Piggyback IOL may be ideal for postoperative residual hyperopia
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Our IOL power estimation is reasonably accurate, with most modern formulas being able to deliver about 80% of patients to within 0.5 D of the intended target.
With newer artificial intelligence methods such as the Ladas Super Formula 2.0 AI, many surgeons can achieve greater than 90% accuracy. However, this still means that on occasion we will have a patient in whom the postop refractive target is missed, with the need for a second procedure to address the residual refractive error. While corneal excimer laser ablation is easy and accurate for a myopic miss, performing a piggyback IOL is often a better option for residual hyperopia.
Piggyback IOL vs. IOL exchange
A piggyback IOL refers to a second IOL that is placed in the eye so that there are now two lens implants. Usually, the first IOL is placed in the capsular bag, and then at a later date, the piggyback IOL, a three-piece design, is placed in the ciliary sulcus. This is a relatively easy way to add dioptric power to the eye without having to exchange the original IOL. While an IOL exchange can also be done to achieve the same result, it can sometimes be a challenge to dissect the old IOL from the capsular bag. In addition, if the first IOL has a toric design, it may not be possible to perform an IOL exchange while keeping the haptic position precise for an accurate astigmatic result. There is usually plenty of room for the piggyback IOL because the original human crystalline lens is 4 mm or more in anterior-posterior thickness, while a typical IOL placed in the capsular bag is just 1 mm thin. This allows for the three-piece piggyback IOL to be placed into the ciliary sulcus.
Piggyback IOL power calculation
The calculation of the piggyback IOL power can be determined on the refraction with about 1.5 times the power needed for the IOL as compared with the refraction spherical equivalent. For example, if the desired correction is +2 D, then the piggyback IOL with a power of +3 D is placed in the sulcus. For myopic postop refractive surprises, I generally prefer doing a keratorefractive procedure such as PRK or LASIK because it avoids a return trip to the operating room as it is not an intraocular procedure. If you decide to perform a piggyback IOL for a myopic surprise, then cut down the factor to 1.3 times for the piggyback IOL power needed to avoid postop hyperopia. Also, note that these negative-power IOLs can have a thick edge, which may scrape the posterior surface of the iris when placed in the capsular bag.
IOL selection
Because we do not have a specially designated sulcus IOL in the U.S., we tend to use three-piece IOL designs made of acrylic or silicone. These designs have posterior angulated haptics of usually 5° to 10°, which allows the optic to sit more posterior and closer to the capsule while the haptics are secured in the sulcus. While using a three-piece IOL in the sulcus as a piggyback IOL may be considered off label, it is a common practice and well within the standard of care. Note that it is not typically recommended to place a single-piece acrylic IOL in the sulcus because these designs are planar (no angulation of the haptics) and the haptics are quite thick and bulky, which could lead to scraping of the posterior surface of the iris, causing uveitis-glaucoma-hyphema syndrome.
There can be cases of intralenticular opacification in some cases of piggyback IOL placement, particularly when both IOLs are primarily placed in the capsular bag at the time of the original cataract surgery. For this reason, for these highly hyperopic or nanophthalmic eyes that call for an IOL with a power of greater than 40 D, I prefer a stepwise approach. At the time of the original cataract surgery, place the highest-power IOL available in the capsular bag (single-piece acrylic monofocal IOLs are available in powers up to +36 D to +40 D, depending on the manufacturer), and then let the patient heal. After the patient recovers from the original cataract surgery, the residual refractive error can be measured accurately, and then a piggyback IOL in the sulcus can be planned.
Surgical technique
The original cataract surgery can often be carefully opened to allow placement of the piggyback IOL. If not, a new incision can be made, or the prior incision can be cut again. Small aliquots of viscoelastic are injected under the iris in all quadrants to gently expand the ciliary sulcus (Figure 1). The three-piece IOL can then be placed into the sulcus with care taken to ensure the correct orientation (anti-S) to ensure proper posterior angulation of the haptics (Figure 2). Note that the incision may need to be slightly widened to 2.75 mm to allow for placement of the injector tip. Finally, the trailing haptic can be dialed into the sulcus (Figure 3), and now there should be good centration of the piggyback IOL. The pupil can be constricted using a miotic agent, and the viscoelastic is gently removed.
Using a piggyback IOL can be useful to help address a postop refractive surprise, particularly for hyperopia. The procedure is safe and efficient and can produce an accurate correction of a residual refractive error.
A video of this surgery can be found at https://cataractcoach.com/?s=piggyback.
- For more information:
- Uday Devgan, MD, in private practice at Devgan Eye Surgery and a partner at Specialty Surgical Center in Beverly Hills, California, can be reached at devgan@gmail.com; website: www.CataractCoach.com.
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