CATARACT SURGERY FEATURE STORYIOL Station Software
for the OPD-Scan
This wavefront aberrometry system determines corneal, internal, and total-eye aberrations toprovide the optimal axis of alignment for toric IOLs.
BY PAOLO VINCIGUERRA, MD; AND ELENA ALBÈ, MDA

ccuracy of biometric calculations and, more important, of refractive results depends on three main
factors: preoperative biometric data including axial
length, anterior chamber depth, lens thickness, andcorneal curvature power variables; power calculation formulas; and quality and accuracy of the IOL. In the past 15 years,
several million people worldwide have undergone various
refractive surgery procedures for the most disparate visual
defects. These patients will soon be candidates for cataract
removal due to the natural aging process. In this population,
corneal curvature is profoundly modified, and obtaining
reliable biometry becomes complex. Additionally, patients
who have previously undergone refractive surgery are accustomed to a high level of visual quality, translating to highexpectations after cataract surgery.
All available biometric devices, even the most sophisticated, are designed for use on normal prolate corneas,
for which keratometry measurement based on 4 to 6
points is considered enough to accurately determine corneal curvature. These points are measured several millimeters from the corneal center; however, after refractive
surgery, the corneal gradient changes dramatically acrossthe corneal surface, from the pupil center to the periphery. The postoperative course may therefore be full ofTAKE-HOME MESSAGE• The postoperative course in cataract patients who
have previously undergone refractive surgery may
be full of surprises due to inaccurate determinationof corneal curvature using biometric devices andstandard measurements.
• Preoperative topographic and wavefront analyses
can be just as advantageous in cataract surgery as
they have proved to be in refractive surgery.
• The OPD-Scan with IOL Station software measuresand collects postoperative data and provides asynthetic single-document printout of all essential
information that can be hung in the operating room.

surprises due to inaccurate determination of corneal
curvature using these devices and standard measurements. The same situation tends to occur in individuals
whose corneas have been subjected to other surgicaltreatments that affect corneal curvature, such as corneal
transplantation, radial keratotomy, deep anterior lamellar keratoplasty, Descemet-stripping automated endothelial keratoplasty, and phototherapeutic keratectomy.
In comparison, topography can accurately detect themean pupillary power rather than just 4 to 6 points in themedium periphery. Topography measures the actual powerof the entire pupillary area that is involved with visual acuity.
INTRODUCTION OF WAVEFRONTTECHNOLOGYGreat attention has recently been given to the accurate
analysis of irregular optical systems with the introductionof wavefront analysis, a type of evaluation once belonging
exclusively to the territory of astronomy, into common
ophthalmic practice. Preoperative topographic and wavefront analyses of the total power of the eye can be justas advantageous in cataract surgery as they have proved
to be in refractive surgery in the past decade. Both canbe used to analyze the parameters necessary for successwith modern IOL technology and therefore answer theincreasing demands for optimal postoperative visual quality. These parameters include the following categories,described below.
Total, corneal, and internal spherical aberration.
These can be used to select the best aspheric IOL.
Total and internal astigmatism. The latter is determinedby the lens that will be surgically removed, resulting inchange in the total astigmatic power and axis of the eye. The
availability of toric IOLs makes wavefront assessment essential. If the total astigmatism is corrected with a toric IOL, theastigmatic component of the crystalline lens is removed, andthe patient will end up with iatrogenic astigmatism.
Angle kappa. Angle kappa (angle K) is the difference

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CATARACT SURGERY FEATURE STORY

Figure 1. Vinciguerra Summary, obtained with the Nidek OPD-Scan.
Red: The MPDist (angle K) provides information on the distance
between pupil center and the visual axis in photopic and scotopic
conditions. Data are color-coded: normal = green, suspect = yellow,
danger = red. In this case, the Mdist value is abnormal (red).

Figure 2. Vinciguerra Summary, obtained with the Nidek
OPD-Scan. Presentation of IOL data. Green: the power of two
aspheric IOLs for a target refraction of -3.00 D. It also
estimates the postoperative residual spherical aberration.

Figure 3. Vinciguerra Summary, obtained with the Nidek OPDScan. The final printout is used in the operating room.

Figure 4. Vinciguerra Summary, obtained with the Nidek
OPD-Scan. Presentation of visual quality with various types ofaspheric lenses. Residual spherical aberration is also calculated.

between the pupil center and the visual axis. In patients withhigh angle K, implantation of aspheric, multifocal, and hightoricity IOLs may lead to unsatisfactory results. Even if the IOL
is centered in the bag, the optical center of the IOL will be far
from the visual axis, with bad visual results. Therefore, a highangle K may be a contraindication for these types of IOLs.
Determination of different refractive powers according
to two pupil diameters, corresponding to photopic andscotopic conditions. The refractive power of the cornea varies
from center to periphery, often leading to two different refractions in scotopic and photopic conditions. This difference ismore pronounced in patients with a large scotopic pupil size,
and the information is vital when there is a specific request for
optimization of vision in photopic or scotopic conditions.
For these reasons, a topography-aberrometry device
allows not only appropriate patient selection but also
objective evaluation of the success of the implant.

BIOMETRY INTEGRATED WITH
ABERROMETRY CALCULATION
Devices such as the OPD-Scan (Nidek Co.), which
combines the functions of an autorefractometer, keratometer, topographer, pupillometer, and aberrometer(based on skiascopy) and measures accommodative
amplitude, visual axis, and keratometry, can be used tocalculate internal aberrations. Another factor to consider
is that biometric calculations are based on corneal power
data provided by ophthalmometry. The axial algorithm
is the closest to these data.
The OPD-Scan’s user-friendly printout acts as a guidefor the surgeon in the operating room, as this single document includes all the essential and necessary information
for the procedure. Each formula has increased efficiency
in a certain range of refraction, but the Holladay 2 andCamellin-Calossi formulas can be adapted to any refractive

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CATARACT SURGERY FEATURE STORYTABLE 1. DATA PRESENTED IN THE IOL STATIONSOFTWARE: PRINTED SUMMARY FOR CATARACT
1.
2.
3.
4.
5.

Two IOL calculations (first and second choice)State of the cornea (eg, after refractive surgery)
Pachymetry
Endothelial cell counts
Refraction, visual acuity, and intraocular pressure ofboth eyes
6. Axis of astigmatism superimposed onto topographic
map and pupillometry
7. Summary of biometric data
8. Type of IOL
9. Keratorefractive indices10. Position of the surgeon
11. Vision from the point of view of the surgeon

situation by introducing corneal power and lens thickness into the calculation. Moreover, these formulas neednumerous other data to be properly calculated.
In the process of patient preparation, mistakes canreduce the accuracy of the assessment, sometimes distorting the results. By using a single tool such as theOPD-Scan for all the necessary calculations, the surgeon
can generate a printout that acts as a guide in the operating room. However, surgical errors can originate not
only from wrong biometric calculations but also becauseof an inability to access to all relevant information.
Therefore, a unique printout serves as a synthetic single
document with all essential information that can behung, for example, on the operating microscope.
IOL STATION SOFTWARE
One component of the Nidek OPD-Scan is the IOL
Station software. This program generates a printout called
the Vinciguerra Summary (Figures 1 through 4), providing
step-by-step instructions to be used after the acquisition of
topography and wavefront data. It calculates the corneal
power in both eyes in relation to pupillary area and position, crystalline thickness and anterior chamber depth, corneal thickness (after introduction of pachymetric values todetermine refractive index), previous corneal surgery (withseparate calculations for incisional refractive surgery, phototherapeutic refractive procedure, and corneal transplant),
the power of previous refractive surgery (ie, the surgicallyinduced refractive change), information regarding primaryor secondary implantation (with different calculations due
to different IOL positions), and basic data (visual acuity,intraocular pressure, endothelial cell counts, previous surgery in the contralateral eye, notes).
The printout (Table 1) orients the map to the sur-geon’s point of view (superior or temporal approach),overlaps the axis of astigmatism onto the dilated pupilwith the arrangement of iris crypts as a more reliablereference for toric IOL implantation, and shows a second
IOL choice with appropriate A-constant.
Because the OPD-Scan is also an aberrometer, it determines the spherical total, corneal, and internal aberrations and provides an internal database of the best IOL
choice to compensate each patient’s spherical aberration. Additionally, the device divides the total astigmatism into corneal and internal components, allowing
detection of the optimal axis for toric IOL implantation.
It can also simulate the patient’s vision with two different IOLs, depicting how each compensates for sphericaland cylindrical errors. Finally, the OPD-Scan gives themean pupillary power for different pupil diameters.
CONCLUSIONThe OPD-Scan with IOL Station software is a reliable
tool to measure and collect postoperative data, in caseany issue arises after cataract surgery. Surgeons finally haveone machine that can accurately determine preoperative
biometric data, provide IOL power calculation formulas,and determine the quality and accuracy of IOL selection.
We believe that the OPD-Scan will improve the accuracy
not only of our biometry calculations but also of our postoperative refractive results. nElena Albè, MD, is a Consultant in theDepartment of Ophthalmology, Cornea Service,Istituto Clinico Humanitas Ophthalmology Clinic,Milan, Italy. Dr. Albè is a member of the CRST
Europe Editorial Board. She states that she has nofinancial interest in the products or companies mentioned. She
may be reached at e-mail: elena.albe@gmail.com.
Paolo Vinciguerra, MD, is the Chairman of theDepartment of Ophthalmology, Istituto Clinico Humanitas,Milan, Italy. Dr. Vinciguerra is a member of the CRST
Europe Editorial Board. He states that he has no financial
interest in the material presented in this article. He may bereached at e-mail: paolo.vinciguerra@humanitas.it.
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