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The IOL flip: rescue for foldable lens implantation gone wrong
  1. C Y W Khng,
  2. K-T Yeo
  1. Singapore National Eye Centre
  1. Correspondence to: Dr Christopher Y W Khng, Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751; cgkhng{at}

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Phacoemulsification surgery offers many advantages in comparison with extracapsular cataract extraction (ECCE). In particular, faster visual rehabilitation and better control over surgically induced astigmatism are well established benefits over ECCE.1,2 These advantages are largely due to the small size of the cataract incision.3

Inadvertent insertion of a posterior chamber intraocular lens (IOL) with a reversed front to back orientation is a surgical dilemma that will present occasionally. Anecdotal evidence suggests that while this problem is not common, it is not a rare event. Reported data place the frequency between 1.0–1.3%.4–6

Often, IOL inversion is only recognised after the optic has unfolded within the eye. The small phacoemulsification wound, while acting as an ally in the postoperative recovery of the patient, has in this situation become a foe to the surgeon. Faced with this situation, the surgeon has a few options. The simplest would be to leave the IOL inverted. Indeed, this has been advocated by some authors.4 The second would be lens explantation and exchange. However, this often involves sacrificing the IOL7 and is difficult to perform. Alternatively, enlarging the cataract incision to the size of the optic would allow extraction and reinsertion without damage to the IOL. Unfortunately, this would diminish the benefits inherent within the small cataract wound. A better option would be to flip the IOL in situ without enlarging the wound, thus retaining all the advantages of small incision cataract surgery.


This simple technique is easy to perform even for the first time, and has good repeatability. It is recommended only for soft foldable IOLs, and should not be used for rigid one piece poly(methyl methacrylate) (PMMA) lenses. PMMA IOL implantation is usually through an enlarged incision, and it would be simpler to dial out the superior haptic and reimplant the lens. The haptics of PMMA IOLs are also much stiffer than foldable IOLs and can damage both the posterior capsule and the endothelium during the flipping process. This manoeuvre is also not recommended for cases where the integrity of the capsular bag is lost or in doubt, as there is a potential for worsening any capsular rent.

The idea of the technique is to cause a rotational movement about the diameter of the IOL optic, similar to flipping a coin, while at the same time protecting the corneal endothelium and posterior capsule. The technique proceeds as follows:

(1) The anterior chamber is deepened with viscoelastic to create space between the optic/haptics and the endothelium. The capsular bag behind the optic is distended with viscoelastic to facilitate safe flipping of the IOL.

(2) This step flips the IOL. The rotational force on the optic is generated by the careful placement of two intraocular instruments. Non-sharp instruments are preferable, such as a Sinskey hook and mushroom. Their long horizontal segments ensure a controlled rotation of the optic about the central axis. For the right handed surgeon, a Sinskey hook held in the left hand is gently placed anterior to, and on the left of, the optic centre, while a mushroom in the right hand is placed behind the optic, to the right of the optic centre (Fig 1A). To initiate the flip, the mushroom is then raised towards the cornea while simultaneously the Sinskey hook is pushed posteriorly. These movements take place about an axis passing through the diameter of the optic (Fig 1B), forcing the IOL to flip. The haptics then do a 180 degree slow, controlled sweep into the correct position, lagging slightly behind the optic. The manipulation should be completed in one smooth action. It is important to ensure that flipping occurs in the anticlockwise direction so that the leading haptic’s free end does not point towards and threaten the posterior capsule. There is usually adequate room between the corneal endothelium and posterior capsule in most eyes to accommodate the vertical position of the optic during the flip. Although it is possible to perform this manoeuvre with the lens held by the Kelman-McPherson forceps, slight misalignment of the jaws, which often is present, could result in sudden and uncontrolled twisting and an uncontrolled flip so this is not recommended.

Figure 1

(A) Positioning of instruments for IOL flip. (B) Section through plane A-A.


Most of the problems causing IOL inversion are related to inadequate attention to details during lens insertion. The use of injectable IOL systems, particularly those that require elaborate rotational movements on the part of the surgeon in order to correctly place the IOL into the capsular bag may result in an inverted IOL. Correct insertion of the IOL within the cartridge is no guarantee of correct placement into the eye. In the AMO Unfolder system, particular care has to be taken to avoid inversion. During injection, the free end of the leading haptic has to be directed to the surgeon’s left, with the loop held in the horizontal position at all times via a series of pronation movements of the right handed surgeon’s wrist, in order for the IOL to be correctly oriented. Failure to pronate the wrist in an adequate and timely fashion will result in an incorrect placement. Other systems that do not require complicated manipulations may reduce the possibility of incorrect implantation.

Forceps insertion of foldable IOLs also may lead to reversed placement. The correct orientation of the IOL should be checked before folding in all cases, particularly if the lens has been dropped during transfer. Incorrect orientation is indicated by an “S” configuration formed by the lens haptics and optic. Recognition of the “S” must signal to the surgeon to “stop” and check. Occasionally the trailing haptic may be trapped within the incision by the jaws of the inserting forceps, inducing spontaneous flipping within the eye. Recognised early, this can be aborted by placing the forceps tips over the optic to prevent further rotation, while releasing the trapped haptic with Kelman-McPherson forceps.

Although inverted lens implantation is eminently preventable with proper attention at each step of lens implantation, it still is a problem that occurs with enough frequency to be of concern. Should the surgeon decide that correction of the reversal is appropriate, the IOL flip offers a simple, quick and safe way out of a tight spot.


The authors are grateful to Paul Chua of the Medical Illustration Department of the Singapore National Eye Centre for his assistance with the illustrations.


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