Presbyopia / SPO - 3.2.3.6. Intraoperative aberrometry

3.2.3.6. Intraoperative aberrometry

Joaquim Murta 1,2,3, Miguel Raimundo 1,2, Andreia Rosa 1,2,3 e Maria João Quadrado 1,2,3

1 - Integrado Centro de responsabilidad en Oftalmología (CRIO), el Hospital y la Universidad Coimbra (Chuc), Portugal.

2 - Facultad de Medicina de la Universidad de Coimbra (FMUC), Portugal

3 - Unidad de Oftalmología de Coimbra (UOC) - IdealMed, Portugal.

INTRODUCTION

Parallel to the remarkable developments that continue to occur in the field of preoperative biometrics, with new measuring devices and formulas for calculating spherical and cylindrical intraocular lens (IOL) power, intraoperative aberrometry emerges as a new tool with the enormous potential to increase the accuracy and predictability of the refractive component of cataract surgery.

FUNDAMENTALS AND FUNCTIONING

Wavefront analysis consists of studying the distortion of light through an optical system. The difference between the theoretical wavefront in an aberration-free system and the actual wavefront, observed in an optical system such as the human eye, defines the aberrated wavefront, a surface that can be mathematically characterized with the definition of low- (such as myopia, hyperopia and regular astigmatism) and high order aberrations.

Wavefront analysis devices are already integrated into regular clinical practice within the framework of laser corneal refractive surgery. These devices apply wavefront analysis based on Hartmann-Shack interferometry. Although very accurate, this technology is difficult to miniaturize so its incorporation into an operative microscope is difficult1 and no commercially available intraoperative aberrometer utilizes this technology.

In parallel, the first commercially available intraoperative aberrometry system (ORA™, Alcon) (Figures 1 and 2) uses Talbot-Moiré interferometry that simply processes the wavefront reflected by the dispersion analysis (fringe pattern) of the reflected light as it passes through a pair of filters (gratings) of the device1,2.

This technology allows the creation of a small device capable of rapid measurements, to be incorporated in any operating microscope and allowing the evaluation of the vast majority of IOLs on the market.

Figure 1 - ORA™ (Alcon) mounted on an operating microscope and operating monitor with 3 visualization cameras.

Figure 2 - Visualization cameras during an exam (wide field, refraction and focus).

The second commercially available device for performing intraoperative aberrometry (HOLOS IntraOp, Clarity) (Figures 3) uses wavefront sequential analysis technology through the interaction between the reflected wavefront, a rotating mirror (MEMS, microelectro-mechanical mirror system) and a photovoltaic detector with high spatial resolution3,4.

As opposed to Hartmann-Shack’s and Talbot-Moiré’s interferometry, this technology does not require the use of a photographic sensor, so measurement is faster and can be done continuously during surgery.

With both these devices it is possible to perform aberrometry (and consequently refraction) during surgery, both in aphakia and pseudophakia, information that is incorporated for the choice and confirmation of the spherical and cylindrical power of the IOL, as well as its orientation in the case of toric IOLs.

The first commercially available device (ORA™, example of use in Figures 4-8) allows, according to the information provided by the manufacturer, measurements between -5.0 D and +20.0 D, with a spherical and cylindrical error margin of less than 0.25 D and 0.2 D, respectively, an axis accuracy of approximately 4° and a measurement time of less than 2 seconds.

Obtaining a reliable and reproducible measurement depends on several factors, both technical and clinical. The anterior chamber and the capsule should be completely clean and free of cortical debris, the anterior segment fully filled by the same substance (to obtain a homogeneous refractive medium, BSS or cohesive viscoelastic), the incisions watertight but not excessively hydrated, the lacrimal film replenished, the intraocular pressure, measured with Barraquer's tonometer at 21 mmHg, and there should be no traction by the blepharospasm or surgical field, in order not to influence the results.

The quality of the measurement also depends on clinical criteria, such as those related to stable fixation capacity during measurement and media transparency, and may also be used in patients subjected to peri- or retrobulbar blockade as well as anesthetic sedation.

Thus, by way of example, patients with progressive retinal pathology, decreased corneal transparency (e.g., advanced Fuchs’ dystrophy or others, large pterygium, scarring), severe dry eye, asteroid hyalosis, nystagmus, among others, are not good candidates for the use of intraoperative aberrometry.

Figure 3 - Holos IntraOp (Clarity) Aberrometer mounted on the operating microscope and Operating Monitor.

Figure 4 - Intraoperative aberrometry measurement capture using ORA™ (Alcon) with correct and centered focus of the 3 cameras.

Figure 5 - Incorrect capture of intraoperative aberrometry using the ORA™ (Alcon) (viscoelastic visible in the wide field and refractive cameras interferes with the measurement).

Figure 6 - Intraoperative aberrometry using ORA™ (Alcon) in the implantation of a multifocal toric lens. Confirmation of the spherical power of the IOL (measurement in aphakia).

Figure 7 - Selection of the cylindrical power of the IOL measured in aphakia.

Figure 8 - Final measurement with pseudophakic refraction, with residual astigmatism and spherical equivalent evaluation. In this case, the system confirmed the correct position of the implanted IOL axis that does not coincide, sometimes, with the axis evidenced in the Verion.

APPLICATIONS

From our experience and published evidence (described below), intraoperative aberrometry is a particularly important tool in premium cataract surgery (multifocal and/or toric IOLs) and in biometrically atypical or difficult eyes:

Decreased refractive "surprises", especially in eyes where current formulas tend to be less precise:
Eyes previously submitted to laser refractive surgery
Biometrical extreme eyes (high myopia or hyperopia)
Corneal ectasia (primary or after refractive surgery)
Confirmation and adjustment of IOL spherical power evaluated in the preoperative biometry, particularly useful in the case of multifocal IOLs where effective multifocality requires a low margin of error in the residual spherical equivalent
Confirmation and adjustment of the IOL cylindrical power evaluated in the preoperative biometry, as well as the real-time correction of its orientation

CLINICAL EVIDENCE

The pioneering studies with the first commercially available intraoperative aberrometer (ORA™, Alcon) suggest that there is a strong correlation between intraoperative pseudophakic refraction and manifest refraction obtained one month after surgery5 or refraction obtained by auto-refractometer one week after surgery6. Both of these studies were performed with the first generation of this device. Subsequent versions will, according to the manufacturer, have a higher level of accuracy, although there are no published studies with these data yet.

An analysis of the optical influence of the type of viscoelastic used during intraoperative aberrometry has recently been published7. Six different viscoelastic types were tested and compared as anterior segment filling with BSS (six patient groups, in each group a measurement with BSS and one type of viscoelastic was recorded).

The authors concluded that two types of viscoelastic (Amvisc Plus and Discovisc) were associated with a systematic measurement error of about 0.5 D (in the IOL plane), whereas the remaining four types (Provisc, Amvisc, Healon and Healon GV) did not change the measurements significantly. This study emphasizes the importance of choosing the viscoelastic in order to obtain a precise measurement by intraoperative aberrometry, as well as the influence that circumstantial factors to the measurement act may have on the refractive result.

Regarding the role of intraoperative aberrometry in the choice of toric power and IOL axis adjustment, a first study by Hatch et al in a non-randomized, retrospective design, showed that the group of patients in whom intraoperative aberrometry was used had a 2.4 times higher probability of presenting a residual astigmatism of less than 0.5 D8. Another prospective, randomized study compared refractive outcomes in patients undergoing bilateral cataract surgery with a toric lens implant9. Randomly, in one eye the choice of the lens and the surgery was done with the aid of intraoperative aberrometry, whereas in the fellow eye only conventional preoperative methods (online calculator) were used. The use of intraoperative aberrometry significantly increased the proportion of eyes with residual astigmatism less than 0.50 D (89.2% vs 76.6%, p = 0.006).

In none of these studies a toric calculator incorporating Barrett's algorithm, which makes a theoretical compensation for posterior astigmatism based on the standard anterior keratometry obtained from biometrics10,11, was used in the control arm8,9.

In this sense, a study was performed by our group that evaluated the predictive error in residual astigmatism using Barrett's toric calculator compared with intraoperative aberrometry. It was observed that in 26 of 52 eyes (50%) there was a mismatch in the toric power suggested by these two methods, and the predictive error was significantly lower using intraoperative aberrometry (absolute median error: intraoperative aberrometry 0.44 D, Barrett's toric calculator 0.73 D, p = 0.028)12,13.

Since the introduction of intraoperative aberrometry in clinical practice, its potential has become obvious in the case of eyes previously submitted to laser refractive surgery. In a large retrospective series, Ianchulev et al demonstrated that the predictive error in eyes previously submitted to PRK or myopic LASIK was significantly lower using intraoperative aberrometry compared to the Shammas method or the Haigis-L formula (absolute median error with intraoperative aberrometry 0.35 D, Haigis-L 0.53 D and Shammas 0.51 D, p <0.001), with 67% and 94% of eyes with a margin of error of less than 0.5 D and 1.0 D, respectively14.

A subsequent study by Fram confirmed the good results of intraoperative aberrometry (absolute median error of 0.29 D), although in this series there were no statistically significant differences compared to the Haigis-L formula, the Masket regression formula, and the formula derived from the OCT of Optovue RTVue (Optovue Inc)15.

With regard to other biometrically difficult eyes, a recent study evaluated the accuracy of intraoperative aberrometry compared to new formulas based on preoperative biometry in eyes with axial myopia (axial length >25 mm)16.

Intraoperative aberrometry was superior to all formulas included in the study (Hill-RBF, Barrett Universal II, SRK/T, Holladay 1, Holladay 1 optimized by axial length and Holladay 2), with significantly lower predictive errors, a higher proportion of eyes with predictive errors of less than 0.5 D and a lower proportion of hyperopic refractive results.

As a final note it is important to highlight that the total of the published evidence with intraoperative aberrometry is still relatively scarce and, in some particular clinical situations (for example in keratoconus or high hyperopia), it is absent. In addition, all evidence published in the literature concerns a single device (ORATM, Alcon), and no published study yet exists on the other commercially available intraoperative aberrometer (HOLOS IntraOp, Clarity)

CONCLUSION

The last two decades were marked by remarkable advances in cataract surgery that today allow, in addition to the correction of opacity of media, a complete refractive solution through the correction of myopia, hyperopia, astigmatism and presbyopia. Thus, the requirement placed on the cataract surgeon was never greater. In the opinion of the authors, intraoperative aberrometry decreases the uncertainty associated with the refractive component of cataract surgery, either in premium surgery, where the margin of error is very low, or in biometrically atypical or difficult eyes, where traditional methods of calculation still present shortcomings (namely after laser refractive surgery). Being a relatively recent technology, more studies are still needed to fully understand all its capabilities and limitations.

REFERENCES

Hemmati HD, Gologorsky D, Pineda R. 2nd. Intraoperative wavefront aberrometry in cataract surgery. Semin Ophthalmol 2012; 27(5-6): 100–6.
Sarver EJ, Van Heugten TY, Padrick TD, Hall MT. Astigmatic refraction using peaks of the interferogram Fourier transform for a Talbot Moiré interferometer. J Refract Surg 2007; 23(9): 972–7.
Su W, Zhou Y. Adaptive sequential wavefront sensor and its applications US Patent. 7815310, 2010 [cited 2017 Nov 4]. Available from: https://www.google.com/patents/US7815310.
Krueger RR, Shea W, Zhou Y, Osher R, Slade SG, Chang DF. Intraoperative, real-time aberrometry during refractive cataract surgery with a sequentially shifting wavefront device. J Refract Surg 2013; 29(9): 630–5.
Donnenfeld ED. Intraoperative wavefront aberrometry during cataract surgery as a predictor of postoperative refractive results (abstract 415280). 2008 ASCRS ASOA Symposium & Congress; 2008.
Chen M. Correlation between ORange (Gen 1, pseudophakic) intraoperative refraction and 1-week postcataract surgery autorefraction. Clin Ophthalmol 2011; 5: 197–9.
Masket S, Fram NR, Holladay JT. Influence of ophthalmic viscosurgical devices on intraoperative aberrometry. J Cataract Refract Surg 2016; 42(7): 990–4.
Hatch KM, Woodcock EC, Talamo JH. Intraocular lens power selection and positioning with and without intraoperative aberrometry. J Refract Surg 2015; 31(4): 237–42.
Woodcock MG, Lehmann R, Cionni RJ, Breen M, Scott MC. Intraoperative aberrometry versus standard preoperative biometry and a toric IOL calculator for bilateral toric IOL implantation with a femtosecond laser: One-month results. J Cataract Refract Surg 2016; 42(6): 817–25.
Abulafia A, Barrett GD, Kleinmann G, Ofir S, Levy A, Marcovich AL, Michaeli A, Koch DD, Wang L, Assia EI. Prediction of refractive outcomes with toric intraocular lens implantation. J Cataract Refract Surg. 2015; 41(5): 936–44.
Abulafia A, Hill WE, Franchina M, Barrett GD. Comparison of Methods to Predict Residual Astigmatism After Intraocular Lens Implantation. J Refract Surg 2015; 31(10): 699–707.
Raimundo M, Rosa A, Quadrado MJ, Murta J. Prediction of residual astigmatism using intraoperative wavefront aberrometry vs a toric IOL calculator (Free Paper Session 89). AAO 2018; 2018; New Orleans.
Raimundo M, Azenha C, Martins A, Rosa A, Quadrado MJ, Murta J. Intraoperative Wavefront Aberrometry – A Comparison of Intraocular Lens Power Calculation Methods. J Refract Surg 2018 (submitted for publication).
Ianchulev T, Hoffer KJ, Yoo SH, Chang DF, Breen M, Padrick T, Tran DB. Intraoperative refractive biometry for predicting intraocular lens power calculation after prior myopic refractive surgery. Ophthalmology 2014; 121(1): 56–60.
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 Corretion. Ophthalmology 2015; 122(6): 1096–101.
Hill DC, Sudhakar S, Hill CS, King TS, Scott IU, Ernst BB, Pantanelli SM. Intraoperative aberrometry versus preoperative biometry for intraocular lens power selection in axial myopia. J Cataract Refract Surg 2017; 43(4): 505–10.

Report abuse