Intraoperative aberrometry (IWA) is a technique that measures wavefront aberrations during cataract surgery to confirm and optimize intraocular lens (IOL) power and align toric IOLs. It serves as an additional tool that allows real-time assessment of the refractive status of the aphakic and pseudophakic eye in the operating room, complementing preoperative measurements and formula-based IOL power calculations.
IOL power can be confirmed and adjusted using intraoperative aberrometry in both aphakic and pseudophakic states. It is also considered useful for aligning toric IOLs 1). However, whether intraoperative aberrometry consistently improves postoperative outcomes is not clear 1).
It is not essential for routine uncomplicated cataract surgery. It is particularly useful in eyes with prior refractive surgery or those requiring astigmatism correction. Combined use with preoperative measurements is recommended.
A wavefront refers to the surface of propagation of light rays. In an ideal eye, the wavefront converges precisely on the retina, but in actual eyes, optical irregularities cause distortion. This distortion is called aberration.
Aberrations are classified into the following two types.
To evaluate high-order aberrations, the pupil diameter must be specified. A 4 mm diameter reflects photopic visual function, while 6 mm reflects scotopic visual function. Typically, when the pupil diameter is increased from 4 mm to 6 mm, high-order aberrations increase by about twofold. Spherical aberration is often associated with halo phenomena, and coma aberration with glare and starburst phenomena.
Wavefront aberration is mathematically described by Zernike polynomials. In a pyramid-like arrangement, important low-order aberrations are placed at the bottom and high-order aberrations at the top. The result is reported as the root mean square (RMS), which represents the average difference between the actual wavefront and the theoretical planar wavefront as a single numerical value.
The main intraoperative aberrometry devices currently used in clinical practice are shown below.
ORA System
Manufacturer: Alcon (formerly WaveTec)
Measurement principle: Talbot-Moiré interferometry. Analyzes spherical power, cylindrical power, and cylinder axis from fringe patterns generated by two gratings.
Features: Uses a superluminescent diode light source. Integration with AnalyzOR enables comparison of preoperative, intraoperative, and postoperative data.
Measurement range: -5 to +20 D
HOLOS IntraOp
Manufacturer: Clarity
Measurement principle: High-speed rotating MEMS mirror and quad detector. Directly measures the magnitude of wavefront displacement.
Features: Capable of high-speed measurement up to 90 times per second.
Measurement range: -5 to +16 D
The ORA System was introduced in 2012 as the successor to ORange, with improvements to the optical system, interface, and algorithms. In 2014, Alcon acquired WaveTec.
There are multiple types of wavefront sensors that serve as the foundation for intraoperative devices.
Early studies using ORange showed good postoperative spherical error of 0.36±0.30 D. However, in eyes without complications, research results are not conclusive whether intraoperative aberrometry is superior to conventional formulas. There is no consensus on the usefulness of intraoperative aberrometry in routine cataract surgery.
Eyes with a history of refractive surgery such as LASIK or PRK present unique challenges in determining intraocular lens power.
Intraoperative aberrometry is considered useful in eyes with a history of refractive surgery (PRK or LASIK), but its utility is low in eyes after radial keratotomy1).
In eyes that underwent LASIK after cataract surgery, less than 55% achieved within ±0.5 D of emmetropia, which is inferior to the 70% in eyes without prior refractive surgery. Recent studies using ORA have reported improvements, with a median absolute error of 0.35 D, 67% within ±0.5 D, and 94% within ±1.0 D.
| Calculation method | Median absolute error |
|---|---|
| ORA | 0.35 D |
| Surgeon choice | 0.6 D |
| Haigis-L | 0.53 D |
| Shammas | 0.51 D |
Toric intraocular lenses require high precision in alignment, as each 10-degree misalignment reduces the astigmatism correction effect by one-third.
Intraoperative aberrometry provides accurate axis measurement in the aphakic state and allows confirmation of alignment in the pseudophakic state. It has been reported that toric intraocular lens placement guided by intraoperative aberrometry increases the likelihood of postoperative residual refractive astigmatism less than 0.5 D by 2.4 times.
In a study of intraoperative aberrometry-guided toric intraocular lens placement in eyes with prior refractive surgery, the mean prediction error of ORA was 0.43, outperforming IOLMaster (0.77) and ASCRS calculator (0.61). It was estimated that 80% of eyes were within ±0.75 D of spherical equivalent when using ORA, compared to only 53% with preoperative measurements alone.
In a guide for corneal limbal relaxing incision (LRI) using ORange, the mean residual refractive astigmatism after surgery was reported to decrease by 5.7 times. However, this trend was not statistically significant.
Approximately one-third of the astigmatism correction effect is lost for every 10 degrees of axis misalignment. Since accurate axis alignment directly affects postoperative visual function, real-time confirmation using intraoperative aberrometry is useful.
Multiple factors affect intraoperative aberrometry measurements. To maximize accuracy, these factors need to be controlled.
There is a significant difference in astigmatism values immediately after surgery and at one week postoperatively. This is due to changes in the incision, corneal stromal hydration, and intraocular pressure fluctuations. Intraoperative measurements are only reference values and may deviate slightly from the final refractive outcome.
Corneal aberrometry is useful for intraocular lens selection and may help determine the suitability of advanced lenses such as multifocal intraocular lenses 1).
With aging, the spherical aberration of the crystalline lens shifts in a positive direction, adding to the positive spherical aberration of the cornea and reducing contrast sensitivity. Aspheric intraocular lenses correct this spherical aberration and improve contrast sensitivity and visual function under twilight and dark conditions 1).
Care is needed when evaluating wavefront aberrations in eyes with multifocal intraocular lenses. In refractive multifocal IOLs, the rapid change in refraction within the pupil results in large higher-order aberration values. In diffractive types, reduced diffraction efficiency for near-infrared light displays results only for the distance focus portion.
New-generation devices such as HOLOS IntraOp achieve high-speed measurements up to 90 times per second using MEMS mirror technology. Improved measurement speed is expected to contribute to more efficient intraoperative workflows.
The ORA system now integrates the AnalyzOR platform, enabling comprehensive comparison and analysis of preoperative, intraoperative, and postoperative data. Continuous refinement of algorithms based on accumulated data is expected to improve prediction accuracy.
The added value of intraoperative aberrometry in uncomplicated routine cataract surgery remains controversial. Large-scale prospective studies are needed to validate its utility.
It is already widely used in eyes with a history of refractive surgery or when using toric intraocular lenses. Its usefulness in routine cataract surgery has not yet been established, and further accumulation of evidence is needed.
