Cataract surgeons address needs, expectations of aging patients after refractive procedures

More than 30 years have passed since the first PRK procedures were performed, followed by LASIK a few years later. An increasing number of keratorefractive patients are now old enough to have visually significant cataract, and surgeons need to be prepared to approach them and deal with their specific requirements and expectations.

“Managing expectations is one of the challenges of doing cataract surgery in this group of patients,” OSN Cataract Surgery Section Editor John A. Hovanesian, MD, FACS, said. “These are people who are accustomed to very good vision who at one point in their life chose to pay out of pocket to be spectacle independent and expect the same to be maintained to some extent after cataract surgery. They are likely to be well informed and to know that we have the technology to provide excellent vision.”

Hovanesian’s approach is to treat patients as partners in the effort to improve their vision, being frank and transparent with them about challenges and options. To illustrate, he uses corneal topography maps to explain how the patient’s cornea is different from a virgin cornea.

Source: David F. Chang, MD

“I show them that this is an eye that has been surgically altered, where it is still possible but more difficult to achieve perfect vision. I show them what a normal cornea looks like and what their cornea looks like. I explain by the different color pattern why it is more difficult to calculate the power of the lens we are going to implant. I tell them that there are special formulas to calculate lens power but that they may not be completely accurate and predictive of the results that we want. And we talk about enhancement and the need for it. I reassure them that the end result will be good, but it is more of a challenge and may take a little longer to achieve,” he said.

In this way, from the beginning, patients know that there are challenges and, having discussed this previously, will maintain their trust in the relationship with their physician, even if the immediate result does not hit the target and needs adjustment.

Lens power calculation

IOL power calculation is rendered less accurate in post-LASIK/PRK eyes. The post-LASIK IOL Calculator, available on the American Society of Cataract and Refractive Surgery website, is a popular and versatile resource that every cataract surgeon should become familiar with, according to David F. Chang, MD.

“I have found that the Barrett post-LASIK formula is the best predictive algorithm, and this is what I primarily base my preoperative selection on. It does not require the patient’s clinical LASIK history, which is often unobtainable or inaccurate. I then use intraoperative wavefront aberrometry (ORA, Alcon) to confirm or slightly adjust this power selection,” he said.

The IOLMaster 700 (Carl Zeiss Meditec) now computes each individual’s total keratometry by separately determining both the anterior and posterior corneal curvature. The Barrett formulae for the IOLMaster 700 have been adjusted to use the total keratometry measurement instead of assuming a theoretical value for posterior corneal astigmatism. This theoretically should be beneficial because LASIK alters the anterior corneal curvature but not the posterior corneal curvature, and most formulae assume the posterior corneal curvature based on the anterior keratometry measurement, Chang, an OSN Cataract Surgery Board Member, explained.

Finally, knowing that the calculation is less reliable in this population, it is better to err on the myopic side for a monofocal or extended depth of focus (EDOF) IOL, he said.

Optical biometry with machines such as the IOLMaster or the Lenstar (Haag-Streit) can be fairly accurate, but it is advisable to double-check that power against the topography-based method using the best-fit sphere in the central cornea, Hovanesian said. Being familiar with topographers and their capabilities is mandatory in these cases. Physicians should therefore consult with the manufacturers to understand the specific capabilities of the systems they use.

“The Pentacam (Oculus), for example, has the Holladay package that you can use as a simple topographer and just look at the axial power as in the center of the cornea. That’s going to be relatively predictive of what the anterior cornea surface power is,” he said.

In general, an advanced formula should be used for planning these procedures.

“Latest-generation formulas are accurate. The Haigis is popular, and I have had very good luck with the Barrett True K formula. In general, Barrett formulas work well for high myopes and high hyperopes and very well for post-refractive cases because they include measurements of anterior chamber depth, a parameter that you cannot ignore in post-refractive cases,” Hovanesian said.

The ASCRS as well as the European Society of Cataract and Refractive Surgeons online calculators allow surgeons to see the results of multiple formulas.

“There is a bit of guesswork because sometimes you will see varying results and it is not absolutely clear which formula is right, but usually the results cluster around a couple of lens powers,” Hovanesian said.

Wavefront aberrometry

According to Hovanesian, intraoperative aberrometry may be helpful, but with caution because it is subject to some errors in eyes with high irregular astigmatism such as post-radial keratotomy.

“There can be inaccuracies even if used in the best way possible. Results should be looked at with reasonable suspicion, mostly as a confirmatory step,” he said.

Chang performs ORA aberrometry routinely during surgery with refractive IOLs.

“In addition to topography, I perform preoperative wavefront aberrometry using the iTrace (Tracey Technologies), which is able to quantify corneal higher-order aberrations (HOA) across the same diameter as the patient’s undilated pupil in a dimly lit exam room. Most post-LASIK patients have significant corneal HOA when calculated across the 6-mm optical zone, but if the pupil diameter is normally 3 mm to 4 mm or less, then it is more relevant to quantify HOA for a 4-mm optical zone,” Chang said.

Eyes that previously underwent a larger myopic ablation will generally have more corneal HOA, which can reduce the patient’s contrast sensitivity and quality of vision. These HOA may also create more unwanted images at night when the pupil is larger. Chang recommended explaining these implications to the patient preoperatively because symptomatic HOA will not be corrected with spectacles. Corneal HOA will be exacerbated by dry eye and ocular surface disease, and appropriate treatment should be addressed and initiated preoperatively, he said.

After SMILE

In general, patients who underwent prior refractive surgery have two main problems. The first is change in total and anterior corneal curvature, which results in false anterior chamber depth. The second is effective lens position, Ahmed El-Massry, MD, PhD, said.

“The effective lens position calculated after refractive surgery is not true because the machines rely on the flat cornea that has been created. This flatter anterior curvature will create a hyperopic shift of the intraocular lens if regular calculations are used,” he said.

El-Massry has a lot of experience with small incision lenticule extraction, with more than 20,000 procedures performed since 2011. SMILE is a relatively young procedure, but a few patients are now starting to present for cataract surgery.

“SMILE only corrects myopia or myopic astigmatism, so the dilemma of calculation is a little less than for patients post-PRK or LASIK. Apart from this, changes in the cornea are the same as for the other refractive procedures, with the anterior corneal curvature becoming flatter than normal,” he said.

Another advantage is that preoperative data such as Pentacam and keratometry are generally available, which may not be true for older PRK and LASIK procedures. Calculations can be done more accurately, using more than one formula to be sure of the lens power, El-Massry said.

After presbyopic laser surgery

One particular group of refractive patients is those who have undergone laser vision correction for presbyopia. According to Dan Z. Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, it is important to understand the difference between Presbyond Laser Blended Vision (LBV) (Carl Zeiss Meditec) and other laser techniques that create a multifocal cornea, such as presbyLASIK, Intracor (Bausch + Lomb) or PresbyMAX (Schwind).

“Presbyond improves the depth of field by controlling spherical aberration. Therefore, the lens power calculation after Presbyond is very easy. Providers would use the exact same formulae of choice as for a normal post-refractive eye. On the other hand, in a multifocal corneal situation, the mean corneal power and keratometry calculation will be different in different zones, so the standard post-refractive IOL power formulae are likely to be inaccurate,” Reinstein said.

In his practice, 98% of presbyopic patients without visually significant cataract are treated with Presbyond.

“Not only does this provide excellent distance, intermediate and near vision to meet their current visual demands, but it has a benefit for those who need to have cataract surgery later in life,” he said.

Over the last 11 years, he has performed cataract surgery after previous Presbyond LBV LASIK in 89 patients. Because the depth of field is already in the cornea, they were simply implanted with a monofocal IOL while employing micro-monovision in the reading eye, which they were already well adapted to.

“They retain the majority of their range of vision without risking the side effects that multifocal IOL patients complain about, including glare, halo, decreased contrast sensitivity and waxy vision,” Reinstein said. “Because our patients receive monofocal IOLs, which are slightly more forgiving, we rarely need to perform LASIK re-treatments.”

Premium IOLs

There is still debate on whether or how often multifocal IOLs should be used in eyes that have previously undergone refractive surgery. Multifocal IOLs could potentially allow patients to continue being spectacle free, but corneal HOA and reduced IOL power calculation accuracy make most post-LASIK eyes poor multifocal IOL candidates.

“However, because the post-LASIK cornea is already somewhat multifocal, mini-monovision with monofocal IOLs can work quite well. If the first eye ends up more myopic than targeted, we get another shot at emmetropia with the second eye,” Chang said.

The EDOF optical design appears to be better tolerated in these eyes.

“Compared to multifocal IOLs, this platform is optically more forgiving of small residual refractive error and is designed to preserve contrast sensitivity. After excluding severe corneal HOA, my post-LASIK patients have generally been pleased with the Symfony EDOF IOL (Johnson & Johnson Vision),” Chang said.

If the keratometry, topography and Barrett formulae are in agreement, Chang is comfortable using toric IOLs but believes that most post-keratorefractive patients will be ideal candidates for adjustable IOLs once they become available.

“This will allow us to adjust the intraocular IOL power based on the postoperative refraction, and the patient can also try out different amounts of myopia for mini-monovision before we adjust the IOL accordingly,” he said.

Low-add multifocal IOLs are a good option if the patient has a fairly regular cornea and low previous correction, according to Hovanesian.

“Both the Tecnis (Johnson & Johnson Vision) and the ActiveFocus (Alcon) are great options,” Hovanesian said. “If you are using those low-add lenses, you might need to do a bit of monovision, depending on the patient’s desire. Fortunately, a lot of patients have had monovision with their prior refractive surgery, at least the older patients have, and for those patients monovision is a good option.”

Single-focus optics

The Crystalens accommodating IOL (Bausch + Lomb) may also be an appropriate choice for post-keratorefractive patients, particularly the toric model of the lens, which allows correction of a high amount of irregular astigmatism.

“The rule is that if you have a significant irregular cornea, you want to use a single-focus lens, which may be a monofocal toric lens or the Crystalens, which has the added benefit of providing some correction for presbyopia,” Hovanesian said.

“My choice has been mainly restricted to monofocal IOLs. The more advanced technology of the IOLMaster 700 provides more accurate measurements, but I am still cautious,” El-Massry said.

Aspheric IOLs can be used after SMILE or myopic LASIK/PRK because the myopic correction does not change the asphericity of the cornea. For the opposite reason, the same lenses are not suitable for hyperopic refractive procedures.

El-Massry discusses with his patients the monovision option, which they usually accept and tolerate well within an average of 1 D difference between the two eyes. Before surgery, they test monovision with contact lenses.

“This is currently the best solution because these are usually demanding patients who want to maintain the privilege of not wearing glasses. I expect that in the near future we should be able to offer trifocal or multifocal lenses, thanks to the advancements in the technology for IOL power calculation,” he said.

Enhancement options

There are many options to treat residual refractive error after IOL surgery. The treatment choice depends on many factors including the type of primary corneal procedure, how long ago it was performed, residual stromal tissue and the number of previous treatments, Reinstein said.

“Most of our LASIK patients have had thin flap (110 µm or less) femtosecond flaps. In these patients, it is very easy to create a slightly larger and deeper flap and perform a second LASIK procedure. If we find any reason that gives us pause for performing LASIK, such as residual stromal thickness, we can always fall back to PRK. For patients who have had previous SMILE, we would follow our standard re-treatment protocol of performing LASIK with a thin flap after confirming there is sufficient space between the epithelium and the SMILE interface by VHF digital ultrasound or OCT imaging,” he said.

PRK is the best enhancement technique to address residual refractive error after cataract surgery, according to Hovanesian.

“Typically, not a large amount of correction is needed, maybe 1 D or 2 D. PRK has the advantage of being easy for the patient to go through and has a low risk of causing significant dry eye. It is accurate, and you can use a smaller optical zone if the patient has a smaller pupil. That means smaller epithelial debridement and quicker healing. You usually get the job done very quickly, and it allows astigmatic enhancement as well,” he said.

Limbal relaxing incisions are another feasible option in patients with mixed astigmatism. For small amounts of myopic error, some surgeons use mini-RK, a procedure that is a “little bit dated” but works reasonably well at a low cost, Hovanesian said.

Follow-through

The time interval between cataract surgery and enhancement depends on how the eye reacts to surgery. If the patient has significant dry eye, healing is inhibited, and it is advisable to wait at least 1 month.

“Usually 2 months is the ideal time and is what I prefer if the patient can wait that long,” Hovanesian said.

Waiting, however, can be frustrating for both patient and physician. Whatever patients expect before surgery, they do not react well when told they need an enhancement.

“Regardless of what you told them before surgery, they won’t blame themselves — they will blame you. They’ll say you put the wrong lens in and will tell their friends that you did. They are frustrated, and the more you wait before fixing the problem, the more you increase their frustration,” Hovanesian said.

The best approach is a calm approach, again partnering with the patient and together looking ahead to the end result.

“As a surgeon, you know your job is not done and that your patients are not happy with the results, but what you also know is that in the long run they will be very happy,” Hovanesian said. “You need to ask them to be patient, to forgive of their imperfect eye and understand that eventually you will get there. Most patients thank you for that after it is all done.” – by Michela Cimberle

• References:
• Arce CG, et al. J Refract Surg. 2009;doi:10.3928/1081597X-20091117-05.
• Canto AP, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130617-07.
• Fram NR, et al. Ophthalmology. 2015;doi:10.1016/j.ophtha.2015.01.027.
• Ianchulev T, et al. Ophthalmology. 2014;doi:10.1016/j.ophtha.2013.08.041.
• Krueger RR, et al. J Refract Surg. 2013;doi:10.3928/1081597X-20130819-04.
• Packer M, et al. J Cataract Refract Surg. 2004;doi:10.1016/j.jcrs.2004.02.075.
• Patel RH, et al. Int Ophthalmol Clin. 2016;doi:10.1097/IIO.0000000000000106.
• Reinstein DZ, et al. J Refract Surg. 2012;doi:10.3928/1081597X-20120723-01.
• Savini G, et al. Eye Vis (Lond). 2018;doi:10.1186/s40662-018-0110-5.
• Vrijman V, et al. J Cataract Refract Surg. 2017;doi:10.1016/j.jcrs.2017.06.028.
• Vrijman V, et al. J Cataract Refract Surg. 2018;doi:10.1016/j.jcrs.2018.01.030.
• Vrijman V, et al. J Refract Surg. 2019;doi:10.3928/1081597X-20181119-01.

• For more information:
• David F. Chang, MD, can be reached at 762 Altos Oaks Dr. Suite 1, Los Altos, CA 94024; email: dceye@earthlink.net.
• Ahmed El-Massry, MD, PhD, can be reached at Alexandria Faculty of Medicine, Department of Ophthalmology, Alexandria, Egypt; email: ahmad.elmassry@gmail.com.
• John A. Hovanesian, MD, FACS, can be reached at Harvard Eye Associates, 24401 Calle De La Louisa, Laguna Hills, CA 92653; email: drhovanesian@harvardeye.com.
• Dan Z. Reinstein, MD, MA(Cantab), FRCSC, DABO, FRCOphth, FEBO, can be reached at London Vision Clinic, 138 Harley St., London W1G 7LA, United Kingdom; email: dzr@londonvisionclinic.com.

Disclosures: Chang reports he is a consultant for Johnson & Johnson Vision, Carl Zeiss, Perfect Lens and RxSight. El-Massry reports no relevant financial disclosures. Hovanesian reports he is a consultant for Bausch + Lomb, Johnson & Johnson Vision, Alcon and Carl Zeiss Meditec. Reinstein reports he is a consultant for Carl Zeiss Meditec and has a financial interest in Artemis Insight 100 VHF digital ultrasound (ArcScan Inc.).

Click here to read the , “Is intraoperative aberrometry an essential tool in cataract surgery?”