Scleral lenses may be a great option for patients when other contact lens modalities fail to provide adequate comfort or vision. However, residual astigmatism (RA) can pose challenges in environments that demand optimal vision.

A New Hobby Demands a New Lens

A 51-year-old male with a history of keratoconus and recurrent corneal erosions presented for a contact lens evaluation. He was fit with a soft toric contact lens OD after undergoing phototherapeutic keratectomy (PTK) and intracorneal ring segment surgeries to normalize and strengthen his corneal surface. The left eye was fit into a piggyback system. Recently, he started a new hobby of long-distance desert car racing; this prompted him to inquire about other lens modalities that would provide optimal vision and less lens ejection in this environment.

Possible Options Multiple contact lens options are available to optimize vision of patients who have irregular astigmatism. If corneal toricity or irregular astigmatism is mild, soft toric contact lenses may provide adequate vision. Corneal and scleral GP lenses are designed to mask corneal-induced astigmatism; however, despite this masking, RA can persist.

Large amounts of RA can limit contact lens options in patients who have more significant amounts of corneal toricity. If patients are willing to wear spectacles, a spherical GP lens with overlay spectacles that incorporate the RA can provide crisp vision without concern about a lens’ rotational stability.

If spectacles are not indicated, front-surface (F1) toric corneal or scleral GP lenses are the main alternatives. Because astigmatism correction is located on the front surface, rotational stability may be achieved with back-surface-toric haptics (for scleral lenses) or with prism ballast (for corneal GP contact lenses).

Before fitting an F1 toric contact lens, first incorporate the spherical equivalent and determine whether a patient benefits from a simpler spherical change in prescription.

Troubleshooting RA

Due to our patient’s off-road racing hobby, the possibilities for lens selection were limited by the desert dust and the patient’s helmet restrictions. He was interested in pursuing a scleral lens fit because racing conditions caused excessive movement of his corneal GP lens and dryness with his soft toric lens, leading to significant blur and discomfort while racing.

During the scleral lens fitting, we found a significant amount of RA in his left eye. After accounting for lens rotation and performing a spherocylindrical over-refraction (SCOR), –2.25DC was incorporated, and the patient reported very crisp vision. Unfortunately, he noticed bothersome, superimposed double images that differed significantly from the haloes and shadows that he normally experienced with his other lenses. The center thickness of the lens was changed to decrease the likelihood of lens flexure, and the lens material was changed; however, this higher-order visual phenomenon persisted. After re-evaluating the amount of RA in the SCOR, only –1.25DC was incorporated into the lens, resolving the visual phenomenon.

A patient’s hobbies may limit contact lens options for proper correction of irregular astigmatism, especially with significant amounts of RA. Precautions should be made when incorporating high amounts of cylindrical prescription into an F1 toric contact lens. As with a high-cylinder soft toric lens, rotational instability can cause significant visual blur. In addition, high-astigmatism F1 toric lenses may induce higher-order aberration-like phenomena.

Therefore, it is important to weigh the benefits and potential consequences of a high-cylinder F1 toric contact lens. It is also imperative that patients have reasonable expectations about the vision that they will achieve with an F1 toric GP lens. CLS