Peer Review | May/June '17

Intraoperative Wavefront Aberrometry

In the past 2 decades, there has been a substantial amount of research focused on increasing the precision and accuracy of IOL selection in cataract surgery.1 Accuracy of optical biometry is essential to successful refractive outcomes.

One of the latest developments in optical biometry is intraoperative wavefront aberrometry. This technology provides real-time intraoperative refractive information to increase the precision and accuracy of IOL selection under aphakic and pseudophakic conditions after removal of a cataractous lens in normal eyes, post–refractive surgery eyes, and post-radial keratotomy (RK) eyes. Intraoperative wavefront aberrometry can also aid surgeons in selecting the correct axis for toric IOLs as well as placement of limbal relaxing incisions (LRIs) for astigmatism correction.1

The first commercially available intraoperative wavefront aberrometer was the ORange (WaveTec Vision), which was later updated to the Optiwave Refractive Analysis (ORA) system (Alcon). This device projects light onto the retina, and the reflected images pass through the optical system of the eye, distorting its wavefront, which is subsequently analyzed according to optical and mathematical principles proprietary to the device. The ORA takes into account parameters such as posterior corneal astigmatism and higher-order aberrations, allowing the surgeon to confirm or revise the IOL power chosen according to preoperative biometry.1,2

The ORA uses a super luminescent light-emitting diode and Talbot-Moiré interferometer to take 40 measurements in less than 1 minute. The ORA analyzes and combines data from the central 4-mm optical zone and has a dynamic range of -5.00 D to +20.00 D. The Talbot-Moiré fringe patterns are produced by the reflected wavefront after it passes through two gratings placed at a specific distance and angle to each other. The resulting fringe patterns provide information about the spherical, cylindrical, and axis components of the refractive error.1-3

This article reviews the existing literature for use of the ORA system in normal eyes, in post–refractive surgery eyes, and for astigmatism correction.

NORMAL EYES

The role of intraoperative aberrometry is not well defined in routine cataract surgery for normal eyes. One study using ORA’s predecessor, ORange, in routine cataract surgery found a low postoperative spherical error of 0.36 ±0.30 D in 215 eyes, compared with 0.53 ±0.44 D for traditional formulas such as the Holladay 1, Hoffer Q, and SRK.1

However, other studies have questioned the superiority of intraoperative wavefront aberrometry over traditional formulas in uncomplicated eyes due to factors influencing the quality of aphakic readings, including appropriate intraocular pressure, corneal hydration, tightness of the lid speculum, and patient fixation.4 Stringham et al5 found a significant change in cylinder, greater than 0.50 D, induced by lid speculums, suggesting that refractive changes inherent to routine cataract surgery manipulation may affect measurements between respective steps. Although the evidence for ORA use in routine cataract surgery is encouraging, more studies are needed to establish standardized conditions to optimize measurements and improve precision.

POST–REFRACTIVE SURGERY EYES

Eyes that have previously undergone refractive surgery pose a challenge for accuracy of IOL power calculations. Using the measured average keratometry readings after myopic RK, PRK, or LASIK in traditional IOL formulas commonly results in undercorrection and a postoperative hyperopic surprise.6 The traditional formulas fail to accurately measure anterior corneal curvature and effective lens position.6 A variety of correction factors for formulas have been developed to reduce hyperopic errors in post–refractive surgery eyes. In a study of 173 eyes, McCarthy et al found that more than 45% of post–refractive surgery eyes fell outside ±0.50 D of the intended target refraction, despite these correction factors.7

Ianchulev et al8 evaluated the efficacy of ORA in calculating IOL power in 246 eyes that had previously undergone myopic LASIK or PRK and compared it with the Haigis L formula, Shammas formula, and a combination of all clinical data based on surgeon’s choice. ORA was found to have the greatest predictive accuracy (P < .0001), with a median absolute error of 0.35 D, compared with 0.60 D of surgeon’s choice, 0.53 D with Haigis L, and 0.51 D with Shammas.

Another study compared IOL power calculations in eyes with previous laser vision correction using the ORange to the power predicted by the SRK-T formula using keratometry and axial length measurements from the IOLMaster (Carl Zeiss Meditec), average central keratometry from corneal topography, and average IOL power predicted by the ASCRS website.9 The ORange outperformed the other methods, achieving ±0.50 D of emmetropia 37% of the time, compared with 30% with SRK-T and IOLMaster, 26% with keratometry, and 17% with ASCRS prediction.9

Despite evidence supporting the use of ORA in post–refractive surgery eyes, it is worth noting that one study with a small sample size (n = 39) comparing ORA with optical coherence tomography (Optovue), IOLMaster calculation with the Haigis-L formula, and IOLMaster calculation with Masket regression formulas found no statistically significant difference among methods.10

ASTIGMATISM CORRECTION

LRIs. The success of astigmatism correction using LRIs depends on the location, depth, and length of the incision. Traditionally, corneal topography has been used to aid in determining the location of the limbal incision. However, it is often imprecise and fails to take into account surgically induced astigmatism from the clear corneal incision.1

Packer compared the rate of excimer laser enhancement after astigmatism correction with LRIs in patients treated with intraoperative aberrometry versus conventional corneal topography (control group).2 The excimer laser enhancement rate was found to be 3.3% in the aberrometry group compared with 16.2% in the control group. The mean postoperative cylinder was 0.37 D for the aberrometry group versus 0.48 D for the control group.2 This difference, while not significant (P = .12), represents a 5.7-fold reduction in odds ratio of subsequent excimer laser enhancement in the aberrometry group when compared with the control group.2

Toric IOL Alignment. In patients requiring a toric IOL, the magnitude and orientation of astigmatism has been traditionally calculated using preoperative keratometry.11 Available methods include autorefraction, corneal topography, or optical biometry; however, there is poor correlation between keratometric and refractive astigmatism using these method.11 In addition, for every 10° of toric malrotation, approximately one-third of cylindrical correction is lost.

The ORA can be used for toric IOL placement in aphakic and pseudophakic conditions. Generally, the aphakic reading will provide the desired axis, while the pseudophakic reading confirms it. The ORA calculates the true refractive astigmatism of an eye, including posterior corneal astigmatism.

Wiley et al12 compared the magnitude of residual cylinder using intraoperative aberrometry to the traditional methods of toric IOL placement. The mean residual refractive cylinder was 0.16 ±0.22 D in the ORA group and 0.61 ±0.54 D in the control group (P = .0005). Approximately 96% of eyes in the intraoperative aberrometry group achieved a target refraction within 0.50 D, compared with 56% of eyes in the control group.

Similarly, Hatch found that toric IOL placement guided by automated keratometry, standard optical biometry, and an online calculator and refined by intraoperative wavefront aberrometry showed a 2.4x increase in likelihood that the postoperative residual astigmatism would be less than 0.50 D when compared to the same method with no corresponding intraoperative wavefront aberrometry refinement.13 Another study looking at the outcomes of implanting a Trulign toric IOL (Bausch + Lomb) in 40 eyes using ORA found that, at postoperative month 1, uncorrected distance and intermediate visual acuity was 20/25 or better in 95% of eyes.14

CONCLUSION

No consensus exists regarding the current role of intraoperative wavefront aberrometry during routine cataract surgery. Although early studies may be promising, standardized operative conditions should be sought to optimize precision and accuracy during calculation, and more data are needed using newer-generation intraoperative wavefront aberrometry technologies, including ORA.

The use of ORA in post–refractive surgery eyes, however, is supported by more robust evidence, suggesting a viable role for ORA in eyes with previous laser correction. ORA may also serve a purpose in the correction of astigmatism, with studies suggesting a role for ORA to guide toric IOL alignment and LRIs during cataract surgery.

1. Wiley WF, Bafna S. Intra-operative aberrometry guided cataract surgery. Int Ophthalmol Clin. 2011;51(2):119-129.

2. Packer M. Effect of intraoperative aberrometry on the rate of postoperative enhancement: Retrospective study. J Cataract Refract Surg. 2010;36(5):747-755.

3. Hemmati HD, Gologorsky D, Pineda R. Intraoperative wavefront aberrometry in cataract surgery. Semin Ophthalmol. 2012;27(5-6):100-106.

4. Huelle JO, Katz T, Druchkiv V, et al. First clinical results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol. 2014;98(11):1484-1491.

5. Stringham J, Pettey J, Olson RJ. Evaluation of variables affecting intraoperative aberrometry. J Cataract Refract Surg. 2012;38(3):470-474.

6. Seitz B, Langenbucher A. Intraocular lens power calculation in eyes after corneal refractive surgery. J Refract Surg. 2000; 16: 349-361.

7. McCarthy M, Gavanski GM, Paton KE, Holland SP. Intraocular lens power calculations after myopic laser refractive surgery: a comparison of methods in 173 eyes. Ophthalmology. 2011;118(5):940-944.

8. 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.

9. Canto AP, Chhadva P, Cabot F, et al. Comparison of IOL power calculation methods and intraoperative wavefront aberrometer in eyes after refractive surgery. J Refract Surg. 2013;29(7):484-489.

10. Fram NR, Masket S, Wang L. Comparison of intraoperative aberrometry, OCT-based IOL formula, Haigis-L, and Masket formulae for IOL power calculation after laser vision correction. Ophthalmology. 2015;122(6):1096-1101.

11. Holladay JT, Moran JR, Kezirian GM. Analysis of aggregate surgically induced refractive change, prediction error, and intraocular astigmatism. J Cataract Refract Surg. 2001;27(1):61-79.

12. Wiley WF. Use of real time refractive measurements to improve outcomes with toric IOL. Paper presented at: the American Society of Cataract and Refractive Surgery meeting. March 25-29, 2011; San Diego, CA.

13. Hatch KM, Woodcock EC, Talamo JH. Intraocular lens power selection and positioning with and without intraoperative aberrometry. J Refract Surg. 2015;31(4):237-242.

14. Epitropoulos AT. Visual and refractive outcomes of a toric presbyopia-correcting intraocular lens. J Ophthalmol. 2016;7458210. doi.org/10.1155/2016/7458210.

author
Isi Esquenazi, MD
  • Third-year resident, Baylor College of Medicine, Houston, Texas
  • esquenaz@bcm.edu
author
Andres Parra, BS
  • Third-year medical student, Baylor College of Medicine, Houston, Texas
  • asparra@bcm.edu
author
Zaina Al-Mohtaseb, MD | Section Editor
  • Assistant Professor of Ophthalmology and Associate Residency Program Director, Baylor College of Medicine, Houston, Texas
  • zaina@bcm.edu
  • Financial disclosure: Consultant (Alcon)

NEXT IN THIS ISSUE