Tear Film Considerations With And Without Contact Lens Wear

This book summarizes current understanding of the scientific, clinical, and technical issues surrounding the use of contact lenses. It discusses the special occupational conditions experienced by military personnel, particularly in extreme environments, that give rise to the question of whether or not to use contact lenses. Experts in optometry, ophthalmology, visual psychophysics, and engineering describe recent developments in design and use; and representatives of the military services provide examples of actual situations in aerospace settings. Considerations in Contact Lens Use Under Adverse Conditions will be of particular interest to those involved in the design of contact lenses and those responsible for occupational safety and health matters in the private sector.

The field of contact lenses continues to evolve at a rapid pace, with new optical designs and vision correction options continually being developed. Additionally, the rapid expansion of clinical instrumentation offers eye care practitioners a wide choice of investigative techniques for assessing in-eye contact lens performance and diagnosing adverse reactions. Now in its fourth edition, Contact Lens Practice has been thoroughly updated and revised to capture these developments and more, and translate them into an organised and easily digestible resource. Written and edited by award-winning author, researcher, and lecturer, Professor Nathan Efron, this title provides a comprehensive, evidence-based overview of the scientific foundations and clinical applications of contact lens fitting. The text has been refreshed by the inclusion of five new authors – a mixture of scientists and clinicians, all of whom are at the cutting edge of their specialty. Serves as an essential companion and guide to current thinking and practice in the content lens field, ideal for use by optometrists, ophthalmologists, orthoptists, opticians, students, and contact lens industry professionals. Presents subject matter in a clear and logical format to allow the reader to quickly identify and comprehend key information. Features highly illustrated chapters in full colour, helping the reader to visualize core concepts. Includes completely rewritten chapters, by new authors, on scleral and corneo-scleral contact lenses, high ametropia, therapeutic applications, post-surgical lens fitting, and practice management. A new chapter on Post-Surgery Management consolidates core information on post-operative management involving contact lenses.

Abstract: Successful contact lens wear is dependant on many factors including the tear film. Adequate quality and quantity of tears must be present to provide a stable, uniform coating over the contact lens making it a smooth optical surface, and to provide comfort and lubrication. Placing a contact lens on the eye disrupts the normal tear film dynamics and increases symptoms of dry eye. Dryness is one of the main factors leading to a decrease or discontinuation of contact lens wear. Contact lens induced dry eye (CLDE) is considered to be evaporative in nature although the exact mechanisms are not yet understood. Tear film interferometry is a non-invasive technique used to measure the thickness and thinning rate of the tear layer in front of the contact lens also known as the pre-lens tear film (PLTF). Using interferometry the thickness and thinning rate of the PLTF were collected and compared under evaporative (open air) and non-evaporative (closed chamber) conditions to determine the relation between PLTF thinning and CLDE, and the effect of evaporation on the tear film of dry eye (DE) and non-dry eye (NDE) subjects. One hundred and sixty-nine subjects (169) completed Part 1 of this study examining the relation between CLDE and rate of PLTF thinning. Forty (40) of the original 169 subjects returned for the second, Part 2, visit to investigate what amount evaporation contributes to PLTF thinning and symptoms of dry eye in contact lens (CL) wearers. No significant difference was found between the PLTF thinning rates of dry eye (DE) and non-dry eye (NDE) subjects in Part 1 of this study (Z = -0.13, p = 0.90). A significantly higher rate of PLTF thinning in DE subjects was found in Part 2 of this study (Z = -2.84, p 0.004). These inconsistent results may indicate high inter-subject variability. Under non-evaporative conditions, the average rate of PLTF thinning decreased greatly and there ceased to be a significant difference in PLTF thinning rates of DE and NDE subjects (Z = -0.90, p 0.93). This suggests that the majority of PLTF thinning is due to evaporation, and that evaporation may play a larger role in dry eye subjects than in non-dry eye subjects.

During the past several decades, a significant international research effort has been directed towards understanding the composition and regulation of the preocular tear film. This effort has been motivated by the recognition that the tear film plays a critical role in maintaining corneal and conjunctival integrity, protecting against microbial challenge and preserving visual acuity. In addition, research has been stimulated by the knowledge that alteration or deficiency of the tear film, which occurs in numerous individuals throughout the world, may lead to desiccation of the ocular surface, ulceration and perforation of the cornea, an increased incidence of infectious disease, and potentionally pronounced visual disability and blindness.

In this thoroughly revised and updated third edition of Contact Lens Practice, award-winning author, researcher and lecturer, Professor Nathan Efron, provides a comprehensive, evidence-based overview of the scientific foundation and clinical applications of contact lens fitting. The text has been refreshed by the inclusion of ten new authors – a mixture of scientists and clinicians, all of whom are at the cutting edge of their specialty. The chapters are highly illustrated in full colour and subject matter is presented in a clear and logical format to allow the reader to quickly hone in the desired information. Ideal for an optometrist, ophthalmologist, orthoptist, optician, student, or work in the industry, this book will serve as an essential companion and guide to current thinking and practice in the contact lens field. Highlights of this edition include a new chapter on myopia control contact lenses, as well are completely rewritten chapters, by new authors, on keratoconus, orthokeratology, soft and rigid lens measurement and history taking.