EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/78721
18 EW NEWS & OPINION January 2012 Complicated cataract cases Phacoemulsification after radial keratotomy by Mark Packer, M.D., F.A.C.S. A I ncisional keratotomy patients are far less abundant than LASIK and PRK patients, but they're out there. Unlike the latter, the num- bers of RK patients is not increasing. Hexagonal keratotomy, a procedure to treat mild hyperopia, was uncommon even in its heyday, and the number of patients who will come to cataract surgery is small. The number of RK pa- tients coming to cataract surgery, on the other hand, will be larger, and many of them are seek- ing cataract surgery now. Lens power calculation is difficult following radial keratotomy, just as it is after LASIK and PRK, but there are differences. LASIK and PRK change the anterior curve of the cornea without changing the posterior curve, absent ectasia. Ra- dial keratotomy, on the other hand, produces changes in the curvatures of both surfaces. Lens power formulas that are useful for LASIK and PRK cannot be applied to radial keratotomy. The ASCRS website has a post-refractive surgery IOL calculator (iol.ascrs.org) that is useful for the three most common types of keratorefrac- tive patients: myopic LASIK/PRK, hyperopic LASIK/PRK, and RK. In his article, Dr. Packer discusses the two most important challenges facing the cataract surgeon who operates on post-RK patients, the challenge of calculating IOL power accurately and the challenge of staying clear of the radial corneal incisions. As he notes, difficulty in avoiding RK in- cisions goes up as the incision number increases. As with all post-keratorefractive patients, counseling is critical. These patients need to be warned about the likelihood of a lens power cal- culation error and the greater surgical difficulty that the corneal incisions impose. It's important not to plan a lens exchange, piggyback IOL, or keratorefractive enhancement until any hyperopic shift in the cornea that cataract surgery might have caused has settled. Hyperopic shifts can be minimized by not overpressurizing the eye during surgery, especially at the time of incision closure. Kevin Miller, M.D. complicated cataract cases editor Watch this video on your smartphone or iPad using your QR code reader. (Scanner available for free at your app store.) Or view the video at www.eyeworld.org/replay.php. s radial keratotomy pa- tients are aging and devel- oping progressive hyperopia and cataracts, it is increasingly impor- tant to master safe and effective ways to treat these patients. Eyes that have undergone radial kerato- tomy (RK) present two separate chal- lenges to the refractive cataract surgeon. First, the altered and often irregular curvature of the cornea after RK renders standard keratome- try and routine IOL calculations in- accurate. Second, the altered anatomy of the post-RK cornea with its compromised structural integrity leads to technical challenges during phaco surgery. Linear RK incisions were typi- cally made in a spoke-like pattern extending from a 3-4 mm central optical zone peripherally to within 1-2 mm of the limbus. The incisions were made to 90-95% corneal stro- mal depth and numbered from 2 up to 32 or higher in some extreme cases. Most spherical myopic RK treatments involved 4-16 radial inci- sions arranged in a symmetric wagon wheel spoke pattern over the cornea. Various incisions for the treatment of astigmatism were often added as T-cuts or other small con- centrically arranged incisions placed between and perpendicular to the radial cuts. At the time that RK was in wide- spread use, cataract surgery was still mainly performed via scleral inci- sions either in the form of extracap- sular cataract extraction or scleral tunnel phaco surgery. Consequently, there was little worry at the time about how these peripherally lo- cated corneal RK incisions would in- terfere with future clear corneal cataract surgery. Unfortunately, we now find ourselves dealing with this unintended legacy as we take care of an increasing number of post-RK presbyopic hyperopes and cataract patients. The development of computed corneal topography in the 1980s fa- cilitated understanding of the effects of radial keratotomy on corneal re- fractive power. The resultant flatten- ing of the central cornea violated the central assumption of keratome- try, relatively perfect sphericity of the anterior corneal surface within the 3 mm optical zone. Fortunately, rePlay online content Figure 1. The left-hand clear corneal 1.2-1.4 trapezoidal incision is placed between two RK incisions Figure 2. The right-hand incision is placed between RK incisions in this 16-cut cornea Figure 3. Utilizing the 20-gauge Tsuneoka front-end irrigating chopper in the left hand and a 30-degree bevel 20-gauge straight phaco needle in the right hand, a pie-shaped segment is mobilized with high vacuum (270 mm Hg) and zero ultrasound power corneal topography has also enabled improved measurement of the cen- tral corneal power so that a measure- ment of the effective refractive power can be used in IOL power cal- culation formulas. The latest genera- tion of formulas, such as the Holladay II, allow use of the "double K" method, in which average or pre- keratorefractive values are used to help determine the effective lens po- sition while topographically meas- ured post-keratorefractive values are used for the corneal power. The key to clear corneal inci- sions in these post-RK patients is to avoid the crossing of phaco incisions and RK incisions. If a clear corneal phaco incision is made through an RK incision, there is a high likeli- hood that the roof of the phaco inci- sion will split open along the RK incision due to manipulation during the course of the procedure. The split roof of the clear corneal inci- sion will prevent a good seal at the incision and allow excessive outflow of fluid and consequent chamber in- stability during phacoemulsification. An unstable chamber can lead to multiple complications including iris damage, endothelial damage, capsule rupture, and vitreous loss. A split incision roof can also lead to Figure 4. The slit beam retroillumination feature of the operating microscope (Carl Zeiss Meditec) highlights a posterior subcap- sular plaque while the front-end irrigation stream from the chopper puts the posterior capsule on stretch and facilitates polishing with the silicone-coated 0.3 mm aspiration tip Figure 5. The 2.7 mm temporal incision for IOL insertion is constructed at the limbus, posterior to the RK incisions; the incision is sized generously to avoid pressure on the roof during IOL insertion difficulty in closing the corneal inci- sion at the end of the case. Often multiple sutures are required to achieve a watertight closure. The added sutures can create astigma- tism and patient discomfort. A poorly sealing corneal incision may also increase the risk of endoph- thalmitis. When seeking to optimize safety and outcomes, there are multiple surgical options to consider for post- RK phaco patients. Standard clear cornea (2.5-3.0 mm): If the number of RK incisions is small, there may be enough space