What is OrthoK?

OrthoK has been around for a long time, from around 1962 in fact which is when the first scientific journal paper on the topic was published. Back then practitioners found they could correct myopia (short-sightedness) by getting patients to wear progressively flatter rigid lenses manufactured in PMMA (Perspex) material. It was well known that wearing rigid lenses caused corneal distortion, …

Correcting astigmatism with OrthoK

When it comes to astigmatism, the research shows that approximately 40% of the initial astigmatism remains post treatment when using spherical OrthoK lenses.1 Following this research, -1.25DC is likely to end up at -0.50DC which, in most cases would be considered clinically acceptable. By the same conversion -1.50DC would give a predicted outcome of -0.60D, which, while not much different, is beginning to push …

What makes an OrthoK lens?

While there are variations across different OrthoK lens designs, there are some components that are shared across all designs. All myopic OrthoK lens designs have a back-surface optic base curve that is fitted flatter than corneal curvature, some form of reverse curve to bring the lens back into contact with the cornea, and peripheral alignment curves to provide a comfortable edge lift and tear …

What is the Jessen Factor?

George Jessen was the first to publish on OrthoK in his 1962 paper on Orthofocus Techniques that described the concept of using rigid PMMA to temporarily correct myopia, hyperopia and astigmatism.1 The concepts Jessen introduced evolved to the OrthoK designs and approach to fitting used today. It is the calculation of the base curve for an OrthoK lens described in this …

Sag based approach to lens fitting

Sagittal (sag) height describes the height of the cornea at a given point. If you imagined resting a completely flat surface onto the front of the eye there would be no gap between the flat surface and the cornea at the apex, as this is where it is resting on the eye. Move 2mm away from the apex though and …

Importance of good tear film when measuring corneal topography

Most corneal topographers in clinical practice use Placido disk image capture technology and typically come in two different versions: either bowl type like the Oculus Keratograph; or cone type like the Medmont E300. There are other approaches to measuring topography, like slit scanning (B&L Orbscan) and Scheimpflug (Oculus Pentacam) systems, each with their own differences in methodology but essentially, they …