Inventory set OrthoK systems

Inventory sets typically contain a large range of over 100 lenses that have different base curves and sag heights. The commonality across these designs is that changing the base curve alters the amount of refractive change made while changing sag height alters the fit. Make the base curve flatter to increase the myopic correction change. Increase the sag height and …

Trial set OrthoK systems

Relative to inventory systems, trial lens-based designs make a compromise in only containing a range of lenses with different sag heights to reduce the number of lenses to only around 25 that need to be stocked. In a sense this makes them synonymous with many rigid contact lens trial sets in that they provide just enough lenses for you to …

How corneal eccentricity impacts refractive change from OrthoK

In general, corneas with greater eccentricity offer greater potential for OK induced refractive change than more spherical corneas, which was shown quite nicely by John Mountford in his landmark paper published in 1997.1 John established a regression formula to associate induced refractive power change to change in corneal eccentricity that had a high correlation. He also stated that the endpoint of …

How cornea curvature influences outcomes from OrthoK

In a previous post, I covered how the degree of corneal eccentricity needs to be taken into consideration when evaluating the extent of refractive change can be achieved from Orthok in an eye. In this post, I am going to cover how corneal curvature also has its part to play. The generally accepted wisdom is that steeper corneas tend to …

How corneal toricity influences OrthoK lens fit

Before digging deeper into this topic, clarity is needed on the difference between corneal toricity and corneal astigmatism. When using the term toricity we are referring to the physical shape of the cornea and specifically how corneal curvature differs between the flat and steep meridians that are perpendicular to each other. In general, this will be the difference in curvature …

Initial lens fit patient interview

Having reached lens fit stage your patient is likely to already know the basics, but it is worth taking some time to reiterate what successful ongoing vision correction with OrthoK is going to require. That is continued ongoing overnight wear of lenses, with the lenses removed on waking, properly cleaned and stored during the day so that they are ready for wear …

OrthoK lens selection at initial fit

By now you will have your patient’s spectacle prescription to hand, measured their corneal topography and have conducted an anterior eye exam to make sure it is safe to proceed, assuming of course that you have already recently assessed the rest of their eye health to ensure that all other parts of their visual system are healthy and in good …

Improving accuracy of first fit selection

This is where we turn to the multiple topography maps that in an earlier post I suggested you capture, because through averaging we can obtain a more reliable measure and remove potentially poorly captured maps. Hopefully your corneal topography software will do this for you, otherwise, it is not too hard to work out by adding up the individual K values …

Teaching OrthoK lens insertion

The approach here is much the same as for standard rigid lenses, which is to place the lens directly on the cornea in whichever manner the patient feels comfortable and is most proficient. You also need to demonstrate how to handle a lens that doesn’t end up where intended and displaces onto the conjunctiva, and before leaving your office your …