The truth about torics

The first option for astigmats

When Siddiqi sees new potential astigmatic contact lens wearers in practice, she will ensure that the patient is fully informed on the benefits of toric contact lenses over spherical ones.

Siddiqi explained that this creates parity between the eye care provided to spectacle wearers and contact lens wearers.

“If they haven’t had contact lenses before I will go in first with the toric discussion,” she said.

“The reason I keep that as a first option is that we always provide astigmatic correction in glasses – so why should it be different with contact lenses?” Siddiqi said.

She shared that even in patients with low levels of astigmatism (of 0.75DC or more), a toric contact lens would be her first recommendation.

“There is a common misconception that contact lens astigmatism can be masked with a spherical lens, but that is not the case,” Siddiqi emphasised.

She highlighted that low levels of uncorrected astigmatism can reduce reading speeds and create visual challenges outside of the high-contrast environment of a testing room – such as extended digital device use or driving during the evening.

Nadia Siddiqi

Nadia Siddiqi, professional affairs consultant at Johnson & Johnson Vision

This may mean that the patient experiences eye strain throughout the day and may eventually avoid wearing contact lenses for certain tasks.

“We need to consider the patient as a whole and think about whether toric contact lenses would really improve the quality of their visual experience and comfort,” Siddiqi said.

Siddiqi also takes time to demonstrate to astigmats wearing spherical lenses, the difference that a toric lens can make to their vision.

“It’s a really nice way of showing a patient what their vision can be like in comparison to their current lenses,” she said.

Design considerations

Siddiqi shared that in order to provide individualised care to patients, it is important to understand the benefits and limitations of different toric contact lens designs.

“Every individual is unique and it is really important that we look at the patient in front of us,” she said.

When communicating the advantages of a toric contact lens to patient, Siddiqi will avoid using jargon and relate the benefits of the lens to the individual hobbies and physiology of the patient in her chair.

She highlighted that understanding the design of a lens is important when troubleshooting why it may not be performing on-eye as hoped.

“If you understand how something is designed, you are better placed to then figure out why it may not be working for a particular patient,” Siddiqi said.

“It also means that when you’re trying to resolve an issue, you don’t then refit them with something that’s very similar,” she shared.

Reflecting on design considerations for monocular astigmats, Siddiqi emphasised the importance of understanding the different types of stabilisation methods used across different toric lenses – including prism-based and eyelid stabilised designs.

She highlighted that if a monocular astigmat is fitted with a prism stabilised toric lens in one eye, there is a risk of inducing differential vertical prism. In some cases, Siddiqi highlighted that this could be close to one dioptre vertical prism.

“With the monocular astigmats, I would avoid fitting them with a prism stabilised lens, because you could be solving one problem, but could be introducing another,” Siddiqi said.

The idea is that we are stepping into the shoes of the resident for the day

A word on CAAS/LARS

When it comes to assessing the rotation of a toric lens, Siddiqi emphasised the need to measure this rather than estimate it.

If the rotation is not accounted for, then the patient can end up with an unintended induced cylinder because for every 10-degree rotation, a third of the cylinder power is additionally induced with the axis in the opposite direction.

“It’s really important to accurately measure the amount and direction of rotation, rather than estimating it - no matter how experienced the practitioner is,” Siddiqi highlighted.

“It’s super quick to simply rotate the slit beam to align with the lens marking, measure it and then you know the correct angle before applying the ‘Clockwise Add, Anti-clockwise Subtract (CAAS)’ or ‘Left Add, Right Subtract’ (LARS) rule,” she said.

Siddiqi highlighted the importance of record keeping when adjusting for CAAS/LARS – particularly for a locum optometrist who may not return to the same practice.

She observed that if this adjustment is not recorded once done, the next practitioner to see the patient may also think they have to adapt for the rotation of the lens as the position of the toric marker remains offset.

“The position of the toric marker on the eye will not change – by adjusting for CAAS/LARS you are purely rotating the prescription to the correct orientation within that design of lens.” Siddiqi cautioned.

Another important step that can be missed by practitioners is adapting for back vertex distance in both meridians.

“It’s important to consider the prescription in its power cross form and consider if back vertex distance needs to be considered in just one or both meridians – online calculators often do this for you and can be a very useful tool,” Siddiqi said.