Residual refractive errors may be preoperative culprits.
This article was reviewed by Scott M. Macrae, MD
Refractive surgeons have a number of options from which to choose when considering presbyopia-correcting IOLs.
Trifocal IOLs continue to gain in popularity in Europe. One has been approved in the United States, the AcrySof IQ PanOptix trifocal IOL (Alcon). However, the downside with these IOLs is that surgeons must be attuned to the presence of residual refractive errors, which seems to be the issue associated with this technology. Those refractive errors can constitute a make or break for patients.
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According to Scott M. MacRae, MD, it is mandatory to correct any residual refractive errors before attacking the presbyopia.
“After IOL implantation, when a patient is 20/happy, they see well at all distances; if they are 20/unhappy, I evaluate the residual refractive errors and, if found, try to refine them,” said Dr. MacRae, professor ophthalmology and visual sciences, Flaum Eye Institute University of Rochester, Rochester, NY.
Sometimes there is no residual refractive error, and the unhappiness may result from the presence of retinal issues, such as cystoid macular edema, epiretinal membranes, cystoid macular edema; posterior capsular opacification; irregular astigmatism resulting from anterior basement macular dystrophy or dry eye; or unrealistic expectations.
“However, the one that we can treat the best is the residual refractive error,” he noted.
Dr. MacRae credited Richard Lindstrom, MD, with raising the consciousness about the importance of the residual refractive error when he pointed out that between one and three months postoperatively, over 57% of eyes with premium IOLs may not have achieved the full benefit of the implants because of the bugaboo, the residual refractive error.
The multifocal IOLs are particularly sensitive to residual refractive errors, in that 10.8% to 25% of eyes treated with a multifocal IOL required a re-treatment such as a lens exchange, LASIK, or PRK (Potvin et al. Clinical Ophthalmol 2016;10:365-71; Goes J Refract Surg 2008;24:243-50. doi: 10.3928/1081597X-20080301-05). Dr. MacRae pointed out.
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Focus on focus
Dr. MacRae pointed out that he could not overemphasize the understanding of the patient’s optics. One factor in the optics is the corneal topography. He recounted the case of a patient with anterior basement membrane dystrophy causing irregular astigmatism, who had undergone implantation of a multifocal IOL.
The patient was unhappy with her outcome and required a superficial keratectomy and PTK to improve her vision. Another patient had had contact lens-induced corneal distortion and, he noted, likely should not have received a multifocal IOL.
Some success was achieved with partial correction of the regular astigmatism.
“However, cases such as this are difficult to correct, and multifocal IOLs are best avoided,” Dr. MacRae said.
Another factor is measurement of the postoperative manifest refraction. In Dr. MacRae’s practice, the technicians dig deep to identify as little as 0.75 D of hyperopia or 0.50 D of myopia. If this is uncovered, that amount of refractive error is put into a trial lens frame to allow the patient to test the impact of the refraction in the real world.
A positive evaluation after that with a near card then determines if the refractive error correction solves the problem. If it is, a PRK or LASIK can be performed. If the patient is unsure, he or she uses a soft contact lens or spectacles containing the refractive error for a few weeks before a determination is made, he explained.
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In addition to the multifocal IOLs, diffractive and extended-depth-of-focus IOLs also are particularly impacted by small amounts of residual refractive errors, especially astigmatism.
As noted, 0.75 D of astigmatism can wreak havoc with visual quality and performance, but when combined with subtle irregular astigmatism or posterior capsular opacification, large angle kappa, dry eye, and anterior basement membrane dystrophy, there is an additive effect that reduces image quality, he said.
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“Surgeons should be very aware of this,” he advised.
Dr. MacRae and colleagues performed a study at the University of Rochester in which they compared three multifocal IOLs (ReSTOR3D, ReSTOR3D; Micro F diffractive trifocal, FineVision; and Mplus refractive bifocal IOL, Oculentis) to the AcrySof monofocal IOL.
The investigators corrected the refractive errors and added increasing amounts of astigmatism to determine the through-focus image quality of the IOLs.
“We found that 0.75 D and 1 D of astigmatism dramatically reduced the image quality compared to the monofocal IOL,” he said. “Therefore, correcting even that small degree of astigmatism is important for these patients if they are symptomatic.”
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Correcting the focus
What’s the best way? LASIK, PRK, and relaxing incisions are all good methods depending on the need.
Dr. MacRae performs LASIK in health eyes, and even older patients experience rapid visual recovery. PRK is useful to correct residual refractive errors in post-LASIK eyes. He noted that he likes to perform a mini-PRK for refinement, in which the epithelium with a 7-mm diameter is removed instead of removal of epithelium with a diameter of 8.5 mm, a 30% decrease. This approach allows quicker recovery by one day, less risk of an epithelial defect, and less patient discomfort.
Limbal relaxing incisions are effective in cases with mixed astigmatism of less than 1.25 D. In these cases, he advised against going too centrally (8 mm or less) on the cornea because of the potential for development of coma and less efficient wound healing.
Dr. MacRae summed up his pearls. First, rule out and correct any accompanying issues such as posterior capsular opacification and retinal problems as well as the refractive error.
“Most importantly, inform the patient preoperatively that the possibility of IOL refinements may be necessary postoperatively,” he concluded. “Rather than considering this a treatment failure, consider it as an anticipated refinement.”
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Scott M. Macrae, MD
Dr. Macrae has no financial interest in the topic of this report.