Article

Refractive Surprise in Glaucoma Patients

New data can help surgeons plan ahead.

With the increasing adoption of microinvasive glaucoma surgery (MIGS), it is important for both cataract and glaucoma specialists to know whether MIGS can be done with premium cataract surgery. There are few studies published to date that explore the question of refraction post phacoemulsification and MIGS; however, a study by University of Colorado researchers published in the Journal of Cataract and Refractive Surgery recently evlauated this.1 In this Q&A, Glaucoma Physician editor in chief Nate M. Radcliffe, MD, talks with the paper’s corresponding author, Leonard K. Seibold, MD, from the University of Colorado School of Medicine, about optimizing patient outcomes in this population.

Dr. Radcliffe: Dr. Seibold, it is important for surgeons to understand that there is some variability inherent in patients with glaucoma and that MIGS is not always the cause of refractive surprise. I’d also like to get tips from you to empower surgeons who are doing MIGS with premium cataract surgery but not getting the results they want. Does this study, or your clinical experience, give you any ideas for improving the process?

Dr. Seibold: Yes. Our study was a retrospective study of our database at the University of Colorado looking at refractive outcomes in patients that underwent cataract surgery. We wanted to look at whether glaucoma patients specifically compared to those without glaucoma had similar refractive outcomes or if they were at higher risk of having a refractive surprise after surgery. The second aim of the study was to see if the addition of a MIGS procedure at the time of cataract surgery contributed to the risk of having an undesirable refractive outcome.

We had 206 eyes in the glaucoma group and 1,162 in the control group. We looked at refractive surprise defined as either 0.5D above or below their target refraction based on the IOL calculation or above or below 1D as well. For both categories, there was a significantly greater chance of having a refractive outcome that was outside that range, in patients who had glaucoma compared to those who didn’t.

We found 2 subtypes of glaucoma had the highest risk of having a refractive surprise: chronic angle-closure glaucoma with an odds ratio of 14.54 and pseudoexfoliation glaucoma with an odds ratio of 7.27. In other words, chronic angle closure and pseudoexfoliation patients had a 14 and 7 times greater chance, respectively, of having a refractive surprise after cataract surgery, whereas primary open-angle glaucoma did not seem to have as much of a risk of that refractive surprise. The only other demographic feature that showed an increased risk was an axial length greater than 25 mm. But that was true not only for glaucoma patients, but control patients as well.

Specifically looking at patients with glaucoma who had a MIGS procedure in addition to their cataract surgery, there was no difference in the rate of refractive surprise between them and the eyes with glaucoma who were just having cataract surgery. We looked at iStent (Glaukos) and endoscopic cyclophotocoagulation (ECP) specifically, or a combination of both. There was no additional risk of refractive surprise with the addition of MIGS, which was nice to see.

We looked at the IOP change as an independent risk factor for refractive surprise and it was not significant. We also looked at keratometry and preoperative IOP. Previous studies have shown that eyes with filtration surgery, post-trabeculectomy or tube specifically, with very low pressure, tended to have a higher risk of refractive surprise.2 We only had 19 patients in this study that had prior filtration surgery. We looked at that specifically, and we looked at the eyes that had pressure less than 10 mmHg. None of these were found to be a significant risk factor for refractive surprise. But we weren’t really powered for that, so it’s hard to draw definitive conclusions.

Dr. Radcliffe: How does this inform your preoperative counseling vs preoperative management?

Dr. Seibold: It is important to discuss with glaucoma patients who are preparing to have cataract surgery that they are at an increased risk of having a refractive surprise or maybe not having the exact refractive outcome that their calculations are designed to give them. They may be more likely to need either postoperative spectacles or contact lenses to correct any residual refractive error. Additionally, they might be at a higher risk of needing an IOL exchange or refractive surgery to correct any large refractive error.

We should emphasize this risk to those patients with pseudoexfoliation or chronic angle-closure glaucoma, whom we found to have the highest risk for a refractive surprise. Especially those with perhaps a more shallow anterior chamber or who have phacodonesis preoperatively. Those would be the ones I would specifically emphasize the increased risk of not hitting the target exactly each time and needing some other correction later, in the form of glasses, lens exchange, or refractive surgery.

Also, make sure that your IOL calculations are as accurate as can be. Many of these patients have poor ocular surface from their drops, so it’s important to make sure that the ocular surface is optimized as much as possible before surgery. Looking for any other macular changes preoperatively with OCT can be helpful.

Dr. Radcliffe: I don’t think you were able to pick up any signals regarding dry eye, but we do know 40% of people with glaucoma have dry eye, and part of the reason we want to do MIGS is to get patients off some of those drops. How do you prepare a patient who, for example, is on 3 drops and is going to have cataract surgery?

Dr. Seibold: Unfortunately, the scope of our paper didn’t uncover all the factors that led to these refractive surprises. If they had a high axial length, pseudoexfoliation or chronic angle closure, those would be at higher risk. But based on clinical experience and other data, I treat dry eyes a lot more aggressively in these patients preoperatively, even in patients without glaucoma, to try and tune up that ocular surface. Basically, from the time that I sign them up for cataract surgery, if they have any signs of dry eye I strongly emphasize artificial tear treatment. Sometimes I’ll start a prescription dry eye medicine as well to optimize their ocular surface ahead of time before they go in for the IOL measurement.

Pay close attention to your IOL calculations, particularly the keratometry readings and axial length readings, to make sure they’re reliable. If something doesn’t make sense preoperatively, have a low threshold to further treat their dry eye and have them come back another day to repeat the measurement before surgery, specifically if you’re doing a premium IOL, like a toric or multifocal lens. I also discontinue contact lens wear 2 weeks to 4 weeks before calculations and make sure keratometry readings are stable before proceeding with surgery. We did not uncover anything new that we should be doing postoperatively.

Dr. Radcliffe: What are the takeaways here in terms of premium IOLs?

Dr. Seibold: In the right patient, I think using a premium lens like a toric or multifocal lens, but especially toric lenses, can be a great option for glaucoma patients. Multifocal lenses, with their decrease in contrast sensitivity, should be used judiciously and probably only in very mild disease with appropriate discussion of the risks. The silver lining is, when you’re using a premium lens in a patient with glaucoma and combining it with a MIGS procedure like we often do, that the addition of MIGS doesn’t necessarily increase the risk of refractive surprise or having your calculation be off. You can more confidently recommend a MIGS procedure, like iStent and/or ECP, knowing that based on these data they’re probably not going to be at any higher risk of having a refractive surprise compared to just cataract surgery alone. In contrast, a previous study did find a trend toward more myopic results with cataract surgery combined with ECP, but this was only in angle closure eyes, which we know from our study have a high risk of refractive surprise.3

Dr. Radcliffe: I know you’ve done a lot with the Kahook Dual Blade (New World Medical), which is a trabecular procedure. Is there anything you can share from your experience related to refractive surprise?

Dr. Seibold: Anecdotally, my experience has been very similar to the 2 procedures that we included in this study. I haven’t noticed any increased refractive error or refractive surprise using the Kahook Dual Blade in addition to cataract surgery. Our unpublished data also back that up, but it wasn’t specifically looked at in this paper.

Trabectome has also been looked at in terms of refractive outcomes.4 Refractive outcomes were similar between cataract surgery alone and cataract surgery with trabectome. That aligns well with our data as well. GP

References

  1. Manoharan N, Patnaik JL, Bonnell LN, et al. Refractive outcomes of phacoemulsification cataract surgery in glaucoma patients. J Cataract Refract Surg. 2018;44:348-354.
  2. Yeh OL, Bojikian KD, Slabaugh MA, Chen PP. Refractive outcome of cataract surgery in eyes with prior trabeculectomy: risk factors for postoperative myopia. J Glaucoma. 2017;26:65-70.
  3. Wang JC, Campos-Moller X, Shah M, et al. Effect of endocyclophotocoagulation on refractive outcomes in angle-closure eyes after phacoemulsification and posterior chamber intraocular lens implantation. J Cataract Refract Surg. 2016;42:132-137.
  4. Luebke J, Boehringer D, Neuburger M, et al. Refractive and visual outcomes after combined cataract and trabectome surgery. Graefes Arch Clin Exp Ophthalmol. 2015; 253:419-423.
  5. Flowers BK. Effect of supraciliary microstent implantation concurrent with cataract surgery on the accuracy of IOL calculations in patients with open-angle glaucoma. Presented at: the 2018 American Society for Cataract and Refractive Surgeons annual meeting; April 17, 2018; Washington, DC.

NO SURPRISE HERE By Jennifer Ford, senior managing editor

An abstract presented at the 2018 American Society of Cataract and Refractive Surgery meeting by Brian E. Flowers, MD, described a retrospective review evaluating whether Cypass stent (Alcon) implantation at the time of cataract surgery affects refractive outcomes of cataract surgery. He compared refractive outcomes of 43 consecutive combined cataract/stent surgeries to a group of 43 similar patients who underwent cataract surgery alone. All 86 patients had open-angle glaucoma and were operated on by a single surgeon. The control group was selected from the same time period and was similar in demographics as well as axial length. The researchers evaluated the difference in the preoperative predicted refractive error compared to the postoperative spherical equivalent (SE) at various time points up to 6 months postoperatively.

In the stent group, the mean difference in postoperative SE compared to the preoperative predicted refractive error at 1, 3, and 6 months was -0.23, -0.22, and 0.20, respectively. This compares to -0.11, -0.08 and 0.03, respectively, for cataract surgery alone. The percentage of patients that were within 0.75D of the predicted postoperative SE was 74%, 76%, and 74% at 1, 3, and 6 months in the stent group, compared to 79%, 81%, and 83%, respectively, for control. No statistically significant differences were found between the 2 groups.5

“We had a few more data points by the time of the presentation, thus the numbers are slightly different,” Dr. Flowers told Glaucoma Physician. “There are studies that show patients with glaucoma are less likely to hit their refractive targets after cataract surgery. We did multiple subgroup analyses looking for risk factors for missing refractive targets (myopic or hyperopic). There seemed to be an emerging trend for low IOP to be associated with myopic shifts, but the numbers were too small. The only statistically significant thing we could find was that patients with IOP <10 and axial length <23 or >25 were more likely to experience a myopic shift at all time points.”