The Next Wave in Cataract Surgery: Intraoperative Measurement of Sphere, Cylinder, and Aberrations

Louis Nichamin, MD


July 12, 2010

Evolution of Refractive Cataract Surgery

Refractive cataract surgery has evolved around 3 basic tenets: safety, efficacy, and patient satisfaction. Patient satisfaction requires a delicate balance of the best possible outcome mixed with the appropriate patient expectations.

Historically, the goal of early keratorefractive surgery was "functional" vision. Uncorrected visual acuity (UCVA) of 20/40 or better with accuracy to target of ± 1.00 diopter (D) was considered a good outcome.

Today's patient lives in a world full of technological advances and personal gratification, and the latest generation of excimer lasers provide laser-assisted in situ keratomileusis (LASIK) patients essentially complete spectacle independence, with outcomes of 20/20 vision or better and accuracy to target of ± 0.50 D.

The biggest question faced by refractive cataract surgeons today is how to provide LASIK-like outcomes for lens-based surgical patients.

Wavefront Aberrometry-based Technology

With the development of the ORange® intraoperative wavefront aberrometer (WaveTec Vision Systems, Aliso Viejo, California), surgeons now have the ability to dynamically measure the refractive state of the eye intraoperatively.

The ORange® device uses wavefront aberrometry-based technology and fits on the operating room microscope. It allows the surgeon to perform measurements at any point during surgery to determine the refractive status of the eye, both from a spherical standpoint and as an astigmatic reading. This tool provides surgeons with unprecedented refractive data and the ability to refine the results. Eventually surgeons will also be able to ascertain higher-order aberration states intraoperatively.

Intraoperative Measurements Lead to Improved Accuracy

Studies are showing that the use of intraoperative measurements has the potential to significantly improve patient outcomes.

In a comparison study, accuracy to target and mean prediction error in a cohort of 643 eyes that were operated on without the use of the ORange® device showed 46% of eyes at ± 0.50 D and 85% of eyes at ± 1.00 D, with a mean prediction error of 0.52 ± 0.44 D. In the cohort of 153 aphakic eyes that were operated on using ORange® Gen II, the accuracy to target was 75% of eyes at ± 0.50 D and 94% of eyes at ± 1.00 D, with a mean prediction error of 0.38 ± 0.31 D. These results remained consistent over several brands and types of intraocular lenses (IOLs). Controlled studies were completed with the following IOLs: Bausch & Lomb (Crystalens®), AMO ZCB00 (TECNIS®), Alcon SN60WF (AcrySof®), and Bausch & Lomb MI60L (Akreos™), and all show improved refractive predictability with the Orange® device.[1]

It was also found that the axial position of the implant at the end of surgery actually correlates closely to its final resting position (effective lens position [ELP]). Whereas the axial position was always considered to be an inconstant variable that would probably not correlate with the final ELP, data now show that the ELP can be predicted with a high degree of accuracy.

Leading experts in the field of intraoperative lens power calculations and refractive outcomes put the theoretical limit for accuracy at 0.18 D. In other words, in the case of a perfect keratometry reading and a perfect axial length position, with everything else ideal, 0.18 D is the best range of error that can probably be achieved. With the ORange® device, surgeons are coming in close approximation of that range, opening up the possibility of a new level of refractive accuracy.

Astigmatism Applications

Investigators performed a prospective, multicenter, randomized study of the ORange® intraoperative wavefront aberrometer in astigmatic patients with cataracts undergoing cataract surgery with IOL implantation combined with peripheral corneal relaxing incisions.[2]

The control group had 37 eyes at 3 months of follow-up and preoperative keratometer measurements of 1.42 ± 0.43 D (0.80 to 2.60 D). Surgery was performed without the use of ORange® measurements. Results showed that 8 of 37 eyes (21.6%) had ≥ 1.00 diopters of cylinder (DC) at 3 months after surgery.

In comparison, the treatment group had 30 eyes at 3 months after surgery, with preoperative keratometer measurements of 1.56 ± 0.52 D (1.00 to 2.70 D). The ORange® device was used intraoperatively, and limbal relaxing incision enhancements were left to the discretion of the surgeon. The results in this group showed that 10 of 30 eyes were enhanced, and 3 months after surgery 4 of 30 eyes (13.3%) had ≥ 1.00 DC.

These data indicate that the investigators statistically significantly refined the astigmatic outcomes when the ORange® device was used intraoperatively to measure the results of limbal relaxing incisions and then enhance on the basis of the intraoperative reading (as opposed to not taking a reading and just doing what would normally be done with standard nomograms).

The field of astigmatism management is very complex, with multiple variables. It is encouraging to see that this new technology can begin to be used to refine the outcomes.

Toric intraocular lenses. William Wiley, MD, assisted in the investigation of the application of the ORange® device with toric IOLs. In a study that compared outcomes of toric IOLs placed with the assistance of the ORange® device,[3] 23 eyes were operated on without and 24 with the assistance of the intraoperative wavefront aberrometer. Preoperative demographic characteristics and keratometer measurements were similar in both groups.

In the group that was not measured with the ORange® device, manifest refraction at 1 month after surgery was 0.61 ± 0.54 D and residual cylinder was 0.00 to 1.75 D. In addition, 13 of 23 eyes (56.5%) had ± 0.50 diopters of sphere (DS), 20 of 23 eyes (86.9%) showed ± 1.00 DS, and 3 of 23 eyes (13.1%) eyes showed > 1.00 DS.

In comparison, the group that was measured intraoperatively with the ORange® device showed manifest refraction at 1 month after surgery of 0.16 ± 0.22 D and residual cylinder of 0.00 to 0.50 D. Final results of the ORange® cohort showed 23 of 24 eyes (95.8%) with ± 0.50 DS, and all eyes (100%) with ± 1.00 DS. No eyes in the ORange® cohort had > 1.00 DS.

Wiley's data are impressive in showing the improvements being made in cylinder and sphere.