This article was originally published in a sponsored newsletter.

Approximately 28% of contact lenses prescribed globally correct for astigmatism. This percentage has increased since the beginning of the century, likely due to improved availability of toric lens parameters, enhanced lens quality and reproducibility, and practitioners’ increased confidence.¹However, the full amount of astigmatism is not always prescribed when fitting soft toric contact lenses, unlike other types of refractive correction such as spectacles, refractive surgery, or intraocular lenses. Soft toric contact lenses can correct astigmatism in most instances, but may be an expensive option when using daily disposables. For a more cost-effective option for low-to-moderate astigmatism, a spherical contact lens is fit with the spherical equivalent power of the manifest refraction. However, fitting a spherical equivalent lens has reduced visual acuity.

A single-blind study evaluated if full astigmatism correction with soft toric contact lenses in individuals who had low-to-moderate astigmatism offered a significant improvement in visual performance compared to spherical contact lens prescriptions.² The contact lenses used in this study were Precision 1 and Precision 1 for Astigmatism (Alcon Laboratories, Inc, Fort Worth, TX; 49% verofilcon A, 51% water; ø = 14.2mm; Base Curve = 8.3mm). 

The study divided 56 neophyte contact lens wearers into two fitting groups (toric and spherical) of 28 subjects each. Patients in both groups were an average age of 22 years old. The spherical group included 12 males and 16 females, and the mean power of spherical contact lens correction was –2.7 ± 0.9D. The toric group included 10 males and 18 females. The mean power of spherical contact lens correction was –2.3 ± 1.3D and the mean power of cylindrical contact lens correction was –1.0 ± 0.4D. To avoid potential bias, subjects were randomly selected for each group and were not notified about the type of contact lens correction.

Visual performance was evaluated using standard visual acuity and contrast sensitivity tests. Additionally, subjects were evaluated on new functional tests simulating everyday tasks. They had to compose an e-mail to a specified address and include three attachments from a populated desktop screen. For the reading test, subjects read two paragraphs of 92 and 97 words divided into six lines on a screen. Reading performance parameters including time, number and duration of fixations, number and ratio of regressions, and magnitude of saccades were recorded using an eye tracking device. In the level test, subjects poured 50mL of blue water from a graduated test tube into a different graduated test tube to the specified level of 35mL. In the lock test, patients used a key to open a lock box. They then placed a bolt in the box and drew a mark on the bolt.

The results demonstrated that subjects with toric lenses had significantly better visual acuity and contrast sensitivity compared to spherical lens wearers, though the functional tests did not demonstrate significant differences between groups. The authors proposed that this finding was based on several factors: the visual demand of the functional tests, the dynamic blur due to misalignments, and small differences between the available and measured axes of the astigmatic contact lens.

A key learning from this study is that soft toric daily disposable contact lenses provide better optical and visual quality, which is especially important for precision tasks, compared to correcting only the spherical equivalent in daily contact lens wearers who have low-to-moderate astigmatism.

REFERENCES

1. Morgan PB, Woods CA, Tranoudis IG, et al. International Contact Lens Prescribing in 2022. Contact Lens Spectrum.January 1, 2023. Available at https://www.clspectrum.com/issues/2023/january-2023/international-contact-lens-prescribing-in-2022. Accessed July 17, 2023.

2. Gil P, Farcas A, Benito A, Tabernero J. Functional visual tests to evaluate the effect of small astigmatism correction with toric contact lenses. Biomed Opt Express. 2023 Jun;14:2811-2820. 

Melissa Barnett, OD, FAAO, FSLS, is the director of optometry at the University of California, Davis in Davis, specializing in anterior segment disease and specialty contact lenses. She is the past president of the Scleral Lens Education Society. She is an advisor to and/or has received honoraria or travel expenses from AccuLens, Alcon, Allergan, Bausch + Lomb, Bruder, Contamac, CooperVision, Johnson & Johnson Vision, Ocusoft, ScienceBased Health, Shire, Tarsus, and Visus Therapeutics.