Case Report

Effect of arcus senilis on intraocular lens power calculation with intraoperative aberrometry

Lin, Wonchon MD; Lam, Peter MD; Kim, Terry MD*

Author Information
Journal of Cataract and Refractive Surgery Online Case Reports: July 2018 - Volume 6 - Issue 3 - p 51-54
doi: 10.1016/j.jcro.2018.04.001
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Abstract

Intraoperative aberrometry has been shown to accurately predict intraocular lens (IOL) power in complex cases.1–4 The use of intraoperative aberrometry in normal eyes is more debatable.5 As newer generation IOL formulas have become progressively better at predicting IOL power, the addition of intraoperative aberrometry has provided another tool to confirm and/or enhance IOL power prediction. The Optiwave Refractive Analysis device (Alcon Laboratories, Inc.) requires the user to input optical biometric measurements such as axial length (AL), keratometry (K) values, lens thickness, anterior chamber depth, and white-to-white (WTW) diameter; however, how these parameters are used to predict the IOL power is unknown. In addition, other factors, such as intraocular pressure (IOP), corneal thickness, external pressure from the lid speculum, and patient's fixation, might affect the accuracy of IOL power calculation with intraoperative aberrometry.6–8 These parameters might not be factored into the device's IOL power calculation. We describe a case of arcus senilis affecting accuracy of intraoperative IOL power calculation.

CASE REPORT

A 75-year-old white woman was referred for cataract surgery. The patient had no significant medical or ocular history. The corrected distance visual acuity (CDVA) was 20/40 in the right eye and 20/30 in the left eye.

On slitlamp examination, the patient was noted to have arcus senilis and 2+ nuclear sclerotic cataracts with vacuoles in both eyes as well as a small nasal pterygium in the right eye (Figures 1 and 2). Table 1 shows the preoperative biometry.

Figure 1.
Figure 1.:
Right eye has a large area of arcus senilis.
Figure 2.
Figure 2.:
Left eye.
Table 1
Table 1:
Preoperative biometry measurements.

Based on the IOL power calculation with the Barrett Universal II formula using optical low-coherence reflectometry (OLCR) (Lenstar, Haag-Strait AG), the tentative plan was to place a +21.50 diopter (D) multifocal IOL (Restor +2.50 SV25T0, Alcon Laboratories, Inc.) in the right eye. Intraoperative aberrometry was performed using the Optiwave Refractive Analysis device, which predicted a +20.00 D IOL for the right eye (Figure 3). The large discrepancy between the preoperative and intraoperative IOL power calculation presented a dilemma as to which IOL to implant in the eye. Of note, the arcus senilis encompassed a larger surface area in the right eye than in the left eye. The WTW measured with OLCR was 8.62 mm in the right eye, which was 2.08 mm greater than that in the left eye (10.70 mm). The WTW in the right eye was manually measured as 11.00 mm using intraoperative calipers. This measurement was inputted into the intraoperative aberrometer, which then calculated an IOL power of +21.50 D (Figure 4). The intraoperative measurement after implantation of the IOL confirmed that +21.50 D was the correct choice. Postoperatively, the CDVA was 20/20 in the right eye and the patient stated she was happy with the IOL and the outcome.

Figure 3.
Figure 3.:
Intraoperative aberrometer measurement predicting the +20.00 D multifocal intraocular lens.
Figure 4.
Figure 4.:
Intraoperative aberrometer measurement predicting the +21.50 D multifocal intraocular lens after the white-to-white diameter was adjusted.

DISCUSSION

This case shows that dense arcus senilis can interfere significantly with the Optiwave Refractive Analysis aberrometer's intraoperative IOL power calculations by giving a false WTW. The preoperative IOL power calculations with the Barrett Universal II formulaA predicted the correct IOL the very small WTW resulting from arcus senilis. The Barrett Universal II formula, which incorporates the WTW measurement in its calculation, predicted a power of +21.50 D. On the other hand, the intraoperative aberrometer, which uses an algorithm that integrates multiple parameters (including WTW) to calculate the target IOL power,4,9 predicted a much different IOL power of (+20.00 D).

The intraoperative aberrometer used in our case determines the effective lens position (ELP) by calculating what is termed the Wavetec factor, which is the product of combining 4 regression coefficients.B These regression coefficients are tied to an individual patient's AL, mean K values, aphakic spherical equivalent (SE), and WTW. The Wavetec factor is then combined with the intraoperative aberrometer lens constant (ie, the surgeon factor) to calculate the ELP for that specific eye. In our case, given that the WTW resulted in a significant difference in the predicted IOL power, the WTW measurement likely is more important in the intraoperative aberrometer's calculations than in the Barrett II formula.A Other formulas that take WTW into account include the Holladay II10 and Hill Radial Basis Function.CTable 2 shows the predicted SE of implanting a +21.50 D Restor SV25T0 multifocal IOL for different formulas with a WTW of 8.62 mm or 11.00 mm. For our patient, inaccuracies in the WTW appear to significantly affect the intraoperative aberrometer Optiwave Refractive Analysis device and Holladay II calculations more so than those of the other formulas.

Table 2
Table 2:
Predicted SE of different formulas with 8.62 mm WTW versus 11.00 mm WTW for +21.50 D IOL.

We hypothesized that the intraoperative aberrometer predicted a much lower target IOL power because of the smaller WTW. After the WTW intraoperatively measured with calipers was inputted into the intraoperative aberrometer, the aberrometer's IOL power prediction aligned with that of the Barrett Universal II formula,A confirming our hypothesis. Thus, it is imperative to review all preoperative measurements for symmetry between fellow eyes and identify any outliers because these might cause unexpected predicted IOL powers during surgery. This is especially important in cases in which premium IOLs, such as multifocal IOLs, are implanted. In such cases, achieving the refractive target is of very important. To our knowledge, this is the first report of arcus senilis affecting the accuracy of intraoperative aberrometry.

To conclude, although newer IOL formulas and technologies continue to be developed, the predictive accuracy of IOL power calculation remains a challenge and requires continued and active review by the surgeon preoperatively and intraoperatively. Also, this case shows that surgeons should be cognizant of the WTW in addition to other factors that affect the accuracy of intraoperative IOL power calculations. These other factors include patient fixation, increased corneal thickness, IOP, external pressure from the lid speculum, and the capsulorhexis diameter.6–8 Future studies should evaluate other factors that might affect intraoperative IOL power calculations.

Disclosures:

Dr. Kim is a consultant to Alcon Laboratories, Inc. None of the other authors has a financial or proprietary interest in any material or method mentioned.

REFERENCES

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5.Davison JA, Potvin R. Preoperative measurement vs intraoperative aberrometry for the selection of intraocular lens sphere power in normal eyes. Clin Ophthalmol 2017; 11:923-929. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5440073/pdf/opth-11-923.pdf. Accessed May 10, 2018
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8.Huelle JO, Druchkiv V, Habib NE, Richard G, Katz T, Linke SJ. Intraoperative aberrometry-based aphakia refraction in patients with cataract: Status and options. Br J Ophthalmol 2017; 101:97-102. Available at: http://bjo.bmj.com/content/bjophthalmol/101/2/97.full.pdf. Accessed May 10, 2018
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10.Holladay JT. Holladay IOL Consultant User's Guide and Reference Manual. Houston, TX, Holladay Lasik Institute, 1999

OTHER CITED MATERIAL

A.Barrett GD. Barrett Universal II Formula. Singapore, Asia-Pacific Association of Cataract and Refractive Surgeons. Available at: http://www.apacrs.org/barrett_universal2/. Accessed May 10, 2018
B.Alcon Laboratories, Inc. Product Specification 028, personal communication, March 21, 2018
C.Hill WE. Hill-RBF calculator version 2.0. Available at: http://rbfcalculator.com/online/index.html. Accessed May 10, 2018
© 2018 by Lippincott Williams & Wilkins, Inc.
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