Refractive Error After Cataract Surgery

Key Points at a Glance

Key Points of This Disease

• Refractive error after cataract surgery is a deviation from the target refraction, including myopic/hyperopic surprises and residual astigmatism.
• The proportion of patients whose postoperative refraction falls within ±0.5 D of the target is about 50–70%, making improvement of IOL calculation accuracy an important issue.
• Currently, the Barrett Universal II, Hill-RBF, and Kane formulas have the highest accuracy for IOL power calculation, surpassing the conventional SRK/T formula.
• After corneal refractive surgery (LASIK, PRK, RK), accurate measurement of corneal power becomes difficult, often leading to refractive errors.
• Preoperative corneal astigmatism of 1 D or more is observed in about one-third of patients, and correction with a toric IOL or corneal relaxing incision is considered.
• For residual astigmatism, glasses or contact lenses are the first choice. Excimer laser is effective for surgical correction, but facilities are limited.
• Axis misalignment of a toric IOL can be easily corrected within the early postoperative period (1–2 weeks), and it is important not to miss the timing.

1. What is refractive error after cataract surgery?

In cataract surgery (phacoemulsification), an important goal is to bring the postoperative refractive value close to the target when removing the cloudy lens and inserting an intraocular lens (IOL). However, due to errors in IOL power calculation, intraoperative factors, and patient anatomical characteristics, a “refractive error” that deviates from the target refractive value may occur.

Refractive surprise refers to a condition in which an unexpected residual refractive error remains after surgery, potentially requiring additional measures such as glasses, contact lenses, corneal refractive correction, or IOL exchange¹⁾.

It has been reported that the proportion of patients achieving a postoperative refractive error within ±0.5 D of the target is approximately 50–70%, and within ±1.0 D it is 79–94%. Based on EUREQUO, European guidelines reviewed clinical processes using data from 523,921 cataract surgeries ¹¹⁾. Preoperative corneal astigmatism of 1 D or more is present in about one-third of cases, and appropriate IOL power selection and reduction of postoperative astigmatism are important for improving patient satisfaction.

Classification of Refractive Errors

• Spherical error: Myopic surprise (IOL effective position more anterior than predicted) or hyperopic surprise (IOL effective position more posterior than predicted)
• Residual astigmatism: Undercorrection of preoperative corneal astigmatism, surgically induced astigmatism from the incision, or misalignment of a toric IOL
• IOL decentration or tilt: Deviation of the IOL optical center from the pupil center or tilt in the anteroposterior direction

Q Is it possible that glasses will be needed after cataract surgery?

A

Glasses may still be needed after surgery. The target refraction (emmetropia or mild myopia) is set preoperatively, but errors can occur in IOL power calculation, and preoperative corneal astigmatism may remain. If the postoperative refraction differs from the target, the basic approach is to use glasses or contact lenses.

2. Main Symptoms and Clinical Findings

Subjective Symptoms

Symptoms due to refractive error vary depending on the type and degree of error.

• Poor vision (distance and near vision): The greater the deviation from the target refraction, the more likely dissatisfaction occurs.
• Asthenopia and difficulty seeing: Residual astigmatism is often the main cause.
• Photophobia, glare, halo: May be enhanced by the combination of multifocal IOL and refractive error
• Monocular diplopia: Occurs when irregular astigmatism or higher-order aberrations are present

Clinical Findings

Postoperative refractive error is evaluated using a combination of the following tests.

• Visual acuity test and refraction (manifest refraction): Quantification of corrected visual acuity and residual refraction
• Slit-lamp examination: Confirmation of IOL position, tilt, and decentration. IOL position confirmation using the transillumination method under mydriasis is particularly useful for multifocal IOLs and EDoF IOLs
• Corneal shape analysis: Separation of corneal and internal components of postoperative astigmatism. Irregular cornea is also evaluated using topography and tomography.

If there is concern about postoperative vision

If you feel that your vision is “poor” after surgery, first check with your doctor whether it is temporary (corneal edema/inflammation) or persistent. Even if you are told that “you will get used to it,” we recommend that you see your doctor again if it does not improve after several weeks.

3. Causes and Risk Factors

The causes of refractive error are broadly divided into preoperative measurement errors, IOL calculation errors, intraoperative factors, and postoperative factors.

Preoperative measurement errors

• Axial length measurement error: A 1 mm measurement error corresponds to a refractive error of 3.4 D in short eyes (≤22 mm), 2.9 D in average eyes, and 1.6 D in long eyes (≥26 mm). Accuracy within 0.2 mm is required. Optical biometers (e.g., IOLMaster, LENSTAR) are non-contact, highly accurate, and have low inter-examiner variability. Devices equipped with swept-source OCT may be able to measure even in mature cataracts ²⁾
• Underestimation or overestimation after corneal refractive surgery: After LASIK, PRK, or RK, the shape of the anterior and posterior cornea is altered, and standard K-value calculations do not accurately determine refractive power ³⁾
• Irregular cornea (keratoconus, staphyloma): Corneal topography evaluation is essential
• Examples of optical biometers available in Japan: IOLMaster (Carl Zeiss), OA-1000 (Tomey), LENSTAR LS900 (Haag-Streit), AL-Scan (Nidek), and ALADDIN (Topcon) are five representative models

IOL calculation error

• Prediction error of effective lens position (ELP): Error in estimating the anteroposterior position where the IOL will be located postoperatively. This is the largest source of calculation error
• Formula selection error: Using an inappropriate formula for long or short eyes (e.g., misusing the SRK/T formula for short or long eyes) can cause large errors.
• Insufficient consideration of posterior corneal astigmatism: Not accounting for posterior corneal astigmatism reduces the accuracy of toric IOL calculations⁸⁾.
• Formula misuse, data entry errors, and surgeon mistakes (e.g., mixing up left and right eyes) can also cause refractive errors.

Intraoperative factors

• Residual ophthalmic viscosurgical devices causing IOL position changes.
• IOL placement in the ciliary sulcus (sulcus-fixated IOLs result in a 0.5–1.0 D power reduction in average eyes)²⁾.
• In short axial length eyes (AL < 22mm), high-power IOLs (+30D or more) may be difficult to obtain in 0.5D steps ³⁾

Postoperative factors

• IOL decentration/tilt over time: especially common with short total length IOLs
• Long axial length eyes (AL > 25mm): prone to postoperative hyperopia; it is important to fully explain the target refraction and potential error preoperatively ³⁾

Axial length	Recommended formula (standard)	Special notes
Short axial length (≤22mm)	Hoffer Q, Holladay 2	Holladay 2 is best for ≤20mm
Medium (22–26mm)	Holladay 1, Barrett II	Standard cases
Long axial length (≥26mm)	SRK-T, Holladay1, Holladay2	Caution for postoperative hyperopia

Q Is there a high risk of refractive error when undergoing cataract surgery after LASIK?

A

In eyes after LASIK, the anterior corneal curvature is altered, making standard keratometry inaccurate. After myopic LASIK, hyperopic refractive errors are more likely postoperatively, while after hyperopic correction, myopic errors are more common³⁾. Dedicated formulas (Barrett True-K, Haigis-L, etc.) can improve accuracy but cannot fully compensate, so it is important to thoroughly explain this to patients preoperatively³⁾.

4. Diagnosis and Examination Methods

Selection of IOL Power Calculation Formula

IOL power calculation formulas are classified by generation as follows.

• 1st generation: Fyodorov formula, Binkhorst formula, Colenbrander formula (theoretical formulas)
• 2nd generation: SRK formula (1980), SRKII formula (regression formulas)
• 3rd generation: SRK-T formula, Holladay1 formula, HofferQ formula (theoretical + regression)
• 4th generation: Holladay2 formula (multivariable)
• New generation (equivalent to 5th generation): Barrett Universal II, Hill-RBF (AI + radial basis function), Kane formula (AI + theoretical optics)

ESCRS guidelines recommend against using older generation formulas (SRK-II, SRK, Binkhorst, Hoffer, etc.) and recommend using new generation formulas (GRADE +)³⁾. ESCRS meta-analysis data reports Barrett Universal II MAE 0.314D (within ±0.5D: 82.1%), Haigis 0.346D (76.1%), Holladay2 0.351D, SRK/T 0.389D, Hoffer Q 0.409D, indicating superiority of new generation formulas³⁾.

For extremely long axial length (AL ≥30mm), AI-driven formulas significantly outperformed SRK/T: Kane formula MAE 0.51D, Hill-RBF 0.52D, Barrett II 0.66D, SRK/T 0.96D. For AL ≥32mm, Kane formula MAE 0.44D, with incidence of >±1.0D error reported as 42.5% for SRK/T versus 7.5% for AI-driven formulas⁴⁾.

For the MN60MA IOL group in extremely long axial length cases, the following results have been reported⁴⁾.

IOL formula	MAE (D)	MedAE (D)
SRK/T	0.86	0.77
Barrett Universal II	0.62	0.54
Hill-RBF	0.54	0.45
Kane formula	0.49	0.41

For short axial length and shallow anterior chamber (ACD < 2.5mm), HofferQ is recommended; for long axial length and deep anterior chamber (ACD > 3.5mm), Haigis; for steep cornea (>46D) or flat cornea (<38D), Barrett II (TK) and EVO (TK) are recommended³⁾. ESCRS online IOL calculator tool (https://iolcalculator.escrs.org/）の利用も推奨されている³⁾。

IOL calculation after corneal refractive surgery

In eyes after LASIK/PRK, the following points affect calculation accuracy.

• Underestimation of corneal power (after myopic correction) or overestimation (after hyperopic correction)
• Selection of correction algorithm: Barrett True-K (MAE 0.36D after myopic correction), Haigis-L (MAE 0.41D) are relatively accurate³⁾
• Double-K method, anterior segment OCT ray-tracing software (OKLIKUS), Calossi formula (IOL-Station), etc. are also used.
• Intraoperative aberrometry is useful after LASIK/PRK but has low accuracy after RK²⁾
• After radial keratotomy (RK), 83.4% show hyperopic error when targeting emmetropia. Changing to a myopic target can reduce hyperopic error to 42.0%³⁾

Evaluation for Toric IOL

Preoperative corneal astigmatism ≥1.5 D is found in 15–29% of cataract patients²⁾. Consider toric IOL for corneal astigmatism ≥1.0 D (GRADE ++)⁹⁾.

• Using formulas that measure and account for posterior corneal astigmatism (PCA) further reduces residual astigmatism⁸⁾
• Preoperative evaluation: corneal topography/tomography, posterior corneal astigmatism measurement with Scheimpflug camera, SIA nomogram
• Intraoperative aberrometry (OIA) can also be used for toric IOL alignment²⁾

5. Standard Treatment

Management of Residual Spherical Refractive Error

Glasses or contact lenses: First-line treatment for residual refractive error. Noninvasive and reliable. If contact lens use is difficult in elderly patients, consider surgical treatment.

Excimer laser (LASIK/PRK): Effective for cases with small residual refractive error. Can correct astigmatism and spherical error simultaneously. However, facilities with laser equipment are limited²⁾.

Femtosecond laser-assisted peripheral corneal incisions: Can correct astigmatism. Characterized by better incision accuracy and predictability compared to manual LRI.

IOL exchange: Optimal within 2–3 weeks postoperatively before anterior capsule closure begins. Most safe within 4 months postoperatively. The incidence of IOL dislocation/removal/exchange is reported to be 0.19–1.1% ²⁾.

Piggyback IOL (add-on lens): An option for high hyperopia when the available power range is exceeded. Placing one IOL in the capsular bag and one in the ciliary sulcus reduces the risk of intercapsular membrane formation. Refractive errors are less likely because the power can be determined based on subjective refraction ²⁾.

Suture removal: An effective method for reducing astigmatism when tight sutures cause significant induced astigmatism after extracapsular cataract extraction.

Precautions for IOL exchange

IOL exchange is recommended within 4 months postoperatively, but after 1 month, anterior capsule closure becomes stronger, making the procedure more difficult. If the capsular bag is damaged, suture fixation may be required, and there is a risk of decreased visual function compared to before surgery. The indication should be determined after thoroughly considering alternatives such as glasses or laser.

Management of residual astigmatism

眼鏡・コンタクトレンズ：保存的治療の第一選択。

トーリックIOL軸ずれ修正術：日本では6,431眼中42眼（0.653%）に施行されている。目標軸からの平均ずれは32.9 ± 15.7°（10〜74°）で、初回手術から平均9.9 ± 7.5日後に実施されている。術後1〜2週間以内なら水晶体囊との癒着はほとんどないため処置が容易。1度の軸ずれで矯正効果が約3%減少し、30度ずれで効果が消失する。長眼軸・直乱視眼では特に注意が必要である。

角膜弛緩切開術（LRI・AK）：少量の残余乱視に対して有効。白内障手術と同時施行が多く、高価な装置が不要という利点がある。ただしCochraneレビューでは、トーリックIOLの方が術後乱視0.5D以内を達成しやすい可能性が示されている¹⁰⁾。

エキシマレーザー（LASIK・PRK）：残余乱視が大きい場合に有効²⁾。

Q 両眼同日手術か、片眼ずつ手術するかで屈折誤差への対応は変わるか？

A

両眼手術を予定している場合、1眼目の屈折誤差を確認したうえで2眼目のIOL度数を調整できる。そのため1週間程度間隔を空けて手術することで屈折誤差を補正しやすくなる。特に多焦点IOL使用例や角膜屈折矯正手術後では間隔を設けることを検討すべきである。

Q By when should IOL exchange be performed?

A

The most convenient and ideal timing is within 2–3 weeks after surgery. It can be performed relatively safely within 4 months postoperatively. After that, fibrosis and adhesion of the anterior capsule become stronger, making the procedure difficult. If the refractive error is large and difficult to correct with glasses or other methods, it is important to consult the surgeon early.

6. Pathophysiology and Detailed Mechanisms

Mechanisms of IOL Power Calculation Error

IOL power calculation mainly depends on the following factors.

• Axial length (AL): Optical biometers have the advantages of being noninvasive, highly accurate, and free of inter-examiner variability. They are more accurate than ultrasound A-scan. Since optical biometers apply a single refractive index to the entire eye, they tend to overestimate axial length and underestimate IOL power in highly myopic eyes. Wang-Koch AL adjustment can be applied, but it is unnecessary for Barrett II, Hill-RBF, etc. ^{2, 7)}
• Corneal refractive power (K value): Calculated from anterior corneal curvature. Ideally, total corneal refractive power including the posterior cornea should be measured.
• Effective lens position (ELP) prediction: Estimation of the anteroposterior position where the IOL will be located postoperatively. Current formulas estimate ELP from axial length and K value, but this is the largest source of calculation error.

Conventional regression formulas (e.g., SRK/T) assume an average eye shape, leading to larger errors in cases of extremely long or short axial length, or flat or steep corneas. Barrett Universal II uses a multi-factor theoretical eye model, Hill-RBF uses radial basis function AI pattern recognition, and the Kane formula incorporates AI regression, theoretical optics, and sex, achieving higher accuracy especially in outlier axial length cases^{1, 4, 5, 6)}.

Hill-RBF shows no correlation with axial length (ρ = -0.088, p = 0.439) and is stable, whereas Barrett II shows a moderate positive correlation (ρ = 0.406), with some reports indicating a tendency toward hyperopic shift in longer eyes⁴⁾.

Mechanism of refractive error after corneal refractive surgery

In eyes after myopic LASIK, the anterior corneal surface is flattened and the refractive power ratio between the anterior and posterior surfaces changes. Standard keratometers cannot accurately capture this change, leading to underestimation of corneal power and resulting in postoperative hyperopic refractive error³⁾.

After hyperopic LASIK, the opposite phenomenon occurs, and the corneal refractive power is overestimated, making myopic errors more likely ³⁾.

Refractive error due to IOL decentration or tilt

When a 3-piece IOL is placed in the ciliary sulcus, anterior displacement of the IOL optic causes a myopic shift (0.5–1.0 D in an average eye) ²⁾.

7. Latest research and future perspectives (research-stage reports)

For patients: Please read this

The following content is currently in the research or clinical trial stage and is not standard treatment available at general hospitals. This is reference information for professionals regarding future medical developments.

光線調整レンズ（Light Adjustable Lens：LAL）

RxSight社のLALは、IOL挿入後に特定波長の光（紫外線）を照射することでIOLの屈折力を術後に調整できる光重合性シリコーン製レンズである。術後の調整により92%の患者で球面等価が±0.5D以内に収まり、91.6%で20/25以上の裸眼視力が達成されたと報告されている²⁾。球面・円柱成分の調整が可能であり、lock-in処理で最終屈折値が固定される。

なお、屈折率整形（refractive index shaping）と呼ばれるフェムト秒レーザーによるアクリルIOLの化学的変化を用いた手法も研究されており、球面・円柱・焦点数の変更が理論上可能とされているが、現時点では未市販である²⁾。

術中収差解析（Intraoperative Aberrometry：OIA）

術中に実際のIOL挿入前後の屈折状態をリアルタイムに計測し、IOL度数を最終選択する技術。949眼の検討では±0.5D以内がOIA 82%（Barrett II 84%）と同等であった¹²⁾。角膜屈折矯正手術後の症例での有用性が期待されており、トーリックIOLの軸合わせにも応用されている²⁾。

AI駆動IOL計算の今後

AI-driven formulas (Kane, Hill-RBF) significantly outperformed SRK/T in extremely long axial lengths (AL ≥ 30mm), reducing the incidence of refractive errors exceeding ±1.0D from 42.5% with SRK/T to 7.5% with AI formulas⁴⁾. Hill-RBF is expected to achieve further accuracy improvements through real-time data learning. Future large-scale studies are expected to further clarify the superiority among new-generation formulas³⁾.

8. References

1. Abdelghany AA, Alio JL. Surgical options for correction of refractive error following cataract surgery. Eye Vis (Lond). 2014;1:2. PMCID: PMC4604120. doi:10.1186/s40662-014-0002-2.
2. American Academy of Ophthalmology. Cataract in the Adult Eye Preferred Practice Pattern. Ophthalmology. 2021;128(1):P1-P228.
3. European Society of Cataract and Refractive Surgeons. ESCRS Guideline for Cataract Surgery. 2024.
4. Suzuki Y, Kamoi K, Uramoto K, Ohno-Matsui K. Artificial intelligence driven intraocular lens power calculation in extreme axial myopia. Sci Rep. 2025;15(1):36921. doi:10.1038/s41598-025-20899-6. PMID:41125680; PMCID:PMC12546796.
5. Melles RB, Holladay JT, Chang WJ. Accuracy of intraocular lens calculation formulas. Ophthalmology. 2018;125:169-178. doi:10.1016/j.ophtha.2017.08.027.
6. Savini G, Taroni L, Hoffer KJ. Recent developments in intraocular lens power calculation methods - update 2020. Ann Transl Med. 2020;8(22):1553. doi:10.21037/atm-20-2290. PMID:33313298; PMCID:PMC7729321.
7. Koch DD, Hill W, Abulafia A, Wang L. Pursuing perfection in intraocular lens calculations: I. Logical approach for classifying IOL calculation formulas. J Cataract Refract Surg. 2017;43(6):717-718. doi:10.1016/j.jcrs.2017.06.006. PMID:28732602.
8. Koch DD, Jenkins RB, Weikert MP, Yeu E, Wang L. Correcting astigmatism with toric intraocular lenses: effect of posterior corneal astigmatism. Journal of cataract and refractive surgery. 2013;39(12):1803-9. doi:10.1016/j.jcrs.2013.06.027. PMID:24169231.
9. Kessel L, Andresen J, Tendal B, Erngaard D, Flesner P, Hjortdal J. Toric Intraocular Lenses in the Correction of Astigmatism During Cataract Surgery: A Systematic Review and Meta-analysis. Ophthalmology. 2016;123(2):275-286. doi:10.1016/j.ophtha.2015.10.002. PMID:26601819.
10. Lake JC, Victor G, Clare G, Porfirio GJM, Kernohan A, Evans JR. Toric intraocular lens versus limbal relaxing incisions for corneal astigmatism after phacoemulsification. Cochrane Database Syst Rev. 2019;12:CD012801. PMID: 31845757. PMCID: PMC6916141. doi:10.1002/14651858.CD012801.pub2.
11. Lundström M, Barry P, Henry Y, et al. Evidence-based guidelines for cataract surgery: guidelines based on data in the European Registry of Quality Outcomes for Cataract and Refractive Surgery database. J Cataract Refract Surg. 2013;39:1485-1497.
12. Raufi N, James C, Kuo A, Vann R. Intraoperative aberrometry vs modern preoperative formulas in predicting intraocular lens power. Journal of cataract and refractive surgery. 2020;46(6):857-861. doi:10.1097/j.jcrs.0000000000000173. PMID:32176162.