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Cataract surgery after radial keratotomy can be challenging
Inaccurate IOL calculations, extended postop recovery and patients’ mindset create the possibility of a difficult procedure.
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Many of the patients who had radial keratotomy surgery in the ’80s and ’90s are now developing visually significant cataracts.
Because of their irregular corneas, even mild cataracts can induce visually significant aberrations at an earlier stage than would be expected for a traditional patient. This is a difficult subset of patients for many reasons: The IOL implant calculations can be inaccurate, the surgical procedure can be challenging, and the postoperative recovery can be prolonged. However, the greatest challenge is often the mindset of the refractive patient. These patients often have high demands and are frequently intolerant of residual refractive errors.
IOL selection
 Uday Devgan |
Many formulas and techniques have been described for calculating IOL power in post-radial keratotomy (RK) patients. This tells me that there is no single method that yields great results. The principal error in calculation is overestimation of the corneal power, which results in implantation of a lower power IOL and postop hyperopia. Because these patients have typically been myopic their entire lives, leaving them with residual hyperopia is particularly uncomfortable and bothersome. To help prevent postop hyperopia, a more myopic result can be targeted, such as –0.75 D instead of the typical –0.25 D.
In patients with no old records, the method that I use most often to calculate corneal power was proposed by Robert K. Maloney, MD. It uses the central corneal power as measured by topography and therefore does not depend on history. The power of the cornea is a combination of the anterior corneal power and the posterior corneal power. By converting the overall central corneal power from topography back to the anterior corneal power, then subtracting the expected posterior corneal power, we can achieve a fairly accurate estimation for our IOL calculations. This formula is:
Estimated K power = (Central K power on topography × 376/337.5) – 6.1
Because of the irregular corneas, I prefer to avoid multifocal IOLs, instead preferring single focus lens implants. Aspheric IOLs may be a particularly good choice in these patients because of their significant corneal aberrations.
Implanting a negative spherical aberration aspheric IOL can help to offset the large amount of positive spherical aberration often seen in RK corneas. In this case, I prefer the Advanced Medical Optics Tecnis IOL, as it has the best ability to offset large degrees of corneal positive spherical aberration. When the corneal aberrations are not known and a degree of irregularity and other higher order aberrations are suspected, I prefer the Bausch & Lomb SofPort Advanced Optics, as it has zero spherical aberration and is the “do no harm” IOL that will not confound the aberrations.
Intraoperative considerations
The RK incisions are weak and are prone to opening during surgery. Any incisions made during cataract surgery must avoid intersecting the existing RK incisions, lest they unzip and cause excessive fluid leakage during surgery. In patients with previous 8-cut RK, clear corneal incisions can be made between the existing RK incisions. (Figure 1). In patients with 16-cut or more RK, it becomes difficult to avoid the existing RK incisions unless a scleral tunnel cataract incision is used (Figure 2).
To be gentle on the weakened cornea, I prefer lower flow and a lower bottle height with a smaller phaco needle to ensure that the fluid inflow still stays greater than the fluid outflow. If the RK incisions open during surgery, be aware that there could be sudden instability and shallowing of the anterior segment, and the chance for capsule rupture is increased. At the end of these surgeries, I like to paint the entire cornea with fluorescein dye to check for any leaks, which can easily be sutured while the patient is in the operating room.
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Images: Devgan U |
Postop recovery
The RK incisions swell during even the gentlest cataract surgery, and this swelling can induce central corneal flattening, which results in excessive hyperopia immediately postop. These RK patients will experience fluctuations in their refractive state for many weeks after their cataract surgery, so a mild amount of initial hyperopia should not be a cause of concern. After waiting at least 6 weeks, if the patient is still significantly hyperopic, a second procedure can be performed.
Perhaps the most important issues in RK patients with cataracts are explaining to them that their IOL calculations are, at best, estimations and that their surgery and postop recovery will likely be more challenging for the surgeon and the patient.
For more information:
- Uday Devgan, MD, FACS, is in private practice at Devgan Eye Surgery in Los Angeles, Beverly Hills, and Newport Beach, California. Dr. Devgan is Chief of Ophthalmology at Olive View UCLA Medical Center and an Associate Clinical Professor at the Jules Stein Eye Institute 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 and Bausch & Lomb, and is a stockholder in Alcon Laboratories and formerly in Advanced Medical Optics.