POINT/COUNTERPOINT: DOES INTRAOPERATIVE ABERROMETRY MATTER?

Point: For those who consider themselves refractive cataract surgeons, this technology helps to nail the target refraction.

Technology helps bring the wow factor to cataract surgery.

Stephen G. Slade, MD

With an almost endless supply of new high-tech instruments in ophthalmology, it is important to separate those that merit capital investment from those that do not. Cataract surgery is the most common surgery performed worldwide, with an estimated 19 million procedures annually.¹ With numerous premium options in lens designs and surgical technologies available to our patients, cataract surgery is a procedure that can be very profitable for surgeons. In order for this to remain true, however, patients must be wowed by their outcomes. In my opinion, real-time aberrometry is the keystone in the arch of patient satisfaction.

Clarity Medical Systems has released the Holos IntraOp, a wavefront aberrometer that provides a continuous video stream of wavefront data to allow assessment of refraction changes during cataract surgery in real time. This technology uses a patented sequential scanning system that provides qualitative and quantitative information regarding the patient’s sphere, cylinder, and axis measurements.

ADVANTAGES

Selecting a lens. The aim of intraoperative aberrometry is to reduce residual refractive error by refracting the aphakic eye and allowing the surgeon to confirm or revise the IOL selection that was made based on preoperative biometry. This is particularly advantageous for patients who have previously undergone refractive surgery, which renders conventional biometry methods less predictable; it is also useful in patients who have a dense cataract or posterior subcapsular cataract, as both situations make it difficult to obtain a correct biometric reading.

Aphakic refraction also takes into account posterior corneal astigmatism. One study of 715 eyes of 435 patients found that posterior corneal astigmatism averaged -0.30 D.² Picking a toric IOL power based on anterior surface measurements alone can underestimate total astigmatism by 0.22 D at the 180º meridian, resulting in overcorrection in eyes that have with-the-rule astigmatism and undercorrection in eyes that have against-the-rule astigmatism.

Optimizing lens location. Toric IOLs must be correctly aligned to be effective, as each degree of rotational misalignment reduces the toric effect by 3.3%.³ Intraoperative aberrometry can be used to refine toric IOL alignment following implantation. Although preoperative alignment techniques can be accurate, they ignore three elements that are potential sources of error: (1) posterior corneal astigmatism, (2) surgically induced astigmatism, and (3) tilting or head misalignment during preoperative testing. By contrast, real-time aberrometry can measure the eye’s toricity on the table and as the surgeon rotates the lens; these results can be seen in real time. When the image indicates that cylinder is no longer present, astigmatism has been neutralized.

Tailoring arcuate incisions. Another helpful function of intraoperative aberrometry is to tailor arcuate and limbal relaxing incisions (LRIs). Nomograms and calculators for astigmatism-correcting incisions can be helpful, but, just as preoperative keratometry (K) is not always precise, there is still some guesswork with these incisions, and there may be an impact on the degree of astigmatism induced by the cataract incision. Intraoperative refraction can correlate to the arcuate incision, and the surgeon can use the refraction to determine if the incisions should be opened to achieve their maximum effect.

IMPACT ON RESULTS

Peer-reviewed evidence for the efficacy of intraoperative aberrometry is lacking; however, numerous surgeons have reported in personal accounts that nearly all of their patients leave with less than 0.50 D of pseudophakic refractive error. These surgeons also report that intraoperative aberrometry decreases the number of patients who return for enhancement procedures.

The greatest use for intraoperative aberrometry appears to be in the premium channel. Patients who pay extra for premium IOLs and/or laser-assisted cataract surgery (LACS) do so with incredibly high expectations. This is especially true of post-LASIK and post-PRK patients, as they are accustomed to investing in their sight and expect the types of outcomes common with refractive surgery. IOL technology has enabled better visual acuity with greater contrast sensitivity and fewer visual distortions than ever before, but this has only increased the need for highly precise biometry.

Emmetropia may be the goal for all of our patients, but predictability is what every surgeon craves. Intraoperative aberrometry adds a greater level of control to the surgical procedure, allowing physicians to promise—and then deliver—excellent outcomes.

Stephen G. Slade, MD, practices at Slade and Baker Vision in Houston, Texas. Dr. Slade states that he has no financial interest in the products or companies he mentioned. He may be reached at tel: +1 713 626 5544; e-mail: sgs@visiontexas.com.

1. Trikha S, Turnbull AM, Morris RJ, et al. The journey to femtosecond laser-assisted cataract surgery: new beginnings or false dawn? Eye (Lond). 2013;27:461-473.
2. Koch DD. Contribution of posterior corneal astigmatism to total corneal astigmatism. J Cataract Refract Surg. 2012;38(12):2080-2087.
3. Novis C. Astigmatism and toric intraocular lenses. Curr Opin Ophthalmol. 2000;11:47-50.

Delivering optimal refractive results can grow your refractive cataract surgery practice.

Jonathan H. Talamo, MD

In my practice, the ORA System with VerifEye (WaveTec Vision) is an essential component in achieving optimal refractive outcomes in cataract surgery.

I rely on intraoperative aberrometry every time I implant a presbyopia-correcting or toric IOL and in any eye that has undergone corneal refractive surgery. Because it increases the accuracy of IOL power selection, the ORA System with VerifEye is the perfect complement to the precision of LACS.

According to data compiled from multiple users, ORA has reduced costly retreatments by 50% and increased surgeons’ premium IOL conversions by 41% on average. Nearly all users (98%) said the system saves them from refractive surprises, as often as at least once a week (55%).¹ My experience is similar, which is why I consider ORA a crucial adjunct technology for refractive cataract surgery.

For me, the proof of ORA’s value is in the frequency with which it affects surgical decision-making. In a recent analysis of our toric IOL cases, my partner and I found that we changed the spherical IOL power in 35% of eyes and the cylinder power in 24% based on intraoperative ORA refraction. After implantation, we rotated the lenses in 33% of eyes, with a few (8%) requiring more than three rotations to fully eliminate astigmatism. In those eyes, the lens power we selected or the initial axis position would have resulted in a poorer outcome had we not used ORA.

A recent case illustrates this point. A male patient presented with high astigmatism and mild keratoconus. Manual K indicated 2.00 D of astigmatism at 13°, but K readings with the IOLMaster (Carl Zeiss Meditec) were considerably higher (2.71 D). I was undecided whether to implant a Tecnis ZCT300 or ZCT400 lens (Abbott Medical Optics). The aphakic ORA refractions indicated astigmatism of 2.84 D at 23°, so I implanted the higher-powered toric lens (Figure 1). Pseudophakic ORA refraction showed that 0.54 D of astigmatism remained, almost exactly as predicted by the aphakic measurement, and recommended a clockwise rotation (Figure 2). Had I gone with my preoperative calculations alone, I may have put in the ZCT300 and gotten an undercorrection. Thanks to the intraoperative measurements, I was more confident that the ZCT400 was the right choice in this eye. One week after surgery, UCVA was 20/25+3, and manifest refraction of +0.50 -0.75 X 65º yielded acuity of 20/20, confirming that the IOL selection and positioning were appropriate.

EVOLVING TECHNOLOGY

More than 170,000 cases have been performed with the ORA System, contributing to a significant database that helps users optimize lens constants for better results. Now in its third generation, the ORA System has been tested and refined with multiple software and hardware upgrades. The latest upgrade, VerifEye, has further improved accuracy and sped up measurements. Also, the preview screen provides a full field of view, including a live video display of the eye and streaming refractive information so the surgeon can monitor crucial parameters throughout the procedure. For example, I am able to confirm that the eye is stable and that no extrinsic factors (eg, a speculum) are affecting the measurement http://eyetube.net/?v=ifese.

The streaming data include sphere, cylinder, axis, spherical equivalent, and lens power recommendation. Each measurement is an average of the best three of five consecutive measurements, captured within a matter of seconds.

LATEST RESULTS

Reducing the prediction error (PE) in refractive cataract surgery is a crucial component of achieving excellent UCVA postoperatively. Ideally the PE should be no more than 0.50 D; published studies, however, report this level of accuracy achieved less than 60% of the time.^2,3

The mean PE with the ORA System with VerifEye is 0.29 ±0.25 D, compared with 0.34 ±0.29 D with preoperative calculations alone, according to a large global data set of nearly 5,000 eyes.⁴ With ORA, users have achieved a PE of 0.50 D or less in 84% of eyes, whereas they would have achieved this level of accuracy in only 77% with preoperative measurements alone (Figure 3).⁴

When only eyes implanted with presbyopia-correcting IOLs in this database (n=1,655) are considered, the PE was 0.28 D, and 85% achieved a postoperative refraction within ±0.50 D of the intended correction.⁴ The results when ORA was used to guide astigmatic correction were similar. In 1,303 eyes in the database with mean preoperative keratometric astigmatism of 1.72 ±0.79 D, the mean postoperative astigmatism was 0.42 ±0.40 D following implantation of a toric IOL with ORA guidance for lens power and positioning (Figure 4).⁴

Analysis of our own results with and without intraoperative aberrometry showed a statistically significant difference in cylinder reduction (75% vs 57%) when ORA was used compared with eyes in which it was not.⁵ Ultimately, we were 2.5 times more likely to reduce refractive cylinder to no more than 0.50 D if ORA was used.

I have also been impressed by the results of intraoperative aberrometry in eyes after refractive surgery (eg, PRK and LASIK). Standard IOL power calculation methods in these eyes are inadequate and do not provide patients with the good UCVA to which they have become accustomed. In a recently reported series of 248 postrefractive surgery eyes, the mean absolute PE with ORA was 0.47 D, compared with 0.71 D when the surgeon’s best choice of preoperative biometry methods was used. With ORA, 67% were within ±0.50 D and 94% within ±1.00 D of the intended refractive outcome; with preoperative biometry, 46% and 76%, respectively, achieved the same outcomes.⁶ All differences were statistically significant.

CONCLUSION

So, does intraoperative aberrometry matter?

If you are satisfied with 60% of patients achieving a refractive result within ±0.50 D of intended correction, perhaps it does not. If you do not mind a relatively high enhancement rate in premium lens cases, maybe you do not need ORA. If your patients are content to wear glasses after surgery, then the answer is no, intraoperative aberrometry does not matter.

But for anyone who considers himself or herself a refractive cataract surgeon, the ability of intraoperative aberrometry to increase accuracy, improve outcomes, and grow a premium practice matters a great deal. With VerifEye, the ORA system can make good surgeons better.

Jonathan H. Talamo, MD, is Medical Director of Surgisite Boston and an Associate Clinical Professor of Ophthalmology at Harvard Medical School, Boston. Dr. Talamo states that he is a consultant to WaveTec Vision. He may be reached at tel: +1 781 890 1023; e-mail: jtalamo@lasikofboston.com.

1. Spectacle Network. 2014 Laser Cataract Surgery User Survey. Accessed August 8, 2014.
2. Gale RP, Saldana M, Johnston RL, et al. Benchmark standards for refractive outcomes after NHS cataract surgery. Eye. 2009;23:149-152.
3. Narvaez J MD, Zimmerman G, PhD, Stulting RD, et al. Accuracy of intraocular lens power prediction using the Hoffer- Q, Holladay 1, Holladay 2, and SRK-T formulas. J Cataract Refract Surg. 2006;32(12):2050-2053.
4. Data on file, WaveTec.
5. Hatch KM, Talamo JH. Toric IOL selection and positioning with and without intraoperative aberrometry. Paper presented at: the American Academy of Ophthalmology Annual Meeting; November 16-19, 2013; New Orleans, Louisiana.
6. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology. 2014;121:56-60.

Counterpoint: Intraoperative aberrometry is not yet the best answer to guide the surgical refractive plan in cataract surgery.

By Jan O. Hülle, BSc(Hons), MD; and Stephan J. Linke, MD

Modern microincision phacoemulsification techniques have increased the expectations of both patients and surgeons that accurate refractive outcomes can be achieved after cataract surgery. However, those expectations are not always met, especially in patients who have undergone previous refractive surgery.^1,2 Real-time biometry during cataract surgery could potentially address this shortcoming by informing, and thereby improving, the surgical outcome. Experiments have demonstrated that objective refraction methods based on wavefront aberration maps can accurately predict the outcome of subjective refraction and may be even more precise.³

Numerous studies demonstrate the feasibility of intraoperative wavefront aberrometry (IWA), and some surgeons argue that it can be used to guide the surgical refractive plan in cataract surgery.^4-6 However, to date, the quality and precision of IWA have not been assessed systematically. We recently explored these vital parameters and concluded that the time is not yet ripe for clinical application of IWA.⁷

QUALITY AND PRECISION OF IWA

At seven defined steps during routine cataract surgery in 74 eyes, we attempted aberrometry measurements of sphere, cylinder, and axis with a Hartmann-Shack device that was mounted to the surgical microscope. The mean age of patients was 69 years (standard deviation [SD], 11.3 years) and the mean baseline manifest refraction was 0.31 D of sphere (SD, 2.90 D) and -1.10 D of cylinder (SD, 1.05 D). To determine wavefront quality, we calculated the wavefront map’s percentage in a standardized automated procedure. Repeated threefold measurements were taken in aphakia and pseudophakia.

Quality. In our sample, IWA succeeded in only 56.8% of all measurement attempts during cataract surgery (462 readings out of 814 measurement attempts). In a lower-powered study, this ratio was as low as 25%.⁸ On its own, this statistic points to severe feasibility and quality issues with IWA. In our attempt to understand this trend, we examined the impact of certain variables on measurement failure by calculating the odds ratios from logistic regressions. Except for preoperative distance BCVA, no variable had a statistically significant impact on measurement success.

Also, the quality of the measurements showed considerable variation across the defined steps of the surgical procedure (Figure 1). The highest total number of successful readings (n=63) was achieved in aphakia with an ophthalmic viscosurgical device (OVD) in the anterior chamber. The highest (50.63%; SD, 20.23%) and lowest (29.19%; SD, 13.94%) qualities of wavefront maps were found, respectively, after the clear corneal incision and in pseudophakia with an OVD in the anterior chamber. With increasing wavefront quality, more precise measurements were achieved.

Precision. Reproducibility and repeatability are two sides of the same coin, and both are markers of precision. ⁹ Repeatability describes variability in repeated measurements under constant conditions; for example, in our study, the variability seen in the IWA recordings in aphakia. Reproducibility is used when conditions are not constant—when there is a change from one measured point to another; for example, in our study, comparing the IWA scores before and after IOL implantation determined reproducibility.

In terms of reproducibility, our data showed high accuracy across most intraoperative measurement points. Interestingly, IWA quality scores were slightly higher when the anterior chamber was filled with an OVD (as compared with balanced saline solution) in aphakia and pseudophakia. It may be possible that an OVD enables a more homogeneous filling of the anterior chamber than balanced saline, resulting in more stable measurement conditions. In our view, stable anterior chamber conditions are key for successful IWA measurements.

In terms of repeatability, our study showed that repeated IWA measurements in aphakia were highly reliable (Figure 2). However, the clinical interpretation of the agreement range, which is vital to the limits-of-agreement approach,9 showed that spherical equivalent (SE) in aphakia varied from 0.69 to -0.72 D, a range that seems too large to use as a basis for intraoperative IOL calculation. The large range of this example is derived from a small sample in which all measurements succeeded (n=27); a bigger sample size should provide a more accurate assessment of those limits of agreement.⁹

SIX FACTORS

We identified six factors that may impair the precision and quality of the vulnerable IWA measurements and, thus, for the time being, we advocate against using this modality to guide the surgical refractive plan in cataract surgery.

Factor No. 1: The supine position of the patient on the table. We noticed a shift in SE of -0.37 D and significant cyclotorsion between the preoperative IWA assessment on a seated patient versus the first measurement on the same patient supine in the operating room. We recommend, therefore, that IWA not be the sole source for surgical decisions on astigmatic corrections but rather should always be supplemented by conventional marking methods.¹⁰

Factor No. 2: The lid speculum. The lid speculum can be responsible for significant changes in cylinder power and axis depending on how much the patient squeezes.⁸

Factor No. 3: Topical anesthesia and corneal and vitreous wound hydration. These factors may alter corneal curvature and refractive indices, resulting in significant changes of refraction.

Factor No. 4: Capsulorrhexis size. A varying effective IOL position, for instance in a slightly more anterior position in an eye with a large capsulorrhexis, may influence IWA measurements.

Factor No. 5: Eye movements. As surgery must be performed under topical anesthesia to enable fixation for IWA measurements, patients’ eye movements are a potential source of error.

Factor No. 6: The intraoperative state is not physiologic. Hence, anterior chamber depth (ACD) may vary greatly during surgery. For instance, an increase in ACD during aphakia can lead to significant alterations of the refractive state of the eye.

This last factor is the most important argument against using IWA to guide the surgical plan. It should be mentioned, however, that some of the variables listed above can be controlled through methods such as intraoperative OCT measurements of ACD and real-time monitoring of intraocular pressure. Further, an automated eye-tracking function in IWA would be highly desirable in order to overcome fixation problems, and a combination of IWA with a laser-assisted phacoemulsification technique seems to hold promise in the advancement of standardized surgical techniques.

CONCLUSION

Before IWA can be used to guide the surgical plan (eg, for astigmatism correction during cataract surgery, as described with Talbot-Moiré interferometry⁶) or to generate constant dynamic data for intraoperative biometry,¹¹ further efforts are needed to enhance the measurement precision and quality of IWA. While waiting for more reliable devices, we should not neglect available conventional options to optimize biometry, such as second-eye refinement.¹²

To judge the success of an objective method of refraction, a gold standard for comparison is required;¹³ to date, however, none exists for intraoperative refraction. Some authors have used intraoperative autorefractive retinoscopy for IOL power estimation,^14-16 but difficulties arise when comparing manifest refraction, autorefraction, and aberrometry-based refraction with one another, such as different reference plane distances of refraction and different wavelengths of the light source.¹⁷ In the quest for a gold standard in intraoperative refraction, future studies should seek to establish benchmarks by comparing different methods of intraoperative autorefraction in randomized, controlled trials.

Our latest study has shown that more efforts are required to improve the precision and quality of IWA before it can guide the surgical refractive plan during cataract surgery.

Jan O. Hülle, BSc(Hons), MD, is an ophthalmologist at the South West Peninsula Deanery, United Kingdom. Dr. Hülle states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: jan.huelle@doctors.org.uk.

Stephan J. Linke, MD, is an Associate Professor and Lead Consultant at University Medical Center Hamburg-Eppendorf, Germany. Dr. Linke states that he has no financial interest in the products or companies mentioned. He may be reached at e-mail: slinke@uke.de.

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2. Ianchulev T, Hoffer KJ, Yoo SH, et al. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology. 2014;121(1):56-60.
3. Thibos LN, Hong X, Bradley A, et al. Accuracy and precision of objective refraction from wavefront aberrations. J Vis. 2004;4(4):329-351.
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5. Cervino A, Hosking SL, Montes-Mico R, et al. Clinical ocular wavefront analyzers. J Refract Surg. 2007;23(6):603-616.
6. Packer M. Effect of intraoperative aberrometry on the rate of postoperative enhancement: retrospective study. J Cataract Refract Surg. 2010;36(5):747-755.
7. Huelle JO, Katz T, Druchkiv V, et al. First clinicial results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol. 2014. doi:10.1136/bjophthalmol- 2013-304786.
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10. Popp N, Hirnschall N, Maedel S, et al. Evaluation of 4 corneal astigmatic marking methods. J Cataract Refract Surg. 2012;38(12):2094-2099.
11. Krueger RR, Shea W, Zhou Y, et al. Intraoperative, real-time aberrometry during refractive cataract surgery with a sequentially shifting wavefront device. J Refract Surg. 2013;29(9):630-635.
12. Sheard R. Optimising biometry for best outcomes in cataract surgery. Eye (Lond). 2014;28(2):118-125.
13. Thibos LN. Unresolved issues in the prediction of subjective refraction from wavefront aberration maps. J Refract Surg. 2004;20(5):S533-S536.
14. Ianchulev T, Salz J, Hoffer K, et al. Intraoperative optical refractive biometry for intraocular lens power estimation without axial length and keratometry measurements. J Cataract Refract Surg. 2005;31(8):1530-1536.
15. Wong AC, Mak ST, Tse RK. Clinical evaluation of the intraoperative refraction technique for intraocular lens power calculation. Ophthalmology. 2010;117(4):711-716.
16. Leccisotti A. Intraocular lens calculation by intraoperative autorefraction in myopic eyes. Graefes Arch Clin Exp Ophthalmol. 2008;246(5):729-733.
17. Martin J, Vasudevan B, Himebaugh N, et al. Unbiased estimation of refractive state of aberrated eyes. Vision Res. 2011;51(17):1932-1940.