Cataract surgery in myopic eyes requires extra attention

Although the patients are often highly satisfied, cataract surgery in myopic eyes poses particular challenges and risks.

Uday Devgan

Cataract surgery is one of the most effective forms of refractive surgery, because the new lens implant can correct just about any degree of hyperopia, myopia and even astigmatism at the time of surgery. The highly myopic patients are often the happiest, because a lifetime of nearsightedness is finally cured with successful cataract surgery. However, these myopic eyes pose challenges and additional risks during surgery and in the perioperative period.

Preoperative evaluation

Myopic eyes have a higher risk of retinal complications, such as retinal detachment, compared with emmetropic eyes. During the preoperative exam, look carefully for any retina breaks, holes or weaknesses, 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 postoperative vision achieved and may influence the development of postoperative complications such as cystoid macular edema. If any posterior segment issues are noted, referral to a vitreoretinal colleague for treatment is recommended before cataract surgery.

In addition to the typical cataract evaluation, care must be taken to accurately assess the retinal status and measure the axial length of the eye. Highly myopic eyes often have a posterior staphyloma, which can give an erroneously long axial length when measured with the standard A-scan ultrasound. This would cause an error in lens calculations and residual postop hyperopia, resulting in an unhappy patient. Using an optical method for measurement tends to be more accurate, as it measures directly at the fovea. The IOL calculation formulae are less accurate at the extremes, and this is particularly true for highly myopic eyes. Of the two-variable formulae, the SRK/T tends to perform particularly well, as do more complex formulae such as the Haigis and Holladay 2. A postoperative refractive goal of a mild amount of residual myopia, such as –0.5 D, can be helpful to avoid a hyperopic surprise.

The selection of the IOL depends on each patient’s ocular status and needs. Patients with large degrees of myopia and corneal astigmatism are particularly well suited to toric IOLs, while others may do well with multifocal or accommodating IOL designs. Multiple manufacturers make an extended range of IOLs, including minus power lenses that can correct patients with up to –30 D of preoperative refractive myopia. Examples of these lenses are the Abbott Medical Optics Sensar AR40M acrylic IOL (as low as –10 D), the Alcon AcrySof acrylic IOL (as low as –5 D), the STAAR AQ5010V silicone IOL (as low as –4 D), the Bausch & Lomb Crystalens AO (as low as +4 D) and the Hoya Surgical Optics iSymm (as low as +6 D).

Surgical technique

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 posteriorly. With an overly deep anterior chamber, surgery becomes difficult and uncomfortable for both the surgeon and patient. To address this issue, the infusion pressure can be decreased by lowering the bottle height; however, this will result in less inflow of fluid and a higher tendency for surge. A better solution is to break the reverse pupillary block by making sure that there is fluid flow under the iris to equalize the anterior and posterior chamber pressures. By neutralizing this pressure gradient, the cataract will not be pushed so deeply within the eye, and adequate infusion pressure can be used. 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. Alternatively, a single nasal iris hook can be placed for the duration of the surgery.

A detailed examination of the retina before cataract surgery is important to identify posterior segment pathology. Myopic degeneration can affect the macula while peripheral retinal weakness can increase the risk of a postoperative retinal detachment. Despite the retinal changes noted in this photo, the patient achieved 20/20 vision after successful cataract surgery. Images: Devgan U

Highly myopic eyes are prone to excessive deepening of the anterior chamber upon pressurization during cataract surgery due to a reverse pupillary block. (A) In this figure, the nucleus has been removed and is ready for cortical cleanup; (B) The anterior chamber becomes overly deep upon insertion of the probe; (C) The chopper is used to briefly tent up the iris to break the pupillary block and equilibrate the anterior and posterior chamber pressures; (D) Removal of the remaining cataract material can be completed in a safe manner with restoration of the normal anterior chamber anatomy.

Myopic patients 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 irrigation and aspiration probe from the eye. Once the anterior chamber collapses from lack of infusion, the posterior capsule and vitreous have a tendency to move anteriorly, often quite abruptly and significantly. This can be avoided by one simple technique: fully inflating the eye with viscoelastic via the paracentesis before 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.

Postoperative management

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, inflammation can be controlled using topical steroids and NSAIDs. During the postoperative period, a repeat dilated fundus examination is indicated in order to search for possible retinal breaks or weaknesses 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 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.

While cataract surgery in myopic patients can pose many challenges, these patients tend to be among the happiest of all. In a safe, efficient surgery that has taken just minutes, their cataract has been removed, their myopia has been treated, and they can now enjoy a lifetime of excellent vision.

• Uday Devgan, MD, FACS, is in private practice at Devgan Eye in Los Angeles, chief of ophthalmology at Olive View UCLA Medical Center and an associate clinical professor at the UCLA School of Medicine. Dr. Devgan can be reached at 11600 Wilshire Blvd., Suite 200, Los Angeles, CA 90025; 800-337-1969; fax: 310-388-3028; e-mail: devgan@gmail.com; Web site: www.devganeye.com. Dr. Devgan is a consultant to Abbott Medical Optics, Bausch & Lomb, Hoya Surgical Optics, and a stockholder in Alcon Laboratories and formerly in STAAR Surgical.