What defines toric IOL misalignment?

A toric lens sitting away from its intended axis Misalignment means the toric intraocular lens lies off its intended axis, which leaves residual astigmatism and defeats the purpose of the implant.

A toric lens implanted with the wrong cylinder power

A toric lens decentred out of the visual axis

A toric lens captured in the anterior capsulorhexis

By roughly how much does toric IOL effective power fall per degree of axis error?

About 3 percent The effective cylindrical power of a toric lens drops by approximately 3 percent for every degree of misalignment from the planned axis.

What happens to refractive cylinder once a toric IOL is rotated beyond about 30 degrees?

The lens begins adding astigmatism, exceeding the preoperative amount A 30-degree error removes the benefit entirely, and beyond that the lens starts to add astigmatism so the patient may have more cylinder than before surgery.

The cylinder axis flips to the opposite meridian without changing magnitude

The correction is preserved but shifts toward spherical equivalent

The cylinder becomes fully corrected by corneal compensation

When does most rotation of an implanted toric intraocular lens occur?

In the first days to weeks after surgery Most rotation takes place in the first days to weeks and usually stops once capsular fibrosis contracts around the lens and fixes it in position.

Between six and twelve months postoperatively

Only after Nd:YAG capsulotomy is performed

Gradually and steadily over several years

Which eye feature permits greater postoperative rotation of a toric intraocular lens?

An axial myopic eye with a large capsular bag A large capsular bag, as in an axial myopic eye, gives the lens more room to move and so predisposes to rotation.

A shallow anterior chamber with a thick lens

A densely pigmented iris with posterior synechiae

A short hyperopic eye with a small corneal diameter

Why should corneal reference marks for a toric IOL be placed with the patient sitting upright?

Cyclotorsion on lying down shifts the apparent axis Marking while the patient sits upright avoids the axis error introduced by cyclotorsion when the patient lies down; image-guided registration of iris and limbal landmarks is an alternative.

Tear film spreads more evenly in the upright position

Topical anaesthetic penetrates the epithelium more reliably

Pupil size is more stable when the patient is seated

Which intraoperative step reduces toric IOL rotation in the first postoperative hours?

Removing all viscoelastic from behind the lens Retained viscoelastic behind the lens lets it rotate in the first postoperative hours, so complete removal is essential; a capsulorhexis that overlaps the optic edge also helps.

Leaving a viscoelastic cushion behind the optic

Creating a capsulorhexis smaller than the optic

Placing the haptics in the ciliary sulcus

When is surgical repositioning of a misaligned toric intraocular lens most straightforward?

Within the first few weeks, before capsular fibrosis Repositioning is best performed in the operating room within the first few weeks, since later surgery may need more manipulation to break adhesions between capsule and lens.

After six months, once the refraction has fully stabilised

Only at the same time as an Nd:YAG capsulotomy

At the slit lamp during the first postoperative day

A toric IOL sits on its planned axis yet significant astigmatism persists. What is the next option?

Limbal relaxing incisions or laser refractive surgery When the lens is correctly placed but astigmatism persists, limbal relaxing incisions or laser refractive surgery can be considered; exchange is reserved for uncorrectable power or position.

Rotate the lens 45 degrees clockwise

Repeat the rhexis to recentre the optic

Observe indefinitely without further intervention

In which eyes does the posterior corneal surface matter most for toric IOL planning?

Eyes with against-the-rule astigmatism The contribution of the posterior corneal surface is most important in eyes with against-the-rule astigmatism, which is why two independent keratometry methods should be compared.

Eyes with a previous Nd:YAG capsulotomy

Eyes with pseudoexfoliation of the capsule

Toric IOL Misalignment: Detection and Repositioning

Toric IOL misalignment occurs when a toric intraocular lens lies away from its intended axis, and the result is residual astigmatism that undermines the purpose of the implant.

A few degrees of rotation are common and tolerable, but larger errors reduce the correction and can add astigmatism.

Recognizing the problem early gives the surgeon the chance to reposition the lens before the capsule seals it in place.

How Much Toric IOL Misalignment Matters

The effective power of the toric lens falls by about 3 percent for each degree of misalignment.

A 10-degree error leaves roughly a third of the astigmatism uncorrected, and a 30-degree error removes the benefit.

Beyond about 30 degrees the lens starts to add astigmatism, and the patient can end up with more cylinder than before surgery.

These figures are approximate, and they depend on the power of the lens, but the relationship is steep enough that axis accuracy deserves attention.

Causes

Marking errors: incorrect reference marks on the cornea, especially with cyclotorsion when the patient lies down
Biometry and keratometry errors: an inaccurate axis or an incorrect assessment of the posterior cornea
Intraoperative misplacement: an error in aligning the lens in the capsular bag
Postoperative rotation: movement of the lens in the early postoperative days, before capsular fibrosis fixes it
Large capsular bag: an axial myopic eye with a large bag allows more movement
Lens design and material: haptic configuration and surface properties influence stability

Most rotation takes place in the first days to weeks, and it usually stops when the capsule contracts around the lens.

Test your knowledge 10 questions from this article

Detecting Misalignment

The main symptom is blur and a refractive result that does not match the plan.

Check the uncorrected acuity, the manifest refraction, and the keratometry.

If the residual cylinder is higher than expected, dilate the pupil and examine the lens at the slit lamp with a narrow beam, noting the axis marks on the optic.

Compare the lens axis with the planned axis, using a protractor eyepiece or an image captured with a smartphone or a camera.

Online calculators can estimate the best repositioning angle based on the refraction and the current lens axis.

Take care to examine the cornea, because corneal irregularity, dry eye, or an error in the keratometry may explain the findings and would not be corrected by rotating the lens.

Management

Reposition the lens when the residual astigmatism is significant and the lens is out of axis by a meaningful amount.

The procedure is performed in the operating room, with a viscoelastic and a spatula or a hook, and it is best done within the first few weeks, before capsular fibrosis.

Later repositioning is possible, but it may require more manipulation to break the adhesions between the capsule and the lens.

If the lens is correctly placed and the astigmatism persists, consider limbal relaxing incisions or laser refractive surgery, as appropriate.

A lens exchange is reserved for cases in which the power or the position cannot be corrected.

Before surgery, patients should be told that toric implants can rotate and that a second operation is occasionally needed.

Review all measurements after surgery to improve the planning of future cases (see phacoemulsification).

Clinical eye photograph illustrating Toric Iol Misalignment

Preventing Misalignment

Precise preoperative measurements are the foundation of a good toric result.

Use two independent keratometry methods and compare them, and consider the effect of the posterior corneal surface, which matters most in eyes with against-the-rule astigmatism.

Mark the cornea with the patient sitting upright to avoid errors from cyclotorsion, or use an image-guided system that registers the iris and limbal landmarks.

During the operation, remove all viscoelastic from behind the lens, because retained material allows the lens to rotate in the first postoperative hours.

Choose a lens with a stable haptic design, and take care to center it within a capsulorhexis that overlaps the optic edge.

Postoperative Checks

Examine the lens axis at the first visit and again at one to two weeks, with the pupil dilated if necessary.

If the lens has rotated and the surgeon plans to reposition it, it is easier to do so early, which is why the first examinations matter.

Patients should be told to avoid rubbing the eye and to report a sudden blur after the first weeks.

Counselling After a Disappointing Result

Explain that the astigmatism is not permanent, and that options exist for correction.

A clear plan, including the proposed surgery and the likely outcome, helps patients to remain confident in their surgeon.

References

Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while controlling axis. J Cataract Refract Surg. 1994;20:523-526.
Kessel L, Andresen J, Tendal B, et al. Toric intraocular lenses in the correction of astigmatism during cataract surgery: a systematic review and meta-analysis. Ophthalmology. 2016;123:275-286.
Salmon JF. Kanski’s Clinical Ophthalmology: A Systematic Approach. 9th ed. Elsevier; 2020.
American Academy of Ophthalmology. Basic and Clinical Science Course, Section 11: Lens and Cataract. AAO; current edition.

Test yourself

A few questions straight from this article.

1 / 10 0 correct

What defines toric IOL misalignment?
Misalignment means the toric intraocular lens lies off its intended axis, which leaves residual astigmatism and defeats the purpose of the implant.
By roughly how much does toric IOL effective power fall per degree of axis error?
The effective cylindrical power of a toric lens drops by approximately 3 percent for every degree of misalignment from the planned axis.
What happens to refractive cylinder once a toric IOL is rotated beyond about 30 degrees?
A 30-degree error removes the benefit entirely, and beyond that the lens starts to add astigmatism so the patient may have more cylinder than before surgery.
When does most rotation of an implanted toric intraocular lens occur?
Most rotation takes place in the first days to weeks and usually stops once capsular fibrosis contracts around the lens and fixes it in position.
Which eye feature permits greater postoperative rotation of a toric intraocular lens?
A large capsular bag, as in an axial myopic eye, gives the lens more room to move and so predisposes to rotation.
Why should corneal reference marks for a toric IOL be placed with the patient sitting upright?
Marking while the patient sits upright avoids the axis error introduced by cyclotorsion when the patient lies down; image-guided registration of iris and limbal landmarks is an alternative.
Which intraoperative step reduces toric IOL rotation in the first postoperative hours?
Retained viscoelastic behind the lens lets it rotate in the first postoperative hours, so complete removal is essential; a capsulorhexis that overlaps the optic edge also helps.
When is surgical repositioning of a misaligned toric intraocular lens most straightforward?
Repositioning is best performed in the operating room within the first few weeks, since later surgery may need more manipulation to break adhesions between capsule and lens.
A toric IOL sits on its planned axis yet significant astigmatism persists. What is the next option?
When the lens is correctly placed but astigmatism persists, limbal relaxing incisions or laser refractive surgery can be considered; exchange is reserved for uncorrectable power or position.
In which eyes does the posterior corneal surface matter most for toric IOL planning?
The contribution of the posterior corneal surface is most important in eyes with against-the-rule astigmatism, which is why two independent keratometry methods should be compared.