REFRACTIVE SURGERY FEATURE STORY Safety Considerations for Phakic IOLs Avoid potential problems by paying attention to these points. BY GWyn SAMUEL WILLIAMS, MRCS; AND MOHAMMED MUHTASEB, FRCOPHTH n the decades since their introduction in the 1950s, phakic IOLs have become a compelling option for the correction of refractive error. There are, however, potential problems that can result from electing a Iphakic IOL as part of a refractive solution. Consequently, various safety parameters have been devised to mini- mize risks. But before complications can be properly addressed, it is important to distinguish among the avail- able phakic IOLs and differentiate those problems associ- ated with each lens design. TYPES OF PHAKIC IOL Initial phakic IOL designs were angle-fixated lenses Figure 1. The Artisan lens is the longest-serving example of intended for implantation in the anterior chamber.1 an iris-supported lens. Unfortunately, the first 5-year follow-up study demon- strated a high rate of angle recession, glaucoma, hyphe- Posterior chamber phakic IOLs. The move to the pos- ma, endothelial cell loss, and decentration, leading to terior chamber began in the 1980s, when surgeons began removal in up to 60% of cases.2 Subsequent lens designs fixating iris-supported lenses on the posterior rather than improved, and today, in addition to anterior chamber the anterior face of the iris but continued to place the phakic IOLs, posterior chamber phakic IOLs are also optic in the anterior chamber.6 These so-called anterior- available. posterior lenses were associated with pupil block and Anterior chamber phakic IOLs. Phakic IOLs designed daytime photophobia in bright light, as the pupil could for the anterior chamber are either angle-supported or not constrict beyond a certain size due to the protrud- iris-supported. Angle-supported lens models include ing optic.6 The only such lens in use today is a one-piece the AcrySof Cachet one-piece foldable lens (Alcon meniscus PMMA lens, the Nikai IOL (Soleko). Laboratories, Inc.) and the two-piece Kelman Duet After this experience, lenses placed entirely in the Implant (Tekia).3 Several rigid PMMA angle-supported posterior chamber were developed in the early 1990s. lenses are still used in Europe, notably the ZSAL-4 The first lens of this design was what is now called the (Morcher GmbH). With its flexible haptics, this lens is Implantable Collamer Lens (ICL; STAAR Surgical);7 others designed to disperse compressive forces, reduce move- followed, including the Sticklens (IOLTech Laboratories). ment, and thus, decrease endothelial damage.4 Iris-supported lenses were developed to avoid the POTENTIAL PROBLEMS complications seen with angle-supported lenses in their AND SAFETY CONSIDERATIONS early years. The longest-serving example is the Artisan Endothelial cell count. Arguably the two most lens (Ophtec GmbH; Figure 1), a one-piece PMMA lens important parameters for contraindication of phakic that fixates onto the anterior surface of the iris. A fold- IOL implantation are anterior chamber depth (ACD) able version of this lens, the Artiflex, is also available. less than 2.8 mm and endothelial cell count (ECC) lower Studies have shown that endothelial loss rates with this than 2,500 cells/mm2 at 20 years of age or 2,000 cells/ lens are no higher than natural atrophy.5 mm2 at 40 years of age.3 However, these parameters are 30 CATARACT & REFRACTIVE SURGERY TODAY EUROPE JULY/AUGUST 2012 REFRACTIVE SURGERY FEATURE STORY A calculation based on the ECC, the age of the patient, and the natural endothelial cell death rate can be used to determine safety. risk for decompensation.15 The usual rule is that these indices stabilize after initial postoperative decompensation as rates of hexagonal cells increase.11 Reversal of this trend may be an indication for explantation. Angle considerations. A stable refraction and good ocular health are also important criteria. For posterior Figure 2. Evaluating endothelial morphology is important in chamber phakic IOLs, an open angle is the most impor- determining the potential risk of phakic IOL surgery. tant factor; Shaffer grades 3 and 4 are the least problem- atic angles.16 no longer absolute and should be considered on a case- Age. Declining endothelial cell counts and increasing by-case basis. A calculation based on the ECC, the age of crystalline lens thickness, which both occur with aging, the patient, and the natural endothelial cell death rate reduce ACD. Current thinking suggests 50 years of age (14 cells/mm2/year) can be used to determine safety.8 is the upper-age limit for phakic IOL implantation.3 One All intraocular procedures entail some degree of endo- must also bear in mind that phakic IOL implantation thelial cell loss, and insertion of a phakic IOL induces preserves the crystalline lens, and therefore, in a younger between 2.1% and 7.6%.3 Postoperative endothelial loss patient, preserves accommodation. In patients of pres- is also an important issue. In one study, the Artisan lens byopic age, this advantage is void, and the surgeon must was associated with endothelial cell loss of 1.06% at consider whether these patients would not be better 1 year, with an average yearly endothelial cell density served by clear lens extraction and placement of a pseu- change of -1.7% over the course of 3 years9 compared dophakic lens such as a multifocal.17 with the natural average change of -0.6%.10 Another Crystalline lens rise. Another recently recognized safety study showed 1-year endothelial loss rates of 3.5%; how- criterion proposed for anterior chamber phakic IOLs is ever, the loss rate stabilized over 5 years and the percent- crystalline lens rise,18 defined as the distance between the age of hexagonal cells increased, indicating stability.11 For anterior pole of the crystalline lens and the horizontal the ICL, the 1-year endothelial cell loss rate was 5.17% plane joining the opposite iridocorneal recesses. Among in one study,12 and, in another, a cumulative decrease of 87 eyes implanted with an Artisan IOL, little risk of pig- 7.7% was seen in endothelial cell density over 5 years.13 ment dispersion was found when the crystalline lens rise The reason for the discrepancy is possibly due to chronic was less that 600 µm. Beyond this level, the incidence low-grade inflammation.14 jumped to 67%. Postoperative checks are vital to detect higher-than- Additionally, due to natural thickening, the anterior expected rates of endothelial cell loss, and the lens pole of the crystalline lens moves forward by 20 µm each should be removed if the loss rate is too high.3 There is year, and for every 1.00 D of accommodation the ante- debate as to how high the cell loss rates must be before rior pole moves forward by 30 µm.19 Anterior segment one contemplates removal, with the options based on optical coherence tomography (OCT) can be used to an absolute ECC or on cumulative loss compared with calculate whether a phakic IOL—and which model—is preoperative values. safe to implant.20 Endothelial morphology. A high rate of hexagonal cells Cataract formation. The incidence of nuclear cataract indicates endothelial stability. During pre- and postopera- 4 years after angle-supported phakic IOL implantation tive evaluation of the endothelium, check for signs of poly- has been reported as 3.42%.21 In one series of posterior megathism and pleomorphism, which are variations in the chamber IOLs,22 8.2% of 170 patients developed some size and shape of the cells, respectively (Figure 2). Corneas degree of anterior subcapsular opacity, which was symp- with high rates of polymegathism and pleomorphism do tomatic in five patients (2.3%) and required phacoemul- not tend to do well after intraocular surgery, and the pres- sification in two patients (1.2%). As 86% of these anterior ence of less than 50% hexagonal cells is considered high subcapsular elements presented within 7 months of the JULY/AUGUST 2012 CATARACT & REFRACTIVE SURGERY TODAY EUROPE 31 REFRACTIVE SURGERY FEATURE STORY TAKE-HOME MESSAGE Mohammed Muhtaseb, FRCOphth, is a Consultant Ophthalmic Surgeon at the Royal • Insertion of a phakic IOL induces between 2.1% and Glamorgan Hospital, Wales, United Kingdom. 7.6% endothelial cell loss. Dr. Muhtaseb states that he has no financial • During pre- and postoperative evaluation of the interest in the products or companies men- endothelium, check for polymegathism and tioned. He may be reached at tel: +44 7949 235 666; pleomorphism. e-mail: [email protected]. • Anterior segment OCT can indicate whether a Gwyn Samuel Williams, MRCS, is a Specialist phakic IOL is safe to implant, and which one. Registrar at the Royal Glamorgan Hospital, • The most vital preoperative consideration is Wales, United Kingdom. Dr. Williams states accurate calculation of the phakic IOL power. that he no financial interest in the products or companies mentioned. He may be reached at operation and tended to be within the first group of tel: +44 1792 797398; e-mail: gwynwilliams@ patients operated upon by individual surgeons, the study doctors.org.uk. authors posited that surgical technique and adequate sizing were more relevant to cataract formation than the 1. Brown CA. Anterior chamber implants with the Ridley tripod lens. Proc R Soc Med. 1976;69:908-911. 2. Barraquer J. Anterior chamber plastic lenses. Results of and conclusions from five years’ experience. Trans presence of the lens in the posterior chamber. Cataract Ophthalmol Soc UK. 1959;79:393-424. formation does not always occur; one of the first patients 3. Lovisolo CF, Reinstein DZ. Phakic intraocular lenses. Surv Ophthalmol. 2005;50:549-587. 4. Jiminez-Alfaro I, Garcia-Feijoo J, Perez-Santonji JJ, et al. Ultrasound biomicroscopy of ZSAL-4 anterior chamber who underwent posterior chamber phakic IOL implanta- phakic intraocular lenses for high myopia.