. Homeostatic balance leads to stability of the tear film, that makes possible to realize its functions as lubrication, nutrition and protection of ocular surface [3, 6]. Nonetheless, this stability can be disturb in tear film layers deficiencies, defective spreading of the tear film, in some general diseases and during application of some systemic and/or topical medications and dry eye disease evolves as a consequence of it. These review focused on physiology of the tear film, it's meaning for the ocular surface stability and analyzed influence
