It is well known that the majority of eyes exhibit some degree of astigmatism.

In training, all students are exposed to “Javal’s Rule” (Asiedu et al, 2016). A study from China of 1,463 schoolchildren, aged 6 to 9 years old, found clinically significant astigmatism in 22.4% of participants (Lin et al, 2019). Another study from Spain found that astigmatism occurs in as much as 85% of the population (Vinas et al, 2012).

Whatever the actual rate, practitioners soon find that some patients have difficulty adjusting to cylindrical correction for the first time or when changes are made to the habitual correction, whether in spectacles or contact lenses.

Recurring Themes

A study by Hughes and colleagues (2021) of 22 patients, aged 21 to 71 years (mean age 43), found that 10% of patients found their new prescription “unacceptable.” In that study, the authors discovered recurring themes: trust, conflict, and “part of me.”

Trust This starts with trust in the practitioner, including the continuity of care received and the ability to develop a long-term relationship. Patients want to feel heard. It also means that patients have trust in themselves and their ability to adapt.

Conflict This occurs when patients receive advice that differs from their experience. The perception of conflict also influences expectations regarding the new prescription.

“Part of Me” The researchers described this as how patients felt about themselves.

The conclusions in the study were that many ECPs underestimate the physical, behavioral, and emotional aspects that adaptation to a new prescription sometimes requires.

Contact Lens Implications

What does this mean for eyecare practitioners when they are making recommendations for contact lenses as the primary means of correction?

Patients who have low amounts of astigmatism (e.g., less than 0.75D) will generally do well in a soft contact lens with the spherical equivalent. In the range of 0.75D to 2.25D, visual acuity will benefit from a toric correction (Barnett, 2018).

If the patients’ astigmatism is mostly corneal and they express a desire for optimum vision, I usually discuss the benefits of a corneal GP lens. In a previous column, I discussed the importance as assessing not only axial or tangential maps of curvature change but also differences in elevation (Arnold, 2022). When the elevation difference between the high and low points of the cornea is less than 150µm, corneal lenses work well.

This last feature is important in regards to lens centration. Bitoric contact lenses will be more comfortable, center better, and provide superior vision as opposed to a contact lens that has a spherical base curve (Chang, 2013) (Figure 1). Lenses that are fit too flat, in an effort to attach to the upper lid, may cause significant distortion of the cornea resulting in significant spectacle blur (Lee et al, 2017).

In Conclusion

A well-fit contact lens for astigmatism correction, whether soft or rigid, will provide patients with an alternative and adjunct to spectacle lens wear. After all, improving the “quality-of-life” of our patients is one of the joys of our wonderful eyecare profession (Pesudovs et al, 2006). CLS

References

1. Asiedu K, Kyel S, Ekow-Ampiah E. Autorefraction, Retinoscopy, Javal’s Rule and Grosvenor’s Modified Javal’s Rule: The Best Predictor of Refractive Astigmatism. J Ophthalmol. 2016;20163584137.
2. Lin Y, Jiang D, Li C, et al. Simultaneous Changes in Astigmatism with Noncycloplegia Refraction andOcular Biometry in Chinese Primary Schoolchildren. J Ophthalmol. 2019 Jun 23;2019:5613986.
3. Vinas M, Sawides L, de Garcia P, Marcos S. Perceptual Adaptation to the Correction of Natural Astigmatism. PLoS One. 2012;7:e46361.
4. Hughes A, Fylan F, Elliot D. What are patients’ beliefs and experiences of adaptation to glasses and how does this affect wearing habits. Ophthalmic Physiol Opt. 2021 Sep;41:1034-1046.
5. Barnett M. How to Effectively and Efficiently Present the Toric Lens Option. Toric Tips for Successful Fits. 2018 Mar. Available at clspectrum.com/newsletters/toric-tips-for-successful-fits/march-2018 . Accessed July 6 ,2022.
6. Arnold T. Heads or Tails? Contact Lens Spectrum. 2022 Apr;37:12. Available at clspectrum.com/issues/2022/april-2022/prescribing-for-astigmatism . Accessed July 6, 2022.
7. Chang A, Lam D. A Toric GP primer. Contact Lens Spectrum. 2013 Dec;28:22-27. Available at clspectrum.com/issues/2013/december-2013/a-toric-gp-primer . Accessed July 6, 2022.
8. Lee AC, Vo AM, Edrington TB. Spectacle Rx Considerations for Irregular Astigmatism. Contact Lens Spectrum. 2017 Dec;32:50. Available at clspectrum.com/issues/2017/december-2017/prescribing-for-astigmatism . Accessed July 6, 2022.
9. Pesudovs K, Garamendi E, Elliot D. The contact lens impact on quality of life (CLIQ) questionnaire: development and validation. Invest Ophthalmol Vis Sci. 2006 July;47:2789-2795.