An Instrument for All Surgeons

The new features of the OPD-Scan III will be a valuable asset to your armamentarium.

By Farrell “Toby” Tyson, MD, FACS

Some say lightning doesn‘t strike twice, but in the case of Marco‘s OPD-Scan III, lightning has struck three times. I‘ve been enthralled with my OPD II (3D Wave) for several years—it‘s my favorite piece of diagnostic equipment—so I didn‘t feel there was much to improve upon, but Marco has proven me wrong. With the OPD-Scan III, Marco didn‘t simply release a new software update with a new screen. The manufacturer, Nidek, actually took a clean slate approach and reworked the diagnostic machine from the chassis on up.

Giving Doctors What They Want

The OPD-Scan III continues the tradition of being an excellent multifunctional ophthalmic device. It combines a corneal topographer, autorefractor, wavefront refractor, wavefront analyzer, internal optical path difference analyzer (OPD) and light/dark pupillometer. In addition, the OPD-Scan III has the ability to record retro-illumination images, provide a toric IOL summary, calculate the effective central corneal power in postrefractive patients, calculate the modular transfer function of the optical system and provide a visual acuity simulation of corrected and uncorrected vision. These capabilities help fill out the spectrum of diagnostic tests that refractive cataract surgeons need and want.

Starting with corneal topography, they almost doubled the number of acquired data points from 6840 with the 3D Wave to 11,880 with the OPD-Scan III. This was aided by expanding the placido disc from 19 rings with the 3D Wave to 33 rings with the OPD-Scan III (Figure 1). By increasing the number of rings, the density of data points in the central cornea has increased significantly, which allows for more precise data in the area of the cornea that are most affected by postrefractive surgery and most crucial in IOL calculations. The addition of this extra data hasn‘t slowed down the acquisition process. Actually, the process to obtain a complete scan has been cut in half—from 20 to 10 seconds. Some of this improvement stems from the fact that the placido disc has been changed from red light rings to blue light rings, which are less startling to patients. If there‘s less startle, blink errors are reduced.

Figure 1. The OPD-Scan III has 33 rings for 11,880 data points. The blue light topography is much easier on patients during measurement.

The 3D Wave had an infrared camera that allowed the user to help align the unit with the eye. It was easy to visualize pathology on the cornea, iris or lens. The OPD-Scan III has taken this ability and expanded on it, allowing the user to record and print this information. The increase in managed care and the use of medical advisory boards has made this data more crucial to obtain and save. This documentation of cortical or posterior subcapsular cataracts or posterior capsular opacification may make the difference between an approved surgical procedure or a denied claim. In addition, some medical carriers will reimburse for this photography under the external ocular photography CPT code.

Additional Features

The OPD-Scan III has taken infrared photography one step further by integrating it with the corneal topographer, providing a highly functional toric IOL summary. Most surgeons enter the preop data into the appropriate toric IOL calculator and take the printout to surgery. While in the preop area, the patient is then crudely marked with ink on the limbus. While this method works for the most part, the ink often spreads over a 5° axis or there may be unaccounted cyclorotation. The OPD-Scan III allows surgeons to obtain an infrared image of the eye in a dilated or undilated state, illuminates the blood vessel on the sclera for landmarking, then superimposes the keratometric astigmatism and the surgical toric IOL placement over the image (Figure 2). This method eliminates the time-consuming process of marking patients on the surgical day and allows placement based on anatomical landmarks such as vessels, iris crypts and iris nevi. Postoperatively, this same process can be used to evaluate the surgical outcome or determine if rotation has occurred over time.

Figure 2. The toric IOL Summary allows you to accurately mark cornea based on landmarks, such as vessels, iris crypts or iris nevi.

Catch the Wavefront

The wavefront analysis function of the OPD platform has been very beneficial to refractive cataract surgeons because of its ability to calculate corneal spherical aberration. This helps guide the proper IOL selection based on the spherical aberration correction of the IOL. This is important in working toward the goal of leaving the post-cataract surgery patient with as little total spherical aberration as possible, allowing for maximal contrast sensitivity, which is extremely important for the highly demanding diffractive multifocal IOL patients and post-refractive cataract patients. In an effort to present more data for the surgeon, the OPD-Scan III has allowed the acquisition of wavefront data over a 9.5-mm area as compared to the 6.0-mm area of the 3D Wave. This increased area provides information where blend zones and treatment edges of LASIK take place.

A wavefront analyzer helps us understand the mysteries of refractions. In the past, all we had were topographers and autorefractors. On occasion, we see a patient without pathology whose vision doesn‘t significantly improve with refraction. Usually, at this point, your autorefractor is over-cycling and maybe your corneal topographer is displaying asymmetric astigmatism. This is usually a clue that something more than lower-order aberrations are at play. The OPD-Scan III does a great job of presenting the higher-order aberrations in a multitude of displays. Explaining higher-order aberrations to patients is easier with the OPD-Scan III, because it has the ability to show comparative images with and without higher- and/or lower-order aberration corrections (Figure 3). This visual presentation greatly simplifies the discussion with patients, so more time can be spent on the discussion of treatment options.

Figure 3. The visual acuity display on the OPD-Scan III provides comparative images with and without higher- and/or lower-order aberration corrections.

As time marches on, more and more of our cataract surgery patients will also be post-refractive surgery patients. The alterations to the cornea present many problems to the surgeon—from IOL surprise to induced spherical aberration. Many patients inform the surgeon that they‘ve had previous LASIK surgery, but they have no documentation—many don‘t even know if they had a myopic or hyperopic correction. This is easily elucidated with corneal topography, but the IOL calculations can still be tricky as effective lens position is altered by the alteration in corneal keratometry values. In order to obtain more accurate results, several different methods have been developed to help select the appropriate post-refractive IOL. The OPD-Scan III is able to calculate the effective central corneal power (ECCP) to provide a K-reading for IOL calculations. The software takes the 3 mm and 4.5 mm corneal power centered over the pupil from the corneal topography and compares it to the periphery, around a 9 mm zone. This information allows the software to calculate what the central corneal curvature power would have been before the myopic ablation and can modify it to compensate for the posterior radius of the cornea. With these values, the software computes the new ECCP.

These modifications and improvements have taken a very robust device and made it even more useful in a more complex ocular surgical environment. We no longer need to fear the postrefractive patient. Toric IOLs will require less intervention with greater reproducibility. Monofocal patients can benefit from spherical aberration optimization. Even standard eye exams benefit from the OPD-Scan III and its ability to highlight wavefront aberrations that limit the effectiveness of spectacles. This one device has become the gateway to our clinic. ■