What Are the Problems with Toric Lenses for Cataract Surgery?

Toric intraocular lenses (IOLs) are commonly used in cataract surgery to correct astigmatism, offering patients clearer vision without heavy reliance on glasses. While effective, these lenses present challenges that can impact surgical outcomes and patient satisfaction.

Understanding these potential drawbacks is essential for both patients and surgeons.

Axis Misalignment Issues

The effectiveness of toric IOLs depends on precise alignment with the patient’s corneal astigmatic axis. Even slight deviations reduce the lens’s corrective power, leading to suboptimal visual outcomes. For every one-degree misalignment, the toric effect decreases by approximately 3.3%, meaning a 10-degree rotation results in a 33% loss of astigmatic correction (Visser et al., Journal of Cataract & Refractive Surgery, 2011). This sensitivity underscores the need for meticulous surgical planning.

Accurate alignment relies on preoperative measurements from corneal topography, optical coherence tomography (OCT), and keratometry. Variability in these measurements, often due to tear film instability or irregular corneal surfaces, can introduce errors before implantation. Additionally, intraoperative factors such as cyclotorsion—eye rotation when a patient moves from a seated to a supine position—complicate alignment. Surgeons use digital marking systems or intraoperative aberrometry to address these challenges, but perfect alignment remains difficult.

Postoperative misalignment can occur due to lens rotation within the capsular bag, particularly in the early healing phase. Capsular bag contraction during healing can exert uneven forces on the IOL, causing it to shift. Lens materials and haptic designs influence rotational stability, with hydrophobic acrylic lenses generally adhering better to the capsular bag than hydrophilic materials (Koch et al., American Journal of Ophthalmology, 2020). Despite advancements, postoperative rotation remains a concern, sometimes requiring realignment procedures if vision is significantly affected.

Residual Astigmatism

Some patients experience residual astigmatism after cataract surgery despite toric IOLs. This can result from inaccuracies in preoperative measurements, surgically induced astigmatism (SIA), or limitations in toric power increments. Even when correctly positioned, discrepancies between predicted and actual postoperative corneal shape can leave uncorrected refractive error.

A primary contributor is variability in corneal measurements. Preoperative assessments using keratometry, corneal topography, and OCT each have margins of error. The posterior corneal surface, which plays a smaller but significant role in total astigmatism, is particularly difficult to measure accurately. Failing to account for posterior corneal astigmatism can lead to over- or underestimation of the required toric power, resulting in unexpected residual error (Koch et al., Journal of Cataract & Refractive Surgery, 2012).

Surgically induced astigmatism further complicates outcomes, as corneal incisions alter curvature. The extent of these changes varies based on incision location, size, and individual healing responses. While modern techniques aim to minimize these effects, even small deviations impact the final refractive result. Some surgeons attempt to compensate for SIA preoperatively, but individual variability makes precise prediction difficult.

Another limitation is the discrete power steps available in toric IOL models. Manufacturers offer lenses in set cylindrical powers, which may not perfectly match a patient’s exact needs. Surgeons must choose the closest available option, sometimes leaving minor uncorrected astigmatism. Even a 0.25-diopter difference can be noticeable, particularly for tasks requiring fine detail, such as reading or night driving.

Rotational Stability

The long-term effectiveness of toric IOLs depends on their ability to maintain alignment, but rotational stability remains a challenge. Even slight shifts reduce astigmatic correction, making stability a key factor in surgical planning. While modern toric IOL designs aim to minimize rotation, factors such as capsular bag contraction, lens material properties, and individual healing responses introduce variability.

The capsular bag contracts in the weeks following surgery, driven by fibrosis and cellular proliferation. This process can exert uneven forces on the IOL, causing rotation. The extent of contraction varies among patients, influenced by age, surgical technique, and preexisting ocular conditions. A smaller capsulorhexis—where the anterior capsule opening is sized to overlap the IOL edge—can enhance stability by promoting uniform contact between the lens and capsule (Ophthalmology, 2015). However, excessive contraction in some cases may induce late-stage rotation.

Lens material significantly affects adherence to the capsular bag. Hydrophobic acrylic lenses, which form stronger adhesions, generally offer better stability than hydrophilic materials. Haptic design also plays a role—plate-haptic designs have been associated with reduced rotation, whereas open-loop haptics may be more prone to movement depending on capsular fibrosis. Manufacturers continue refining haptic architecture and surface coatings to enhance friction and reduce misalignment over time.

Visual Disturbances

Some patients report visual disturbances after receiving toric IOLs, including glare, halos, and reduced contrast sensitivity, particularly in low-light conditions. While these symptoms can occur with any IOL, the optical design of toric lenses introduces additional factors that contribute to visual side effects.

Unlike spherical IOLs, toric lenses correct astigmatism by redistributing light based on precise alignment. Even minor decentration within the capsular bag can lead to optical aberrations, such as ghosting—where a faint secondary image appears alongside the primary image, particularly in high-contrast settings like reading black text on a white background.

Pupil size also affects visual disturbances. In dim lighting, pupil dilation allows more peripheral light rays to enter the eye. If the toric IOL’s optical zone does not fully accommodate these wider angles, patients may experience halos around bright lights or increased glare, especially while driving at night. Some individuals adapt over time, but for others, these disturbances persist enough to impact daily activities.