Toric IOL misalignment: 5 causes and how to fix them

Ophthalmology

Toric intraocular lenses (IOLs) are widely used during cataract surgery to correct preexisting corneal astigmatism and improve uncorrected distance visual acuity (UDVA). Their effectiveness depends on accurate preoperative measurements, appropriate IOL selection, precise intraoperative alignment, and maintenance of the intended axis after surgery. Even small deviations from the planned orientation can leave residual astigmatism and compromise visual outcomes and patient satisfaction. Understanding the factors responsible for toric IOL misalignment is therefore essential for achieving predictable refractive results.[1][2][3]Five causes of toric IOL misalignment and strategies to address themInaccurate preoperative measurements: Errors in assessing corneal astigmatism can result in selection of an inappropriate toric IOL model or implantation axis. Both anterior and posterior corneal astigmatism should be considered during planning. Three-dimensional corneal topography and swept-source biometry can provide detailed corneal measurements and biometric parameters to support toric IOL selection and axis calculation[1] Incorrect IOL model or axis selection: Selecting an unsuitable toric power or orientation can prevent adequate correction of the preexisting astigmatism. Advanced calculation algorithms can help determine the appropriate toric model and intended axis using preoperative measurements. Accurate planning is particularly important because residual astigmatism can affect visual acuity and patient satisfaction, even when the remaining error is relatively small[1][3]Errors during manual axis marking: Manual marking is commonly used to guide toric IOL alignment, but it is susceptible to human error. Furthermore, cyclotorsion may cause the eye to rotate by up to 12 degrees when the patient moves from a sitting to a supine position. Digital image-guided systems can help reduce marking errors and account for cyclotorsion, supporting more accurate alignment[3]Intraoperative misalignment: The implanted IOL may not match the intended axis at the completion of surgery. Accurate positioning is essential because each degree of misalignment can reduce astigmatic correction by approximately 3.3%, while a 30-degree rotation can completely nullify the intended correction. Manual marking, iris fingerprinting, image-guided systems, and intraoperative aberrometry-based methods can support accurate positioning[2]Postoperative IOL rotation: The lens may rotate after implantation, particularly during the early postoperative period. Differences in IOL orientation have been observed between the completion of surgery and the first postoperative day. The unfolding speed of a one-piece toric IOL, which depends on its material composition and haptic design, influences how rapidly the haptics establish contact with the capsular bag. Evaluating IOL orientation early after surgery helps identify postoperative changes from the intended axis[1]Clinical considerations for residual astigmatismResidual astigmatism may persist despite toric IOL implantation and can necessitate postoperative spectacle correction. The following considerations help place the refractive impact in context.[1][2][3]Clinical parameterRelevance to surgical planningPreexisting astigmatismAstigmatism greater than 1 D occurs in approximately 30% of eyes undergoing cataract extraction, and approximately one-third of these eyes have astigmatism exceeding 2 D.Lower degrees of astigmatismCorneal incisions, paired opposite clear corneal incisions, limbal relaxing incisions, and arcuate keratotomies may be considered for correction of astigmatism up to 1.5 D, although outcomes may be less predictable and regress over time.Postoperative refractive errorResidual astigmatism of 0.25–0.5 D may affect visual acuity and patient satisfaction.ConclusionToric IOL alignment is a critical determinant of refractive outcomes after cataract surgery. Inaccurate measurements, inappropriate IOL selection, manual marking errors, intraoperative misalignment, and postoperative rotation can compromise astigmatic correction. Accurate preoperative assessment, appropriate calculation methods, image-guided alignment where available, and early postoperative evaluation can help identify and address these factors. Maintaining the intended IOL axis remains central to achieving optimal visual outcomes.Reference(s):1. Nishimura T, Minami K. Misalignment After Implantation of One-Piece Hydrophobic Toric Intraocular Lenses: Comparison Among Manufacturers and Generations. Clin Ophthalmol. 2026;20:591237. Published 2026 Apr 1. doi:10.2147/OPTH.S591237. https://pmc.ncbi.nlm.nih.gov/articles/PMC13050970/2. Sachdev MS. Commentary: Toric intraocular lens alignment: Going markerless. Indian J Ophthalmol. 2020;68(4):587-588. doi:10.4103/ijo.IJO_1877_19. https://pmc.ncbi.nlm.nih.gov/articles/PMC7210851/3. Kandavel R, Dredge J, Jackson H, et al. Intraoperative Degree Misalignment in Toric Intraocular Lens Implantation When Using Conventional Compared to Digital Marking. Clin Ophthalmol. 2026;20:572712. Published 2026 Mar 16. doi:10.2147/OPTH.S572712. https://pmc.ncbi.nlm.nih.gov/articles/PMC13003956/