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Forensic analysis, case review help define causes of IOL explantation
Dislocation, incorrect lens power and IOL opacification are the three main causes of explantation.
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A study based on an extensive review of cases and forensic analysis of explanted IOLs provided reliable scientific data for the classification of causes that lead to explantation.
“IOL explantation is an infrequent but serious event that deserves attention. Knowing the causes of explantation is epidemiologically important because they might reflect inadequate surgical practices, inadequate materials or design. From knowing the causes, we get important insights on how to improve manufacturing, selection and implantation techniques,” Jorge L. Alió, MD, PhD, said.
About 8 years ago, Alió created jointly with 20 other centers in Spain the Iberian National Biobank of intraocular explanted material. This biobank is located in the facilities of Vissum Instituto Oftalmologico de Alicante under the supervision and auspices of the University Miguel Hernandez, as it is a part of the structure of the cooperative network for clinical research Oftared, sponsored by the Spanish government. It now has more than 2,000 specimens collected from several centers in Spain together with the information about the reason for explantation and the outcomes of surgery. In recent studies published by Alió and the Oftared group, 257 explanted lenses were studied, and dislocation, incorrect lens power and opacification were found to be the main causes of explantation.
IOL dislocation
“Late dislocation accounted for 60% of the cases of explantation. With the growth of the pseudophakic population and longer life expectancy, it is likely that late dislocation may become increasingly common in the future,” Alió said.
Progressive zonular dehiscence, occurring several years after cataract surgery, is the cause of dislocation in most cases. Pseudoexfoliation is the most recognized predisposing factor, followed by connective tissue disorders, uveitis, retinitis pigmentosa and high myopia.
Interestingly, the incidence of pseudoexfoliation appeared to vary according to geographic location in Spain, ranging from 0.5% in the Madrid area up to 25% to 30% in the northern regions.
“In our study, high myopia, more often than [pseudoexfoliation], was associated to dislocation,” Alió said. “Myopic eyes undergo thinning and degeneration processes in several layers of tissues and may be more prone to zonular failure due to elongation of the zonular fibers.”
Highly myopic patients also had explantation at a younger age as compared with other groups.
Repositioning a dislocated IOL may not be always possible, but it is desirable to avoid enlarging the corneal would for exchange. Scleral suturing is the most widely used technique in these cases. IOL exchange was reported to have variable complication rates, from as high as 42% in some studies to below 20% in other studies, depending on the patients’ conditions and the surgeons’ abilities. In many cases, patients may experience deterioration of vision after surgery.
Incorrect lens power
Unsatisfactory visual outcomes, as a result of incorrect lens power, may still be a reason for explantation. In Alió’s series, this accounted for about 13% of the cases. Inaccurate biometry, the limitations of calculation formulas when dealing with high refractive error as well as the incorrect positioning of the lens may be the causes.
“In most of our cases, we are not far from hitting the target, but emmetropia is reached in only about half of the eyes planned for that goal, as shown by the analysis of more than 17,000 cases in the Swedish National Cataract Register,” Alió said.
Without reopening the eye, residual error can be corrected by excimer laser procedures, but not all surgeons have the equipment to do so in their centers. Lens procedures may include IOL exchange or piggyback IOLs.
“In a retrospective comparison of the three methods, we found that LASIK, on top of being safer, was also better in terms of refractive outcomes and predictability. However, lens-based procedures should be a choice in case of extreme ametropia and corneal abnormalities,” Alió said.
IOL opacification
Many cases of IOL opacification were related to the manufacturing process of specific hydrophilic acrylic IOLs, such as the Hydroview (Bausch + Lomb), the MemoryLens (Ciba Vision), the SC60B-OUV (MDR) and the Aqua-Sense (Ophthalmic Innovations International). Although these lenses are no longer on the market, cases of late opacification and explantation are still reported 10 years after primary surgery. Other cases occurred in a recent hydrophilic IOL with a hydrophobic surface, associated with medical conditions such as diabetes, hypertension and glaucoma.
“Lens opacification leads to decreased visual acuity and loss of quality of vision. Obviously, there are no other options than explantation and IOL exchange, which after so many years is often difficult and has a high risk of complications. In our study the success rate was high, but vitrectomy had to be performed in one-third of the eyes and the new IOL was implanted in the ciliary sulcus in more than 60% of the patients,” Alió said.
According to Alió, there is still too little focus on long-term biocompatibility issues when new lenses are manufactured.
“Materials should be tested more and for prolonged periods before large-scale use,” he said.
Explantation of multifocal IOLs
The explantation of multifocal IOLs deserves specific attention, and research should be done to identify the lenses that have a higher rate of explantation, according to Alió.
“Multifocal technology has improved over the years, but problems with tolerance still occur and are still a reason for failure. The problems in most cases are not related to the lenses themselves, but rather to our selection criteria and identification of risk factors,” he said.
The good news is that explantation of multifocal lenses is generally easier and safer than explantation due to other causes because problems manifest early and the decision is made within a few months from surgery, when scarring processes have not yet occurred. In addition, multifocal IOLs are implanted in healthy eyes, which are less exposed to complications.
“The real problem in these cases is the decision of whether or not to explant, of whether the procedure is worthwhile. Visual symptoms and contrast sensitivity improve, but refraction might worsen and potential complications have to be taken into account,” Alió said.
Techniques
There are several techniques for IOL explantation, and surgeons should be able to use them all and adapt them to specific cases. Mostly, techniques that can be performed through small incisions are preferred today.
“We rarely explant the whole lens today because it requires wound enlargement, and rarely we deal with old, rigid lenses that cannot be cut or folded,” Alió said.
The lens can be cut inside the eye in different ways, by bisecting, partially bisecting or trisecting it. Lens haptics can be cut manually or with a YAG laser to facilitate removal of the optic. In some cases they are left inside the eye when they are held tight by fibrotic tissue and the risk of removing them would be too high.
“Refolding the lens and extracting it through a minimally enlarged incision is another option, but it requires a lot of manipulation. The risk of damaging the endothelium and reducing the cell count is quite high,” Alió said.
Finally, Alió emphasized the importance of performing forensic studies when a lens is explanted.
“Each surgeon might have just two or three cases in 1 year, but globally it is a problem worth analyzing. Historically, forensic studies have given a lot of information in medicine and can help us understand why lenses fail and how we can prevent failure,” he said. – by Michela Cimberle
- References:
- Alió JL, et al. J Refract Surg. 2015;doi:10.3928/1081597X-20141202-01.
- Bompastor-Ramos P, et al. J Cataract Refract Surg. 2016;doi:10.1016/j.jcrs.2016.06.032.
- Fernández-Buenaga R, et al. Eur J Ophthalmol. 2015;doi:10.5301/ejo.5000615.
- For more information:
- Jorge L. Alió, MD, PhD, can be reached at University Miguel Hernandez, Vissum Instituto Oftalmologico de Alicante, Avenida de Denia, s/n, 03016 Alicante, Spain; email: jlalio@vissum.com.
Disclosure: Alió reports no relevant financial disclosures.