Cataract surgery is the most common operation performed by ophthalmologists. Although it has a very high success rate, certain complications may occur. 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). Posterior dislocation of an intraocular lens (IOL) is an uncommon complication of cataract surgery and Nd:YAG posterior capsulotomy.
See What the Eyes Tell You: 16 Abnormalities of the Lens, a Critical Images slideshow, to help recognize lens abnormalities that are clues to various conditions and diseases.
IOL dislocation can be subdivided into early and late dislocation. Early dislocation refers to dislocation occurring within 3 months of cataract surgery, whereas late dislocation occurs more than 3 months after cataract extraction.
Posterior dislocation of an IOL may occur during or shortly after cataract surgery. In these cases, posterior capsular rupture or zonular dialysis usually is present. It occurs because of improper fixation within the capsular bag and instability of the IOL–capsular bag complex. The implementation of a continuous curvilinear capsulorrhexis (CCC) during phacoemulsification has decreased the rate of early IOL dislocation. CCC gives support to the IOL optic for 360 degrees and permits excellent IOL fixation. Prior to CCC, most IOL dislocation occurred secondary to asymmetric IOL fixation or IOL malposition within the capsular bag. Rarely, it may occur following Nd:YAG capsulotomy or beyond the immediate postoperative period. Trauma may be a precipitant in these cases.
Late IOL dislocation has been noted to occur more frequently than previously thought.[1, 4, 5] Late IOL dislocation results from zonular weakness since the IOL is adequately fixed within the capsular bag. Several risk factors, including pseudoexfoliation syndrome, trauma, prior vitreoretinal surgery, and connective tissue disorders, have been associated with zonular weakness. In a retrospective case series of 86 late IOL dislocations, the IOL dislocated on average 8.5 years after phacoemulsification and IOL implantation. These same authors reported that patients with any type of IOL were at risk for late in-the-bag IOL dislocation. A population-based study of patients by Pueringer et al found that after cataract extraction, the long-term risk of late IOL dislocation was low and had no significant change over the almost 30-year study period.
The IOL rarely dislocates completely onto the retinal surface. It usually lies meshed into the anterior vitreous with one haptic still adherent to the capsule or iris. It may cause a vitreous hemorrhage by mechanical contact with ciliary body vessels. The IOL may be related to retinal detachment or cystoid macular edema secondary to vitreous changes and may cause pupillary block or corneal contact with secondary corneal edema. On many occasions, it does not cause any complications and may be left alone if the patient is able to use aphakic spectacles or contact lenses.
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 posterior chamber IOLs (PCIOL) than with anterior chamber IOLs (ACIOL) or iris-supported lenses. However, since posterior chamber IOLs constitute most lenses implanted, decentered and dislocated posterior chamber IOLs have become more prevalent.
The frequency appears to have increased in the past few years because of the following reasons: (1) phacoemulsification has a steep learning curve, and, as it becomes more popular, more complications are occurring; (2) anterior segment surgeons are becoming more reluctant to place anterior chamber intraocular lenses (ACIOLs); (3) aggressive placement of posterior chamber IOL in the presence of capsular tears has become more common; and (4) silicone plate IOLs have become popular.
A longitudinal study reported that, in 85% of posterior chamber IOL exchange cases, the indication was decentration/dislocation of the lens.
Pseudoexfoliation syndrome, by virtue of its weakening effect on the zonules, is one of the most common conditions associated with late IOL dislocation. The pseudoexfoliation syndrome is commonly seen in people with Scandinavian heritage.
The most common presenting complaint of a decentered IOL 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 PCIOL may reduce the quality of vision, it is less likely than malposition of an ACIOL to cause mechanical injury or inflammatory sequelae. Pain and red eye are more common complaints in patients with ACIOL decentration if there is inflammation as a consequence.
A sudden loss of vision due to uncorrected aphakia, retinal detachment, cystoid macular edema, or vitreous hemorrhage occurs with dislocated IOL.
If the IOL is mobile in the vitreous cavity, the patient may complain of unusual floaters or optical effects.
In patients with ACIOL 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 ACIOL size may cause a mobile lens.
ACIOL 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.
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.
The posterior capsule usually has an obvious defect.
Zonular dialysis may be present.
The IOL may be freely mobile in the vitreous cavity; it may be in apparent contact with the retina; or it may have one haptic attached to the posterior capsule, iris, or ciliary body.
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.
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 ACIOL 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.
The pathogenesis of PCIOL 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, PCIOLs 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 PCIOL 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.
In general, the main cause of dislocation is lack of capsular support for the IOL. This may be caused by any of the following:
Unrecognized posterior capsule rupture
Progressive zonular dehiscence: Patients with pseudoexfoliation syndrome are at risk of developing zonular dehiscence. Late in-the-bag IOL dislocation is associated with pseudoexfoliation in more than 50% of cases.
Silicone plate lenses deserve special attention. It is believed that progressive contraction of the capsular bag increases the tension on the IOL and causes it to bow posteriorly. Progressive contracture of the anterior capsulorrhexis opening (pursestring) may occur more commonly with silicone plate IOLs. Dehiscence anywhere in the capsular bag allows release of tension through expulsion of the implant. Silicone plate IOLs have been known to dislocate in the following situations:
Following an extension of a radial notch tear in the anterior capsular rim
Following a YAG capsulotomy, particularly if a large capsulotomy is made and if the haptics are placed asymmetrically or the IOL optics are too small; interval from YAG capsulotomy to dislocation ranges from immediately to many months
Following an equatorial capsular break from a YAG iridotomy
In a retrospective interventional case series, possible major predisposing factors for in-the-bag IOL dislocation were pseudoexfoliation, retinitis pigmentosa, prior vitrectomy, trauma, and a long axis. For out-of-the-bag dislocation, predisposing factors included secondary IOL implantation, surgical complications, mature cataract, and pseudoexfoliation.
Studies in cadaver eyes indicate that transscleral sutures must exit the sclera 0.8 mm posterior to the limbus in the vertical meridian and 0.46 mm posterior to the limbus in the horizontal meridian to be within the true ciliary sulcus.
Postmortem studies disclosed that scarring does not occur in the vicinity of the sutured IOL. The haptics are surrounded by a thin fibrous capsule at their attachment site. The transscleral portion of the suture is characterized by the lack of inflammation. In addition, the suture tip usually is exposed externally. If the fixation sutures were cut, the IOL would dislocate back into the vitreous cavity. It was concluded that the stability of the IOL was primarily a result of intact transscleral sutures and not fibrous encapsulation or ciliary sulcus placement of the haptics.
Selection of treatment in the case of a decentered IOL 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 ACIOL 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 PCIOL 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.
Observation may be recommended in dislocated IOLs if the following conditions are met:
The IOL is not mobile.
There are no retinal complications.
The patient is satisfied with aphakic spectacle correction or contact lenses.
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 decentered 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, repositioning 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: The 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 ACIOL, a sulcus-fixated IOL with or without McCannel sutures, a transsclerally sutured PCIOL, or a posterior iris-claw IOL.
To determine whether the risk-to-benefit ratio favors IOL exchange over observation, the surgeon should consider the following:
Severity, duration, and chronology of the 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
Several indications for surgical intervention exist for a dislocated IOL. If the patient is not satisfied or cannot tolerate aphakic spectacle correction or contact lenses or if there is concomitant retinal pathology, such as a retinal detachment, surgery must be considered.
Several surgical options are available. These options include removal, exchange, or repositioning of the IOL. A multitude of techniques has been described on how to grasp, suture, and place the IOL. Repositioning of the IOL into the ciliary sulcus or over capsular remnants with less than a total of 6 clock hours of inferior capsular support is not a stable situation, as many of those repositioned IOLs will end up dislocating again. Transscleral suturing or IOL exchange (removal of the dislocated IOL and placement of a flexible open loop ACIOL) is recommended in these cases.
In 1996, Kelman proposed a technique called posterior-assisted levitation, in which nuclear fragments or dislocated IOLs into the anterior vitreous are retrieved through a pars plana sclerotomy and the insertion of a cyclodialysis spatula, a needle, or a viscosurgical device. However, this maneuver can be complicated with retinal detachment or cystoid macular edema and should not be performed at all.
If transscleral suturing of the IOL is planned, modifications to the usual placement of the sclerotomies are made. Two triangular scleral flaps are made 180 degrees apart in the horizontal meridian. Then, two sclerotomies are made 1-1.5 mm posterior to the limbus under the flaps. The infusion cannula is sutured to the usual position. A complete vitrectomy is performed, paying close attention to removing all vitreous and capsular attachments to the IOL, making it freely mobile. The posterior hyaloid, if still attached, is peeled. This allows the IOL to gently fall over the posterior pole of the eye.
If the IOL does not have positioning holes, the edge of the IOL is elevated with a lighted vitreoretinal pick or hook. If positioning holes are present, the IOL may be engaged through them by the pick or hook. The IOL is elevated into the midvitreous cavity, and the optic is grasped with serrated jaw foreign body forceps or diamond-coated forceps. The haptics should not be grasped, or they will be bent.
Aspiration through the silicone soft tipped cannula also has been used in the retrieval and manipulation of the IOL, but this technique may result in inadvertent vitreoretinal traction.
Silicone plate lenses are difficult to manipulate, and, in certain cases, standard techniques will not suffice. The endocryoprobe has been used to engage the IOL, but diamond-coated forceps are much safer. It is recommended that the gas pressure be lowered to 525 psi to avoid freezing the entire shaft. Another problem is that transscleral suturing is not an option because cheese wiring through the silicone will occur.
Liquid perfluorocarbons, such as Perflubron, can be used to float the IOL to the pupillary plane.
Once the IOL is engaged and elevated, it is brought to the posterior chamber. One haptic may be brought in front of the iris. The other haptic may be positioned in the sulcus. Using a Sinskey hook either through a limbal stab incision or through the sclerotomy, the IOL is rotated into place. If more than a total of 6 clock hours of capsular support are present inferiorly, one may elect to reposition the IOL into the sulcus without suturing it.
If there is not enough capsular support, either transscleral sutures or iris sutures are necessary. Several techniques have been described.
If the IOL has positioning holes, the haptics are rotated until they are in the vertical meridian. Single armed 9-0 Prolene sutures are grasped with intraocular forceps and introduced through the sclerotomies. They are passed through the positioning holes from posterior to anterior. The sutures are tied to the sclerotomies under the scleral flaps.
With the intraocular snare, one of the haptics may be looped, and, at the same time, a 7-0 Prolene suture can be tied to it.
Another option is to temporarily externalize the haptics through the sclerotomies so that they can be tied with 10-0 Prolene sutures. This technique may cause peripheral retina breaks or bleeding. The IOL is repositioned into the sulcus, and the sutures are secured to the sclerotomy.
Needle-guided techniques also have been described where a 9-0 or 10-0 Prolene suture may be threaded retrograde up the bore of a five-eighths-inch 25-gauge needle. The end of the suture that is not threaded is retrieved through the hub of the needle. This results in a suture loop. The needle with the suture is inserted through the base of the scleral flap. As the IOL is being grasped by forceps, the haptic is manipulated into the loop; then, the suture is tied under the scleral flaps.
Under certain situations, an IOL must be exchanged. For instance, if the dislocated IOL is damaged (ie, broken haptic), it must be removed. The damaged IOL may be removed through the pars plana or through a limbal incision at the surgeon's discretion. Pars plana removal increases the risk of retinal detachment and severe choroidal bleeding.
The surgeon has the choice of suturing a posterior IOL or inserting an ACIOL. Modern flexible open loop ACIOLs do not appear to result in the complications seen with older types (ie, corneal decompensation, uveitis-glaucoma-hyphema syndrome).
Another option is to manipulate the dislocated IOL into the anterior chamber and leave it there. Potential drawbacks of this option are endothelial cell and trabecular meshwork damage. This technique works well with 3-piece polymethyl methacrylate (PMMA) IOLS but requires a peripheral iridectomy to prevent pupillary block.
Perfluorocarbon liquids are very useful if a retinal detachment is also present. The perfluorocarbon liquid bubble displaces the subretinal fluid through the retinal breaks reattaching the retina and, at the same time, serves as a cushion between the IOL and the retina. Thus, the retina is protected from potential damage from IOL impact during surgical manipulation. If a silicone plate lens is dislocated, special care with the use of perfluorocarbon liquids is necessary. It has been reported that these lenses often "skate or glide" on the bubble across the retina. In addition, perfluorocarbon liquids make the grasping of the IOL somewhat more difficult by making the IOL more slippery. If the retina is not detached, the use of perfluorocarbon liquids probably is not necessary.
On certain cases, an ACIOL is present in addition to the dislocated IOL. Surgical management of these cases is made more difficult by the presence of the ACIOL, especially if a concomitant retinal detachment is present. The vitreoretinal surgeon has several options.
The surgeon may opt to remove the ACIOL, reposition the dislocated IOL, or suture the dislocated IOL.
Another option is to leave the ACIOL and remove the dislocated IOL. The dislocated IOL may be removed via the pars plana or through a limbal incision. If pars plana removal is entertained, a 7-mm partial-thickness scleral groove is created 3 mm posterior and parallel to the superior limbus. This groove should be contiguous with one of the superior sclerotomies. 8-0 silk sutures should be preplaced through the lips of the scleral groove. Once the IOL is ready to be extracted, the microvitreoretinal (MVR) blade is used to extend the sclerotomy into the scleral groove to make it full thickness. After the IOL is removed, the preplaced sutures are tied. This area is inspected by indirect ophthalmoscopy. If needed, retinopexy is applied.
If extraction through a limbal incision is planned, the ACIOL must be removed first. Then, the dislocated IOL is brought to the anterior chamber and removed through the limbal wound. The ACIOL is reinserted. The limbal wound is closed with 10-0 nylon sutures. The sclerotomies are closed in the usual fashion.
Although dislocated foldable IOLs were traditionally treated with removal of the lens and exchange to a PMMA IOL, one report demonstrates the feasibility of using existing surgical techniques to reposition the dislocated foldable IOLs.
A sutureless technique has recently been described. A 27-gauge needle is passed through the ciliary sulcus, allowing externalization of the IOL haptics. A lamellar scleral dissection is performed, and the haptics are then fixed into this scleral tunnel. Using this technique, the authors report minimal tilt and other complications.
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.
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.
The anterior segment surgeon should be advised to avoid implantation of a flexible silicone plate IOL if there is a break in the posterior capsule, radial notch, or tear in the anterior capsular rim or zonular dialysis.
Small capsulorrhexis openings should be avoided.
Current models of ACIOLs often do not result in the same types of complications as older models. These lenses should be considered if adequate capsular support is lacking rather than risking a posterior dislocation of an IOL.
Complications associated with ACIOL, iris-fixated IOLs, and older PCIOLs are much more severe than those encountered with modern PCIOL decentration. Corneal edema and inflammatory consequences such as uveitis-glaucoma-hyphema syndrome and chronic CME were common reasons for explanation in the above cases.
Complications from a dislocated IOL
Complications associated with dislocated IOL include the following:
Retinal detachment has been estimated to occur in at least 2% of cases. It frequently is caused by attempts at relocation by the cataract surgeon or as a complication of vitreoretinal surgery.
Cystoid macular edema
Uncorrected aphakia, glare, or distortion
Complications from transscleral suture fixation
Late endophthalmitis through the suture track has been reported.
IOL torque may occur. In addition, to place the IOL truly in the sulcus, the suture must be placed 0.8 mm posterior to the limbus in the vertical meridian and 0.46 mm in the horizontal meridian. The effective lens power is probably less than the desired one.
Vitreous hemorrhage may occur if the major arterial circle of the iris is pierced inadvertently during the maneuvers required to suture the IOL. In addition, these maneuvers also may raise the risk of a postoperative retinal detachment.
Erosion of the suture through the conjunctiva also has been reported in cases where scleral flaps were used. An attempt to melt the eroded sutures with the argon laser has been recommended. The sutures cannot be removed because the IOL haptics do not scar into place if placed in the ciliary sulcus. Once the sutures are removed, the IOL will redislocate.
With proper vitreoretinal techniques, excellent visual results and a low complication rate is possible. Long-term prognosis is highly dependent on the prevention of retinal detachment and choroidal hemorrhage secondary to surgical manipulation.