Contact Lens Complications E-Book

Nathan Efron

• Publisher: Elsevier
• Year: 2018
• ISBN:
  9780702078828
• Edition: 4
• Topic: Medizin
• Subtopic: Augenheilkunde & Optometrie

In this thoroughly updated fourth edition, award-winning contact lens author, lecturer, and researcher, Professor Nathan Efron, presents an easily accessible, systematic account of how to identify, understand, and manage contact lens complications. Professor Efron is renowned for his ability to distil often-complex principles of ocular physiology and pathology into a clinically-friendly format. The subject matter is arranged logically by tissue structure – which is the way practitioners naturally approach clinical problems. Beautifully presented and lavishly illustrated with full-color schematic diagrams and clinical pictures, this book can serve as both a practical chair-side manual and authoritative reference.

• Thoroughly revised, capturing the latest advances and concepts in contact lens related ocular pathology.
• Updated 'Complications quick-find index' at the beginning of the book, constituting a valuable practitioner aid to formulating a rapid diagnosis and treatment plan, and serving students as a useful examination study aid.
• Incorporates findings from the Dry Eye Workshop II (DEWS II) and the International Workshops on Meibomian Gland Dysfunction and Contact Lens Discomfort.
• Two new chapters – "Lid Wiper Epitheliopathy" and "Lid-Parallel Conjunctival Folds."
• Over 1, 500 references cited as the basis of a thorough evidence-based approach.
• 60 superb new clinical pictures and schematic diagrams, making over 650 in total.
• Grading scales for 16 contact lens complications, making this the most comprehensive and widely-used grading system available today.
• Grading morphs computer program as a computer-based aid to assessing condition severity.
• Self-help grading tutor computer program to help you hone your grading skills.
• Pictorial tear film classification system.

Part 1

Examination and Grading

1

Anterior Eye Examination

Abstract

Investigation of contact lens complications requires careful examination of the anterior eye. The slit lamp biomicroscope is the primary instrument used for examining the anterior ocular structures, and a variety of illumination and observation techniques can be employed. A number of specialised instruments are available to supplement slit lamp examination. These include anterior eye optical coherence tomography, laser-scanning confocal microscopy, corneal topography, specular microscopy, pachometry and corneal aesthesiometry.

Keywords

Slit lamp biomicroscopy; anterior eye optical coherence tomography; laser-scanning confocal microscopy; corneal topography; specular microscopy; pachometry; corneal aesthesiometry

The slit lamp biomicroscope has been the primary instrument for examining the anterior ocular structures since its invention in the early part of the 20th century. In particular, this versatile instrument is invaluable in assessing the effect of contact lens wear on the tear film, cornea, conjunctiva and eyelids. Other simple 20th century optical instruments which were developed to aid contact lens fitting, such as the Burton lamp, or to enhance our ability to assess the tear film, such as the Tearscope, are still in common use today.

As a result of developments in digital electronics, optical technology, still and video capture imaging and computer-assisted image-analysis techniques, a range of sophisticated ophthalmic instruments have been developed over the past two decades and have expanded our capacity to examine the anterior eye. Such instruments that have been demonstrated to have considerable utility in this regard are the specular microscope, corneal confocal microscope, optical coherence tomographer, corneal topographer, pachometer and aesthesiometer. These devices provide valuable capability that supplements visual examination using slit lamp biomicroscopy.

The aim of this chapter is to review the various instruments that are now available to facilitate examination of the anterior eye and determination of anterior ocular dimensions and which have been used to capture the majority of images presented in this book. Primary attention is given to the slit lamp biomicroscope, as this technique has always been, and is likely to remain, the mainstay of ocular examination in contact lens practice.

Burton lamp

A number of manufacturers make a special hand-held magnifying device for contact lens work. This device is usually referred to as the ‘Burton lamp’, after the company that manufactured the original version (Burton Manufacturing Co., Chicago, Illinois, USA). The Burton lamp is essentially a large magnifying lens of about + 5.00 diopters (D) housed in a broad frame, within which is mounted a combination of 4 watts (W) white light and ultraviolet light fluorescent tubes, each 11 cm long. The operator can switch between the two light sources for white light and fluorescein stain examinations. A key advantage of this instrument is that both eyes of the patient can be viewed simultaneously, facilitating inter-ocular comparisons in the course of contact lens fitting. The Burton lamp is also useful for conducting an initial screening examination (Fig. 1.1).

Fig. 1.1 Burton lamp being used in ‘white light mode’. (Courtesy Lyndon Jones.)

The main disadvantage of the Burton lamp is that it is not possible to view fluorescein fitting patterns of rigid contact lenses made of material containing ultraviolet absorbing properties. This is because the Burton lamp has its highest emission in the 300 to 400 nm range, and this short-wavelength blue light is attenuated by the lens material, resulting in decreased fluorescence.

Slit lamp biomicroscope

The slit lamp biomicroscope (Fig. 1.2) is a combined illumination and observation system that allows the eye to be examined from close distance at different magnifications. With the appropriate application of supplementary lenses and/or viewing techniques, the instrument may be used to assess the condition of the vitreous, lens and retina from the posterior pole to the ora serrata. Various ancillary instruments that enable examination of the tear film, anterior chamber angle and retina and measurement of intra-ocular pressure, corneal sensitivity and corneal thickness can be attached. Since this book is concerned with the assessment of ocular complications of contact lens wear, the discussion that follows will relate primarily to the use of the slit lamp biomicroscope in examining the anterior ocular structures.

Fig. 1.2 Slit lamp biomicroscope.

It has long been recognised that it is not possible to sensibly prescribe and fit contact lenses, or provide ongoing care to contact lens patients, without access to a slit lamp biomicroscope.¹ This instrument is used virtually every time a contact lens patient is seen, including during the initial examination, fitting and aftercare visits. Certainly, the vast majority of complications of contact lens wear cannot be detected or assessed without the aid of a slit lamp biomicroscope. It is therefore imperative that contact lens practitioners have access to this instrument and are well versed in its operation.

This section will outline the design and construction of the slit lamp biomicroscope, review key techniques of ocular illumination and examination inasmuch as they relate to contact lens practice and suggest a recommended examination procedure.

General construct

The general construct of a slit lamp biomicroscope is indicated by its name; that is, there is a separate illumination system (the slit lamp) and a viewing system (the biomicroscope). These two components are mechanically linked (Fig. 1.3) so as to create a common focal point and centre of rotation; however, the mechanical linkage can be unlocked to allow the focal illumination to be directed away from the focal point of the viewing system, and this is an essential requirement for some observation techniques, such as ‘sclerotic scatter’ (see later). The mechanically linked illumination and observation systems are always moved simultaneously – up and down with a height control, and focusing (in and out) and lateral (side to side) movements with a joystick. This linked control system facilitates rapid and accurate positioning of the slit bea...