Before attempting cataract surgery on an astigmatic eye, what pertinent information do we surgeons need to know? Crucial data include (1) determining if the astigmatism is regular or irregular; (2) the astigmatism’s magnitude and axis angle; (3) the presence of any corneal aberrations that would alter the astigmatism’s value or axis; (4) the health of the cornea—eg, the presence of dry eye disease (DED); and (5) controversially, it is helpful to know the pupil’s size and the line of sight (eg, whether we should aim for angle kappa or alpha). The OPD-Scan III from NIDEK assists with all these preoperative calculations and performs several more useful functions.
AT-A-GLANCE CALCULATIONS
I worked with the NIDEK team for more than 18 months to develop a diagnostics system that could display both corneal and intraocular measurements on a single page to help us quickly determine if further diagnostics were warranted before any surgery. These data are also useful as an educational tool and help us explain to patients which parts of their eyes require treatment. The OPD-Scan III incorporates a point spread function (PSF), which simulates how a pinpoint source of light appears on each part of the eye.
The data on the left side of the printout pertain to the cornea: corneal power, the magnitude of astigmatism, simulated K readings, and the average SimKs (Figure 1). The right-hand column shows intraocular data, including internal aberrometry, astigmatism, magnitude, and axis. Not only can the OPD-Scan III indicate the refractive error centrally, it can also calculate refraction based on pupil size. Additionally, the amount of spherical aberration and coma will change with pupil size, and the values with a mesopic pupil are very useful.
Figure 1. An example of a summary printout from the OPD-Scan III, codeveloped with Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed), FRCOphth. This display shows three columns of data from each ocular scan (corneal optics, overall ocular optics, and internal optics), which may be used for presurgical evaluations, surgical planning, and postoperative diagnostics. The device comes with several pre-registered summaries, and users may also register customized summaries.
IOL SELECTION AND ALIGNMENT
Corneal asphericity is very important to consider in choosing an IOL, as is the eye’s potential visual acuity. In addition to toric data, the OPD-Scan III provides pupillary data that include photopic and mesopic pupil sizes; white-to-white measurements, and the offset, the so-called angle kappa (displayed in mm). Furthermore, the device includes wavefront data derived from corneal topography. I consider these data critical in aligning IOLs over astigmatism correction. The OPD-Scan III also illustrates higher-order aberrations visually, making it easy to identify coma or spherical aberration immediately.
Moreover, the OPD-Scan III is a great tool for checking post-refractive alignment, so much so that I no longer dilate post-refractive surgery patients to see if the lens lined up correctly. Instead, I look at the internal astigmatism alignment on the OPD-Scan III.
DRY EYE
Because dry eye disease (DED) is a problem in presurgical eyes, it is important to screen for it in all cases. Sometimes, dry eye can masquerade as astigmatism and interfere with IOL calculations. Traditional methods to evaluate the corneal surface include fluorescein staining, but my staff and I also use the OPD-Scan III’s topography map for DED screening to identify the patients who need to be treated before undergoing surgery (Figure 2).
Figure 2. The OPD-Scan III’s surface regularity index (SRI) will show irregularities in the cornea. In this sample case, there is an irregularity of 1.27 (highlighted in red), which is a dry spot on the cornea.
AN ESSENTIAL TOOL
In my clinic, every patient receives an OPD-Scan III at every visit before I see them. It is impressive to patients when I walk into the exam room with a printout of their ocular data and I say, “Oh, your dry eye’s improved.” They wonder how I know that, and then I show them their surface irregularity map relative to their last visit. It’s a valuable tool for both internal and external optics.
For surgical planning and preoperative evaluation, the OPD-Scan III is incredibly valuable given all the measurements it can take. We use it in conjunction with NIDEK’s AL-Scan for biometry, which is phenomenally accurate, even imaging through hard lenses. Postoperatively, if the patient’s vision is not quite right, the diagnostics of the OPD-Scan III help us find out why. I consider it an essential instrument for performing premium ocular surgery.
