We recently began integrating a new high-definition wavefront aberrometry platform into the clinic where I operate in Dublin, Ireland (Optilase Eye Clinic). The Dublin facility is one of three clinics in a busy corneal refractive surgery practice where we treat about 2,000 eyes per year.
As with any new technology, we wanted to evaluate results in a subset of eyes first before fully transitioning to the new aberrometer for all cases. We treated 95 healthy, normal eyes with LASIK or PRK treatments guided by the iDesign Refractive Studio (Johnson & Johnson Vision) and followed them for three months to make sure that we understood the capabilities of the device and the outcomes we could expect to achieve for patients.
The device was easy for our high volume clinic to integrate, with minimal disruption to the work flow in the first few days of use. Compared to the prior generation aberrometer, the iDesign Advanced WaveScan Studio, the new device proved to be similar or slightly faster for staff to use, given that it offers 1-click rather than 2-click acquisition. With a single capture, the surgeon gains access to more information and more complex maps than previously, which I expect will be a significant advantage, particularly in more challenging cases.
At three months, we have data available for 73 of the 95 eyes. Of these, 88% achieved 20/16 or better uncorrected visual acuity. The mean postoperative spherical equivalent was +0.12 D at 12 feet and -0.12 D at optical infinity (range -0.75 to +1.00 D), with a very tight standard deviation of 0.29 D.
Just as with the previous aberrometer, the device takes up to 1,257 micro-refractions to produce the whole-eye wavefront map. But in addition to the refractive information, the new system also integrates topographical information from each of those spots.
Essentially, it maps how elevated each spot is in relation to all the spots around it, allowing us to study the cornea in much greater detail. My impression is that this significantly increases the accuracy of the wavefront mapping. The visual acuity results in our initial patients demonstrate that the iDesign Refractive Studio is effective in normal, healthy eyes, but the potential for topography-integrated wavefront is even greater in highly aberrated eyes.
Potential in irregular corneas
In eyes with corneal aberrations, including those with keratoconus, prior surgery, or a traumatic injury, the addition of topographical information should help us to make better decisions about surgical candidacy. In the past, in a patient with a high degree of higher order aberrations (HOAs), we could not necessarily tell from the aberrometry alone whether the aberrations were coming from the crystalline lens, the cornea, or the retina. More information allows us to better differentiate the source of the wavefront error and make a better decision between cornea and lens surgery.
The high dynamic range (the system can image eyes from -16.00 to +12.00 D sphere and 0.00 to 8.00 D cylinder) also gives surgeons confidence in the accuracy of the refraction and imaging in both normal eyes and abnormal eyes.
I had the opportunity to examine a patient who worked as a mechanic and whose cornea had been perforated by a screwdriver. Surgeons had sutured the wound and saved the eye but the patient was left with 7 D of cylinder and was considering either topo- or wavefront-guided treatment. We were able to image the eye with the iDesign system and perform a wavefront-guided PRK, highlighting the accuracy of this system in recognizing complex wavefront patterns.
Although this has yet to be confirmed, it is my hope that topo-integrated wavefront technology will allow us to leave behind the difficult dilemma of choosing either wavefront-guided or topography-guided for challenging cases. Topography-guided treatments have been very effective for such eyes but they are difficult to perform and the learning curve is steep.
They also typically require two procedures-the first to regularize the cornea, and the second to treat the refractive error. It would be nice to be able to address both the refractive error and the corneal irregularities with a single procedure.
In addition to integrating topography, wavefront aberrometry, and refraction, the iDesign Refractive Studio also captures keratometry and two pupillometry measures (photopic and meso-scotopic). Like the topography, the keratometry data come from the same source as the wavefront data (the 1,200+ micro-refractions) so there is no misalignment or inconsistency in the data. Having a dynamic range of pupil measurements allows us to better evaluate the change in pupil centroid from dim to bright light.
The system can provide additional metrics, including axial, tangential, and elevation maps, among others, which are helpful in screening for various pathologies.
In cases where we see a slightly suspicious topography, combined with an increase in coma aberrations, for example, that would increase my level of concern about early keratoconus. In such a patient, I might want to defer surgery and monitor a little longer to see if there is any progression, giving this technology an additional use as a screening device.
Another feature that I find very useful is the calculation of angle kappa, or the difference between the center of the pupil and the line of sight. Previously, this information could be obtained only by using multiple devices.
In hyperopes, a large angle kappa might induce more aberrations which can lead to postoperative vision that is not as good as it was preoperatively with glasses. When the angle kappa is between 400-600 µm, I look more carefully at the treatment plan, the amount of astigmatism and total refractive error, and the pupil size.
In short, more information-no matter what the surgeon ultimately decides to do with that information-is always helpful in screening and treatment planning.
Dr Antonio Uceda Montanes
Dr. Uceda-Montanes is a consultant ophthalmic surgeon practicing in Spain and Ireland. He serves as a medical monitor for Johnson & Johnson Vision.
Figure 1 The Hartman-Shack aberrometry image clearly shows the Y-shaped trajectory of an earlier perforating corneal injury. (Figure courtesy of Dr. Uceda-Montanes)