Astigmatism management is a notable contributor to refractive outcomes in refractive cataract surgery and can significantly impact patient satisfaction.1
With this in mind, in this episode of Interventional Mindset, Drs. Preeya K. Gupta, MD, and Eric Donnenfeld, MD, review the foundations of astigmatic keratotomy (AK) and how surgeons can utilize these procedures to reduce corneal astigmatism.
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Why astigmatic keratotomy has persisted through the years
As a long-time educator on astigmatism management, Dr. Donnenfeld began by going back in time 10 to 15 years ago and noted that many ophthalmologists would likely be surprised to hear that current surgeons still perform astigmatic incisions due to the advent of the excimer laser, femtosecond laser, and toric intraocular lenses (IOLs).
He observed that one would most likely think that astigmatic incisions would be on the decline; however, in reality, he is performing them more than ever. The reasons for this are likely that patient expectations have increased, and they tend to be more symptomatic, so he finds that treating low levels of astigmatism is key to meeting a patient’s vision expectations in refractive cataract surgery.
Dr. Donnenfeld recounted an old saying that half a diopter or more of astigmatism can result in glare, blur, or ghosting. However, he finds that even less than half a diopter can cause vision distortions. Consequently, he has “zero tolerance” for astigmatism.
Dr. Gupta agreed, emphasizing that in the past, she has treated as low as 0.25D of astigmatism, which she began to surgically manage after becoming comfortable performing arcuate incisions with the femtosecond laser.
She focused on fully reducing astigmatism in those patients, finding their refraction to be stable, which tended to yield consistently enhanced visual outcomes. This was true not only for patients with trifocal and extended depth of focus (EDOF) IOLs but also for those with monofocal IOLs from “bread and butter” cataract surgery as well.
Improving patient satisfaction with astigmatic keratotomy
Dr. Donnenfeld mentioned a study from Schallhorn et al. that outlined how low levels of residual astigmatism can degrade visual acuity and negatively impact patient satisfaction following cataract surgery.1
The retrospective case series utilized 3-month post-operative outcomes in over 17,000 eyes and compared patient satisfaction in eyes with no residual astigmatism to those with different levels of residual astigmatism. They found that the odds of not achieving 20/20 vision in eyes with 0.25 to 0.50D of residual astigmatism increased by 1.7 and 1.9 in monofocal and multifocal IOLs, respectively (P<0.0001).
This trend continued with 0.75 to 1.00D of residual astigmatism, with an odds ratio of 6.1 for monofocal IOLs and 6.5 for multifocal IOLs (P<0.0001). At this level of residual astigmatism, the odds of patients not being satisfied with their vision increased by a factor of 2.0 and 1.5 in patients with monofocal and multifocal IOLs, respectively (P<0.0001).1
Therefore, Dr. Donnenfeld stated that he often offers adjustments to patients to meet their vision expectations. Considering the presence of preexisting astigmatism of ≥1D is present in up to 47% of cataract eyes;2 Dr. Donnenfeld noted that he would elect to recommend toric lenses once a patient is above the 0.375 to 1.375D threshold.
Dr. Gupta agreed, explaining that astigmatic keratotomies are particularly helpful because T2 toric lenses (i.e., low-power toric IOLs) are not available in the United States. Consequently, managing low levels of astigmatism with AK can get patients closer to their vision goal.
Selecting an astigmatic keratotomy technique
Astigmatic keratotomy can encompass a variety of methods for surgically addressing astigmatism, such as:
- Limbal relaxing incisions (LRIs): Partial-thickness incisions made at the steep axis with a diamond knife near the limbus.
- Arcuate incisions: Corneal incisions that are usually made at the 8 or 8.5mm optical zone. Dr. Donnenfeld stated that he does not feel comfortable performing these incisions free hand due to the proximity to the visual axis, so he elects to use a laser.
- Intrastromal astigmatic incisions: Incisions that do not penetrate to the ocular surface and must be performed with a femtosecond laser.
- Penetrating astigmatic incisions: An incision technique in which a keratome is inserted at the limbus at the steep axis—originally described by Richard MacKool, MD, and developed by Dr. Donnenfeld.
Dr. Gupta’s preferred form of astigmatic keratotomy is arcuate incisions with a femtosecond laser at the time of cataract surgery. Additionally, one of Dr. Gupta’s favorite enhancement tools, when appropriate, is an LRI with a diamond knife, because it can be performed at the slit lamp.
An added benefit of performing LRIs at the slit lamp is having the patient sit up during the procedure, meaning there is no cyclotorsion to factor in, highlighted Dr. Donnenfeld. Of note, the diamond knife used for LRIs was designed by Dr. Donnenfeld and collaborators, with 15° angulation for improved applanation that he utilizes to perform LRIs at the steep axis.
When performing in-office LRIs, he tends to put a phoropter right next to the slit lamp to clearly visualize where to put the incision. He also performs diamond knife LRIs for laser-assisted in situ keratomileusis (LASIK) patients who develop against-the-rule (ATR) astigmatism 1 year after the procedure.
Astigmatic keratotomy with femtosecond laser
As mentioned earlier, Dr. Gupta prefers to perform arcuate incisions with a femtosecond laser due to the repeatability and reliability in depth using optical coherence tomography (OCT) in comparison to manual incisions. She also appreciates that this procedure can be integrated into existing surgical workflows (i.e., cataract surgery) as a natural step to minimize the amount of time patients are operated on.
She added that she and Dr. Wörtz developed the Wörtz-Gupta Formula (which can be accessed at LRIcalc.com) to calculate femtosecond laser arcuate parameters in patients with low levels of astigmatism. In a study, they evaluated whether treating low corneal astigmatism (<1.0D) with femtosecond laser arcuate incisions using their formula improved treatment outcomes.3
They found that using the femtosecond laser for arcuate incisions with the formula provided favorable anatomic and refractive outcomes in patients with lower levels of pre-operative astigmatism at the time of cataract surgery.
Surgical pearls for femtosecond laser-assisted AKs
Dr. Donnenfeld reiterated the accuracy and precision of the femtosecond laser, and added, based on his experience with excimer laser photoablation, surgeons need to consider:
- Cyclotorsion control: Dr. Donnenfeld recommended registering the eye pre-operatively, which can now be done with many available femtosecond lasers by IOLMaster, Cassini, and Pentacam. That way, when the patient lies down for the procedure, the cyclotorsion is already taken into account.
- Include the posterior cornea: Based on findings from Koch et al., it is critical to include posterior corneal astigmatism, especially for low cylinder.4 Dr. Donnenfeld stated that it is important to have both anterior and posterior cornea factored into the calculations. He recommended taking these measurements from IOLMaster or Cassini devices.
- Automate the process: The final key step is to automate the process, as most doctors would prefer not to make these calculations by hand.
Dr. Donnenfeld added that he developed a nomogram for manual LRIs many years ago that is now integrated into the Catalys Precision Laser System so doctors can automatically take pre-operative measurements, control for variables, and place the incision accurately on the eye. Similarly, the Wörtz-Gupta formula is available on the ZEISS Veracity Surgery Planner.
Dr. Donnenfeld mentioned that he designed a website, lricalculator.com, that guides clinicians step-by-step through how to perform an LRI with a video.
Surgical pearls for performing limbal astigmatic keratotomies
Dr. Donnefeld shared that there tends to be little pain or discomfort for patients and a low risk of infection with minimal to no wound healing variables in intrastromal astigmatic incisions. He elects to perform them on patients with small amounts of cylinder (0.375 to 0.75D). However, for the average ophthalmologist, limbal relaxing incisions are “still king” in terms of in-office procedures when it comes to addressing corneal astigmatism, he observed.
For patients undergoing cataract surgery with small amounts of cylinder who don’t have the financial resources for a femtosecond laser-assisted procedure or toric lens, Dr. Donnenfeld often performs a small LRI combined with a non-premium EDOF lens, such as the Eyhance (Johnson & Johnson), the RayOne EMV (Rayner Surgical), and the enVista Aspire (Bausch +Lomb).
These lenses provide 0.3 to 0.4D of near power, and instead of billing for the lens, he bills for the astigmatic keratotomy. He finds that this is a valuable vision-correction package that offers patients better reading distance vision with the AK.
Intra-operative pearls for performing an astigmatic keratotomy
Dr. Gupta emphasized that for surgeons interested in managing low levels of corneal astigmatism, incision placement is key. For example, if a doctor is uncomfortable making an arcuate incision in patients with <0.5D, they could consider changing the axis of the primary incision. This could potentially provide enough of an effect on corneal astigmatism that it results in changes to the patient’s refractive astigmatism.
Additionally, both doctors highlighted the penetrating limbal relaxing incisions (PLRIs) technique, developed by Dr. Richard Mackool, which entails two full-thickness incisions along the steepest meridian as well as the clear corneal incision for phacoemulsification.
For this process, Dr. Donnenfeld uses his LRI nomogram to determine the location of the new axis of cylinder will be: taking into account the posterior corneal astigmatism and the induced cylinder from the primary incision. These calculations determine where the axis is, and then he places an incision with a keratome at the axis manually.
For patients 0.25 to 0.3D, Dr. Donnenfeld elects to use a 2.6-blade, but if he wants to treat for more astigmatism, he uses a 3.0mm keratome to treat 0.5 to 0.75D of astigmatism. He added that it is important to make the incision and not open it to prevent the wound from gaping or leaking.
Astigmatic keratotomy post-operative regimen
Following an LRI, Dr. Donnenfeld prescribes patients steroids and antibiotics because he has observed that patients tend to have some post-operative discomfort. He explained that doctors could prescribe TobraDex (tobramycin and dexamethasone ophthalmic suspension, Alcon) TID or ofloxacin and prednisolone TID for 4 days.
If a patient still has significant discomfort, he recommends that they continue taking the steroid until the pain subsides. Dr. Donnenfeld explained that he has found that pain after the procedure tends to happen only with diamond knife incisions and not penetrating incisions.
Due to the fact that Dr. Gupta typically performs AKs during cataract surgery, she tends to elect for a combination drop with a steroid, non-steroidal anti-inflammatory drug (NSAID), and antibiotic. If she performs an in-office LRI, she opts to put an NSAID drop in the patient’s eye before leaving the office and prescribe a steroid/antibiotic combination drop.
Contraindications for astigmatic keratotomy
Dr. Gupta noted that she is cautious about performing an arcuate incision in a patient with existing severe dry eye because there could be disruption of the corneal nerves. Additionally, she does not perform arcuate incisions in patients with known ectasia as it is contraindicated for this kind of penetrating incision.
Dr. Donnenfeld agreed, explaining that he prefers to implant toric lenses in dry eye patients and those with keratoconus. For corneal transplants, he always makes incisions inside the graft-host interface, allowing for a smaller optical zone.
Conclusion
Both Drs. Gupta and Donnenfeld emphasized that incorporating astigmatism management with astigmatic keratotomy into clinical practice is highly beneficial to both surgeons and patients.
Reducing astigmatism via AK allows doctors to tailor a treatment to the patient’s individual needs and vision goals—improving satisfaction and overall patient care.
