GP lens eye Rounds

HIGH ASTIGMATISM: Empirical GPLI Toric and Spherical Calculator

A highly astigmatic patient was desiring a viable option for achieving high quality vision (OD only)
Refraction: -4.00 – 4.00 x 180
Keratometry: 42.50 @ 180; 46.00 @ 090
A GP bitoric lens was recommended due to the high amount of astigmatism and the desire for high quality vision

- The refractive information was inputted into the GPLI Toric and Spherical Lens Calculator (https://gpli.info/lens-calculator) and the results – including powers, base curve radii, and diameter are shown in Figure 1.

Figure 1: GPLI Toric and Spherical Lens Calculator

Although this is empirical and relies on an accurate refraction and keratometry/simulated K values, this method is recommended for bitoric lenses as the quality of bitoric lens manufacturing is high, and it allows for the patient to likely achieve very good quality of vision with the initial application of GP lenses.
Whereas it is common to design bitoric GP lenses when a patient has ≥ 2.5D of corneal cylinder, you may want to consider this option for as low as 2D of cylinder if topography shows limbus-to-limbus astigmatism.
The CLMA member laboratory and their consultants can assist with the other lens parameters but keep in mind that the diameter, material, and center thickness would be similar to a spherical lens (the latter two based upon the power in the more plus meridian). Toric peripheral curves are often recommended. One philosophy would be to add 1 mm to the base curve radii (BCR) to obtain the toric secondary curve radii (SCR) and add 2mm to the SCR to obtain the toric peripheral curve radii.¹

1. 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, PA, 2020:388–439.