Article

PRESCRIBING FOR ASTIGMATISM

CUSTOM SOFT SUCCESS

Awareness of contact lens technology is building among our patients. It’s not just irregular corneas either; I have also seen growth in the number of patients who have normal corneas and are also seeking better comfort and vision from their lenses. One of my favorite, but perhaps under-utilized, tools are custom soft lenses. With custom soft lenses, practitioners can better fit their patients who have larger and smaller cornea sizes, custom multifocals, high astigmatism, and more, all while allowing patients to stay in a modality that they are comfortable handling and wearing. One reason for using a custom soft lens is for patients who have any amount of astigmatism and are also frustrated with their vision consistency in their standard soft lenses.

Patient Concerns

Patients may comment on “constantly having to spin their lenses” to find good vision. Or, they may comment about their contact lenses being only “marginally comfortable or hard to remove.” All of these patient concerns are good reasons to consider custom soft lenses for a patient who has astigmatism.

Vision Fluctuation If patients complain about vision fluctuation and their vision changes with every blink, it’s highly likely that their current soft lens is not fitting properly and that their cornea is outside of the normal bell-curve in terms of sagittal depth and corneal diameter.

Looking carefully, practitioners may find that the lens does not have adequate drape past the limbus. It also simply does not have enough ocular surface on which to rest, which leads to rotational instability. Note: the issue is not the power nor the prism, it is the lens diameter. A slightly larger lens size, such as 14.8mm or 15.0mm, can solve many concerns about vision fluctuation.

On the other hand, vision can fluctuate from a lens that is too large or too deep. These patients will also comment that their standard soft lenses are hard to remove. Many instruments, such as a topographer, can accurately measure corneal diameter, which can be sent to a lens consultant to select a custom diameter. Because the lens is more appropriate to the cornea size, patients will also notice improved comfort.

Lens Rotation When the surface of the cornea is moderately to highly toric, sometimes even a custom soft lens can rotate with the blink. If the lens diameter appears appropriate, another adjustment that can be made is to add additional prism to the ballasting design of the lens. Sometimes, a small amount of additional base-down prism is just enough weight to bring the optics into place and keep them there during the patient’s wearing time.

Lens Power For normal corneas that have astigmatic refractive error, we can use the manifest refraction to help us determine lens power as we make our design adjustments. Consider holding off on changing lens power significantly until you are satisfied with the appearance of the lens on the eye, as a good fit should provide good vision! A member of your laboratory’s consulting team can help you make adjustments, too.

Summary

While there is a lot of talk about using sclerals for normal corneas that have high refractive error, we shouldn’t forget about the benefits that custom soft contact lenses can bring to the table, especially for astigmats. These lenses require less chair time and are less expensive. They also dictate a planned replacement schedule, which encourages patients to have back-up pairs. This simple prescribing tool is a great way to connect with patients and demonstrate the value of our skill. CLS