Toric IOLs are intraocular lenses (IOLs) 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 model, power, axis of fixation, 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 just lens removal; it increasingly incorporates refractive correction. 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 of 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 the single-piece open-loop hydrophobic acrylic toric IOL (AcrySof), which became widely adopted due to its 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 cataract 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 elective medical treatment (patient pays the difference). Only the difference from a monofocal IOL is borne by the patient; 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 postoperatively, requiring glasses, but using a toric IOL allows many patients to be spectacle-free for distance vision. High success rates are achieved with appropriate patient selection, IOL calculation, and surgical technique. Monofocal toric IOLs are elective 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 direction (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) 1).
| Examination | Key findings |
|---|---|
| Manual refraction | Determine refractive astigmatism with careful examination |
| Keratometer | Check amount and axis of anterior segment astigmatism |
| Corneal topography/tomography | Essential to rule out 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 indication (indicated)
Corneal regular astigmatism: Regular astigmatism is required
Astigmatism amount: Usually 1.0 D or more (recommended by ESCRS; strong evidence for 2.0 D or more) 5)
Expectations: Realistic expectation of being free from distance glasses
Corneal stability: Stable measurements
Relative contraindications / Cases requiring caution
Irregular astigmatism: Unsuitable 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
The ESCRS guidelines (2024) recommend the use of toric IOLs for regular astigmatism of 1.0 D or more, with strong evidence (GRADE++) for 2.0 D or more and moderate evidence for 1.5 D or more 5). For astigmatism of 0.75 D or less, opposite clear corneal incision (OCCI) or adjustment of the main incision position is recommended as an alternative 5). Corneal relaxing incisions (LRI) carry a higher risk of residual astigmatism than toric IOLs 11).
Posterior corneal astigmatism (PCA) has long been overlooked, but it is now recognized as essential to incorporate into calculations 1)2).
Koch et al. (2012) reported a mean PCA of 0.30 D in 435 patients 2). It was also shown that the steep meridian of the posterior cornea is vertically oriented in 87% of patients 2). In with-the-rule (WTR) eyes, PCA reduces anterior corneal astigmatism, while in against-the-rule (ATR) eyes, it enhances it 1).
Calculation methods that incorporate PCA and effective lens position (ELP) may reduce postoperative residual astigmatism compared to those that do not 8). The ESCRS guidelines recommend that toric IOL calculators using measured PCA are potentially superior to predicted PCA in eyes with high PCA 5). The Barrett formula, Goggin Nomogram, and Baylor Nomogram incorporate this correction 1).
Preoperative evaluation before toric IOL implantation requires the following in addition to standard cataract surgery evaluation 5).
Perform multiple measurements and adopt stable values with little variation. Preoperative subjective refractive astigmatism is irrelevant for IOL planning (because lens-induced astigmatism disappears after 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.) are recommended over traditional formulas due to lower trend errors (GRADE+) 5). Calculation methods that include posterior corneal astigmatism and effective lens position (ELP) are recommended, and using these calculations significantly reduces postoperative residual astigmatism 8).
Intraoperative aberrometry: Using intraoperative aberrometers such as ORA or Holos IntraOp enables real-time refraction measurement in the aphakic eye and assists in the alignment accuracy of toric IOLs 6). However, aberrometry does not always improve outcomes 6).
The most important consideration is posterior corneal astigmatism (PCA). Many traditional calculation tools use only anterior corneal data; 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 that incorporate PCA, such as the Barrett formula or the ESCRS calculator. Surgically induced astigmatism (SIA) must also be reflected using vector calculations. In long axial length eyes, the capsular bag is larger and the IOL is more 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 to 6.0 D | Wavefront design |
| enVista Toric (B+L) | Hydrophobic acrylic | 1.25 to 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). Toric multifocal IOLs offer better predictability and rotational stability than spherical multifocal IOLs combined with corneal relaxing incisions 6).
Step 1: Preoperative marking (axis identification)
Place the patient in a sitting (or standing) position and have them look straight ahead while marking the corneal limbus with reference marks. Since 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 axis alignment
After injecting ophthalmic viscosurgical device (OVD), roughly position the IOL about 10–15 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 corneal steep meridian.
Postoperative follow-up:
First, confirm the IOL axis position and postoperative refraction. If axis misalignment is the cause, perform reoperation (repositioning) to rotate the IOL to the correct position, aiming for 2–4 weeks postoperatively. If the IOL cylinder power is inappropriate, IOL exchange or additional surgery is required. If a non-toric IOL was used, options include supplementary toric IOL insertion in the ciliary sulcus or corneal laser enhancement (LASIK, PRK, etc.).
Uncorrected astigmatism reduces visual acuity 1). The effect depends not only on the power but also on the axis direction; 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 correction of 0.5–0.6 D of corneal astigmatism 1). The required cylinder power may change when the spherical power of the IOL changes, 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). For toric IOL power calculation, the residual astigmatism after subtracting SIA is used. SIA is a multifactorial factor depending on incision location, size, and surgeon experience 5).
In an evidence-based review by Goggin (2022), the following outcomes are achievable with appropriate preoperative planning, calculation, and surgical technique1):
In a meta-analysis by Kessel et al. (2016) (13 studies), toric IOLs significantly improved UDVA compared to non-toric IOLs (logMAR MD −0.07 to −0.10), and the rate of spectacle independence for distance was significantly higher (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).
In a systematic review by Rocha-de-Lossada et al. (2023) (155 eyes)3):
In cataract surgery for patients with keratoconus (KC), irregular anterior-posterior corneal curvature ratio, non-orthogonality of axes, and errors in ELP estimation can cause reduced 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 target is only 12–48% 4). The ESCRS guidelines recommend using the Barrett True-K and Kane keratoconus formulas for keratoconus and advise against conventional formulas (e.g., SRK/T) (GRADE+) 5).
In mild to moderate stable keratoconus, toric IOLs may be useful. However, irregular corneal shape reduces the predictive accuracy of astigmatism correction. Systematic reviews report relatively good outcomes in mild to moderate cases (Krumeich I–II), but in advanced keratoconus, the rate of achieving within 1 D of target tends to be low. The ESCRS guidelines recommend using the Kane keratoconus adjusted formula or Barrett True-K.
