In this chapter you will learn how OK has evolved from fitting PMMA contact lenses as an attempt to alter corneal shape, to correcting refractive error into modern reverse geometry designs that provide accelerated effect during overnight wear. Types of OK lens design are covered alongside who you should and should not fit with OK.

OK lenses correct refractive error by temporarily altering corneal topography, which makes measuring and analyzing corneal topography an important skill for you to master. In this chapter you will learn how corneal topography works; tips to capture the best quality topography image; and how to analyze topography maps.

This chapter builds on the first two chapters to understand how baseline corneal topography and refractive error influence lens fit, and the limits of correction that can be achieved from OK. You will then learn the steps to follow to select a first lens, its dispensing and instructions to provide your patient for their first night of lens wear.

The response from the first night of lens wear can be variable, making the first follow-up visit more about ensuring your patient is proficient in lens handling than assessing lens fit and refraction outcomes. In this chapter you will learn what to expect and how to manage the different presentations, and how to manage shortfall in refraction correction while the OK effect improves over the next few days of lens wear.

By one week of wear the full OK effect is expected, requiring you to understand the topography map patterns that represent different lens fit outcomes. Each map type is analysed in detail in this chapter, including description of the map characteristics that define each pattern type and advice on how to modify lens fit to improve fit and refraction outcomes.

With your patient now established in OK, your attention shifts to long term management. In this chapter you will learn when your patient should return for follow-up appointments, and the procedure to follow at these visits to maintain long term success from OK lens wear, alongside maximizing safety and ensuring continued good eye health.