Intraocular Lens Performance
An IOL may be correct in power and may be properly located and centered, and yet may still have certain negative performance characteristics that sometimes necessitate its removal. Certain designs of IOL optics, particularly old-style, 5x6-mm oval-optic PMMA IOLs and double squareedged IOLs, have had significant subjective complaints related to the edge design.[16] These undesirable visual phenomena (dysphotopsias) can be manifest as dark temporal, crescent-shaped relative scotomata (negative dysphotopsias) or as bright temporal arcs of light (positive dysphotopsias).[17,18] Some silicone concentric-ring multifocal IOLs have been removed due to intolerable nocturnal glare manifested as rings or halos around lights at night.[19]
Intraocular lenses have varying degrees of biocompatibility. The degree of tolerance depends on IOL design, material, and location inside the eye. Although intracapsular sequestration, away from uveal and corneal tissue, is believed to be the most biocompatible location for implantation, different designs and materials perform differently inside the capsular bag. PMMA (Figure 13) and silicone, for example, cause more anterior capsular fibrosis than acrylic and hydrogel. Some investigators believe that PMMA and silicone may also cause higher rates of uveitis and cystoid macular edema (CME) than acrylic and hydrogel. Persistent anterior chamber cell or flare reaction, inflammatory precipitates on the IOL surface[20] (Figure 20), posterior synechiae, secondary ocular hypertension, and persistent CME may be indications for removal or replacement of an IOL. An IOL in the ciliary sulcus may cause chronic iridocyclitis and ocular tenderness, particularly if it is too large for the space, as may be seen with 14-mm, one-piece PMMA IOLs, or if the haptics are made of polypropylene. Double square-edged optics in the posterior chamber may cause pigment dispersion from the back of the iris due to chafing of the posterior pigment layer by the sharp anterior optic edge during dilation and constriction of the pupil. Anglefixated PMMA IOLs, if too long, may fixate posteriorly to the scleral spur, resulting in progressive ovalization of the pupil in the long axis of the IOLthis may be associated with ocular pain and tenderness. Conversely, an anglefixated PMMA AC IOL that is too short may move from side to side with ocular saccades, which is the socalled windshield-wiper syndrome form of pseudophakodonesis. Chronic rubbing on the corneal endothelium can cause a marked reduction in endothelial cells, potentially leading to corneal decompensation. Early recognition is crucial and diminishing serial endothelial cell counts may necessitate IOL removal and replacement.
Complete continuous curvilinear capsulorhexis closure by lens epithelial cell fibrosis over a PMMA intraocular lens (courtesy of John Shepherd).
Precipitates on anterior intraocular lens surface consistent with chronic uveitis.
As all man-made implantable material could be considered relatively incompatible, incompatibility has been observed to occur in special situations, such as the combination of silicone IOLs and silicone oil.[21] A posterior segment procedure requiring silicone oil may necessitate silicone IOL removal or replacement in order to avoid the loss of visibility that can occur when IOL silicone and silicone oil bond. A second material incompatibility has been demonstrated when two acrylic-optic IOLs are placed in contact with one another in one capsular bag, piggyback style, with an anterior capsulorhexis opening that is smaller than the diameter of the anterior IOL optic.[22] Lens epithelial cells have been observed to migrate between two acrylic optics and undergo fibrous metaplasia, forming not only visually symptomatic opacification but also a physico-chemical-biologic bond between the two IOLs, which renders them surgically, mechanically inseparable.[23] In such cases, simultaneous explantation of both optics or the entire IOL-capsular complex may be necessary.
The visual performance characteristics of IOL optics may be compromised iatrogenically when pitting of the optic occurs as a result of aggressive Nd:YAG laser posterior capsulotomy. Silicone and PMMA optics are particularly vulnerable to laser marking. In addition, certain IOL materials have been observed to undergo spontaneous discoloration or opacification. Some early generation silicone optics were observed to turn a semi-opaque brown color, a process thought to be related to insufficient curing of the liquid silicone during manufacturing,[24] that did not significantly impair visual function. Early generation hydrophobic acrylic optics were seen to develop glistenings, thought to be actual water vacuoles,[25] which also did not impair visual function significantly to indicate IOL removal. Hydrophilic acrylic has been observed to develop a uniform white opacification of the optic[26,27,28] (Figure 14) and sometimes of the haptics as well in the case of onepiece hydrophilic acrylic design. In some of these cases, impairment of visual function did necessitate IOL removal. The hydrophilic nature of these IOLs has also allowed penetration of trypan blue, an intraocular dye used for staining the anterior capsule when no red reflex is present, which could potentially alter color perception. Recently, the back surface of a silicone optic was found to have symptomatic white calcification following Nd:YAG laser posterior capsulotomy in an eye with asteroid hyalosis that necessitated IOL removal.[29] Any of these forms of reduced optic clarity may necessitate IOL removal or replacement.[30,31,32,33]
Opacification of the optic of a hydrophilic acrylic intraocular lens.
The technique of IOL removal and the size of the incision will vary and will depend on the material of the IOL to be removed, the status of the capsule and zonule, and the replacement IOL.
© 2005 Comprehensive Ophthalmology Update, LLC
Cite this: Indications and Techniques of Intraocular Lens Removal - Medscape - Sep 01, 2005.
