A recent reflection revealed how we tend to shift our specialties into segments. As advancements happen, it seems that each segment gets better opportunities to improve care for our patients, and practices keep improving as well. When we know what options are available, possibilities then exist that allow us to make things better for our patients.
Standard One segment to consider is orthokeratology lenses. Some of these are standard lens designs. These lenses are fit based on K readings, refraction, and in some cases based on patients’ horizontal visible iris diameter (HVID). Eyecare practitioners either use a calculator to determine what lens to place on the eye from a fitting set or simply empirically order the first set of lenses. In one study, this was shown to be successful, with 80.5% of the first lenses ordered being the final lens for those patients (Davis et al, 2015). That is very successful indeed, if you ask me.
Some Adjustments In some cases, patients have some corneal elevation differences. This is usually because of corneal toricity, especially closer to the peripheral cornea. In these cases, a more complex lens fit is warranted. Most likely, the lens would include toric curvatures—not to correct power, but rather to get a uniform treatment zone by sealing the lens 360º.
Over the last several years, my fitting has become more refined. I now fit more than 40% of my orthokeratology patients in lenses that have toricity.
Custom Additionally, we have lenses that are custom created. While they can go by various names, most would call these “free-form lenses.” Free-form lenses require corneal mapping, usually with a topographer, and the back surface of the resulting lens most closely matches the shape of the cornea. These lenses are certainly the most customized, allowing for the most precise type of fitting, and some may choose to use them for more complex prescriptions or for corneal irregularities.
I have seen a similar trend happening in the scleral lens arena. Some of our best scleral lens educators continue to encourage me in my fitting techniques. In addition, as I speak to lab partners, scleral designs seem to keep getting more refined. In brief, we again have three levels of scleral lens fitting.
Standard Standard scleral lenses are fit from a fitting set. Eyecare practitioners measure the eye, but the fit is usually refined mostly by placing a lens on the eye and then making modifications based on what they see.
Some Adjustments Next, we have lenses that are fit based on corneal/scleral mapping of some sort. The goal of this fitting technique is to design a lens that most closely matches the shape of the eye based on instrumentation.
Custom Finally, we have ultra-customized lenses that come in two modes: 1) Scleral lenses based on impression patterns; and 2) Scleral lenses that have refined power surfaces to negate visual aberrations. Both types of scleral lenses require advanced knowledge and fitting methods, but both allow for the best of vision and comfort.
I always advocate for practitioners to become comfortable with their everyday options. Doing so encourages us to know how best to use the tools, but sometimes we need more. While you may only use advanced approaches on occasion, I strongly encourage you to become familiar with other fitting modalities so that you can best help patients by either fitting them yourself in a more customized lens or by sending them to a colleague who uses customized approaches more frequently. CLS
For references, please visit www.clspectrum.com/references and click on document #315.