A 36-year-old female came to our office for the first time. She was wearing spherical monthly replacement lenses that were –3.00D in both eyes. An autorefraction performed over the contact lenses resulted in a reading of OD plano –0.75 x 170 and OS +0.25 –0.75 x 010. Her vision with the contact lenses was OD 20/25-, OS 20/25+, and OU 20/20-2. An over-refraction was performed that resulted in the following findings: OD +0.25 –0.75 x 170, 20/20 and OS plano –1.00 x 010, 20/20.
Why Is Astigmatism Uncorrected?
There was a philosophy previously in which eyecare practitioners (ECPs) would fit patients who had low levels of astigmatism by prescribing lenses that were the patients’ spherical equivalent of their sphero-cylindrical refraction. In an era of toric contact lenses with poor stability, this made clinical sense. With contemporary toric lens options, ECPs can fit even low levels of astigmatism reliably and comfortably because of the stability and reproducibility of these designs. But at what level should astigmatism begin to be corrected in a contact lens prescription?
Our office starts to question the need for astigmatism correction at vertexed astigmatism levels of –0.50D. As we are refining cylinder power with the Jackson cross cylinder (JCC), there is a very subtle difference in subjectivity that will determine the final power. If patients don’t get to a level of equivalence in response to the JCC and they transition between two astigmatic powers, clinically we will finalize the cylinder power that is lower. Patients whose final refractive astigmatism is recorded at –0.50D may have been altering responses between –0.50D and –0.75D during the JCC power assessment of the refraction process. As such, their refractive astigmatism is likely between these two powers. Because the power is so close to –0.75D, we will often place contact lenses on the patients’ eyes with just the spherical power. Then, we’ll hold –0.75D of cylinder with loose lenses at the appropriate axis in front of them to determine whether they prefer the vision with the astigmatic correction or without it. If they prefer the vision with the astigmatism correction, we will then fit them with the appropriate toric lenses.
GP lenses provide a logical solution for correcting corneal astigmatism through the creation of a tear lens between the posterior surface of the lens and the cornea. Hybrid lenses provide a similar benefit with the advantage of a soft skirt to help achieve a wearing experience more similar to soft lenses.
An understanding of scleral shape helps ECPs realize that a majority of patients do not necessarily require a spherical landing zone, but rather a toric or other asymmetric design. This type of landing zone stabilizes the lens on the eye, allowing astigmatism correction to be placed in the lens and correcting the vision to higher levels of precision.
Additionally, to correct a presbyope’s astigmatism, we often initially think of GP or hybrid designs, but there are also specialty soft multifocal lens options. This year, expect to see more readily available soft toric multifocal technologies.
With so many options to correct astigmatism successfully, it is incumbent upon ECPs to provide patients with the best vision options. If not correcting astigmatism is the new norm, we don’t want to be normal. CLS