Management of astigmatism calls for complex strategies for best results

Among refractive errors, astigmatism poses the greatest challenge to surgeons. Correcting an irregular shape requires complex treatment plans for lasers, precise alignment strategies for IOLs and nomograms for relaxing incisions. Surgeons have to take into account that long-term results might be jeopardized by the natural repair mechanism of the cornea, which leads to “filling in” irregular gaps, inducing regression and having to deal with the potential threat of IOL rotation.

Often associated with other refractive errors, astigmatism “requires quite a lot of thinking and is never straightforward as a treatment,” Ugo Cimberle, MD, said.

Technological advances have improved the chances of addressing astigmatism with precision and safety. On one hand, corneal topography, wavefront aberrometry and optical coherence tomography allow mapping of astigmatism and the creation of customized treatment plans. On the other hand, the new laser eye trackers with dynamic cyclotorsion compensation allow for precise delivery of laser ablation. IOL technology offers premium toric models with increasingly higher performance. Many methods for accurate sizing and alignment of IOLs have also been developed. In addition, the femtosecond laser promises to revive incisional techniques. However, the surgeon’s mind remains crucial to coordinate, combine, correlate and interconnect information, Cimberle said.

“If we find the right formula, we can give our patients a quality and clarity of vision they would never expect. Well-treated astigmatic patients are the happiest patients,” he said.

Paradigm shifts in laser surgery

According to a recent study of nearly 2,000 healthy eyes of European patients between the ages of 15 years and 100 years, astigmatism of more than 1 D is present in more than 30% of the population.

“Association of astigmatism and spherical refractive error is present in 90% of my laser-treated patients. In 15% of the cases, it is high astigmatism, above 2 D,” Cimberle said.

Off-axis wavefront aberrations, such as asymmetric astigmatism and coma, which may be present with a large angle kappa, have a high negative impact on visual quality. Blurry vision and image distortion may also be associated with asthenopic problems, such as headache, dizziness and fatigue.

“Any astigmatism above 1 D should be considered significant enough to have treatment,” Cimberle said.

In a population of 3,654 people between the ages of 49 years and 97 years, the Blue Mountains Eye Study found that the prevalence of astigmatism increases with age, doubling its rate in people older than 80 years.

“About 30% of my cataract patients have astigmatism,” Günther Grabner, MD, said. “The sheer number of patients that will profit from astigmatic treatment is huge because, starting from 0.7 D, it reduces your uncorrected distance vision significantly.”

Cimberle defined astigmatism as “the optical transposition of an irregular corneal morphology that we name toricity. The section is an ellipse, often not asymmetric because the four hemimeridians have different curvature gradients.”

Corneal topographers and wavefront aberrometers, he said, have introduced a paradigm shift in the way astigmatism is evaluated.

“We can now see and analyze the morphology of the cornea, while in the past we could only address its optical transposition. We can also do precise wavefront analysis. Combining topography and aberrometry, we can produce accurate, individualized treatment plans for the laser,” Cimberle said.

Laser surgery for a high degree of astigmatism was first confronted with the problem of regression, Michael Assouline, MD, PhD, said.

“The cornea has a memory of shape, and when you change the curvature of one meridian too much, it tends to go back to where it was. With modern technologies, this problem has been overcome. The new laser algorithms have enabled us to produce ablation profiles with smooth transition zones and to work simultaneously on both meridians,” he said.

A second problem of older lasers was the alignment with the anatomical axis of astigmatism during ablation.

“This has been greatly improved with the use of eye trackers with capabilities for limbal and iris recognition, as well as pupil recognition. The last step in this quest has been the ability to dynamically address cyclotorsional movements during surgery. All this has been achieved and has dramatically improved the success of astigmatic correction with laser,” Assouline said.

Best practices for best results

Compensating for static and dynamic cyclotorsion is critically important in astigmatic correction, Massimo Camellin, MD, said. Torsional movements, particularly in hyperopic astigmatic patients, can be up to 15° or 20°. Positioning errors can add a further 10°, leading to a possible 30° of rotation.

“With a 30° rotation, there will be no astigmatic correction. Surgical error should never be beyond 5° for good results,” Camellin said.

Precise topography mapping is the first step to achieve this level of accuracy. The patient’s head needs to be perfectly vertical with no rotation, the light in the room has to be adequately calibrated as required by the topographer, and at least four consecutive measurements must be taken to achieve the lowest standard deviation, Camellin recommended.

“Topographic data are then translated into wavefront data. Individual aberrations need to be isolated and quantified separately,” he said.

Low-order aberrations, ie, sphere and cylinder, are included in the treatment algorithm, and compensation by internal aberrations is assessed.

 The nomogram needs to be further adjusted to include the patient’s subjective refraction, carefully measured by using small increments, with both natural and dilated pupils.

“Optical zone diameter and transition zones are then set accordingly,” Camellin said. “Low-toricity corneas can be addressed by smaller-diameter ablations, but large optical zones are generally better because we need to distribute the treatment over the entire cornea to obtain a regular profile.”

According to Assouline, one of the pitfalls in the laser correction of astigmatism is related to the size of the optical zone.

“For high degrees of cylinder, since you are removing on a different diameter in the steep and flat meridians, the optical zone will be oval. When the small axis is on the horizontal meridian, in some patients, especially in hyperopes, the fixation point will not always be very well-centered in this small optical zone because of the angle kappa. If you don’t take this into account, you’ll have severe problems with quality of vision,” he said.

Another issue with optical zone size might occur with LASIK because if the hinge is positioned on the longer diameter of the ablation, the periphery might be undercorrected, again with a significant impact on quality of vision and efficacy of correction due to occurrence of coma aberration.

In these cases, surface ablation with PRK or LASEK might therefore be better indicated than LASIK. Regression can be effectively prevented with the use of mitomycin C, Assouline said.

“Regression used to occur in the past with PRK due to the sharp transition zones, but now this problem has been overcome. LASIK not only has a significantly higher risk of iatrogenic ectasia, but it can also induce astigmatic changes due to the cut, though femto-LASIK has now minimized complications,” Cimberle said.

Assouline has five different excimer lasers in his private clinic in Paris and has been able to compare how they correct astigmatism.

“Top rank is the Bausch + Lomb 217 Zyoptix Z100 laser, which is a little tedious in terms of alignment but provides incredible results with high astigmatism, both in the wavefront and subjective mode. For myopes, I use the aspherical treatment modality based on wavefront analysis, and in hyperopes, I use the tissue-saving mode that is based on iris recognition but not on the wavefront. I also use the Carl Zeiss Meditec Mel 80 laser and the Alcon WaveLight EX500, but not for high degrees of astigmatism,” he said.

Both Cimberle and Camellin use the Schwind Amaris laser platform for astigmatic correction.

“The Amaris embodies all the best contemporary technology for astigmatic, customized treatments, including a six-dimensional eye tracker, which compensates for static and dynamic cyclotorsion during surgery,” Camellin said.

Grabner performs LASIK with the iFS femtosecond laser (Abbott Medical Optics) and the Mel 80 excimer laser, and he is in the process of acquiring the Schwind laser.

Phakic lenses

Camellin said that he has gradually reduced the range of correction with laser.

“Over 8 D of myopia, I now prefer phakic lenses, and I never treat with laser hyperopic astigmatism over 3 D or 4 D. Steepening a flat cornea leads to creation of a peripheral step, which ends up being filled by the epithelium,” he said.

Spectral domain OCT now has facilities for epithelial mapping, allowing close monitoring of epithelial reaction and the prevention of regression with corticosteroids. However, phakic lenses are a safer option in these patients.

“I use the Visian toric ICL (STAAR Surgical) with success,” Camellin said.

Assouline also uses the Visian toric.

“It is very comfortable, predictable and accurate in the correction of even high degrees of astigmatism. If accurately sized, it is stable in the sulcus. It doesn’t rotate, which is, of course, extremely important with toric lenses,” he said.

Cimberle uses the Visian ICL, but not the toric model.

“I prefer avoiding problems that may come from axis alignment. For high degrees of correction, which may not be safely treated with laser, I implant the spheric lens, wait 2 to 3 months, and then address the astigmatism and any residual spherical error on the cornea with laser because the astigmatism is ‘on the cornea.’ Should I have to remove the ICL at any time to do cataract surgery, I’d have the astigmatism already treated. These patients are young, and I don’t need to achieve the full result with just one treatment. As a matter of fact, there are quite a few of my patients who are so happy just after the phakic lens correction that don’t want me to laser them,” he said.

For high refractive error, Grabner uses the Artiflex toric iris-claw lens (Ophtec).

“I’ve used it since it was introduced in 2001. I have implanted approximately 300. Results are fast, and patients are very happy. It is a reversible procedure, which is a further advantage,” he said.

“The only problems we had were inflammation in two patients who did not use their topical treatment properly, and partial disenclavation in another two cases: a man who did Power Plate and a lady who did trampoline jumping. I wouldn’t do bungee jumping, either. Now I tell patients that these are the three things they should not do if they have this lens implanted,” Grabner said.

Toric IOLs for cataract surgery

In patients who need cataract surgery, toric IOLs are an option that is encountering high appreciation among surgeons.

“With just one treatment, they provide the advantages of a clear lens, astigmatic correction and even some near vision because the toric component helps gain a small degree of multifocality. They are very good lenses and work extremely well,” Cimberle said.

“Toric IOLs are the true premium lenses, in my opinion. They give amazing results. A variety of them are available; some are customizable, like the Tecnis toric (Abbott Medical Optics) and the AT LISA (Carl Zeiss Meditec). I use both but prefer AT LISA because the plate haptics allow for better stability,” Camellin said.

Grabner uses toric versions of the AcrySof (Alcon), the Tecnis, the Rayner T-flex and the HumanOptics IOLs.

“All of them are good lenses with different injectors. I don’t really have preferences,” he said. “I implanted a fair number of them in patients with astigmatism more than 1.5 D who want to get rid of glasses. However, I tend not to use them in very old patients who have had glasses all their life. I prescribe new bifocal spectacles, and they are happy, unless they want to play sports like skiing, golf or use the bicycle a lot.”

Assouline uses the Lentis Mplus toric (OcuLentis) and the AT TORBI 709m (Zeiss) and had the opportunity to work with the PhysIOL Ankoris, a lens with a hydrophobic surface and innovative haptic design aimed at improving rotational stability.

Alignment and stability are crucial issues with toric IOLs. A 10° axis deviation reduces astigmatic correction by one-third, 20° by two-thirds, and lens misalignment greater than 30° will increase the net astigmatic error. Manufacturers are working to further improve features to reduce misalignment.

“Toric IOL markings that should help us align the lens are not expanded enough toward the center to be of comfortable use with small pupils. Manufacturers should think that not all patients are well-dilated, and it would be good to have markings that extend more towards the center. Sometimes the haptics give you a clear indication of where the lens is but not all of the haptics,” Assouline said.

He also noted that very similar designs do not behave in the same way for stability. Lens material and volume, as well as overall length, are likely to contribute to the different outcomes.

“The ideal lens would have a hydrophobic surface and hydrophilic core, high volume and long length to make sure that the design will indent into the periphery of the capsule, in the equator, and be stable. But maybe a smaller lens will induce less rotation because it puts less pressure. We don’t know yet what the winning combination is,” Assouline said.

A wide variety of new technology platforms, such as Callisto eye (Carl Zeiss Meditec), Ora (WaveTec Vision) and iTrace (Tracey Technologies), are available to assist surgeons in IOL alignment.

“We have been using for 3 years the SMI Surgery Guidance system (SensoMotoric Instruments), which grabs the image of the frame and vessels of the eye before surgery and intraoperatively projects them into the microscope, using them as landmarks to guide toric IOL orientation,” Grabner said.

The same system is used when implanting toric phakic IOLs.

“It’s like a jet fighter shooting game: grab, track, compare, shoot. Very neat, fast and simple. Very helpful and precise,” Grabner said.

Cimberle and Camellin use their own topography-based methods.

“I take a photo on the slit lamp, carefully orientating the patient’s head. I take blood vessels as reference points and then, using a program I developed with CSO, which superimposes a goniometer to the cornea, I re-track these points on the topography map and draw the lens axis. This allows me to keep within a maximum of 5° error,” Camellin said.

“On the slit lamp, I draw four reference points at the limbus. I retrace these points on the topography map, see where the toric axis is, measure the angle and know exactly where I must place the lens,” Cimberle said. “The Casia OCT (Tomey) uses a similar system, but it’s easy to do it just with a topographer that visualizes the limbus.”

Incisional techniques

Incisional techniques are another traditional way of correcting astigmatism. Instability, imprecision, wound gape and scarring have generated problems with limbal relaxing incisions performed in the past, and not all surgeons currently use them.

According to Assouline, the use of limbal relaxing incisions is still viable if patients are carefully selected.

“Currently this approach is not precise enough compared to toric IOLs, at least with more than 1.5 D. For less than this, a simple pair of limbal relaxing incisions will do the trick. For higher astigmatism, there is the automated relaxing incision device by Moria, but femto is more efficient and precise in terms of depth and extension. The only precaution is to make sure you are dealing with regular astigmatism,” he said.

Intrastromal astigmatic keratotomies with a femtosecond laser might be promising. Grabner performs them with both the iFS laser and the Catalys laser (OptiMedica) for cataract surgery.

“They are safer as compared to anterior penetrating incisions, very precise as to the placement, shape, different options of inclination, and it is very fast surgery. For simultaneous treatment with cataract, it only takes 2 to 3 seconds,” he said.

The range of potential correction is lower compared with penetrating incisions, but effective reduction of corneal astigmatism between 0.5 D and 2.5 D is achieved in a safer way. Results are fairly stable over 1 year, Grabner said.

An ongoing international study is comparing penetrating and intrastromal incisions, but final results are not yet available. A study recently published in the Journal of Cataract and Refractive Surgery evaluated the effects of intrastromal incisions before cataract surgery, after cataract surgery and as a standalone procedure and found “excellent safety profile, rapid recovery, and stability of vision without the known risks associated with incisions that penetrate Bowman membrane.”

“We are currently working at improving nomograms,” Grabner said. – by Michela Cimberle

• References:
• Attebo K, et al. Ophthalmology. 1999;doi:10.1016/S0161-6420(99)90251-8.
• Nemeth G, et al. Eur J Ophthalmol. 2013;doi:10.5301/ejo.5000294.
• Pan CW, et al. Invest Ophthalmol Vis Sci. 2013;doi:10.1167/iovs.13-11725.
• Ruckhofer J, et al. J Cataract Refract Surg. 2012;doi:10.1016/j.jcrs.2011.11.027.
• Rückl T, et al. J Cataract Refract Surg. 2013;doi:10.1016/j.jcrs.2012.10.043.
• For more information:
• Michael Assouline, MD, PhD, can be reached at Centre Iéna Vision, 37 rue Galilée, 75116 Paris, France; +33-1-5367021; email: drassouline@gmail.com.
• Massimo Camellin, MD, can be reached at SEKAL, Via Dunant 10, 45100 Rovigo, Italy; phone/fax: +39-0425-411357; email: cammas@tin.it.
• Ugo Cimberle, MD, can be contacted at CIDIEMME, Centro di Microchirurgia Oculare, Via Berlinguer 14, Ravenna, Italy; +39-054-440-4355; fax: +39-054-440-8956; email: cimberle@alice.it.
• Günther Grabner, MD, can be reached at University Eye Clinic, Paracelsus Medizinische Privat-Universität, PMU, Universitätsklinikum, Müllner Hauptstrasse 48, A 5020 Salzburg, Austria; email: g.grabner@salk.at.

Disclosures: The sources have no relevant financial disclosures.

Will the femtosecond laser revive widespread use of relaxing incisions at the time of cataract surgery?

Laser optimizes precision, may decrease need for toric IOLs

There is one basic reason why I like to use laser arcuate relaxing incisions. As astigmatism usually comes from the cornea, I like to compensate it right on the cornea whenever it is possible and safe, rather than aligning two cylindrical optical elements — the cornea and toric IOL. The optimal optical system should not consist of several cylindrical optical elements with the risk of their future potential misalignment.

I used to perform manual diamond blade arcuate incisions in the past. The results were favorable, but the precision was somehow suboptimal. Laser has the potential to significantly increase the precision of relaxing incisions.

We have been performing laser relaxing incisions for about a year. In our first 21 eyes, the mean preoperative cylinder of 2.28 ± 0.45 D decreased to 0.49 ± 0.44 D at 3 months. In other words, 70% of eyes were within 0.5 D of cylinder correction. I think this is quite an encouraging result. So whenever I deal with astigmatism on otherwise healthy corneas, I tend to treat astigmatism by laser corneal incisions right at the time of cataract surgery. In the near future, we will be able to perform different relaxing incision types with femtosecond lasers for safer and more predictable outcomes. One of the promising applications already in use is intrastromal arcuate cuts, which eliminate postoperative pain and reduce the risk of infection and epithelial ingrowth.

I believe that we will see more femtosecond lasers for cataract surgery in the field. As the surgeons recognize the possibilities of laser relaxing incisions, they will use them more, thus implanting fewer toric IOLs.

Pavel Stodulka, MD, is the head surgeon at Gemini Eye Clinic, Prague, Czech Republic. Disclosure: Stodulka is a consultant for Bausch + Lomb.

Predictability, efficacy higher with toric IOLs, laser photoablation

The femtosecond laser has certainly improved the quality and reproducibility of astigmatic keratotomy. The depth and arc length, as well as the centration and symmetry of the two incisions, can be precisely calculated. Refraction, corneal topography and corneal pachymetry are performed directly in the area of the intended incisions and then programmed into the laser. Similar to the LASIK flap, you can now have the accuracy that you could never achieve by mechanical methods, and this adds a lot to the procedure.

However, there are variables that we are still unable to control, such as elasticity gradient and strength, which vary between individuals and in relation to age. The biomechanical and functional response of the cornea to the treatment, both in the short and long term, remains, to some extent, unpredictable.

Femtosecond lasers are becoming an indispensable tool in any modern practice. The added capability for relaxing incisions is an additional bonus. However, astigmatic keratotomy remains a rough approach to astigmatic correction. It also requires calculating the different spherical equivalent resulting from what you remove from the cylinder and add to the sphere by performing the corneal cuts. Nowadays we have toric IOLs, which work wonders to correct astigmatism in our cataract patients. With careful patient selection and accurate preoperative measurements, they provide perfect outcomes and no surprises. And we have excimer lasers with reliable nomograms and potentiated eye trackers for astigmatism, which can be used for primary procedures or for astigmatic enhancement after IOL implantation. Both toric IOLs and laser procedures are, at present, more reliable methods of addressing astigmatism, with still more accurate and predictable results and fewer complications.

Vikentia Katsanevaki, MD, PhD, is an OSN Europe Edition Board Member. Disclosure: Katsanevaki has no relevant financial disclosures.