Rotational stability of scleral lenses allows for reliable incorporation of front-surface toricity, which can help optimize visual acuity, especially for patients who have reduced visual quality due to corneal irregularity. Stabilization can be achieved with toric peripheral curves and with prism ballast. Front-surface toricity can be incorporated at many stages in the fitting process: upon initial order after diagnostic lens fitting, after establishing rotational stability, or at the end.

Starting with Toric Peripheral Landing Zones

Many diagnostic fitting sets incorporate a standard amount of toricity in the peripheral landing zone (LZ), with distinct curvatures along two perpendicular meridians. One meridian serves as the “flat” meridian and the other as the “steep.” Once applied to the eye, a lens should rotate in place so that the flat meridian of the haptic aligns with the flatter portion of the sclera. Likewise, the steep meridian of the LZ should align with the steeper portion of the sclera. This makes it convenient to evaluate the alignment of the lens to the conjunctiva in two perpendicular meridians (flat versus steep).

Commonly, the flat meridian is denoted by laser markings, which can appear in the form of a hash mark(s) or an “o.” These toric markings allow for an accurate assessment of the overall lens rotation, which is crucial for determining the axis of the toricity to be applied to the front surface of the lens.

It is imperative to allow a toric LZ lens to settle for 10 to 20 minutes to account for lens rotation prior to performing a sphero-cylindrical over-refraction (SCOR). After settling, take note of the location of the toric markings on the lens surface. Providing the lens consultant with a description of the location of these markings (e.g., rotated 30º clockwise from the horizontal plane or toric markings at 4 o’clock) will allow for an accurate calculation of any oblique cross-cylindrical effects when combined with the results of a SCOR performed over the diagnostic lens.

Starting with Spherical Peripheral LZs

If the diagnostic set does not include toricity in the peripheral LZ, it will be difficult to ascertain the degree of lens rotation. Therefore, ordering a lens with astigmatic correction prior to incorporation of a toric peripheral LZ is not recommended because any amount of rotational instability can greatly affect vision. With the initial evaluation of the spherical LZ diagnostic lens, clinical judgement can assist in determining the amount of LZ toricity that is needed prior to incorporating astigmatic correction.

Once the toric LZ lens is received, allow the lens to settle, take note of the lens rotation, and perform a SCOR. Then, provide the laboratory consultant with values of lens rotation in degrees and the full SCOR for the final lens order. The consultant will calculate the new prescription that takes the lens rotation into account to optimize vision for the patient.

Conclusion

Incorporating front-surface toricity to correct residual astigmatism is a useful tool in scleral lens fittings that can help improve visual acuity for patients who have corneal irregularity. Therefore, it is important to understand the most efficient and effective ways to utilize peripheral toric LZs in front-surface toric scleral lens fittings to optimize visual potential. CLS