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Soft Lens Measurement

Introduction The vast majority of soft contact lenses are today mass produced by a double-sided moulding process (see Chapter 5 ). Using such a method of manufacture ensures relatively consistent quality, eliminating the need to measure every lens that comes out of production. This standardization also makes it easier for manufacturers to meet regulatory requirements and for practitioners and patients to have confidence that every lens…

Soft Lens Optics

Introduction Single-vision soft contact lenses have a number of optically attractive features. They centre well on the cornea with only small amounts of lateral movement and hence introduce little additional asymmetric aberration into the lens–eye system. The diameter of their optic zone normally exceeds that of the entrance pupil of the eye under all lighting conditions; thus the ‘haloes’ around light sources that are observed at…

Soft Lens Manufacture

Introduction Three techniques are currently employed to manufacture soft contact lenses – lathe cutting, spin casting and cast moulding. A fourth disruptive technology, three-dimensional (3-D) printing, has also been proposed, but 3-D-printed soft contact lenses have yet to be produced commercially. As medical devices that rest against the highly sensitive eyeball, contact lenses need to be of the highest quality in terms of their physical construction.…

Soft Lens Materials

Introduction Soft contact lenses have had a massive impact on the global contact lens market since they became widely available in the early 1970s. Since their introduction, the number of soft contact lenses being prescribed around the world has steadily increased, and it is mainly the sale of soft contact lenses that is responsible for an industry that has been estimated to reach US$10 billion globally…

Visual Optics

Introduction The human eye is a remarkable optical instrument ( ). Its performance has been honed by millennia of evolution to meet admirably the needs of the neural system that it serves. At its best, few human-engineered photographic lens systems can match its semifield of more than 90 degrees, its range of f -numbers from about f /11 to better than f /3 and its near-diffraction-limited…

Anterior Eye

Introduction A critical aspect of contact lens practice is monitoring the ocular response to lens wear, which ranges from acceptable physiological changes to adverse pathology. To do this, practitioners must possess a thorough understanding of the normal structure and function of the anterior eye, which is the subject of this chapter. In the course of reading other chapters in this book, the reader may need to…

History

Introduction We cannot continue these brilliant successes in the future, unless we continue to learn from the past . Calvin Coolidge, inaugural US presidential address, 1923 Coolidge was referring to the successes of a nation, but his sentiment could apply to any field of endeavour, including contact lens practice. As we continue to ride on the crest of a huge wave of exciting developments in the…

IER Grading Scales: Vision Cooperative Research Centre, Institute for Eye Research, University of New South Wales

Application of Grading Scales Patient management is based on how much the normal ocular appearance has changed. In general, a rating of slight (grade 2) or less is considered within normal limits for a population (except staining). A change of one grade or more at follow-up visits is considered clinically significant. 1. VERY SLIGHT 2. SLIGHT 3. MODERATE 4. SEVERE BULBAR REDNESS LIMBAL REDNESS LID REDNESS…

Addendum

Chapter 2 – Materials Nature of polymers Perhaps the best way of visualising the way in which polymer chains arrange themselves is by taking several pieces of string to represent individual molecules. The usual arrangement is random, with the pieces of string loosely entangled rather than being extended. The interaction and entanglement of the individual molecules in this way gives polymers their characteristic physical properties. By…

History

The History of Contact Lenses Timothy Bowden Jacqueline Lamb Impression Materials Josef Dallos was the first to successfully take an impression of a living eye and use this mould to make a cast and from that cast make a lens. He was visited by many ophthalmologists and practitioners from around the world, one of whom was Theodore Obrig in 1935, who started using started using Negocoll to produce…

Modification Procedures

The Importance of the Practitioner Being Able to Carry Out Modifications Nowadays, when modifications can be carried out relatively quickly and cheaply by laboratories, it is often difficult to impress on students, and even qualified practitioners, the following reasons why contact lens practitioners should be able to carry out their own modifications: ▪ There is no interruption to the patient's wearing schedule or necessity for extra…

Setting Up a Research Project

There are several advantages to undertaking research in everyday practice rather than in an academic setting. The depth of experience of a full-time practitioner may be more attuned to clinical trends that deserve further investigation. Patients in a normal contact lens practice may be more representative of the real world and better motivated towards participating in a given study. Also, a comprehensive practice database can provide…

Legal Issues and Contact Lenses

This chapter will endeavour to cover the legal aspects of fitting and prescribing contact lenses. To do this, an explanation of the tort of negligence (malpractice) is required with recent precedent case law. This is the basis of most claims that are ‘negligence-based’. Examples of the law in its application are given to emphasise certain contact modalities. It is important for practitioners to understand the process…

Contact Lens Standards

Introduction to Standards A standard is a technical specification or other document which is available to the public. Such standards are drawn up with the cooperation and consensus or general approval of all interested parties affected by it. Standards should be based on the consolidated results of science, technology and experience and aimed at the promotion of optimum community benefits and approved by a body recognised…

Contact Lens Manufacturing

This chapter will discuss manufacturing options for producing both soft and rigid gas permeable (RGP) contact lenses, dispensed as either disposable or durable products. Disposable lenses were originally designed to be used for up to 1 month and now as daily, 2-weekly or monthly replacement. ‘Durable’ refers to lenses that are designed to last more than 1 month, typically for quarterly or annual replacement. Contact lens…

Contact Lens Correction and Myopia Progression

This chapter gives a review of the literature which provides evidence that myopia control can be effective and beneficial. Clinical practice can be found on p. 502 of this chapter and in Chapter 19 . Contact lenses have been an effective method of correction for myopia for many decades during which time the prevalence of myopia has increased markedly and reflects the worldwide increase evident in…

Special Types of Contact Lenses and Their Uses

Special types of contact lens not covered elsewhere in this book are described in this chapter. Lenses to Aid Diagnosis and Surgery Various special contact lenses have been developed to assist observation of the eye in diagnosing eye disease. Contact lenses for corneal observation When carrying out specular reflection to examine the corneal endothelium using the slit-lamp biomicroscope, the bright reflection from the tear film is…

Therapeutic Contact Lenses

Introduction Contact lenses can be used for therapeutic purposes to manage a wide range of ocular conditions. When so fitted, they are referred to as therapeutic contact lenses (TCLs) or bandage lenses. TCLs are fitted mainly to protect or promote healing of the cornea, as well as to provide relief from pain and discomfort. They can range from daily disposable lenses to specialist lenses such as…

Cosmetic and Prosthetic Contact Lenses

Introduction In this chapter, coloured contact lenses are differentiated into cosmetic lenses, i.e. tinted contact lenses that simply change the colour of the eyes, and prosthetic lenses, i.e. lenses that change the appearance of an unsightly eye, although the term ‘cosmetic lenses’ is often used for the latter purpose. The fact that contact lenses can provide benefits other than visual is often overlooked, and their ability…