The sclera is commonly referred to as non-rotationally symmetric in the setting of scleral lenses (van der Worp, 2010). That makes sense. However, sometimes putting those words into action can be lost in translation.
According to the Merriam-Webster Dictionary, rotation is defined as rotating around an axis or center. And, according to that definition and taking into account that the sclera has highs and lows, the sclera can indeed be considered non-rotationally symmetric. It may also help to think of fitting the sclera as trying to fit a baseball sometimes or a football at other times. But, how do practitioners actually fit those shapes, and what can be done to impact the outcome of a fit?
Toric Peripheral Curves
Well, when needed, a toric peripheral curve can help. In my last column, I talked about basic principles of toric peripheral curves; now, let’s delve deeper.
The landing zone (LZ) is the section of the scleral lens that rests and/or supports the lens on the eye (Fadel and Barnett, 2017). It is within this zone that practitioners need to focus for problems that may require toric peripheral curves. Simply put: It is not just about the edge!
Signs of Blanching
With a spherical scleral lens on the eye, a toric sclera will likely demonstrate blood vessel blanching or compression at the lens edge and/or sometimes as a band of blanching 1mm or more from the edge (Figure 1).
Second, although not proven, these areas of blanching tend to occur in quadrants (usually two to three clock hours) and linearly or respecting a meridian. For example, if you see blanching at 12 o’clock, look at the area 180º away. Conversely, if you see edge lift in one area, look 180º away. This can help with troubleshooting when communicating with your lab.
The next problem is vessel blanching or compression within the LZ, away from the edge and toward the limbus. While there is not a standard term for this, it is commonly called a “heel” landing or mid-haptic compression (Figure 2).
Looking for these areas and differentiating this presentation from edge problems can be helpful during the fitting process when communicating with your lab. Also, note that these compression areas occur in only one quadrant. In each of these cases, lens settling can add to this phenomenon. Therefore, it is ideal to let the lens settle on the eye before looking for these problem areas.
Finally, if feasible, technology can be your friend. New scleral topographers on the market can be integrated with proprietary designs, and this can further aid eyecare practitioners in obtaining a successful scleral fit. CLS
For references, please visit www.clspectrum.com/references and click on document #281.