21 Intraoperative Aberrometry Abstract Intraoperative aberrometry (IA) is a proven technology to optimize refractive outcomes in cataract surgery. Given the increasing patient expectation for optimal refractive outcomes after cataract surgery, IA may provide significant value for a variety of clinical scenarios. It is used for spherical intraocular lens (IOL) power calculation for normal eyes and may have a unique role for extreme axial lengths (< 22.5 and > 26.5 mm). Additionally, it has been shown to assist in maximizing outcomes with astigmatism management including toric IOLs and limbal relaxing incisions (LRIs). During toric IOL surgery, both the spherical and toric powers are selected in the aphakic state, followed by axis alignment optimization in the pseudophakic state. Both the anterior and posterior contribution to the eye’s cylinder is accounted for as light is projected onto the retina, and the reflected images pass through the optical system of the eye. Femtosecond laser-assisted arcuate incisions as well as manual LRIs can also be optimized with IA. Additionally, IA may play a crucial role in the postrefractive eye in optimizing residual refractive errors. This could ultimately lead to less postoperative excimer enhancements or the need for IOL exchange or piggyback IOLs. The technology does have potential limitations including cost and additional operating room time. Additionally, the readings are sensitive to intracameral bubbles, intraocular pressure, or pressure from the lid speculum, so there is a user learning curve to the device. Keywords: intraoperative aberrometry, refractive cataract surgery, optimization cataract surgery, residual refractive error Intraoperative aberrometry (IA) is a promising technology that aids in optimizing refractive outcomes for cataract surgery. In the era of increasing patient demands for spectacle independence, achieving targeted refractive outcomes is essential to patient satisfaction. Efforts to improve intraocular lens (IOL) outcomes have traditionally focused on optimizing preoperative biometry measurements and IOL power prediction formulas. But even with the most advanced preoperative calculations including noncontact biometry, averages of multiple corneal power measurements, and optimization of a surgeon-specific A-constant for each IOL, it is still not uncommon to have suboptimal refractive results. Even among the most experienced surgeons, only 80% of eyes are within of ±0.50 diopters of intended spherical target.1 Larger deviations from intended target are routinely seen in high myopes,2 high hyperopes, eyes that have undergone prior corneal refractive surgery,3,4 and eyes in which it is impossible to obtain biometry, such as a white or dense posterior subcapsular cataract. IA takes real-time phakic, aphakic, and pseudophakic refractions during cataract surgery. The aphakic refraction provides both a spherical and toric power calculation for optimal IOL power selection. In cases of toric IOL implantation, in additional to the IOL power selection, the optimal axis alignment can be obtained in the pseudophakic state with real-time feedback from the aberrometer to guide fine-tune axis alignment. It can also be used to titrate limbal relaxing incision (LRI) and may have a key role in IOL selection in the postrefractive patient. The first commercially available intraoperative wavefront aberrometer was the ORange (WaveTec Vision), which was later updated to the Optiwave Refractive Analysis (ORA) system (Alcon) in July 2013. Light is projected 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 uses a super luminescent light-emitting diode and Talbot–Moiré interferometer, where the wavefront passes through gratings set at specific distances producing a specific fringe pattern, taking 40 measurements within seconds, while combining data obtained from the central 4-mm optical zone. Aberrations in the wavefront cause distortions in the fringe pattern, which translates to a refractive value using proprietary algorithms, and ultimately determines spherical, cylindrical, and axis components of the refractive error.5,6,7 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 traditional preoperative biometry or with online calculators for toric IOLs.5,6 The advantages of this system are that it is compact and lightweight (allowing easy attachment to the microscope) and can be configured to have a dynamic range of −5.0 to + 20 diopters without degradation of the fringe pattern. Each IOL model goes through a lens optimization process with ORA. Initially, a global set of regression coefficients and manufacturer lens constant is assigned after the following parameters: • ≥ 100 surgeries with at least 10 days of postoperative data. • ≥ 3 surgeons with ≥ 15 surgeries. • No surgeon with greater than 50% of surgeries performed. Once a surgeon has greater than 25 cases with good data, the surgeon-specific optimization can be done and the surgeon-specific IOL constant can be applied. The gold and platinum bars seen on the IOL screen page designate if the IOL has global or surgeon-specific lens optimization ( The use of IA in routine cataract surgery is not well defined. Given that there are variables that can affect the reading including pressure from the eyelid speculum, patient fixation, as well as the intraocular pressure (IOP) or intracameral bubbles, a surgeon learning curve or intra-user error can affect readings. A study by Davison et al showed that IA in eyes with no prior eye surgery did not improve overall clinical outcomes, but it may be helpful when there is a significant difference between IA and preoperative calculations.8 IA for axial myopia and short eyes may also have a role. For axial myopes, defined at axial length greater than 25 mm, when compared to preoperative biometry using Sanders–Retzlaff–Kraff (SRK)/T, Holladay 1 and 2, Barrett Universal II, and Hill-RBF, IA was shown to be better than all formulas and was as effective as the axial length–optimized Holladay 1 formula in predicting residual refractive error and reducing hyperopic outcomes.9 Extreme axial lengths, including short eyes less than 22.5 mm and long eyes greater than 26.5 mm, are also good candidates for maximizing refractive outcomes with aberrometry. Prediction errors have been reduced by software updates that optimize lens coefficients by axial length group. As astigmatism correction with toric IOLs and LRIs at the time of cataract surgery has become more mainstream, and as patient expectations for uncorrected visual acuity after surgery have risen, increased accuracy is also expected. IA assists not only with spherical and toric IOL power in the aphakic state, but also with IOL rotation and ideal axis determination in the pseudophakic state. At the time of surgery, generally patients are marked preoperatively by the surgeon while seated in an upright position using a three-pronged marker to reference axis marks at the corneal limbus. The steep axis can be marked with small femtosecond laser-assisted arcuate incisions (FSAIs) or manually under the operating microscope. During surgery, IA is used initially to obtain an aphakic reading to determine spherical and toric power selection. After the power is chosen and IOL implanted, the reticule function can be turned on to guide initial gross alignment and then subsequent fine-tuning of axis placement. Once the IOL is grossly aligned, pseudophakic refraction is performed while the patient is fixated on a target light to assist with final axis alignment. Prior to this reading, viscoelastic material is removed, the eye is pressurized and a reading is taken, and one of the following recommendations is provided: clockwise, counterclockwise, or NRR (no rotation required). If clockwise or counterclockwise is encountered, the surgeon can opt to reposition the IOL. Pseudophakic rotations, if required, can be repeated with IA measurements until it was decided that astigmatism had been optimally minimized in the surgeon’s judgment. In a small series in a private practice setting, it was found that with the use of IA, postoperative residual refractive astigmatism of ≤ 0.50 diopters was 2.5 times more likely with the use of the ORA compared with standard techniques.10
21.1 Introduction
21.2 IOL Optimization and Normal and Extreme Axial Lengths
Fig. 21.1).
21.3 Astigmatism Management
21.3.1 Toric Intraocular Lens
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