If you have been practicing or have been trained in the past decade or longer, you might remember being taught tips, tricks, and shortcuts to correct astigmatic refractive error with spherical contact lenses.
Even just 10 years ago, constraints like limited parameter availability and unreliable rotation and stabilization systems meant that many eyecare providers (ECPs) would avoid soft toric options.
The perceived unreliability of past soft toric options led some ECPs to believe that soft toric contact lenses took more chair time than they were worth and often did not deliver the desired visual outcomes.
Developments in toric contact lens technology
In today’s contact lens market, however, the soft toric contact lens options available have taken a significant leap forward.
Most brands (both regular and daily replacement modalities) have axes available every 10°, and all brands offer cylinder power up to 2.25 diopters, with some boasting up to 2.75 diopters. As well, when fitting most modern brand options, rotational stability is no longer as much of a concern.
Most lenses stabilize well on the vast majority of eyes, which has led to reports that chair time associated with fitting soft toric lenses is essentially the same as fitting a soft spherical lens and, importantly, that toric fittings can be as successful as spherical fittings.1
It has also been reported that even patients with low amounts of astigmatism tend to prefer and have enhanced outcomes when corrected with a toric compared to a spherical option.1,2
Embracing soft toric contact lenses
Still, soft toric contact lenses seem to be underutilized. It has been reported that about half of all contact lens wearers have 0.75 diopters or more of astigmatism in at least one eye,3 but toric options are only fitted in about 25% of those patients.4 This means that there is an extensive unmet need for soft contact lens wearers.
If a patient has 0.75 diopters or more of astigmatism in either eye, they could benefit from a soft toric contact lens. Correcting as much astigmatism as possible not only can lead to improved visual acuity,5,6 but enhanced other visual factors—like function in low light/glare conditions, contrast sensitivity, performance on digital devices, and overall subjective satisfaction.1,2,5,7
If you have found yourself avoiding soft toric lenses recently, consider the facts above and how many of your patients might be able to wear a toric design successfully. Read on for more facts and tips on modern toric soft contact lenses and how to successfully fit them into your practice.
Rotational stabilization in toric contact lenses
Rotational stability is key to a successful toric soft contact lens fit. Just like a spectacle lens needs to be placed in the correct orientation in a frame, a soft contact lens needs to rotate into a specific position on the eye to correct vision.
Additionally, the lens needs to seat itself in a stable position on the eye—before and after each blink—to potentially maintain clear, consistent vision.
Soft toric lenses are stabilized using two general methods: prism and thin zones. Prism-stabilized designs incorporate base-down prism into a lens, harnessing the weight of the lens and gravity to encourage the appropriate orientation.
Prism ballast and thin zone designs
Lens designs may be described as having a traditional prism ballast design (meaning the prism is located in the optic zone of the lens) or a peri-ballast design (indicating that the weight and prism are actually located in the periphery of the lens). Peri-ballast designs are thought to avoid issues with visual disruption associated with prism being placed in/near the optic zone.8
Thin zone designs achieve appropriate lens orientation by utilizing anatomical pressure from the upper and lower eyelids. Essentially, the lens material is thinned at the superior and inferior portions of the lens.
When applied to the eye, the superiorly and inferiorly thinned zones migrate under the upper and lower lids with the blink. Because a thin zone design stabilizes with the action of the blink, the design is often referred to as “dynamic stabilization.”8
Matching patients with a stabilization system design
The majority of brands on the market today utilize some form of prism or peri-ballast. Notably, all of Johnson & Johnson’s toric options harness a thin zone design. When choosing a lens design for your patient, it is important to remember that most lenses stabilize well on most patients.
If a lens shows unacceptable rotation, it is likely due to the patient’s unique lid and ocular anatomy. Instead of trying to make a lens with poor stability work for your patient, it is best to simply switch to a brand that employs a different type of stabilization system.
Basic toric lens troubleshooting
Most toric lenses will stabilize on most eyes. This fact can empower an ECP to simply try a different lens brand if one does not stabilize. It is possible, though, that you occasionally may need to make lens options work for a patient because of factors like parameter availability, cost, comfort, or modality preference.
There are different strategies for troubleshooting visual dissatisfaction with a soft toric contact lens.8,9 Before considering any strategy, first determine if any observed rotation is stable. Unstable rotation in a soft lens is not something that can be fixed or controlled for. If you are seeing unstable rotation, try a different brand.
Utilizing the LARS strategy to adjust toric lens rotation
If, however, you notice consistently stable rotation, the “LARS” strategy (Left Add, Right Subtract) is arguably the easiest way to quickly and effectively troubleshoot unsatisfactory vision that could be the result of rotational instability.
When evaluating the lens in the slit lamp, observe the direction and magnitude of lens rotation. Note that the direction is that of the observer (i.e., the doctor’s right or left, not the patient’s right or left). If the lens is rotated 10° to the right (Right Subtract), for instance, trial a lens with an axis 10° less than that of the patient's manifest refraction axis.
For example, if the patient’s refraction is -1.00 to 0.75x180, try a new lens with an axis of 170. If left rotation is observed, apply the same strategy but add the rotational magnitude to the axis parameter. LARS theoretically can help troubleshoot any magnitude of rotation.
Clinically, though, large amounts of rotation (15° to 20° or more) should probably be avoided regardless of stability. If large amounts of rotation are observed, consider trying a lens with a different type of stabilization system (i.e., switch from prism ballast to thin zone or vice versa).
Try the toric
There is a vast opportunity for practice growth and for meeting the visual needs of all patients that soft toric options provide for ECPs.
Considering that most soft toric contact lens fittings are straightforward and require minimal to no complex adjustments, ECPs are now primed to possibly upgrade a large portion of existing and new wearers to a modality that optimally can correct their vision.
