IGNORING ASTIGMATISM or under-correcting it can be frustrating for patients who expect clear vision. Fortunately, eyecare providers have several options to correct astigmatism. Here are 3 tips that will help optimally correct for a patient’s astigmatism.
1. Consider Slightly Overcorrecting
Often, practitioners feel limited by the amount of astigmatism that can be corrected, given the limitations of contact lens manufacturers. As an example, –0.75 DC is often considered the minimum amount of astigmatism that can be corrected in contact lenses. There are times when a patient’s refraction is recorded at –0.50 DC of astigmatism, and we do not consider correcting for that astigmatism because it is below the threshold.
If patients are not satisfied with a spherical contact lens correction in this situation, it is useful to demonstrate correction with a –0.75 DC trial lens at the specified axis and demonstrate slight overcorrection vs no correction. The patients can then indicate whether they can appreciate the additional astigmatism and whether they prefer it over having no astigmatism correction. A number of these patients will prefer to have their astigmatism slightly overcorrected as opposed to not being corrected.
2. Correct the Exact Level
For patients who prefer to have the most accurate vision correction and their refractive astigmatism at the plane of the cornea does not match lenses that are readily available commercially, custom lens options are available. Consider custom soft toric lenses for patients who appreciate more precision-based astigmatic correction.
3. Correct Residual Cylinder
Scleral lenses have revolutionized the way corneal ectasia and other corneal irregularities are corrected. When scleral lenses are fit for these conditions, they often correct for the irregular astigmatism. Contemporary scleral lens designs are often created with a toric landing zone allowing for the lens to be stabilized on the eye. This stability on the patient’s eye allows the addition of astigmatism correction in the scleral lens.
It is critical to complete 2 things before introducing astigmatism correction into a scleral lens. First, make sure that you finalize all fitting characteristics such that fit is optimized and the lens is rotationally stable. Second, measure the position/rotation of the lens by assessing the markings on either the steep or the flat meridian of the lens as precisely as possible. Rotating the slit lamp beam so that it aligns with the markings on the lens can be useful for documenting this position (Figure 1).
The Verdict
There are many ways we can now accurately and predictably correct for a patient’s astigmatism, whether they be soft or scleral lenses.
