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Truth or myth: There is no patient benefit to correcting low astigmatism with soft contact lenses

Contact lenses
This month, in our series looking at common myths concerning contact lenses, Dr Jaya Dantam and Quan Wei Ng look at correcting low astigmats

It is not uncommon to fit patients with low amounts of astigmatism with soft contact lenses (CLs). The prevalence of low astigmatism, defined as ≤0.75D, has been reported to be 47.4% in at least one eye versus 24.1% in both eyes.1 Should patients with low amounts of astigmatism be fitted with soft toric CL, or will soft spherical lenses suffice?

First approved by the FDA in 1976, early soft toric CLs had challenges with consistent quality of vision, comfort and reproducibility. The improved quality and reliability of soft toric CLs has since markedly increased, and they have gradually gained acceptance among eye care professionals (ECPs).

In the most recent International Contact Lens Prescribing report (2022), soft toric CLs account for about 28% of all contemporary soft CL fits.2 Despite the evidence, it is not uncommon to come across erroneous and long-held beliefs that thick spherical soft CLs can mask low levels of astigmatism and aspheric lens designs can improve visual outcomes in patients with astigmatism.

 

Professional belief survey results

A recent survey of 1,028 ECPs conducted in 2021 in Russia and in 2022 for the other markets, assessed the prescribing beliefs of ECPs in all six countries. It revealed that, on average, about half of the ECPs surveyed (48%) across all markets preferred to fit a spherical soft CL in patients with 0.75D of astigmatism (figure 1).3

This agrees with the perceived belief that there is no benefit to fully correcting low levels of astigmatism with soft toric CLs. Furthermore, 35% of ECPs also expressed that they routinely under-correct the cylindrical amount with soft toric CLs due to concerns with lens stability.3

 

What the evidence shows

Not correcting 1.00D of astigmatism has been shown to significantly decrease both distance and near acuity, and adversely affect reading speed, reading fluency and stereo acuity.4-6 In addition, this under-correction can also lead to headaches and reduced visual comfort while using digital devices7 and increased symptoms of ocular discomfort, including dry eye.7 Ultimately, the dissatisfaction arising from poor vision may result in CL dropout.8

More importantly, clinical studies have demonstrated that spherical soft CLs cannot consistently or reliably mask astigmatism.9 Likewise, aspheric CLs are also not able to improve visual acuity in patients with low astigmatism compared to toric CLs.10 Given the consequences of uncorrected astigmatism and the erroneous beliefs surrounding the correction of low astigmatism, it is not surprising a large proportion of CL dropouts include astigmats.11

Several studies demonstrate the importance of fitting low astigmats with soft toric CLs. One study reported that in patients with low to moderate astigmatism, soft toric CLs substantially outperformed spherical CLs.12 In fact, when considering visual performance, 95% of patients preferred soft toric CLs over spherical soft CLs.12

Even more clinically relevant is the fact that the correction of 0.75D or 1.00D of astigmatism with soft toric CLs has been shown to improve visual acuity by up to one full line compared to spherical CLs.13 Furthermore, improved visual quality with soft toric CLs has been positively correlated with improved ocular comfort scores.14

 

Conclusion

With the advances in manufacturing technology, a wide range of options are now available in different materials and modalities, offering coverage in up to 96.4% of soft toric CL prescriptions that are present in a typical clinical population.15 Moreover, toric lenses are now easier to fit overall.

One recent masked, crossover study showed that there was no significant difference in the time to fit toric vs spherical soft contact lenses in adults 18-45 (10.2 ±4.3 vs 9.0±6.5 minutes p=0.22).16 Considering the benefits of fully correcting astigmatism, it is paramount ECPs incorporate a proactive approach in recommending and fitting soft toric CLs, including those patients with lower degrees of astigmatism. 

  • Dr Jaya Dantam is a clinical scientist at the Centre for Ocular Research & Education, School of Optometry & Vision Science, University of Waterloo. Quan Wei Ng is associate director, Global Professional Education and Development at Johnson & Johnson PTE Ltd.

 

References

  1. Young, G, A Sulley, and C Hunt, Prevalence of Astigmatism in Relation to Soft Contact Lens Fitting. Eye & Contact Lens, 2011. 37(1): p. 20-25.
  2. Morgan PB, Woods CA, Tranoudis IG, et al. International contact lens prescribing in 2022. Contact Lens Spectrum. 2023; 38: 28-35.
  3. Johnson & Johnson Vision Care. Online survey of 1028 Eye Care Professionals across United States, United Kingdom, Russia, China, Japan and South Korea. Data on file 2021 (Russia) and 2022 (other markets).
  4. Wolffsohn, JS, G Bhogal, and S Shah, Effect of uncorrected astigmatism on vision. J Cataract Refract Surg, 2011. 37(3): p. 454-60.
  5. Wills, J, et al, Effect of simulated astigmatic refractive error on reading performance in the young. Optom Vis Sci, 2012. 89(3): p. 271-6.
  6. Al-Qahtani, H and H Al-Debasi, The effects of experimentally induced graded monocular and binocular astigmatism on near stereoacuity. Saudi J Ophthalmol, 2018. 32(4): p. 275-279.
  7. Rosenfield, M, et al, The effects of induced oblique astigmatism on symptoms and reading performance while viewing a computer screen. Ophthalmic Physiol Opt, 2012. 32(2):
    p. 142-8.
  8. Sulley, A, et al, Retention Rates in New Contact Lens Wearers. Eye Contact Lens, 2018. 44 Suppl 1: p. S273-s282.
  9. McCarey, BE, CF Amos, and LR Taub, Surface topography of soft contact lenses for neutralizing corneal astigmatism. Clao j, 1993. 19(2): p. 114-20.
  10. Morgan, PB, et al, Inefficacy of aspheric soft contact lenses for the correction of low levels of astigmatism. Optom Vis Sci, 2005. 82(9): p. 823-8.
  11. Young, G, et al, A multi-centre study of lapsed contact lens wearers. Ophthalmic Physiol Opt, 2002. 22(6): p. 516-27.
  12. Dabkowski, JA, MP Roach, and CG Begley, Soft toric versus spherical contact lenses in myopes with low astigmatism. International Contact Lens Clinic, 1992. 19(11): p. 252-256.
  13. Richdale, K, et al, Visual acuity with spherical and toric soft contact lenses in low- to moderate-astigmatic eyes. Optom Vis Sci, 2007. 84(10): p. 969-75.
  14. Maldonado-Codina, C, et al, The association of comfort and vision in soft toric contact lens wear. Cont Lens Anterior Eye, 2021. 44(4): p. 101387.
  15. Luensmann, D, et al, Spectacle prescriptions review to determine prevalence of ametropia and coverage of frequent replacement soft toric contact lenses. Contact Lens and Anterior Eye, 2018. 41(5): p. 412-420.
  16. Cox SM, Berntsen DA, Bickle KM, et al. Efficacy of toric contact lenses in fitting and patient-reported outcomes in contact lens wearers. Eye Contact Lens 2018;44(Suppl1):S296-9.