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Ophthalmology > LENS
Intraocular Lens Decentration
Article Last Updated: Aug 24, 2006
AUTHOR AND EDITOR INFORMATION
Section 1 of 9  
Author: Robert H Graham, MD, Senior Associate Consultant, Department of Ophthalmology, Mayo Clinic, Scottsdale, Arizona
Robert H Graham is a member of the following medical societies: American Academy of Ophthalmology, American Medical Association, and Arizona Ophthalmological Society
Coauthor(s):
Vivian Monsanto, MD, Consulting Staff, The Mackool Eye Institute and Laser Center
Editors: Richard W Allinson, MD, Associate Professor, Department of Ophthalmology, Texas A&M University Health Science Center, Scott and White Clinic; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; J James Rowsey, MD, Former Director of Corneal Services, St Luke's Cataract and Laser Institute, Florida; Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri; Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Author and Editor Disclosure
Synonyms and related keywords:
IOL, IOL decentration, subluxated IOL, posterior chamber lens, PCL, anterior chamber lens, ACL
Background
Intraocular lens (IOL) malpositions range from simple IOL decentration to luxation into the posterior segment. Subluxated IOLs involve such extreme decentration that the IOL optic covers only a small fraction of the pupillary space. Luxation involves total dislocation of the IOL into the posterior segment.
Decentration of an IOL may be the result of the original surgical placement of the lens, or it may develop in the postoperative period because of external (eg, trauma, eye rubbing) or internal forces (eg, scarring, peripheral anterior synechiae [PAS], capsular contraction, size disparity).
Basically, 2 types of IOLs commonly are used. Posterior chamber lenses (PCLs) are the standard and are used more frequently. With the advent of PCLs, the use of anterior chamber lenses (ACLs) has declined. However, their implantation is still necessary in certain situations. Iris-supported IOLs are no longer used for implantation after cataract surgery, so they are not included in this discussion. Their use as phakic-IOLs for refractive purposes is currently under further investigation.
Frequency
United States
Clinically insignificant decentration occurs in at least 25% of cases. Clinically significant decentration occurs in about 3% of the cases. The frequency of IOL dislocation ranges from 0.2-1.8%. The rate is lower in eyes with PCLs than with ACLs or iris-supported lenses. However, since PCLs constitute most lenses implanted, decentered and dislocated PCLs have become more prevalent.
History
- The most common presenting complaint is unwanted optical images caused by either a centering hole or the edge of the optic within the pupil.
- Patients may complain of decreased vision, edge glare, diplopia, streaks of light, haloes, photosensitivity, and ghost images.
- Although malposition of a PCL may reduce the quality of vision, it is less likely than malposition of an ACL to cause mechanical injury or inflammatory sequelae. Pain and red eye are more common complaints in patients with ACL decentration if there is inflammation as a consequence.
Physical
- ACL decentration
- In patients with ACL decentration, slit lamp examination and gonioscopy may reveal iris tuck, which can cause uveal inflammation.
- The eye may be red and tender.
- A peaked or oval pupil can be found.
- Inappropriate ACL size may cause a mobile lens.
- ACL malposition may produce ongoing mechanical trauma to the cornea, iris, ciliary body, or anterior chamber angle.
- Chronic inflammation may lead to corneal endothelial cell loss, cystoid macular edema (CME), glaucoma, microhyphema, and pain.
- PCL decentration
- Visual acuity can be compromised by optical aberrations and refractive changes. Slit lamp examination usually does not reveal evidence of inflammation unless contact of a portion of the IOL with the cornea or vitreous prolapse is present.
- Corneal edema from IOL or vitreous touch can be found. In these cases, CME may be a complication.
- Vitreous traction can increase the risk of a retinal detachment, while vitreous to the wound can be implicated in endophthalmitis.
Causes
IOL decentration may occur as a result of factors during the original surgery and lens implantation, or it may develop at a later time as a result of either outside forces such as trauma or internal forces related to capsular dynamics.
- ACL decentration
- Inadequate size: A lens that is too small may be too mobile and cause intermittent damage to the cornea and iris.
- Improper placement during surgery: An improperly placed ACL may be associated with iris tuck and uveal inflammation and PAS.
- Prolapse of a haptic into either wound or iridectomy: This usually requires repositioning at a different angle to avoid recurrences.
- PCL decentration: The pathogenesis of PCL malposition may be related to a variety of locations of haptic fixation, to the forces of capsular contraction, or to a combined mechanism. In a study by Tappin et al, early decentration of the injected IOLs occurred in eyes without a continuous capsulorrhexis. In contrast, late decentration was due to subluxation associated with capsular fibrosis.
- Asymmetric haptic placement: Before the development of capsulorrhexis, it was common for the surgeon to place the inferior IOL haptic within the capsule, while releasing the superior haptic into the ciliary sulcus producing asymmetric haptic fixation. Because significant decentration was expected, PCLs had large optics (7 mm) and long length (13-14 mm). Subsequent healing from capsular fusion and contraction potentially caused the inferior haptic to exert forces on the optic unopposed by forces from the superior haptic within the sulcus. Migration of the optic as a result is termed sunrise syndrome.
- Inadequate zonular or capsular support: This can be due to posterior capsular rupture or zonular dialysis both of which are more prevalent in patients with pseudoexfoliation. A disruption of the superior zonules when the inferior haptic is in the bag and the superior haptic is through the disinsertion also causes a sunrise syndrome as contraction of the bag forces the superior haptic through the disinsertion. Inferior dislocation of a PCL through an unrecognized zonular dialysis is a serious malposition termed sunset syndrome and is usually clinically evident within the first 6 weeks after surgery. A tear in the anterior capsule may allow one or both IOL haptics to migrate out of the capsular bag under the forces of capsular contraction. This has been referred to as "pea-podding."
- Capsular contraction syndrome: Capsulorrhexis is a major surgical advance that contributes to long-term IOL stability and centration. Despite an intact capsulorrhexis, IOL decentration may still occur due to capsular contraction syndrome. Too small a capsulorrhexis has been implicated. Silicone-plate IOL design is particularly susceptible to the forces of capsular contraction and may decenter, rotate, tilt, or buckle. A survey by Mamalis et al cited IOL decentration as the most frequent reason for plate-type silicone IOL removal. Plate-design lenses have a smaller arc of contact with the capsular fornix, reducing anchoring forces that normally reduce potential for rotation and decentration.
- Capsular fusion: An eccentric capsulorrhexis may allow one of its edges to be more peripheral than the optic in one area, with fusion developing, producing decentration away from the area of contact. A large, symmetric, round, central capsulorrhexis is recommended to reduce significant decentration.
- Postoperative trauma
Diplopia
Macular Edema, Irvine-Gass
Red Eye Evaluation
Medical Care
Selection of treatment should be based on the patient's symptoms, needs, and expectations.
- Observation: In the absence of symptoms and no evidence of inflammatory sequelae, observation is an option. In the case of an ACL associated with a peaked or oval pupil, careful observation is warranted if there are no signs or symptoms of intraocular inflammation.
- Miotics: If symptoms from a decentered PCL are infrequent and limited to evening, due to a dilated pupil, these patients may be treated conservatively by using a topical miotic such as pilocarpine 0.5-1% qhs. A trial of miotic agents may be warranted prior to removing or repositioning an implant.
Surgical Care
When more severe and disabling symptoms or if inflammation is present with the potential for further complications in the future, treatment should include either repositioning, explanting, or exchanging the IOL. Selection of treatment is based on the patient's symptoms, visual needs, and expectations, and an assessment of which option is likely to provide the best long-term benefit with the least risk.
- IOL reposition: An IOL may become decentered due to either insufficient zonular support or to irregular fibrosis of the posterior capsule. In the case of inadequate support, early in the postoperative period the surgeon may attempt to rotate the IOL surgically where there is clinical evidence of sufficient capsule and zonules to support the implant. A helpful maneuver is the bounce test where the optic is pushed gently toward each haptic to ensure spontaneous recentration.
- IOL reposition with McCannel sutures: In some cases, reposition may be supplemented by the use of trans-iris IOL fixation (McCannel) suture.
- IOL explantation: Certain circumstances warrant removal of an IOL without secondary IOL implantation. This is determined on an individual basis and taking into account the patient's expectation.
- IOL exchange: Most common indications for removal or exchange of a modern PCL are wrong IOL power and malposition. Deformation of the implant due to irregular capsular fibrosis may make simple rotation insufficient to properly center the IOL. The IOL may be exchanged for an ACL, a sulcus-fixated IOL with or without McCannel sutures, or a transsclerally sutured PCL.
- To determine whether the risk-to-benefit ratio favors IOL exchange over observation the surgeon should consider the following:
- Severity, duration, and chronology of problem
- Response to nonsurgical treatment
- Natural history of a specific IOL
- Likelihood that surgical removal would provide substantial relief or benefits
- Ease of surgical removal and potential for aggravating or creating additional complications
- Status of the other eye
- Patient and family expectations and visual needs
- Life expectancy and overall health of the patient
Pilocarpine hydrochloride sometimes can be used as a trial medication to evaluate symptoms related to edge glare and optical aberrations secondary to IOL decentration.
Drug Category: Miotics
For temporary pupillary constriction to relieve symptoms of optical aberrations.
| Drug Name | Pilocarpine HCL (Akarpine, Ocusert Pilo-40, Pilostat, Piloptic, Salagen) |
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| Description | Pilocarpine, with a chemical name of (3S-cis)-2(3H )-Furanone, 3-ethyldihydro-4-[(1-methyl-1H -imidazol-5-yl)methyl], monohydrochloride, has a molecular weight of 244.72. Pilocarpine HCl ophthalmic solution is a sterile solution for ophthalmic administration having the following composition: a direct-acting cholinergic parasympathomimetic agent, which acts through direct stimulation of muscarinic neuroreceptors and smooth muscle such as the iris and secretory glands. Pilocarpine produces miosis through contraction of the iris sphincter, causing increased tension on the scleral spur and opening of the trabecular meshwork spaces to facilitate outflow of aqueous humor. Outflow resistance is thereby reduced, lowering intraocular pressure. |
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| Adult Dose | 1 gtt in affected eye hs has been recommended in research trials |
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| Pediatric Dose | Not established |
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| Contraindications | Documented hypersensitivity; acute inflammatory disease of anterior chamber; where constriction is undesirable such as in acute iritis |
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| Interactions | May be ineffective when used concomitantly with nonsteroidal anti-inflammatory agents |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Miosis usually causes difficulty in dark adaptation; advise patients to exercise caution in night driving and other hazardous occupations in poor illumination
Not for internal use; to prevent contaminating the dropper tip and solution, take care not to touch the eyelids or surroundings areas with the dropper tip of the bottle |
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Deterrence/Prevention
- A study by Tappin et al examined some of the intraoperative and postoperative factors leading to IOL decentration in patients requiring IOL exchange in an attempt to identify avoidable causes of IOL decentration. They concluded that significant postoperative subluxation of injected silicone IOLs may be minimized by implanting only into a lens capsule bag with an intact capsulorrhexis. The risk of decentration of a small optic (5.5 mm) PMMA IOL may be minimized by positioning the haptics at 90° to any capsulorrhexis tear. After cataract surgery complicated by posterior capsular rupture or zonular dehiscence, it is important to assess the remaining capsular support and, if sufficient, implant a large optic diameter (7 mm) PCL in the ciliary sulcus.
Complications
- Complications associated with ACL, iris-fixated IOLs, and older PCLs are much more severe than those encountered with modern PCL decentration. Corneal edema and inflammatory consequences such as uveitis-glaucoma-hyphema syndrome and chronic CME were common reasons for explanation in the above cases.
Prognosis
- In the absence of inflammatory sequelae prognosis is very good.
Medical/Legal Pitfalls
- Patients undergoing YAG laser posterior capsulotomy must be informed of the possibility of IOL decentration, especially with silicone-plate PCLs.
Special Concerns
- Silicone-plate IOL design is particularly susceptible to the forces of capsular contraction and may rotate, decenter, tilt, or buckle. These lenses have a smaller arc of contact with the capsular fornix, decreasing anchoring forces that normally reduce potential for rotation and decentration.
- A special concern is the potential for dislocation into the vitreous cavity following Nd:YAG laser capsulotomy. A study by Carlson et al reported 10 cases of silicone-plate IOL dislocation, 8 of which occurred even after waiting 3 months following cataract surgery before performing laser capsulotomy. Evidence of capsular tension was present in 6 of 10 patients. This was not specific to an individual surgeon, and there was no correlation with IOL power or axial length. IOL dislocation occurred several days to weeks after the laser procedure.
- Newer plate IOL modifications, such as enlarged holes within the plate or a loop extending from the plate, may provide additional anchoring and increase resistance to forces associated with capsular contraction.
- Some studies have shown that diabetes mellitus, retinitis pigmentosa, and pseudoexfoliation are predisposing factors for excessive IOL tilt, decentration, or both after phacoemulsification with IOL.
- Hayashi et al found a greater incidence of tilt and decentration in patients with glaucoma, particularly narrow angle, than in control patients. They propose an abnormal lens capsule configuration due to unusual anterior segment anatomy in these eyes.
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Intraocular Lens Decentration excerpt Article Last Updated: Aug 24, 2006
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