Although soft lenses are fit in most astigmatic cases, GPs (both corneal and scleral) can be advantageous to patients who have any degree of corneal astigmatism. GP lens wearers often will experience improved vision (compared to a representative soft toric lens), improved long-term comfort (as the GP lens does not dehydrate on the ocular surface like a soft lens might), greater oxygen transmission, and easier care/compliance (Bennett et al, 2020).

An additonal advantage of spherical GP lenses is the lens may rotate clockwise or counterclockwise on the cornea without degrading the vision.

When deciding whether to fit a soft toric or GP lens, a clinician should consider a patient’s residual astigmatism (RA). RA is the astigmatic refractive error that exists following the correction of a patient’s ametropia by a contact lens. Calculated RA (CRA) can be determined by subtracting a patient’s anterior corneal toricity from the total refractive toricity of the eye at the corneal plane (total refractive astigmatism or TRA) (Bennett et al, 2020).

When the CRA is minimal or zero, a spherical GP contact lens or scleral lens is suitable for correcting corneal astigmatism. But what options are available when the CRA doesn’t equal zero or is significant, such as in the following example?

When a patient is predicted to exhibit significant CRA, utilize a front-surface toric, which will provide the best visual acuity. If the patient is not a candidate for GP lenses, a soft toric can correct CRA. Unlike a spherical GP lens, rotation of a front-surface toric GP lens may lead to a significant decrease in visual acuity.

Case Report

A 36-year-old male presented for a contact lens fitting. His chief complaint was blurry distance vision and the feeling that his current contact lenses were rotating. He was wearing non-custom monthly replacement soft toric lenses.

CRA was low for each eye, and the decision was made to continue this patient with soft toric contact lenses since he was a longtime soft lens wearer. Since he was experiencing rotation with his non-custom soft toric lenses, and, unfortunately, the contact lens was not available in alternate base curve, diameter, and/or prism stabilization parameters, he was refit into custom soft toric lenses with the following parameters: OD – base curve (BC) 8.20mm, diameter 14.9mm, power –1.25 –2.50 x 175/1.4 BD prism diopters; OS – BC 8.10mm, diameter 14.9mm, power –1.50 –2.00 x 170/1.4 BD prism diopters.

The patient reported that the custom lenses were more stable on the eye, and he was ecstatic about the improvement in visual acuity noted.

In Conclusion

Clinicians have a variety of contact lens designs in their toolboxes when fitting patients who have astigmatism. Corneal GP or scleral lenses may be ideal for patients who have precise vision demands, while custom soft toric lenses may be valuable for patients who have high levels of ametropia or astigmatism, corneal curvature values or a visible iris diameter outside the normal range, or patients who have been unhappy with the results of their non-custom soft toric contact lenses. CLS

REFERENCES:

1. Morgan, P. et al. International contact lens prescribing in 2021. Contact Lens Spectrum. 2022 Jan;37:32-38.
2. Jones D, Woods J. Soft torics: putting things straight. Contact Lens Spectrum. Sept 2018;33(9):12-13.
3. Bennett ES, Henry VA, Kinoshita BT, Lampa M. Correction of Astigmatism. In Bennett ES, Henry VA. Clinical Manual of Contact Lenses (5th ed.) Wolters Kluwer, Philadelphia, 2020:388-439.