Each semester with third- and fourth-year optometry students, I take the time to discuss the importance of toric contact lens markings. These clinical pearls may seem second nature to seasoned practitioners and clinicians, but for clinicians who are still early in their careers they assist in streamlining astigmatic contact lens fittings.
Although subtle, toric markings are quite useful when assessing the fit of a contact lens and troubleshooting problems that may arise.
Marks the Spot
Toric markings come in all shapes, sizes, and numbers, and are located at different positions on the contact lenses, which vary depending on the brand and design of lens. Some designs have one toric marking, while others can have three or more. The location of the toric markings may also vary. For example, markings may be located at the 6 o’clock position; at 6 and 12 o’clock; or at the 3, 6, and 9 o’clock positions. Additionally, the size and shape of the toric markings can vary from rectangular to circular. Figure 1 illustrates several examples of toric markings on soft, GP, and scleral contact lenses.
Astigmatism markings can be beneficial for several reasons. Often, new patients present at the clinic wearing toric lenses, but they cannot recall the brand or design of the lenses. By identifying the size, shape, and location of the contact lens toric markings, the manufacturer and design of the lens can be narrowed down. If patients have had success with a specific toric lens design, this will allow them to continue in that same brand without unnecessarily being refit with a different toric lens design that may not be as effective.
Get the Best Fit
Toric markings can also be beneficial for patients. Although modern toric contact lens designs exhibit better stabilization methods, it still may take up to several minutes for a contact lens to align properly on the eye, during which time patients may experience blurry vision. When patients are initially fitted with toric contact lenses, they should be educated on the location and positioning of each toric marking, as this will allow them to apply the lens in the correct location, minimizing the blurry vision that may occur as a result of toric contact lens settling.
When measuring toric contact lens rotation, a common observation made when teaching is that student clinicians do not take advantage of toric lens designs that have more than one toric marking. So, if a toric lens design has markings at 6 o’clock and 12 o’clock or 3 o’clock and 9 o’clock, they will often only measure rotation using a single toric marking. To improve accuracy of lens rotation measurements, extend the slit lamp beam so that both markings can be measured simultaneously (Figure 2). This will lead to improved accuracy when quantifying toric lens rotation and determination of the proper prescription adjustments based on the rotation.
Finally, toric markings can be useful when determining how stable a contact lens is on the eye. Carefully observe the toric marking(s) as the patient blinks multiple times, noting if the toric marking is stable, rotates clockwise or counterclockwise, or rotates and then returns to a non-rotated position. If this occurs, an alternative toric stabilization method may need to be considered.
The next time a patient who wears toric contact lenses is in the chair, carefully examine the markings. A wealth of information can be gathered in this way. CLS