Uptight Eyelids Can Increase Astigmatic Contact Lens Success

Soft contact lenses that correct astigmatism are called “Toric” lenses. “Toric” comes from the root word “Toroid”. A toroidal surface in geometry is a surface with two curves at 90° angles to each other.

Toric soft contact lenses have two curves and two powers at right angles to each other. These powers must be rotationally stable on the eye for optimal vision. If the bottom of the contact lens rotates nasally (towards the nose) or temporally (away from the nose), your vision will be compromised. Rotational stability is of paramount importance with toric contact lenses.

Accordingly, soft toric lenses have multiple design features to create rotational stability. The most common design element to encourage this is prism ballasting (or peri-ballasting). Essentially, the bottom of the lens is thicker than the top. This causes the thicker bottom of the lens to ride down. Gravity may play a small role in stabilizing a prism ballast lens, but the main reason the thicker bottom of the lens rides down because the upper eyelid presses harder on the eye during a blink than the lower lid. This causes the thicker part of the lens to move away from the greater force of the upper lid. This is sometimes referred to as the “pumpkin seed effect”.

Often in patients with higher eyelids, standard prism ballast lenses are unstable rotationally. These patients often do better in regards to both vision and comfort with what I call a “double slab-off” toric contact lens. These lenses are thinner on the top and bottom, and are thicker in the middle. Thus the opposing forces of the upper and lower lids stabilize the lens on the eye.

During a contact lens fitting for patients with astigmatism, I usually place both a prism ballast contact lens design and a double slab-off design lens on the patient’s eye. Usually I will prescribe the lens that looks the most rotationally stable on the eye. Often “uptight” lids do best with double slab-off designs, and patients who have loose eyelids or eyes where the upper and lower lids are far apart (large apertures) tend to do better with a prism ballast design.

Steven Lutz, OD
Serving Ann Arbor, Saline, Ypsilanti, Pinckney, Milan, Dexter, Chelsea, Brighton, Howell, Whitmore Lake and surrounding areas since 1988.