Cataract Surgery for Patients With Myopia
Cataract Surgery for Patients With Myopia
Here is how I approach these patients in my own practice.
By UDAY DEVGAN, M.D., F.A.C.S.
Patients with high myopia are often the happiest of cataract patients postoperatively due to the IOL's ability to correct most of the refractive error. However, these patients are more challenging to manage, pre-, intra- and postop. Due to the high volume of patients with myopia in my practice, I have developed guidelines to improve surgical outcomes and deliver high quality vision to these patients.
Myopic patients often have very high demands for their vision and, occasionally, perhaps unrealistic expectations. If corrected for plano, they need to understand that their ability to see a few inches away from their face will be lost. They need to understand that while the cataract surgery can correct much of the myopia, its primary purpose is to correct the cataract and the refractive effect is a secondary benefit. During the informed consent process, tell them of the increased chance of retinal detachment and development of macular disease, as well as ametropia. Also, the IOL calculations in highly myopic patients are less precise than in more emmetropic patients, and the surgeon may need to perform a second procedure, such as an excimer-based ablation, in order to achieve a specific refractive goal, so be sure to inform them of this as well.
Figure 1. (A) Normal anterior chamber depth prior to insertion of irrigation/aspiration probe. (B) Overly deep anterior chamber with posterior displacement of the lens-iris diaphragm due to the infusion pressure and the elastic nature of highly myopic eyes. (C) Use of the second instrument to lift the papillary margin of the iris to allow equalizing of the anterior-to-posterior pressure gradient. (D) Return to normal anterior chamber depth and no posterior displacement of the lens-iris diaphragm.
In addition to the normal work-up, be careful to accurately assess the retina and measure the axial length of the eye. If performing an A-scan ultrasound, be aware that a posterior staphyloma can give an erroneously long axial length, which would then result in postop hyperopia and an unhappy patient. Use an optical method for measurement tends to be more accurate as it measures directly at the fovea. For IOL calculations, use a theoretical formula such as SRK/T, which performs particularly well in eyes with axial lengths greater than 26 mm. Aim for a postoperative goal on the myopic side, such as -0.5 D or even -1 D for axial lengths of greater than 30.0 mm.
I prefer a monofocal or accommodative IOL in these patients so that any future retinal examination can be performed with ease. For extreme myopes, the Sensar AR40M Acrylic IOL (Advanced Medical Optics [AMO], Santa Ana, Calif.) comes in powers as low as –10.0 D, the AQ5010V Silicone IOL (STAAR, Monrovia, Calif.) down to -4 D, the Acrysof Acrylic IOL (Alcon, Fort Worth, Texas) down to -5 D, the SofPort Silicone IOL (Bausch & Lomb, Rochester, N.Y.) down to 0 D, and the Crystalens Five-O (eyeonics, Aliso Viejo, Calif.) down to 3 D. I prefer larger foldable IOLs with three-piece designs as they tend to be a better fit for the large capsular bags found in high myopes. If you do not mind a non-foldable lens, B&L makes the P574UV PMMA IOL, which is available as low as -18 D. The STAAR IOL, due to its configuration and available powers, is well suited as a piggyback lens for cases of postop refractive surprise.
When examining the retina, look carefully for any breaks, holes, or weakness as well as any macular pathology. The highly myopic patients may also have myopic macular degeneration, epiretinal membranes, or other significant changes. These may limit the post-op vision achieved and they may worsen after surgery. I prefer to use the team approach, with the detailed retinal examinations performed by my vitreo-retinal colleagues who have a better ability to detect subtleties.
Preoperative treatment with nonsteroidal anti-inflammatory drugs (NSAIDs) is important for four reasons:
(1) Prevention of intra-operative miosis
(2) Analgesia and patient comfort
(3) Reduction in the postop inflammatory response, and most importantly
(4) Prevention of postop cystoid macular edema (CME). Because of the high incidence of macular pathology in these patients, such as faint epiretinal membranes, use of an NSAID can play an important role in preventing postop CME, which would otherwise significantly limit vision. The important considerations for selection of an NSAID include potency, penetration, clinical efficacy and patient compliance. I like the patients to use the NSAID for 6 full weeks, so having a drop that is dosed just once or twice a day is more advantageous, particularly when it is very potent and has the ability to penetrate these long, myopic eyes.
The advantage of cataract surgery in myopic patients is the larger anterior chamber depth, which allows more working room during phacoemulsification. However, the infusion pressure from the phaco handpiece can cause over-inflation of the anterior chamber and a tendency to push the entire lens-iris diaphragm posterior. With an overly deep anterior chamber, surgery becomes difficult and uncomfortable for both surgeon and patient. To address this issue, we can lower the infusion pressure by lowering the bottle height; however, this will result in less inflow of fluid and a higher tendency for surge. Instead, make sure that there is fluid flow under the iris so that the pressure in the posterior chamber and anterior chamber is equivalent. By equalizing this pressure gradient, the cataract will not be pushed so deeply within the eye and the surgeon can use adequate infusion pressure (Figure 1). I prefer to use the chopper to slightly tent up the iris at the papillary margin in order to establish a channel for anterior-posterior fluid flow.
Figure 2. With twice a day dosing, using a potent NSAID for 6 weeks is easy for the patient and ensures rapid reduction of inflammation.
Patients with myopia are at a higher risk for postop retinal detachment if there is tension or traction on the vitreous base during surgery. The primary culprit is allowing the anterior chamber to collapse when removing the phaco probe or the irrigation and aspiration (I&A) probe from the eye. Once the anterior chamber collapses from lack of infusion, the posterior capsule and vitreous has a tendency to move anteriorly, often quite abruptly and significantly. This can be avoided by one simple technique: fully inflate the eye with a cohesive viscoelastic via the paracentesis prior to removing the phaco probe or I&A probe from the eye. At the end of the case, once the IOL has been placed into the capsular bag, remove the viscoelastic completely and use balanced salt solution via the paracentesis to keep the eye pressurized as the I&A probe is withdrawn. These techniques will prevent collapse of the anterior chamber, increase patient comfort and lessen the risks.
The postop refraction in myopes can take time to stabilize due to the variation in effective lens position as the capsular bag shrink-wraps around the IOL. During this period the physician can control inflammation using topical steroids and NSAIDs. While I only use the steroids for 3 weeks, I like to continue the NSAIDs for a full 6 weeks. This ensures that the inflammation is fully resolved, the post-op discomfort is eliminated and the risk of CME is reduced. I typically prescribe bromfenac (Xibrom, Ista Pharmaceuticals) due to the penetration and potency, comfort without stinging, and b.i.d. dosing that aids in compliance.
Because of the myopic patient's tendency to have thinner and more elastic sclera, there may be a higher risk of incision leakage, and therefore infection, after surgery. Use of a fourth-generation fluoroquinolone is highly recommended both before and after surgery. My goal for the antibiotic is a fast kill time and a full spectrum of microbial coverage, and therefore I typically select gatifloxacin (Zymar, Allergan).
During the post-operative period a repeat dilated fundus examination is indicated in order to search for possible retinal breaks or weakness that may have been created during surgery. Finally, keep in mind that there may be a large degree of anisometropia between the eyes, so performing timely surgery on the fellow eye will minimize the imbalance. While the patients will be functionally emmetropic after bilateral cataract surgery, they will always have the elongated axial lengths and myopic retinal changes that need to be followed on a regular basis.
It Can Dazzle Your Patients
In summary, cataract surgery in patients with high myopia can be challenging, but also very rewarding to both surgeons and patients. There is no greater magic in ophthalmology than neutralizing 20 D of myopia with a surgery that takes only minutes. OM
|Uday Devgan, M.D., F.A.C.S. is in private practice at Maloney Vision Institute, Los Angeles. He is also chief of ophthalmology at Olive View–UCLA Medical Center and assistant clinical professor at Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at (310) 208-3937, or via e-mail at email@example.com. Dr Devgan is a consultant for Allergan, AMO, Bausch & Lomb, eyeonics, Ista Pharmaceuticals and STAAR Surgical.|
Ophthamology Management, Issue: August 2007