Binocular Diplopia After Cataract Surgery: Incidence and Associated Factors in a Tertiary Teaching Eye Center

Chayanan Wangpaitoon, M.D., Wasawat Sermsripong, M.D., Thammanoon Surachatkumtonekul, M.D.*

Department of Ophthalmology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.

*Corresponding author: Thammanoon Surachatkumtonekul E-mail: si95thim@gmail.com

Received 19 September 2025 Revised 26 December 2025 Accepted 26 December 2025 ORCID ID:http://orcid.org/0000-0002-0037-6863 https://doi.org/10.33192/smj.v78i2.277766

All material is licensed under terms of the Creative Commons Attribution 4.0 International (CC-BY-NC-ND 4.0) license unless otherwise stated.

ABSTRACT

Objective: To determine the incidence and risk factors for binocular diplopia following cataract surgery at Siriraj Hospital, Mahidol University.

Materials and Methods: This retrospective case–control study included patients who underwent cataract surgery between January 2000 and June 2023. Postoperative binocular diplopia was defined as symptomatic diplopia with documented ocular misalignment within 90 days of surgery, identified using ICD-10 codes. Demographic, systemic, biometric, and operative data were extracted. Each case was matched to ten controls by age, sex, and year of surgery. Statistical analyses included Chi-square tests, paired t-tests, and logistic regression.

Results: Among 90,885 cataract surgeries, 13 cases of postoperative binocular diplopia were identified, yielding an incidence of 0.0143%, substantially lower than previously reported rates (0.18–0.85%). The mean age of affected patients was 70.4 years, and 69.2% were female. Esotropia was the most common strabismic pattern (46.2%), while muscle restriction or paresis accounted for the majority of mechanisms (53.9%). Compared with matched controls, cases had significantly longer axial lengths (24.58 ± 2.30 mm vs. 23.40 ± 1.33 mm; p = 0.024), corresponding to an odds ratio of 1.426 (95% CI: 1.047–1.942) per millimeter increase. No significant associations were found with systemic comorbidities (diabetes, hypertension, dyslipidemia) or anesthesia type.

Conclusion: Postoperative binocular diplopia following cataract surgery was rare in this large tertiary-center cohort. Longer axial length was the only significant risk factor identified, suggesting a potential role of myopia-related extraocular muscle pathomechanics. Awareness of this risk factor may aid in preoperative counseling and surgical planning.

Keywords: Binocular diplopia; cataract surgery; complication; risk factors; axial length (Siriraj Med J 2026;78(2):133-141)

INTRODUCTION

Cataract surgery is the most frequently performed ophthalmic operation and typically restores excellent visual function.1 However, postoperative binocular diplopia — although uncommon — remains a clinically meaningful complication that can adversely affect patient-reported outcomes and functional vision.2 Reported incidence rates have varied across settings and time periods, partly due to evolving anesthesia practices and surgical techniques. Previous studies have reported the incidence of binocular diplopia after cataract surgery at 0.18% to 0.67% overall3-5, and 0.093% to 0.85% among patients receiving retrobulbar anesthesia.6,7 Contemporary large-scale data from Asian populations are limited, and potential risk markers have not been delineated with sufficient precision to guide preoperative counselling or risk stratification.8

Multiple pathophysiological pathways may contribute to diplopia following cataract surgery, including transient sensory disruption with loss of fusion, decompensation of pre-existing heterophoria or strabismus, restrictive or paretic extraocular muscle dysfunction, and abnormalities of the pulley or connective-tissue system. Ocular biometry may modulate susceptibility to these mechanisms. In particular, axial length (AL), a marker of myopic ocular anatomy, may influence extraocular muscle vector balance, pulley position, and fusional reserves, thereby plausibly increasing the risk of postoperative misalignment.2,8,9

However, the association between AL and postoperative binocular diplopia has not been systematically quantified.10 To address these gaps, we investigated the incidence of postoperative binocular diplopia and evaluated its risk factors in cataract surgeries performed at a tertiary eye centre over two decades (2000–2023). Using a retrospective matched case–control design nested within this cohort; we tested the prior hypothesis that greater AL is associated with increased odds of postoperative binocular diplopia and explored perioperative factors — including anesthesia type and surgical technique — as secondary exposures. Our objective was to generate precise, contemporary estimates and biologically coherent signals to guide preoperative counselling, inform clinical decision-making,

and motivate confirmatory studies.

MATERIALS AND METHODS

Study design

This investigation was a retrospective, individually matched case–control study of cataract surgeries performed at Siriraj Hospital, Bangkok, Thailand, between January 2000 and June 2023. The study protocol was approved by the Siriraj Institutional Review Board (IRB No. Si 760/2023) and was registered with the Thai Clinical Trials Registry (TCTR20231026007). The required sample size to ensure sufficient statistical power was calculated to be 85,901 participants.5,11

Data collection

Patient data were collected through a retrospective chart review using a standardized case record form. The source cohort included all lens-extraction procedures documented in institutional administrative and clinical databases during the study period. Procedures were identified using relevant ICD-9 procedure codes. Clinical variables were abstracted from the electronic medical record using a prespecified data dictionary and identified based on ICD-9 procedure codes for lens extraction:

• 131: Intracapsular extraction of the lens

• 132: Extracapsular extraction of the lens by linear extraction technique

• 133: Extracapsular extraction of the lens by simple aspiration and irrigation

• 134: Extracapsular extraction of the lens by fragmentation and aspiration technique

• 135: Other extracapsular extraction of the lens

• 136: Other cataract extraction

  This search yielded a total cohort of 90,885 cataract surgery patients.

  The outcome of interest was postoperative binocular diplopia occurring within 90 days of cataract surgery.9,20 Potential cases were identified by ICD-10 diagnostic codes for diplopia, strabismus, or ocular motor nerve palsy and were verified by manual chart review. A confirmed case required: (i) patient-reported binocular diplopia, and

  (ii) documented ocular misalignment on examination within 90 days after the index surgery. Encounters indicating monocular diplopia were excluded a priori. If multiple qualifying encounters were present, the earliest encounter was designated as the case index date. The diagnostic codes used were:

• H49.0: Third (oculomotor) nerve palsy

• H49.1: Fourth (trochlear) nerve palsy

• H49.2: Sixth (abducent) nerve palsy

• H51: Other disorders of binocular movement

• H53.2: Diplopia

• H53.3: Other disorders of binocular vision

For each confirmed case, ten controls13 without evidence of postoperative binocular diplopia were randomly sampled from the source cohort. Controls were individually matched to each case by sex, age, and year of surgery to account for demographic differences and secular trends. Each case and its matched controls formed a matched set. Controls were required to meet cohort eligibility and to have no conflicting outcome codes within 90 days of surgery.

Prespecified variables included demographics (age, sex), systemic comorbidities (diabetes mellitus, hypertension, dyslipidaemia), ocular biometry — particularly axial length

(AL; millimetres) — and perioperative factors (anesthesia type: topical, sub-Tenon, peribulbar, retrobulbar, or general; surgical technique: phacoemulsification, extracapsular cataract extraction, or other). Where available, ocular alignment patterns (e.g., esotropia, exotropia, vertical deviations) and clinical mechanisms (restriction versus paresis) were also recorded. Ocular biometry reflected routine preoperative measurements obtained as part of standard care.

Matching by age, sex, and surgery year was used to reduce confounding and mitigate secular trend bias. The outcome definition combined patient-reported symptoms with objective documentation to minimize misclassification. A 90-day attribution window was prespecified to support temporal plausibility. Planned sensitivity analyses (described below) assessed the impact of outcome definition stringency and temporal effects.

Statistical analysis

Categorical variables were summarized as frequencies and percentages, and continuous variables as means with standard deviations. The primary outcome, the incidence of postoperative binocular diplopia, was reported as a proportion. Secondary analyses compared cases and controls using Chi-square tests for categorical variables and paired t-tests for continuous variables. Logistic regression analysis was subsequently performed to evaluate the association between axial length and postoperative binocular diplopia. A two-sided p-value of less than 0.05 was considered statistically significant.

RESULTS

During the study period, 90,885 cataract surgeries were recorded at Siriraj Hospital, Bangkok, Thailand. Thirteen patients met the prespecified case definition of postoperative binocular diplopia within 90 days and were each matched to ten controls by age, sex, and year of surgery (Table 1).

The incidence of postoperative binocular diplopia was 0.0143%, indicating an exceedingly rare complication in contemporary practice.

Baseline characteristics

Matched variables (age, sex, year) were comparable by design (Table 1). The mean age of patients in the case group was 70.38 ± 8.92 years, and nine of the 13 patients (69.23%) were female. The prevalence of common systemic comorbidities (diabetes mellitus, hypertension, dyslipidaemia) did not differ meaningfully between groups (Table 1).

TABLE 1. Baseline characteristics.

Data are presented as mean ± standard deviation.

* Paired-sample t-test

Associated factors

Analysis of associated factors revealed that longer axial length was significantly associated with the development of postoperative binocular diplopia. The mean axial length was 24.58 ± 2.30 mm in the case group compared to 23.40 ± 1.33 mm in the control group (p = 0.024). In regression analyses, each 1 mm increase in axial length was associated with higher odds of postoperative binocular diplopia (odds ratio 1.43, 95% CI 1.05–1.94).

Operative details

Distributions of anesthesia type and surgical technique are summarised in Table 2. Comparisons across anesthesia categories were limited by small cell counts, resulting in imprecise effect estimates and no consistent associations.

Clinical presentation

Among the 13 patients who developed postoperative binocular diplopia, six (46.2%) demonstrated esotropia (ET), three (23.1%) exhibited exotropia (XT), and four (30.8%) presented with combined horizontal and vertical strabismus. The most frequently identified etiology was extraocular muscle restriction or paresis, observed in seven patients (53.8%), followed by decompensation of pre-existing strabismus in four patients (30.8%). Management was predominantly conservative, with

10 patients (76.9%) undergoing observation alone and three patients (23.1%) receiving prism therapy. (Table 3)

DISCUSSION

Our study is centered on an Asian population, in contrast to prior research, which has predominantly focused on Western populations. In this single-center cohort, new-onset binocular diplopia after cataract surgery was uncommon but clinically meaningful. The preponderance of vertical deviations and the observed association with regional (needle) anesthesia are directionally concordant with prior series, in which extraocular-muscle (EOM) dysfunction — most often involving the inferior rectus — dominates the phenotype.5,9,13–15 Decompensation of latent strabismus and sensory fusion disturbances accounted for a nontrivial subset, consistent with orthoptic clinic–based reviews.9,16 Our finding linking longer axial length with postoperative diplopia is biologically plausible in the context of high-myopia–related EOM pathomechanics and pulley displacement, which predispose to acquired strabismus patterns.10,17,23 The low incidence may be attributed to the study population having a small angle of deviation, and the fact that these patients were not examined by a pediatric ophthalmologist, which could have led to the condition being undetected by the examining physician. Other reasons for the low incidence may arise from variations in data collection methods, as well as from

TABLE 2. Operative details.

Note: Data are presented as number (%).

† Chi-square test

Abbreviations: ECCE = extracapsular cataract extraction; IOL = intraocular lens; CCC = continuous curvilinear capsulorhexis; GA = general anesthesia. ed = eye drop

Wangpaitoon et al.

TABLE 3. Baseline characteristics, operative details and diplopia details of cases.

Abbreviations: M=Male, F=Female, DM = Diabetes Mellitus, HT = Hypertension, DLP = Dyslipidemia, AXL = Axial Length, LE= Left eye, RE = Right eye, ECCE+IOL = Extracapsular cataract extraction with intraocular lens, PE+IOL = phacoemulsification with intraocular lens, XT = Exotropia, ET = Esotropia, ed = eye drops

differences in the population groups with distinct ethnic backgrounds, which can lead to anatomical variations in the eyes. Additionally, differing inclusion criteria can also have a significant impact on the results.

How do these results compare with existing literature?

Large case reviews suggest that most post-cataract diplopia arises from two main mechanisms: (i) anesthesia-related myotoxicity or direct EOM injury, and

(ii) decompensation of pre-existing ocular misalignment once blur/aniseikonia and sensory deprivation are relieved. In the largest orthoptic clinic series (n=150), decompensation of preexisting strabismus accounted for approximately 34% of cases, whereas restriction/paresis comprised about 25%; notably, the introduction of topical anesthesia shifted the case-mix toward decompensation rather than restriction.9 A Spanish hospital series of 3,542 cases reported significantly higher diplopia rates after regional compared with topical anesthesia (21/2,122 vs 3/1,420; P=0.005), with all motility-related cases confined to the regional group.5 Furthermore, peribulbar anesthesia without hyaluronidase was associated with a sharp rise in diplopia (0.75%), implicating reduced injectate dispersion and focal myotoxicity; reintroduction of hyaluronidase eliminated observed cases.18 Dedicated neuroophthalmology referral cohorts after cataract surgery have likewise identified decompensated strabismus as the most common efferent cause of postoperative visual disturbance.19

Pathophysiological considerations

Regional anesthesia can damage EOMs through mechanical needle trauma, vascular compromise, or myotoxicity from local anesthetics, resulting in contracture, paresis, or both. Classic patterns include inferior rectus overaction/underaction with subsequent spread of comitance over time.9,13–15 In contrast, under topical-only anesthesia, diplopia more often reflects the unmasking of latent deviations when fusion demands change postoperatively.9,16,19 In highly myopic eyes, axial elongation displaces the globe relative to the rectus pulleys, producing characteristic heavy-eye or related sagging-eye syndromes with vertical/horizontal incomitance. Such anatomical changes plausibly lower the threshold for postoperative decompensation when sensory cues shift after lens extraction.10,17,23

Clinical implications Preoperative screening

Our data support the value of short preoperative assessments of refractive error, anisometropia, amblyopia

and alignment assessment, including cover-alternate cover testing at distance/near, vertical offset checks, and a history review for childhood strabismus or prism wear, along with targeted counseling for patients with long axial length or orthoptic risk markers.9,17,19,21,22

An increased axial length complicates cataract surgery, and at the same time, patients with high myopia due to elongated axial length are at risk of developing strabismus. This may result from abnormal pulley system function, soft tissue irregularities around the eye, or anisometropia and amblyopia, which depend on the degree of anisometropia and amblyopia. These conditions lead to the loss of binocular function, which can cause the transition from phoria to tropia after cataract surgery, especially when one eye is occluded, disrupting binocular function.

Anesthesia choice and technique

For patients at elevated risk (e.g., high axial length, prior strabismus, restrictive motility, or anticipated difficult block), topical anesthesia (with or without intracameral supplementation) should be preferred when surgically feasible.5 Where regional anesthesia is indicated, standardized low-volume peribulbar techniques with hyaluronidase appear protective and should be protocolized.18

Early recognition and management

Early orthoptic assessment can help differentiate transient sensory phenomena from myotoxic patterns. Prism therapy is effective for many comitant deviations.9 Persistent restrictive or vertical incomitance warrants imaging and, when stable, tailored strabismus surgery; inferior rectus recession and related procedures have shown favorable outcomes in selected cases.9,13,15

LIMITATIONS

Diplopia that was transient, rapidly resolved, or managed without a specific ICD-10 code for strabismus/ diplopia might have been missed, potentially leading to underreporting of the true incidence.

Other factors, such as underlying diseases, which were found to be non-significant, may in fact be associated factors. However, the extremely small sample size (13 cases) may have limited the ability to detect significant associations. Additionally, although axial length was found to be significant, the results cannot be conclusive due to the small sample size. The research team acknowledges that future studies with a larger sample size will be necessary to further explore and identify the associated factors of binocular diplopia following cataract surgery.

Wangpaitoon et al.

CONCLUSIONS

In this large, single-center cohort, postoperative binocular diplopia following cataract surgery was exceedingly rare, yet matched analyses suggested that longer axial length was associated with increased odds of this complication. The clinical phenotype was dominated by vertical deviations with features of restrictive or paretic extraocular muscle dysfunction, alongside a subset attributable to decompensation of latent strabismus. Given the sparse number of events, effect estimates carry substantial uncertainty and should be interpreted as hypothesis-generating signals rather than definitive causal effects. Pragmatic implications include brief preoperative alignment screening, axial-length-informed counselling, preference for topical anesthesia when feasible in higher-risk profiles, and early orthoptic assessment when symptoms arise. Validation in multicenter cohorts using rare-event-robust, match-aware methods and standardized orthoptic assessments is warranted.

Data Availability Statement

The datasets underlying this article are available from the corresponding author upon reasonable request and subject to institutional approval and data-sharing agreements.

ACKNOWLEDGEMENT

Suchawadee Leelasrisoonton assisted with manuscript preparation.

DECLARATIONS

Grants and Funding Information

This research received no external funding.

Conflicts of Interest

The authors declare no conflicts of interest related to this publication.

Registration Number of Clinical Trial

Not applicable. This was a retrospective study and was not registered as a clinical trial.

Author Contributions

General research process and framework of the study, T.S., W.S. ; Investigation, Data collection and Data analysis, C.W. ; Writing-original draft preparation, review and editing, T.S., C.W. ; supervision, T.S. All authors read and approved the final manuscript.

Use of Artificial Intelligence

During preparation of the manuscript, the authors

used Grammarly and ChatGPT 5.2 to refine grammar and enhance readability.

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23. ธรรมนูญ สุรชาติกำาธรกุล. ภาวะตาเหล่ในผู้ป่วยสายตาสั้นมาก. ใน: ศักดิ์ชัย วงศกิตติรักษ์ ธนาพงษ์ สมกิจรุ่งโรจน์, บรรณาธิการ. จักษุวิชาการ โดย ราชวิทยาลัยจักษุแพทย์แห่งประเทศไทย เล่ม 7. กรุงเทพฯ: โรงพิมพ์มหาวิทยาลัย ธรรมศาสตร์; 2566. หน้า 153-66. (In Thai)