Had cataract surgery and the vision is not what was planned: understanding refractive surprise, and what can be done

The operation went well, the eye is quiet, and yet distance vision is still blurred, or near vision does not come as expected. Surgeons call this a refractive surprise: the implant that was fitted does not give exactly the correction that was calculated. In the largest European registry, nearly three eyes in four end up within half a dioptre of the target, and seven in a hundred miss it by more than one dioptre. This article explains why this happens, how it is diagnosed, and the four possible responses, from glasses to laser touch-up.

UNDERSTANDING

Why can vision differ from what was planned?

The cataract operation replaces the clouded lens with an implant whose power is chosen before the procedure. This choice rests on a calculation: the length of the eye, the curvature of the cornea and the depth of the anterior chamber go into a formula that predicts where the implant will sit and what power will give the desired vision. A prediction, by its nature, carries a margin of error.

The European EUREQUO registry, which analysed 282,811 operations carried out in 100 centres in 12 countries between 2014 and 2015, gives the order of magnitude: the mean absolute error was 0.42 dioptre, 72.7% of eyes were within half a dioptre of the target and 93.0% within one dioptre (PMID 29685779). In other words, seven eyes in a hundred miss what was planned by more than one dioptre.

The most common causes

The first cause is a faulty measurement before the operation. An irregular cornea, a dry eye that distorts the tear film, an epithelial basement membrane dystrophy: anything that alters the surface of the cornea throws off the keratometry, and therefore the calculation. Two cases published in 2019 describe errors of +1.50 dioptres and of 2.75 dioptres of astigmatism attributed to an epithelial dystrophy that had gone unnoticed (PMID 30879718). One study showed that eyes whose tears are too concentrated have less reproducible keratometry measurements, and more often show a difference in implant power of more than 0.50 dioptre between two measurements (PMID 26432124).

The second cause lies in the eye itself. The very long eyes of highly myopic patients and the very short eyes of hypermetropic patients fall outside the range where the formulas are most accurate. A cornea that has already had laser surgery, a keratoconus or a corneal graft make the prediction more uncertain. The EUREQUO registry identifies precisely these risk factors: poor preoperative vision, associated eye disease, previous eye surgery (PMID 29685779).

The third cause is the final position of the implant. The formula assumes that it will sit at a certain distance from the cornea; if it settles a little further forward or back in the capsular bag, the effective power changes. For a toric implant, a rotation of a few degrees after insertion is enough to leave residual astigmatism. Finally, very rarely, a labelling or implant selection error has been reported.

DIAGNOSIS

Before speaking of refractive surprise, rule out the other causes of blur

A blur after cataract surgery is not always a power error. In a series of patients dissatisfied after a multifocal implant, the blurred vision was due to a refractive error in 29% of eyes, but to posterior capsule opacification in 54% and to dry eye in 15% (PMID 19465282). Another series of 74 eyes found residual refractive error to be the leading cause of complaint, in 57% of cases, followed by dry eye, in 35% (PMID 27784985).

The approach therefore starts with a careful refraction, once the eye has stabilised, and with an examination of everything that can blur the image: the surface of the cornea, the capsule behind the implant, the retina on OCT. A mild macular oedema, common in the weeks after the operation, is treated and usually resolves; it does not justify any touch-up. A dry eye is treated first, and the refraction is repeated afterwards.

Two signs point to a simple power error rather than another cause: vision becomes clear again with a trial lens, and the examination shows no clouding of the capsule, no alteration of the surface and no retinal abnormality. If a lens does not correct everything, the blur has another origin, which must be treated before anything is considered on the implant.

Waiting for the refraction to stabilise

Refraction shifts in the first weeks: the implant settles in, the cornea recovers from the incision, the surface returns to normal. Any decision on correction waits until two successive measurements agree, at the pace of the scheduled checks, at day 2, at one month and then at one year. Dr Tourabaly does not set a fixed delay before the decision: it is the stability of the measurement that triggers it, not the calendar.

A 2021 review sums up the rule: a complete work-up looking for a pathological cause of the blur comes before any correction procedure, and the cause of the error, the type of implant, associated diseases and the patient’s preferences together guide the choice (PMID 33122488). A population-based study of people over 60 also finds a median residual error of 0.50 dioptre in operated eyes, which is a reminder that a small gap is the norm, not the exception (PMID 37206186).

THE RESPONSES

Four ways to correct a refractive surprise

There is no official recommendation on which method to prefer: guidelines acknowledge the possibility of a refractive surprise without ruling on its treatment. A review with meta-analysis published in 2025 in the Journal of Cataract and Refractive Surgery compared the surgical options and concluded that laser correction on the cornea gives the spherical equivalent and the visual acuity closest to the target, ahead of the supplementary implant (PMID 40929562). The choice remains individual.

1. Glasses or contact lenses

This is the first response, and often the only one needed. A gap of half a dioptre is corrected by a pair of glasses, which many patients would have worn anyway for reading. Definitive glasses are prescribed at the one-month check, or three to four weeks after the second eye when both are operated. In the series of 74 eyes cited above, glasses or contact lenses were the most frequent intervention, in 46% of cases (PMID 27784985).

2. A laser touch-up on the cornea

When the patient chose their implant precisely so as not to wear glasses, a laser touch-up corrects the residual gap by reshaping the cornea, exactly like refractive surgery. PRK, which works on the surface, is the most widely used technique in this setting; LASIK is possible on some corneas. A series of 88 eyes treated with surface laser after cataract surgery found, at one year, 68% of eyes within ±0.50 dioptre and 88% within ±1 dioptre of the intended correction, with no sight-threatening complication (PMID 21710952).

A multicentre study comparing the three surgical approaches in 65 eyes found that laser reduced residual astigmatism more than implant exchange or the supplementary implant (PMID 23991761). Even SMILE has been used successfully for residual myopia after a trifocal implant, in a series of 82 eyes (PMID 35643966). Dr Tourabaly performs these touch-ups at the Clinique Laser Victor Hugo, the only place where he performs refractive laser surgery, once the refraction has stabilised and the surface of the eye is in good condition.

3. A supplementary implant

For large gaps, or when the cornea does not lend itself to laser, a second, very thin implant can be slipped in front of the first, in the sulcus, between the iris and the capsular bag. It is called an “add-on” or “piggyback” implant. It exists in a spherical and a toric version, and it can be removed if needed. A 2017 review reports a gain of about two lines of uncorrected acuity after this procedure, in a series of 46 eyes (PMID 29042749). A more recent review judges it safer and more effective than implant exchange for large errors (PMID 33122488).

A special case: the toric implant that has rotated. Residual astigmatism after a toric implant first suggests rotation of the implant within the bag. It is measured with the slit lamp and on topography, and if it explains the gap, repositioning is enough: the implant is turned to the intended axis, without being replaced. This procedure, like exchange, is preferably done early, before the capsule contracts (PMID 33122488).

4. Implant exchange

Exchange consists of removing the implant in place and inserting another of the right power. It is the heaviest procedure, because the implant is already fixed in its capsular bag, and it is preferably carried out in the first weeks, before the capsule contracts around it. It keeps specific indications: a power very far from the target, a poorly tolerated multifocal implant, or a toric implant that cannot be repositioned. In a series of 35 eyes that had a multifocal implant exchange, the prediction error went from 0.22 to −0.09 dioptre on average and all eyes kept a corrected acuity of at least 20/40 (PMID 28732609).

Dr Tourabaly performs the supplementary implant and the implant exchange at the Clinique Sainte-Geneviève, in the 14th arrondissement of Paris, where he operates on cataracts. The procedure takes place under local anaesthesia, as a day case, with the same follow-up as cataract surgery.

IN PRACTICE

How the correction is decided, and how to prevent a refractive surprise

The decision is made in consultation, once the cause of the blur has been identified and the refraction is stable. Three questions guide it: how large is the gap, which implant is in place, and what did you expect from the operation. A gap of half a dioptre in a patient who wears reading glasses without thinking about it is not treated in the same way as an identical gap in a patient who paid for a multifocal implant so as not to wear any.

What reduces the risk before the operation

Refractive surprise is prevented mostly before the procedure. A high-quality optical biometry, performed at the Cachan practice on an IOLMaster 700, combined with corneal topography, detects irregular corneas and astigmatism that needs correcting. Treating a dry eye beforehand makes the measurements reproducible. And taking the history of the eye, in particular any previous refractive surgery, points towards the appropriate formulas.

The choice of implant matters too. An implant with a slightly extended depth of field tolerates a small calculation error somewhat better than a multifocal, whose result depends on a refraction very close to zero. This is one of the arguments for the “plus” monofocal implant in patients whose measurements are less reliable.

Finally, a refractive surprise is not a failure of the operation: the cataract is removed, transparency is restored, and the error can be corrected. What matters is to talk about it at the one-month check rather than to put up with it in silence. A consultation makes it possible to measure the gap and to choose, together, the appropriate response.

Frequently asked questions

Consultations in Cachan, Paris 13 and at the Sorbonne Saint-Michel practice (Paris 5th) · Tel. +33 1 45 47 08 11

Scientific sources

• Lundström M, et al. Risk factors for refractive error after cataract surgery: analysis of 282 811 cataract extractions reported to the European Registry of Quality Outcomes for cataract and refractive surgery. J Cataract Refract Surg. 2018. PMID 29685779
• Kanclerz P, et al. Surgical options for correcting refractive surprise after cataract and lens surgery: review and meta-analysis. J Cataract Refract Surg. 2025. PMID 40929562
• Moshirfar M, et al. Refractive enhancements for residual refractive error after cataract surgery. Curr Opin Ophthalmol. 2021. PMID 33122488
• Fernández-Buenaga R, et al. Resolving refractive error after cataract surgery: IOL exchange, piggyback lens, or LASIK. J Refract Surg. 2013. PMID 23991761
• Gundersen KG, Potvin R. A review of results after implantation of a secondary intraocular lens to correct residual refractive error after cataract surgery. Clin Ophthalmol. 2017. PMID 29042749
• Kim EJ, et al. Refractive outcomes after multifocal intraocular lens exchange. J Cataract Refract Surg. 2017. PMID 28732609
• Semiz F, et al. SMILE for the treatment of residual refractive error after cataract surgery. Ophthalmol Ther. 2022. PMID 35643966
• Kamiya K, et al. Clinical outcomes of photoastigmatic refractive keratectomy for the correction of residual refractive errors following cataract surgery. J Refract Surg. 2011. PMID 21710952
• Hashemi H, et al. Residual refractive errors in pseudophakic eyes and related factors: a population-based study. Int J Ophthalmol. 2023. PMID 37206186
• Ho VWM, et al. Refractive surprise after routine cataract surgery with multifocal IOLs attributable to corneal epithelial basement membrane dystrophy. J Cataract Refract Surg. 2019. PMID 30879718
• Epitropoulos AT, et al. Effect of tear osmolarity on repeatability of keratometry for cataract surgery planning. J Cataract Refract Surg. 2015. PMID 26432124
• Woodward MA, et al. Dissatisfaction after multifocal intraocular lens implantation. J Cataract Refract Surg. 2009. PMID 19465282
• Gibbons A, et al. Causes and correction of dissatisfaction after implantation of presbyopia-correcting intraocular lenses. Clin Ophthalmol. 2016. PMID 27784985

Further reading

• Cataract surgery: the procedure and choosing the implant
• The preoperative assessment for cataract surgery
• PRK, the surface laser
• Astigmatism and cataract: the toric implant

This article is intended to inform and does not replace a medical consultation. Indications, expected benefits and risks depend on each individual situation. If you have any question about your vision, consult an ophthalmologist.