Astigmatism management requires careful analysis, personalized strategies
Astigmatism is the most common and most complex of refractive errors. Management requires careful analysis of many variables and personalized strategies.
“No one-size-fits-all concept can be applied to astigmatism because every astigmatism is different. We need to study each case in depth, diligently look at the data and design a customized strategy for treatment,” Ugo Cimberle, MD, said.
Today’s technology allows for safe and effective management of every degree and type of astigmatism, regular and irregular, and the most severe cases are often those that give the best results and the highest satisfaction.
“Astigmatism can be very invalidating. There are patients who have been struggling for years with spectacles that were never right and see their life change entirely after surgery. I am often amazed myself at the results we are able to achieve,” he said.
There are several factors to evaluate when designing a strategy for astigmatism management. Age and lens status are first because presence of a cataract would immediately qualify the patient for a lens-based strategy.
Other basic determinations are severity and whether the astigmatism is congenital or secondary to trauma or corneal transplantation, regular or irregular, and axisymmetric or not.
“Very high astigmatism post-transplantation is better treated with a lens, but laser enhancement may be required if there is an irregular component that toric IOLs are unable to address,” Cimberle said.
He generally avoids IOL surgery in patients younger than 45 years of age, particularly myopic patients, but there may be exceptions.
“I implanted a toric IOL in a patient who had undergone sliding intrastromal keratoplasty several years ago and had a high degree of astigmatism and a very flat cornea. It changed her life dramatically,” he said.
Toric IOLs can effectively address axisymmetric astigmatism, while irregular astigmatism with a marked non-axisymmetric component requires a well-designed laser treatment. On the other hand, laser treatment has limitations in terms of the degree of astigmatism, and when this is too high, treatment may need to be combined with IOL implantation.
“Associated high hyperopia may also be a limitation for laser treatment because it would require excessive corneal steepening. Mixed astigmatism and myopic astigmatism are more easily treated with laser, but corneal thickness is always a critical parameter,” Cimberle said.
Laser customized treatments
Not only are all cases of astigmatism different, but also all lasers are different and have various characteristics, capabilities and algorithms that lead to a range of outcomes.
“Studies often generalize and say do this and don’t do that, but the dos and don’ts depend on what laser you have. What is not good with your laser may work well with mine or vice versa, and it is extremely important to know your system well,” Cimberle said.
Astigmatic treatments require top-tier eye tracking technology with static and dynamic cyclotorsion compensation because just a few degrees of axis error critically affect the outcomes. With regular astigmatism, standard ablation programs may be adequate, but with other types with asymmetrically steep meridians, decentered corneal vertex and high angle kappa, customized topography-guided and wavefront-guided ablation programs are highly preferable.
“We need specific high-level software to maximize the outcomes. With standard lasers, we can still use methods like bitoric ablation, but they are a bit of a handicraft solution,” Cimberle said.
He uses the Schwind Amaris platform and personally believes there is no better laser for astigmatic treatments.
“The customized ablation treatment profiles of Amaris, based on wavefront analysis, allow us to address, rather than the imperfect morphology of the cornea, the effects of this imperfect morphology on the aberrations. It is extremely precise in the way it tailors the treatment to each eye individually. In combination with very precise and reliable eye tracking, it provides unbeatable results for all types of astigmatism up to 7 D,” he said.
Toric IOLs have also evolved to high standards, and the choice is a matter of subjective preference and habits.
“There are no objective criteria in favor of single-piece vs. C-loop IOLs, and both types have now a good level of rotational stability,” Cimberle said.
Problems may sometime arise with large eyes in which rotation can never be completely ruled out and repositioning may be needed.
“Patients should know that rotation is not frequent but may happen, and we cannot predict if and when it occurs because it depends on how their capsular bag reacts to the implantation. They should know that re-rotation will be needed in these cases,” he said.
Early rotation is easy to adjust, but late rotation due to capsular bag contraction is better managed with laser or implantation of a piggyback lens.
In eyes in which astigmatism may change over time, such as after corneal transplantation, Cimberle suggested piggybacking from the start a toric IOL in the sulcus over a monofocal IOL implanted in the capsular bag.
“As the astigmatism changes, you can more easily reposition the piggyback lens, even a long time after implantation,” he said.
IOL alignment is a crucial step, and while the conventional manual ink-marking procedures based on topography may still be a good option, digital systems such as the Callisto eye (Carl Zeiss Meditec) and the Verion digital marker (Alcon) offer enhanced precision and reliability.
Incisional techniques are no longer part of Cimberle’s armamentarium.
“We have used them for many years, but incisions always weaken and alter corneal biomechanics to some extent. They are easier to perform, but we have two options that work so well, I don’t think we need incisions nowadays,” he said.
A successful astigmatic treatment, whether it is laser or toric IOL implantation, or both, leads to a high degree of patient satisfaction — even more so when astigmatism is high, asymmetric and irregular, and therefore never properly managed by spectacle correction.
“Whether regular or irregular, astigmatism is always worth treating. Even when full correction cannot be achieved, there is always enough improvement to make patients happy,” Cimberle said.
A mild degree of residual astigmatism may be desirable because it can increase the depth of field.
“Be aware of this when you implant a toric IOL in presbyopic patients with cataract because it may worsen near vision. A small degree of against-the-rule astigmatism should be left, as it provides that small degree of multifocality that helps seeing without spectacles. Individualize refractive targeting, bearing in mind that perfection is not always the best choice,” he said. – by Michela Cimberle
- For more information:
- Ugo Cimberle, MD, is head of ophthalmology at Villa Maria Cecilia Hospital, Cotignola, and San Pier Damiano Hospital, Faenza, Italy, and can be reached at Piazza Carlo Luigi Farini, 4 - 48121 Ravenna (RA), Italy; email: firstname.lastname@example.org.