No two eyes are the same. Moreover, no two scleras are the same, even in the same patient. Many studies have shown that the sclera is asymmetric and that its shape is toric (Consejo et al, 2018; van der Worp et al, 2010). Studies have also shown that toric peripheral curves can improve scleral lens comfort (Visser et al, 2006; Visser et al, 2013). However, the question remains as to when to prescribe a spherical scleral lens (spherical periphery) or one with a toric haptic (toric peripheral curves).
Keep It Simple
The sclera changes shape farther away from the limbus. Thus, smaller-diameter lenses may fall within the area of the sclera that is not toric and does not warrant a toric fit. If the fit is adequate and patients are not experiencing complications, a spherical periphery will be just fine.
Look for Signs
A well-fitting scleral lens adequately clears the cornea. Beyond the limbus, the landing zone should be “clean” and free of compression in the midperiphery, meaning that there should be no evidence of blanching. The edge of the lens should align with the sclera and be free of blood vessel impingement. Conversely, edge lift, in which there is a gap between the edge of the lens and the surface of the sclera, should be avoided. If any blanching or edge lift is observed, it can be helpful to switch to a toric peripheral curve.
If there is a need to improve visual acuity with front-surface toric optics, a toric peripheral curve will help stabilize the scleral lens and, likewise, the visual acuity.
Let Symptoms Be Your Guide
Toric peripheral curves often respect one meridian (e.g., along the 180th or 90th meridian/axis). A toric peripheral curve can help improve patient comfort and minimize common symptoms with scleral lens wear. For example, edge lift can result in lens awareness that will cause discomfort or can even lead to scleral lens intolerance. Edge lift may also allow for bubble intrusion. In this case, a toric peripheral curve can bring down the lens edge to better match the profile of the sclera.
Blanching or vessel impingement can be symptomatic or asymptomatic. In patients who are symptomatic, it is common for them to complain of a dull ache with the lens in place or after removal. In this case, switching to a toric peripheral curve can minimize these symptoms and improve long-term success.
Lastly, the fluid reservoir can become cloudy because of debris buildup. While not always successful, toric peripheral curves can minimize debris entrapment and increase patient satisfaction.
How Much Is Enough?
The most challenging part of designing a toric peripheral curve is to determine how much of a change will be enough to achieve the desired results. While there are no studies to support an exact amount, clinically, I have found that a change of ≥ 100 microns is a good start. If practitioners start with less than that, they will not note a change in the fitting relationship.
The most helpful advice is to become comfortable with a few scleral lens designs and to befriend the manufacturing labs, as the labs’ consultants are the best resource in the fitting process. CLS
For references, please visit www.clspectrum.com/references and click on document #278.