Phakic intraocular lenses can be offered as the primary surgical option for anyone who has refractive errors within the available treatment range and meets other screening criteria (discussed later). However, most surgeons reserve PIOL use for patients whose refractive limits are near or beyond the FDA-approved limits for laser vision correction, or who are otherwise not good candidates for keratorefractive surgery. Although excimer lasers can be used to treat high degrees of myopia, many surgeons have reduced the upper limits for laser in situ keratomileusis (LASIK) and surface ablation in their refractive practices because of the decreased predictability, high rate of regression, large amount of stromal tissue removed, increased incidence of microstriae, and night-vision problems that can occur with treatment of a patient with high myopia. Similarly, LASIK and surface ablation for correction of hyperopia greater than +4.00 D and astigmatism greater than 4.00 D of cylinder are less accurate than they are for lower corrections. If surgeons become comfortable with the use of PIOLs, they may also choose to implant them for refractive powers significantly lower than the maximal limits for programmable excimer laser treatments. In addition, due to the rapid visual recovery and low complication rate of currently available PIOLs, increasing numbers of surgeons are implanting these lenses bilaterally on the same day, providing a patient experience similar to bilateral same-day LASIK. The Ophthalmic Mutual Insurance Company (OMIC) has evaluated this practice.
PIOLs are available in powers between –3.00 D and –20.00 D in the United States (see Table 8-1). Outside the United States, PIOLs are available for correcting hyperopia up to +10.00 D. PIOLs may be considered off-label treatment for eyes with irregular topographies from forme fruste or frank keratoconus.
Ophthalmic Mutual Insurance Company (OMIC). Am I covered for performing bilateral same-day RLE or bilateral same-day phakic implant procedures? OMIC website. Updated June 5, 2014. Available at https://goo.gl/bb9IcI. Accessed November 6, 2016.
Phakic intraocular lenses have specific contraindications. These include preexisting intraocular disease such as a compromised corneal endothelium, iritis, significant iris abnormality, rubeosis iridis, cataract, or glaucoma. The anterior chamber diameter, anterior chamber depth, and pupil size must be appropriate for the specific PIOL being considered.
A thorough preoperative evaluation is necessary, as detailed in Chapter 2. PIOLs are not approved in the United States for patients younger than 21 years.
As with any refractive procedure, an informed consent specifically for this procedure should be obtained before surgery. The patient should be informed of the potential short-term and long-term risks of the procedure and of available alternatives; he or she should also be counseled about the importance of long-term follow-up because of the potential for endothelial cell loss over time. The surgeon must also ensure that the patient has realistic expectations about the visual outcomes of the procedure.
Specular microscopy or confocal microscopy should be performed to evaluate endothelial cell count and morphology. Anterior chamber depth must also be assessed because adequate depth is required for safe implantation of a PIOL. If the anterior chamber depth is less than 3.2 mm, the risk of endothelial and iris or angle trauma from placement of an anterior chamber, iris-fixated, or posterior chamber PIOL is increased. Anterior chamber depth can be measured by ultrasound biomicroscopy, anterior segment optical coherence tomography (OCT), partial coherence interferometry, slit-beam topography, or Scheimpflug imaging. In the United States, PIOL implantation is contraindicated in individuals who do not meet the minimum endothelial cell count specified for each PIOL and who do not have a minimum anterior chamber depth of 3.2 mm. Methods for IOL power selection are specific to each PIOL and manufacturer, and some manufacturers provide software for use in IOL power calculation.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.