Using a femtosecond laser to correct astigmatism

Correcting pre-existing astigmatism or preventing the occurrence of surgically induced astigmatism (SIA) is key to achieving effective surgical outcomes and ensuring the highest level of postoperative vision.

Almost all the patients I treat have some degree of astigmatism: a recent study shows that 50% of eyes tested had more than 1.0 D of astigmatism,¹ while resulting astigmatism can have various side effects such as glare, ghosting and halos

In the past, surgeons corrected astigmatism by such manual treatment as limbal relaxing incisions (LRIs) or corneal relaxing incisions (CRIs).² However, many surgeons-including those with lots of experience as well as younger surgeons-are uncomfortable carrying out the manual procedure, particularly as the laser is more predictable and accurate.⁶

In a 2008 survey of 223 surgeons, just 73 were at ease with performing manual LRIs³ because complications are possible, including overcorrection, undercorrection and infection.² Thus, more recent focus has shifted to the use of technology such as the femtosecond laser to better address atigmatism, which can be corrected simultaneously during cataract surgery.

Femtosecond laser incisions

The practice of using femtosecond lasers for cataract surgery has advanced the field hugely. The devices can yield impressive surgical outcomes, such as excellent incision accuracy and reproducibility, compared with LRIs.

Furthermore, these devices are advantageous from a safety perspective, as the risk of collateral tissue damage and its negative consequences is reduced due to the ultraprecise deliverance of ultrashort infrared energy pulses that create a photodisruption effect.⁴

In terms of correcting astigmatism, the laser’s ability to precisely generate arcuate incisions with accurate length, depth and location, is impressive. One study has shown that the corneal incisions created by a femtosecond laser were more stable and easier to replicate than those resulting from traditional techniques.5

As a surgeon, I also consider the safety aspect to be an appealing feature. In my surgical practice, I strive to provide the best visual outcomes for my patients, but equally important is the need for them to be, and to feel, safe when I carry out the procedure.

In my clinic, we use a laser system (Streamline IV, Lensar) that has the capability to link with other preoperative diagnostic instruments (for example, Corneal Analyser OPD-Scan III, Nidek; Aladdin, Topcon Corporation; and Pentacam HR/Pentacam AXL, Oculus).

The coupling between different devices raises the safety profile of cataract surgery as it standardises the procedure.

For example, the manual inputting of patient data is open to many errors – not least, inputting the wrong data for the wrong patient, which can have various undesirable consequences. Instead, by pairing the preoperative device with the laser, the correct data transfer is guaranteed, which enhances the efficiency of the workflow.

Intuitive astigmatism management is a key feature of the system and one of the major benefits is iris registration.

The use of the other preoperative diagnostic instruments to capture a preoperative image of the undilated iris eradicates the need for patient compliance-dependent corneal ink markings and automatically compensates for cyclorotation. This can then be used for comparison with the intraoperative image from the laser to guarantee accurate correction.

Iris registration gives the surgeon confidence with placing the corneal incision by the comparison of preoperative images with those images taken with the laser while the patient is docked

Streamlining astigmatic correction

The femtosecond laser is a useful tool for the implantation of premium IOLs in patients with mild to severe astigmatic error. The use of additional technology provided by the laser system (IntelliAxis-L, Lensar) allows surgeons to make biomechanically stable capsular marks, providing precise alignment for the toric IOL, both intra- and post-operatively. 

The employment of the integrated features of the laser enables optimum astigmatism treatment planning and delivery, which can be customised to individual patients. Corneal toric marks can also be made (using IntelliAxis-C, Lensar).

In addition, the laser makes the process of correcting astigmatism simpler. In cases of residual astigmatism following cataract surgery, the ability to modify the laser arcuate incision means it is easy to achieve the full refractive effect.

In essence, the laser technology gives the surgeon the flexibility to realise its full potential.

The planning of arcuate incisions is possible at the touch of a button and is based on my pre-programmed nomogram data, meaning the astigmatic treatment can be delivered precisely, accurately and to my specifications.

A further benefit is that patients also have a good understanding of how this feature works; when I explain the concept to them, they know exactly what I am going to do and why. This is not often achieved with other techniques, but the ability for patients to visualise the precise elements of the procedure aids the process.

Conclusion

The correction of astigmatism is a fundamental part of refractive cataract surgery, particularly given the number of patients who have the condition. All patients want the best possible visual outcomes-and for many this means spectacle independence-and the modality of laser technology makes this increasingly possible.

In my experience, I consider the main difference between manual and laser techniques to be that manual treatment is an art form, while lasers are science.

References:

1. De Bernardo M, et al. Prevalence of Corneal Astigmatism Before Cataract Surgery in Caucasian Patients. European Journal of Ophthalmology. 2013;24:494-500.
2. Patel AS. Limbal Relaxing Incisions. American Academy of Ophthalmology. (2017).
3. Duffey RJ. US Trends in Refractive Surgery: 2008 ISRS/AAO Survey. Presented at: The International Society of Refractive Surgery and American Academy of Ophthalmology. (2008).
4. Packer M. The LENSAR® Laser System-fs 3D for Femtosecond Cataract Surgery. US Ophthalmic Review. 2014;7:89-94.
5. Nagy ZZ. New Technology Update: Femtosecond Laser in Cataract Surgery. Clinical Ophthalmolog; 8:1157-1167.
6. Lipuma L. Limbal Relaxing Incisions Versus Toric IOLs for Astigmatism Correction. EyeWorld2. 2016.

Dr Detlev Breyer, MD
E: dr.detlev.breyer@gmail.com
Dr Breyer specialises in the treatment of the anterior eye section. He is a global pioneer of micro-incision surgery and ReLEx Smile. He is owner of Breyer, Kaymak und Klabe Augenchirurgie PremiumEyes.