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An Overview of Phakic Intraocularlenses Albert C REVIEW An overview of phakic intraocularlenses Albert C. M. Wong,' FCOphHK, FHKAM, Dimitri Az((J;2 MD, Chi Cheong Wong,' FCOphHK, FHKAM, Clement W N. Chan, 1 FCOphHK, FHKAM 1 Lo Ka Cliow Oplitlialmic Memorial Centre, 1img \\Till Eastem Hospital, Hong Kong, Cliina. 1lllinois Eye and Ear b1jir111aiy, Cliicago, USA. Correspondence and reprint requests: Albert C. M . .ll'ong, 9/F Lo Ka C/iow Oplit/ialmic Memorial Centre, 1img \foll Eastem Hospital, Causeway Bay, Hong Kong, Cliina. Tel: (852) 2162 6888; Fax: (852) 2882 9909; F:-mail: drnlbertc111w@1:111ail.co111 3 6 9 addition to those used for correcting myopia • · and hyper­ 10 12 Abstract opia, · certain lenses are used to correct astigmatism 13•14 and presbyopia.15 The purpose of this article is to review There are 3 types of phakic intraocular lenses: angle­ the different PIOLs and the associated complications. The supported, iris-fixated, and posterior chamber. Implan­ reference articles quoted in this review are collected from tation of phakic intraocular lenses has been common a Medline database search using the key word 'phakic practice in Europe fo r the past decade. With the recent intraocular lens' plus 'complications', 'endothelial loss', approvals by the USA Food and Drug Administration ' pigment dispersion', 'cataract', 'vitreoretinal complication', for the Verisyse and Staar lenses, phakic intraocular lens­ 'surgical technique', and 'visual outcome'. implantation is expected to increase worldwide. Unlike Indications and contraindications the power calculation for conventional intraocular lenses using axial length and keratometry, the power of phakic Indications for PIOL implantation arc moderate to high intraocular lenses is calcul ated from keratometry myopia or hyperopia. The refraction should be stable so readings, anterior chamber depth, refractive error, and PIOLs are usually indicated for patients older than 20 years. ve1tex distance. In this review, different models of phakic For the implantation of anterior chamber lenses, the ante­ intraocular lenses and their indications are addressed. rior chamber depth should be at least 3.0 mm (measured Complications of implanting these lenses include endo­ from the inner part of the cornea). The endothelial cell count thelial cell loss, cataract, pigment deposits, iridocyclitis, should be at least 2000/mm2 preoperatively. For patients with and vitreoretinal complications. T hese complications more than -15.0 D refracti ve error, bioptics can be consid­ should be noted by surgeons before considering the use ered by adding an additional corneal procedure (usually 16 7 of these lenses for refractive cotTection. LASIK). .1 Limitations of the Verisyse toric IOL (Advanced Medical Optics, lnc, Santa Ana, USA) are a cylindrical power of up to 7 .00 D only and an optical zone of 5.00 mm. 13 Key words: lenses, intmocular; l ens implantation. intraocular; Postoperatil'e complications General contraindications for all types of PIOL implanta­ tion include ocular conditions such as corneal dystrophy, Introduction cataract, history of iritis, glaucoma, pigment dispersion syndrome, pseudoexfoliation of the lens capsule, excess iris A phakic intraocular lens (PlOL) is an intraocular lens de­ convexity, large scotopic pupils, ocular hypertension, con­ sig ned for implantation into an eye with phakia. ln 1954, tact sports, presbyopic age (in which refractive lens exchange Strampelli reported the first implantatio n of a minus power is preferred), and ocular conditions associated with diabetes. phakic intraocular lens (PJOL) in the anterior chamber. 1 Small pupil size is a relative contraindication fo r posterior Thereafter, newer and be tte r desig ns of PlOLs we re chamber lens implantation. 18 developed. There are 3 types of PIOL: the angle-supported/ angle-fixated lens (AS PlOL),2 iris-fixated/iris-claw lens With the development of anterior chamber optical coherence 3 4 5 (IF Pl OL), and posterior chamber lens (PC PlOL). • In tomography, a new parameter called crystalline lens rise, 28 HKJOphthalmol ® Vol.10 No.1 REVIEW which is defined by the distance between the anterior pole models,24 the parameters affecting the deviation of IOL of the crystalline lens and the horizontal plane joining the power from the desired power occurred in the following opposite iridocorneal recesses, has been proposed.'9 This order: refraction, vertex distance, ELP, keratometry, and parameter is used to predict the chance of developing pig­ refractive index. PlOLs showed high predictability in eyes ment dispersion after AS PIOL implantation. The safety level with preoperative refractive error between +1 5.0 D to -15.0 has been suggested to be <600 ~un . D. Thus, accurate measurements of preoperative refraction and the corresponding vertex distance, which may often be Power calculations for phakic intraocular neglected in conventional cataract surgery, are important for lens providing accurate desired postoperative refractions. The formula used for the power calculation for PIOL is based Sizing of phakic intraocular lenses on vergence equations: the object vergence is equal to the refractive index of the object medium divided by the object The origi nal design of the Worst-Fechner biconcave iris claw distance (L = n/ I). In 1988, van der Heijde et al published a lens is standardized to 8.5 mm in size, but 7.5-mm or 8.5-mm 3 10 25 26 formu la to determine the IOL power needed for phakic myo­ lenses can now be obtained (Verisyse lens). • · • Other 21 pia and aphakia (hyperopia).20• Holladay later included the lenses such as angle-fixated and posterior chamber lenses desired postoperative refraction (DPostRx) in the equation.22 are available in 3 different sizes with a 0.5-mm step. Accu­ In both formulae, the following parameters were needed: rate sizing of PIOLs is important to minimize complications. the expected/effective lens position (ELP; distance from Limbal white-to-white diameter is usually used to determine corneal vertex to principal plane of IOL), the net corneal the size of the PIOL. The length of anterior chamber PIOLs power (K), the preoperative refraction in D (PreRx), and the (AC PIOLs) is approximated by adding 0.5 mm or 1.0 mm vertex distance (V) [Figure 1). Usually, the manufacturer to the horizontal w hite-to-white diameter for myopia or 6 27 28 calculates the desired power of the lens for the surgeons who hyperopia according to different Jens models. • · For PC provide the parameters. The effective lens position depends PIOLs, 0.5 mm or 1.0 mm is added to the horizontal white­ on the type of Jens and is estimated from the anterior cham­ to-white diameter for myopia, and 0.5 mm is subtracted for 9 11 29 ber depth, measured from the corneal vertex to the anterior hyperopia. • • .JO I 00 MHz ultrasound biomicroscopy (UBM) surface of the lens, rather than using the anatomical anterior and OCT may be helpful for assessing the preoperative and 11 38 chamber depth, which is measured from the corneal endo­ postoperative anatomical conditions. - thelium to the anterior surface of the lens. The white-to-white diameter can be measured by various Holladay's formula works well for all types of lenses. The instruments. The usual manual device is a surgical measur­ Staar Company (Monrovia, USA) has its own software for ing caliper with a scale from 0 to 20.0 mm in 1.0-mm steps. power calculations, but the exact equation was not found in The Holladay-Godwin Cornea Gauge is a hexagonal plate any published articles. Other formulae such as the Olsen­ with a half-circle scale from 9.0 mm to 14.0 mm in 0.5-mm 11 12 Feingold formula9• • ·18•23 have been used for the power increments, and can be held 1.0 mm from the cornea for calculation of PC PIOLs. The basic concept of this fo rmula measurement. Optical devices such as Orbscan II (Orbtek is to take account of the relative position of the PIOL to the Inc, Salt Lake City, USA) and JOLMaster (Carl Zeiss, biometric anterior segment measurements by considering Meditec, Jena, Germany) can detect the border between white the geometric featu res, refractive index, and elasticity of sclera and the darker iris image. lOLMaster shows the best the IOL material. Clinicall y, this formula shows less pre­ correlation with the measurements of video images and has dictability fo r myopia than for hyperopia.23 The accuracy of the highest reliability. 39 the power calculations is mainly governed by the accurate measurements of each parameter. Using mathematical Angle-supported phakic intraocular lenses Examples of AS PIOLs include BaikoffZB (Domilens, Lyon, France), ZB5M (Domilens, Lyon, France), Nu Vita (Bausch 1336 1336 640 lOLe = ------ and Lomb Surgical, Irvine, USA), • ZSAL-4 (Morcher GMBH, 136 136 Stutgart, Germany),41 phakic 6H (Ophthalmic Innovations -- - ELPo - - - ELPo 28 2 1000 1000 International [OII] Inc, Ontario, USA), .4 GBR (IOLTECH, - - - +Ko ---+ Ko LaRochelle, France)NIVARTE foldable (CIBA-Vision AG, 1000 1000 41 - --V - - - - V Embrach, Switzerland), - Kelman Duet (Tekia, Irvine, USA),.w Pre Rx DPostRx I-CARE lens (Corneal, Paris, France), and Thinlens (ThinOptX, Abingdon, USA) LFigure 2]. The Baikoff lenses are polymethyl methacrylate (PMMA) biconcave lenses Figure 1. The power determination of phakic intraocular lens using Holladay's formula.22 that have evolved from the first-generation ZB and second­ Abbreviations: IOL, = expected power of the intraocular lens; generation ZB5M to become the thi rd-generation NuVita DPostHx = postoperative refraction; ELP0 = effective lens implant by altering the size and thickness of the optic.2 The position; 1<0 = net corneal power; PreRx = preoperative refrac­ angulation of the haptics have been reduced from 25° to 20°, tion in D; V = vertex distance. and the optic edge has been thinned to provide an additional HKJOphthalmol ® Vol.10 No.1 29 REVIEW Figure 2. Angle-supported phakic intraocular lenses. (a) Vivarte; (b) Nu Vita MA; and (c) ZSAL-4.
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