Sponsored by NIDEKOPD-Scan III: Powerful Informatics Helps Guide
Preoperative Planning

Analysis of each component of the optical system provides an opportunity to design a surgical plan with a greater
chance of achieving a successful outcome.
BY SHERAZ M. DAYA, MD, FACP, FACS, FRCSED, FRCOPHTH
Preoperative planning is fundamental toensuring accurate outcomes after cataract or
refractive surgery. The technology used by theevaluating surgeon plays a vital role in patient
selection, as well as for choosing the appropriate lens option for cataract surgery or designing the optimal
refractive pattern. Minimizing the potential for a postoperativerefractive surprise has become increasingly important withthe growing popularity of refractive lens exchange (RLE) withimplantation of toric and premium multifocal implants.
The OPD-Scan III (NIDEK) is an advanced diagnostic device
that is well suited to the laser and cataract refractive surgeon.
The device combines autorefraction, corneal topography, ocularaberrometry, pupillography, and white-to-white measurements
in a single platform. The incorporation of all these features
allows evaluation of internal aberrations, potential visual acuity,and modulation transfer function (MTF), each of which may
be useful for analyzing the individual optical components ofthe eye. Armed with this information, the evaluating surgeon
can customize the approach to surgery and thereby reduce thepotential of missing the refractive target.

THE DAYA SUMMARY
I have worked with NIDEK to develop an overview report,
the RLE Cataract Summary, that combines a number ofparameters for surgical planning and postoperative evaluationthat are useful for lens and refractive surgeries.
The cogent summary is divided into three columns. The overall aberrometry, refraction, and quantitative aberrometry arein the central column. The corneal contribution derived from
Placido topography is represented in the left-hand column andthe internal contribution derived by subtracting the corneal
component from the overall aberrometry occupies the righthand column. The bottom half of the report follows the same
columnar format and shows aberrometry-derived astigmatism(axis and magnitude) above and overall higher-order aberrations below. This cleverly shows the overall contribution byeach optical component—corneal versus internal (Figure 1).
Presentation of the data in this manner provides the surgeon
a simplified overview of the influence of corneal aberrations
and internal aberrations to overall ocular aberrations. Dataon refraction, keratometry, visually significant higher-orderFigure 1. The three-column format of the RLE Cataract Summary provides a quick summaryof relevant information for planning lens and refractive surgeries.

aberrations (eg, coma and spherical aberration), and pupillometry can then be evaluated in greater detail.
The role of internal optical features in contributing to total
aberrations is currently underappreciated. The influence ofinternal optical features can be demonstrated in a sample image
from a patient who has myopic astigmatism (Figure 2). At thisstage of the patient’s life, the corneal spherical aberration iscompensating for the internal optical aberrations to ensure
the retinal image is optimized. However, natural changes in thecrystalline lens during the aging process, along with enlargementof the anterior-posterior diameter and increase in stiffness of
the lens, will affect the internal portion, which can negatively
impact image quality, increase total positive spherical aberration,and ultimately lead to loss of visual quality. Another example isseen in Figure 3, where reduction of internal negative aberration
results in a higher level of overall spherical aberration. This eye
may well benefit from an aspheric IOL to improve visual quality.
The OPD-Scan III significantly improves the ability to measureeach relevant portion of corneal, internal, and total aberrations
by combining Placido disk corneal topography (plotted using
SEPTEMBER 2019 | INSERT TO CATARACT & REFRACTIVE SURGERY TODAY EUROPE 1

Figure 2. Sample RLE Cataract Summary from a patient with myopic astigmatism.

Figure 3. Findings on this patient’s report suggest that an aspheric IOL will help to improvevisual quality postoperatively.

11,880 data points over 39 concentric Placido rings) and ocularaberrometry (plotted using 2,520 data points over 9.5 mm to
the 8th Zernike order). Corneal aberrations are subtracted fromthe overall aberrometry to derive the internal contributions. The
resulting maps and data can be used to assess corneal integrity
and determine the source of clinically significant aberrations,each of which can aid in developing a surgical plan. These maps
are also important for postoperative follow-up. For example,
internal aberrometry can be used to evaluate toric lens alignment
postoperatively, conveniently without the need for dilation.

the subepithelial layer, or the stroma. The surface regularity index (SRI) on the report is a good reflection of either thequality of the image taken or surface irregularity from rapid tearfilm evaporation, an irregular tear film, or epithelial basement
membrane dystrophy. These can result in an erroneous IOL
calculation from inaccurate keratometry readings. It is best thatthe cause of the low SRI be determined and treated if at all possible. A persistently poor SRI may well be a contraindication for
implantation of a premium IOL.

ASTIGMATISM CORRECTION

CONCLUSION

Astigmatism is a general term describing deviation fromspherical corneal curvature, and it is further classified as regularor irregular. In an eye with a cataract and regular, stable, andsymmetrical astigmatism, toric IOLs are typically an option. Yet,understanding the magnitude of corneal cylinder and its axis iscritical for accurate placement of a toric lens. This can be easily
accomplished by assessing wavefront-derived astigmatism with theOPD-Scan III using the corneal wavefront axis. Where this method
is very useful is in those patients who, for instance, have forme
fruste or frank keratoconus. Topographic astigmatism is asymmetric and nonorthogonal. It is thus difficult to establish the correct
axis for toric alignment. Again, wavefront aberrometry averages
out overall astigmatism in terms of magnitude and axis. Similarly,
for patients who wish to receive a high-performance premium lens
where the magnitude of astigmatism is low, placement of limbal
relaxing incisions can be determined using similar methodology.
Irregular astigmatism has historically been difficult to manage
in the patient undergoing cataract surgery or RLE. This is because
irregularities may derive from the tear film, the epithelial layer,

The Daya Summary provides a powerful set of data for surgicalplanning, patient counseling, and postoperative evaluation. Otherfeatures available on the OPD-Scan III may help plan the surgicalapproach, including information on pupillary diameter, the pupil’sshape, and the deviation of the visual axis from the pupillary center as well as the point spread function, which is a simulation ofretinal image quality, presented for the overall optical system, andfor the cornea and internal aspects separately. Thorough analysisof the optical components of the eye, overall and separately, helps
minimize the potential for missing the target during cataract surgery, RLE, or refractive surgery, which in turn increases the chancesof a satisfactory outcome for the surgeon and the patient. n2 INSERT TO CATARACT & REFRACTIVE SURGERY TODAY EUROPE | SEPTEMBER 2019SHERAZ M. DAYA, MD, FACP, FACS, FRCSED, FRCOPHTHnM
 edical Director, Centre for Sight, East Grinstead, United Kingdom
n Chief Medical Editor, CRST Europens daya@centreforsight.com
nF inancial disclosures: Consultant (Nidek)