Toric intraocular lenses (IOLs) have revolutionized the management of corneal astigmatism during cataract surgery, offering patients improved uncorrected visual acuity and reduced dependence on spectacles.1
However, the success of toric IOL implantation depends on meticulous attention to detail at every step of the surgical process, from pre-operative planning to post-operative follow-up.
This article highlights five practical pearls for optimizing outcomes with toric IOLs.
Top 5 pearls for toric IOL placement
1. Prioritize patient selection and counseling.
The best surgical technique cannot compensate for poor patient selection or unrealistic expectations.
Toric IOLs are most effective in eyes with regular corneal astigmatism. With few exceptions—where implantation may reduce or “debulk” higher levels of astigmatism—this technology is generally not appropriate in cases of irregular astigmatism, such as that associated with Salzmann nodular degeneration, corneal scarring, or ectatic disorders.
Corneal topography and careful slit lamp examination should be incorporated early in the evaluation process to assess the pattern of corneal astigmatism (regular vs. irregular). Topography also provides valuable information about the status of the ocular surface, helping to identify conditions such as ocular surface disease (OSD) or epithelial basement membrane dystrophy that can distort measurements and compromise visual quality.
These conditions should be diagnosed and treated prior to proceeding, and in some cases may influence whether a toric IOL is the optimal choice.
Patient communication on toric IOLs
Clear pre-operative counseling is critical when discussing toric IOLs. Patients should be informed that, despite meticulous planning and surgical execution, some residual astigmatism may persist. In certain cases, secondary procedures may be required to optimize refractive outcomes.
This is why I emphasize the concept of astigmatism “management” rather than definitive “treatment.” Patients consistently value transparency, and satisfaction is highest when surgical results align with the expectations established during the pre-operative counseling.
2. Attain accurate pre-operative measurements.
The foundation of successful toric IOL implantation is precise measurement of both the magnitude and axis of corneal astigmatism. I incorporate multiple diagnostic modalities to confirm consistency and reproducibility across measurements.
Best practice includes using a combination of:
- Topography
- Topography/tomography
- Optical biometry
- Automated keratometry
I use Scheimpflug imaging (e.g., OCULUS Pentacam) and swept-source optical coherence tomography (e.g., IOLMaster 700) in my practice, and recommend cross-verifying keratometric values between different devices. Outliers or discrepancies should prompt reevaluation before finalizing the IOL power calculation.
Consider posterior corneal astigmatism
Consider the effect of posterior corneal astigmatism (PCA) in determining true total corneal astigmatism (TCA). Most eyes have ~0.3D of against-the-rule (ATR) PCA, though it can range wider in individual cases.2 This tends to reduce the TCA if the anterior corneal astigmatism is with-the-rule (WTR), and increase it if the anterior corneal astigmatism is ATR.
Tomographic devices such as the OCULUS Pentacam, as well as modern optical biometry platforms, are capable of directly measuring posterior corneal curvature and providing total keratometry values. Alternatively, modern toric IOL formulas, such as the Barret Toric Calculator, take PCA into account by estimating its predicted value derived from anterior corneal astigmatism.
OSD algorithm
As discussed in the previous section, ensure the ocular surface is optimized prior to final measurements. I use a combination of ocular lubricants, LACRIFILL canalicular gel, topical steroids, and cryopreserved amniotic membranes, such as Prokera or CAM360 by BioTissue, in cases where ocular surface optimization is needed.
Another good resource is the Pre-Operative OSD Algorithm provided by the American Society of Cataract and Refractive Surgeons.
3. Fully prepare with pre-surgical planning.
Even with accurate measurements, lens selection requires the right computational tools.
Manufacturer-provided calculators have evolved, integrating posterior corneal astigmatism data into their algorithms. I like to use the Barrett Toric Calculator since it accounts for PCA, and I can also customize my incision location and surgically-induced astigmatism (SIA) into its calculation.
SIA is surgeon-specific, and it depends on incision location, length, and surgeon technique. In my planning, I typically assume an SIA of 0.12D, which reflects my own surgical pattern.
Toric IOL power and step size
When selecting toric IOL power, my goal is to achieve the lowest possible residual astigmatism. Since most available toric IOLs in the US come in ~0.75D steps at the IOL plane, it's not always possible to land exactly on zero astigmatism.
So in cases where I need to choose between slightly under- or over-correcting, I prefer to under-correct WTR astigmatism and over-correct ATR astigmatism. This small intentional bias provides better long-term outcomes, as it compensates for the natural age-related shift towards ATR astigmatism.
4. Ensure the axis is precisely marked and aligned.
Accurate toric axis marking is critical for achieving optical outcomes. Even small degrees of misalignment can significantly reduce cylindrical correction of toric IOLs. For instance, a 3° misalignment can result in a 10% loss of the intended correction, while a 10° misalignment can cause a 33% loss.3
Types of axis marking
Manual marking
Traditional manual marking, such as limbal reference marking with a slit lamp or intra-operative ink marks, is relatively simple and widely available. However, they are limited by factors such as patient cooperation, ink smudging, and surgeon-dependent variability.
Despite these shortcomings, they remain an important skill in settings where digital systems fail, and they serve as a reliable backup method that every surgeon should be familiar with.
Digital image-guided marking
Digital systems provide greater precision and consistency by eliminating many of the variables associated with manual marking. Platforms such as the ZEISS Callisto or VERION system allow pre-operative imaging to be superimposed intra-operatively, guiding exact toric alignment.
Femtosecond laser-assisted marking
This is my personal favorite method, and it involves marking directly on the anterior capsule using femtosecond laser platforms such as LENSAR. This approach also integrates iris registration, which automatically compensates for cyclotorsion between upright pre-operative measurements and supine intra-operative positioning.
5. Optimize intra-operative lens stability.
Even if the toric IOL is perfectly aligned at the end of surgery, post-operative rotation can compromise outcomes.
I use the following steps to ensure IOL stability:
- A well-centered, round capsulorhexis with a 360° overlap of the anterior capsule edge to the optic is essential.
- Complete removal of the viscoelastic, particularly from behind the IOL optic, as retained viscoelastic can predispose the lens to rotation in the early post-operative period.
- I remove the viscoelastic with a coaxial irrigation/aspiration (IA) probe through the main corneal incision. In order to minimize the chance of chamber collapse and instability after IA probe removal, I pre-hydrate the main incision before viscoelastic removal.
- When initially positioning the IOL within the capsular bag, I place the lens slightly counterclockwise (undercorrect) relative to the final intended axis. Following viscoelastic removal, the IOL can then be gently rotated clockwise with a Sinskey hook into its exact target alignment. This approach avoids excessive clockwise manipulation.
Conclusion
Toric IOL implantation is among the most rewarding aspects of modern cataract surgery, transforming patients’ visual function and quality of life. Success, however, hinges on meticulous execution across multiple domains.
By focusing on these pearls, surgeons can maximize refractive precision and patient satisfaction in their toric IOL practice.
