A toric IOL is an intraocular lens (IOL) used to simultaneously correct corneal astigmatism during cataract surgery. Astigmatism-correcting IOLs have a structure that adds cylindrical power to conventional IOLs to correct corneal astigmatism. The surgeon uses a calculator on the manufacturer’s website to determine the appropriate astigmatism-correcting IOL model, power, fixation axis, and incision location for the specific case. At the end of surgery, the weak meridian of the IOL is aligned with the steep meridian of the cornea.
Cataract surgery is no longer merely lens removal; its role as a refractive surgery is increasingly emphasized. As patients increasingly desire spectacle-free lives after surgery, the importance of astigmatism correction continues to grow.
The first toric IOL was conceived in 1992 by Shimizu in Japan. It was a three-piece open-loop design made of PMMA with polypropylene haptics 2). Early silicone plate-haptic IOLs (Staar Surgical) had rotational stability issues, with 24% of early cases reporting rotation of 30 degrees or more 2). In 2006, Alcon launched a single-piece open-loop hydrophobic acrylic toric IOL (AcrySof), which became widely adopted due to excellent rotational stability and reduced posterior capsule opacification (PCO) 2).
Corneal astigmatism of 1.0 D or more is present in approximately 30–40% of cataract outpatients, and 1.5 D or more is found in 15–29%. Uncorrected astigmatism is a major cause of reduced postoperative uncorrected visual acuity. Currently, regular astigmatism with cataracts is the main indication, but it is also used in various conditions such as mild to moderate keratoconus, post-keratoplasty, and post-pterygium excision 2).
Insurance system: Toric IOLs are covered under selected medical treatment (patient pays the difference). Only the difference from a monofocal IOL is borne by the patient, while the cataract surgery itself is covered by health insurance.
It is a special intraocular lens that can simultaneously correct corneal astigmatism during cataract surgery. With a standard spherical IOL, astigmatism remains after surgery, requiring glasses, but using a toric IOL allows many patients to be free from glasses for distance vision. High success rates are achieved through appropriate patient selection, IOL calculation, and surgical technique. Monofocal toric IOLs are selected medical treatment (patient pays the difference), while the cataract surgery itself is covered by insurance.
The main subjective symptoms of astigmatism requiring a toric IOL are listed below.
The degree of visual impairment due to astigmatism depends not only on the power but also on the axis (with-the-rule, against-the-rule, oblique) 1). Against-the-rule (ATR) astigmatism is considered to have a greater impact on vision than with-the-rule (WTR) astigmatism 1).
| Examination | Key findings |
|---|---|
| Manual refraction | Determine refractive astigmatism with careful examination |
| Keratometer | Check the amount and axis of anterior segment astigmatism |
| Corneal topography/tomography | Essential for excluding irregular astigmatism5) |
| Optical biometer | Simultaneously measures axial length and anterior chamber depth |
Confirm that the direction and magnitude of astigmatism are consistent across all measurements. Discrepancies between measurements suggest irregular astigmatism or measurement error.
Good indications (appropriate)
Corneal regular astigmatism: Regular astigmatism is required
Astigmatism amount: Typically 1.0 D or more. For 2.0 D or more, the evidence is relatively strong5)
Expectations: Realistic expectations for spectacle independence for distance
Corneal stability: Stable measurements
Relative contraindications and cautionary cases
Irregular astigmatism: Not suitable for corneal scars or corneal ectasia
Zonular weakness: High risk of rotation
Poor pupil dilation: Increases surgical difficulty
History of vitreoretinal or glaucoma surgery: May alter expected outcomes
For regular astigmatism of 1.0 D or more, a toric IOL is a useful option, and for 2.0 D or more, the evidence is particularly strong5). For astigmatism of 0.75 D or less, alternative methods such as opposite clear corneal incision (OCCI) or adjustment of the main incision position are available5). Corneal relaxing incisions (LRI) carry a higher risk of residual astigmatism than toric IOLs11).
Posterior corneal astigmatism (PCA) has long been overlooked, but it is now recognized as essential to incorporate into calculations1)2).
Koch et al. (2012) reported a mean PCA of 0.30 D in 435 patients2). It was also shown that the steep meridian of the posterior cornea is vertically oriented in 87% of patients2). In with-the-rule (WTR) eyes, PCA reduces anterior corneal astigmatism, while in against-the-rule (ATR) eyes, it enhances it1).
Calculation methods incorporating PCA and ELP may reduce postoperative residual astigmatism compared to those that do not consider them8). In eyes with high PCA, toric IOL calculators using measured PCA are potentially superior to those using predicted PCA5). The Barrett formula, Goggin Nomogram, and Baylor Nomogram incorporate this correction1).
Preoperative evaluation before toric IOL implantation requires the following in addition to standard cataract surgery evaluation5).
Multiple measurements are taken, and stable values with little variation are adopted. Preoperative subjective refractive astigmatism is irrelevant for IOL planning (because lenticular astigmatism disappears with surgery)6).
Use the online toric calculator provided by each manufacturer. Input items include corneal astigmatism (cylinder power and axis), surgically induced astigmatism (SIA), axial length, anterior chamber depth, and desired incision location.
Representative calculation tools:
Recommended formula: New-generation formulas (Barrett Universal II, Kane, Hill-RBF, EVO, etc.) have fewer trend errors than conventional formulas and are recommended5). Calculation methods that include posterior corneal astigmatism and ELP are recommended, and calculations that account for these significantly reduce postoperative residual astigmatism8).
Intraoperative aberrometry: Using intraoperative aberrometers such as ORA or Holos IntraOp enables real-time refraction measurement in the aphakic eye and assists in the accuracy of toric IOL alignment6). However, aberrometry does not always improve outcomes6).
The most important consideration is posterior corneal astigmatism (PCA). Many conventional calculation tools use only anterior corneal data, and ignoring PCA can lead to overcorrection in with-the-rule astigmatism and undercorrection in against-the-rule astigmatism. Currently, it is recommended to use tools such as the Barrett formula or the ESCRS calculator that incorporate PCA. Surgically induced astigmatism (SIA) must also be reflected using vector calculations. In eyes with long axial length, the capsular bag is large and the IOL is prone to rotation, so this should be accounted for preoperatively.
Monofocal toric IOLs are primarily intended for distance vision correction. Glasses are needed for near and intermediate vision.
| IOL Name | Material | Cylinder Power (IOL Plane) | Features |
|---|---|---|---|
| AcrySof IQ Toric / Clareon Toric (Alcon) | Hydrophobic acrylic | 1.5–6.0 D | Optic diameter 6 mm, 2.2 mm incision insertion. Most widely used. |
| TECNIS Toric (J&J Vision) | Hydrophobic acrylic | 1.5–6.0 D | Wavefront design |
| enVista Toric (B+L) | Hydrophobic acrylic | 1.25–5.75 D | Aberration-free design |
| Staar Toric | Silicone | 2.0, 3.5 D | Plate-type. Rotational stability is a concern |
Multifocal/EDOF toric IOLs provide simultaneous correction of astigmatism and near-to-distance vision. Representative examples include PanOptix Toric (Alcon), Vivity Toric (Alcon), and TECNIS Symfony Toric (J&J Vision). Compared to spherical multifocal IOLs with corneal relaxing incisions, toric multifocal IOLs offer better predictability and rotational stability6).
Step 1: Preoperative marking (axis identification)
Place the patient in a sitting (or standing) position, have them look straight ahead, and mark the corneal limbus with a reference mark. Since ocular cyclotorsion occurs when lying down, this must be done in the sitting position 1). It is important to identify the axis before anesthesia 1).
Marking methods:
Step 2: IOL insertion and alignment
After injecting ophthalmic viscosurgical device (OVD), roughly position the IOL about 10 to 15 degrees before the final target position (counterclockwise). Carefully remove the OVD, then rotate the IOL to the target position, aligning the IOL’s weak meridian mark with the cornea’s steep meridian.
Postoperative follow-up:
First, confirm the IOL axis position and postoperative refraction. If axis misalignment is the cause, perform repositioning surgery to rotate the IOL to the correct position, ideally at 2–4 weeks postoperatively. If the IOL cylinder power is inappropriate, IOL exchange or additional surgery may be needed. If a non-toric IOL was used, options include supplementary toric IOL insertion in the ciliary sulcus or enhancement with corneal laser (LASIK, PRK, etc.).
Uncorrected astigmatism reduces visual acuity 1). The effect depends not only on the power but also on the axis; against-the-rule astigmatism has a greater impact on visual acuity than with-the-rule astigmatism 1). Since removal of the crystalline lens during cataract surgery eliminates the lenticular astigmatic component, postoperative astigmatism is essentially only corneal astigmatism (anterior + posterior) 6).
A toric IOL has cylinder power on the lens. The lowest-power toric IOL is typically 1.0 D (at the IOL plane), which corresponds to correcting 0.5–0.6 D of corneal astigmatism 1). Changes in the IOL spherical power may alter the required cylinder power, and the effective lens position also affects the correction amount 1).
The cataract surgery incision itself induces mild astigmatism (approximately 0.3–0.5 D with small-incision surgery). Toric IOL power calculation uses the residual astigmatism after subtracting SIA. SIA is a multifactorial factor depending on incision location, size, and surgeon experience 5).
An evidence-based review by Goggin (2022) indicates that with appropriate preoperative planning, calculation, and surgical technique, the following outcomes can be achieved1):
A meta-analysis by Kessel et al. (2016) of 13 studies found that toric IOLs significantly improved uncorrected distance visual acuity (UDVA) compared to non-toric IOLs (logMAR MD −0.07 to −0.10) and significantly reduced the need for distance spectacles (RR 0.51, 95% CI 0.36–0.71)7).
When residual astigmatism remains after insertion of an existing non-toric IOL, an additional toric IOL can be placed in the ciliary sulcus (STIOL) as an option3).
A systematic review by Rocha-de-Lossada et al. (2023) of 155 eyes reported3):
In cataract surgery for keratoconus (KC) patients, factors such as irregular anterior-posterior corneal curvature ratio, non-orthogonal axes, and errors in ELP estimation can reduce accuracy 4). Systematic reviews and meta-analyses report that relatively satisfactory postoperative outcomes can be achieved in mild to moderate keratoconus, but in advanced keratoconus, the rate of achieving within 1 D of the target is only 12–48% 4). For keratoconus, use the Barrett True-K or Kane keratoconus formula, and handle conventional formulas (e.g., SRK/T) with caution 5).
For mild to moderate stable keratoconus, toric IOLs may be useful. However, due to irregular corneal shape, the predictive accuracy of astigmatism correction is reduced. Systematic reviews report relatively good outcomes in mild to moderate cases (Krumeich grade I–II), but in advanced keratoconus, the rate of achieving within 1 D of the target tends to be low. Consider using the Kane keratoconus adjusted formula or Barrett True-K for calculations.
