symptomatic cataracts requiring surgery, and 6 other eyes developed asymptomatic anterior subcapsular cataracts. In a study of more than 500 eyes monitored for an average of 4.7 years, Sanders reported that 6%–7% of eyes developed anterior subcapsular opacities and 1%–2% developed visually significant cataracts.
The incidence of retinal detachment after posterior chamber PIOL insertion is very low. In a series of 16 eyes, surgical reattachment was achieved in 100%, with a mean follow-up of 35.25 months (range, 12–67 months) and a mean postoperative best spectacle-corrected visual acuity of 20/28.
Kohnen T, Knorz MC, Cochener B, et al. AcrySof phakic angle-supported intraocular lens for the correction of moderate-to-high myopia: one-year results of a multicenter European study. Ophthalmology. 2009;116(7):1314–1321. Epub 2009 May 30.
Martínez-Castillo V, Boixadera A, Verdugo A, Elíes D, Coret A, García-Arumí J. Rhegmatogenous retinal detachment in phakic eyes after posterior chamber phakic intraocular lens implantation for severe myopia. Ophthalmology. 2005;112(4):580–585.
Sanders DR. Anterior subcapsular opacities and cataracts 5 years after surgery in the Visian Implantable Collamer Lens FDA trial. J Refract Surg. 2008;24(6):566–570.
Sanders DR, Vukich JA, Doney K, Gaston M; Implantable Contact Lens in Treatment of Myopia Study Group. U.S. Food and Drug Administration clinical trial of the Implantable Contact Lens for moderate to high myopia. Ophthalmology. 2003;110(2):255–266.
Angle-supported phakic intraocular lens
The complications reported most frequently for angle-supported PIOLs are nighttime glare and halos, pupil ovalization, and endothelial cell loss. The risk of pupillary block is low with the use of modern PIOL designs and of iridotomies when needed.
Glare and halos, the most commonly reported symptoms after angle-supported PIOL insertion, occurred in 18.8%–20.0% of patients, but these symptoms appear to decrease by as much as 50% over a postoperative period of 7 years. Endothelial cell loss occurring 1–7 years after angle-supported PIOL insertion ranges from 4.6% to 8.4%. Pupil ovalization can occur because of iris tuck during insertion, or it can occur over time as a result of chronic inflammation and fibrosis around the haptics within the anterior chamber angle. The incidence of pupil ovalization ranges from 5.9% to 27.5% and is directly related to the postoperative interval studied. Ovalization is more likely when the implant is too large. In contrast, endothelial damage and decentration are most often associated with movement of a lens that is too small.
Knorz and colleagues reported on the 6-month to 3-year results of an angle-supported PIOL in 360 eyes with moderate to high myopia. No eyes experienced pupillary block, pupil ovalization, or retinal detachment. The annualized percentage loss in central and peripheral endothelial cell density from 6 months to 3 years was 0.41% and 1.11%, respectively.
Knorz MC, Lane SS, Holland SP. Angle-supported phakic intraocular lens for correction of moderate to high myopia: Three-year interim results in international multicenter studies. J Cataract Refract Surg. 2011;37(3):469–480.
Refractive Lens Exchange
Patient Selection
Indications
The indications for refractive lens exchange (RLE)—that is, removal of the crystalline lens with IOL implantation for the primary purpose of correcting refractive error—are evolving. Refractive lens exchange is usually considered only if alternative refractive procedures are not feasible and there is a strong reason that spectacles or contact lenses are unacceptable alternatives. RLE may be preferable to a PIOL in older patients who no longer have adequate accommodation and in patients with lens opacity that may progress in the relatively near future. RLE is generally not considered medically
necessary and is usually not covered by the patient’s insurance. As all FDA-approved IOLs are approved specifically for implantation at the time of cataract surgery, implantation for RLE is considered an off-label use in the United States.
Informed consent
Refractive lens exchange carries risks and complications identical to those for routine cataract extraction with IOL implantation. Potential candidates must be capable of understanding the shortterm and long-term risks of the procedure. Patients should be informed that unless they are targeted for residual myopia with monofocal, toric, or accommodating IOLs, or have a multifocal IOL implanted, they will not have functional near vision without correction. A consent form should be given to the patient prior to surgery to allow ample time for review and signature. A sample consent form for RLE for the correction of hyperopia and myopia is available from the Ophthalmic Mutual Insurance Company (OMIC) at www.omic.com.
Myopia
Refractive lens exchange can be considered in patients with myopia; however, in addition to the risks associated with cataract surgery, the surgeon must specifically inform the patient about the risk of retinal detachment associated with removal of the crystalline lens. Myopia is a significant risk factor for retinal detachment in the absence of lens surgery, and this risk rises with increased axial length. The risk of retinal detachment in eyes with up to 3.00 D of myopia may be as much as 4 times greater than it is in emmetropic eyes, whereas in eyes with >3.00 D of myopia, the risk may be as high as 10 times that in emmetropia. In the absence of trauma, more than 50% of retinal detachments occur in myopic eyes.
American Academy of Ophthalmology Retina/Vitreous Panel. Preferred Practice Patterns Guidelines. Posterior Vitreous Detachment, Retinal Breaks, and Lattice Degeneration. San Francisco: American Academy of Ophthalmology; 2008. Available at: www.aao.org/ppp.
Hyperopia
If the amount of hyperopia is beyond the range of alternative refractive procedures, RLE might be the only available surgical option. As with correction for myopia, the patient must be informed about the risks of intraocular surgery. A patient with a shallow anterior chamber from a thickened crystalline lens or small anterior segment would not be a candidate for a PIOL and could benefit from the reduced risk of angle-closure glaucoma after RLE. Patients with hyperopia have a lower risk of retinal detachment than do patients with myopia.
Nanavaty MA, Daya SM. Refractive lens exchange versus phakic intraocular lenses. Curr Opin Ophthalmol. 2012;23(1):54–61.
Astigmatism
Patients with significant astigmatism are also candidates for RLE with the advent of toric IOLs that cover an expanded range. In the United States, there are currently no FDA-approved combined toric multifocal IOLs. Thus, US patients planning to undergo implantation of a toric IOL must understand the lack of uncorrected near acuity if targeted for distance; patients considering multifocal IOL implantation should understand that these IOLs will not sufficiently reduce astigmatism. Also, patients need to understand that an additional surgical procedure, usually LASIK or photorefractive keratectomy, may be necessary to maximize spectacle independence and that laser vision correction candidacy should be determined prior to lens-based surgery if it is being considered. Smaller amounts of astigmatism may be managed with corneal incisional surgery.
Surgical Planning and Technique
Although RLE is similar to cataract surgery, there are some additional considerations for planning and performing the procedure because the primary surgical goal is refractive rather than merely reduction of vision loss due to cataract. First, in contrast to keratorefractive procedures, which are usually performed as immediately sequential procedures in the same surgical session, RLE is usually performed as sequential surgery on separate days to minimize the potential for bilateral endophthalmitis. However, this standard continues to evolve, and some surgeons are performing bilateral RLE in the same surgical session.
Preoperative corneal topography is essential to determine the degree of irregular astigmatism present and identify patients with borderline corneal ectatic disorders such as keratoconus and pellucid marginal degeneration. Patients with these conditions may still have RLE performed; however, they must understand the limits of vision correction obtainable, and if there is suspicion of ectatic corneal disease, patients must understand that they are not good candidates for postoperative treatment with LASIK or photorefractive keratectomy to refine the refractive correction.
Surgeons must identify the degree of corneal versus lenticular astigmatism present, as only the corneal astigmatism will remain postoperatively. The patient should be informed if substantial astigmatism is expected to remain after surgery, and a plan should be devised to correct it in order to optimize the visual outcome. Small amounts of corneal astigmatism (<1.00 D) may be reduced if the incision is placed in the steep meridian.
Limbal relaxing incisions with either blade or femtosecond laser may be used to correct residual corneal astigmatism of less than 2.00 D (see Chapter 3). Supplemental surface ablation or LASIK could also be considered (see the following discussion on bioptics). Although glasses or contact lenses are an alternative for managing residual astigmatism, refractive surgery patients frequently reject this option.
Some surgeons obtain preoperative retinal OCT to identify potential macular pathology. Careful attention should be paid to the peripheral retinal examination, especially in patients with higher myopia. If relevant pathology is discovered, appropriate treatment or referral to a retina specialist is warranted. In patients with high axial myopia, retrobulbar injections should be performed with caution because of the risk of perforating the globe. Peribulbar, sub-Tenon, topical, and intracameral anesthesia are alternative options. In a highly hyperopic eye with an axial length <18 mm, nanophthalmos should be considered. Eyes with these characteristics have a higher risk of uveal effusion syndrome and postoperative choroidal detachment.
Many surgeons believe that an IOL should be implanted after RLE in a patient with high myopia rather than leaving the patient with aphakia, even when little or no optical power correction is required. Plano power IOLs are available if indicated. The IOL acts as a barrier to anterior prolapse of the vitreous, maintaining the integrity of the aqueous–vitreous barrier, in the event that Nd:YAG laser posterior capsulotomy is required. Some IOL models also reduce the rate of posterior capsule opacification.
IOL Power Calculations in Refractive Lens Exchange
High patient expectations for excellent uncorrected distance visual acuity (UDVA; also called uncorrected visual acuity, UCVA) after RLE make accurate IOL power determination crucial. However, IOL power formulas are less accurate at higher levels of myopia and hyperopia. In addition, in high myopia, a posterior staphyloma can make the axial length measurements less reliable. Careful fundus examination and B-scan ultrasound imaging can identify the position and extent of staphylomas. The subject of IOL power determination is covered in greater detail in BCSC Section 3, Clinical Optics, and Section 11, Lens and Cataract.