Investigation into the influence of secondary suction within FLACS on the postoperative ocular surface and associated mechanisms

In FLACS, secondary suction may worsen early dry eye. Smaller corneal diameter and significant eye movement are risk factors.

Abstract

Purpose:

To explore secondary suction's impact on postoperative ocular surface, tear factors, and dry eye risk factors in femtosecond laser–assisted cataract surgery (FLACS).

Setting:

Xiamen Eye Center, Xiamen University, Xiamen, China.

Design:

Prospective cohort study; patients grouped by intraoperative secondary suction (no randomization/masking).

Methods:

Age-related patients with cataract undergoing FLACS (December 2023 to May 2024) were included (inclusion: FLACS consent, no prior eye surgery/trauma, and pupil dilation >7 mm; exclusion: ≥3 suction attempts, lens dislocation, pregnancy, psychiatric issues, and poor compliance). Preoperative parameters (corneal diameter and corneal keratometry value) and intraoperative eye movement were recorded. Ocular surface disease index (OSDI), tear meniscus height (TMH), and tear cytokines were assessed preoperatively and at 1 day, 1 week, and 1 month postsurgery.

Results:

41 patients (21 secondary suction, 20 conventional) were analyzed. The secondary suction group had higher 1-week OSDI (6.43 ± 7.96 vs 1.90 ± 5.85; P = .045), higher 1-week (0.04 ± 0.09 vs 0.01 ± 0.07 mm; P = .020) and 1-month TMH (0.07 ± 0.17 vs 0.03 ± 0.07 mm; P = .023), and greater tear interleukin-6 log increases at 1 day (0.44 ± 0.68 vs −0.04 ± 0.78; P = .042) and 1 week (0.01 ± 0.64 vs −0.49 ± 0.89; P = .045). Risk factors: smaller corneal diameter (P = .025) and obvious eye movement (P < .001).

Conclusions:

Secondary suction in FLACS may worsen early-stage postoperative dry eye, but it recovers in 1 month. Key risk factors for secondary suction include smaller corneal diameter and significant ocular movement, which inform targeted prevention strategies to reduce secondary suction incidence.

It is widely acknowledged that cataracts rank as the primary cause of blindness on a global scale.¹ Currently, the sole therapeutic approach for cataracts is the surgical extraction of the opaque lens followed by the implantation of an intraocular lens (IOL).² Cataract surgery may affect the normal physiological structure and function of the ocular surface and lead to a decline in the stability of the tear film, which may manifest in dry eye symptoms subsequent to phacoemulsification.^3–5 In the contemporary era, where cataract surgery has stepped into the age of femtosecond lasers, the demands of individuals regarding visual quality and ocular comfort have witnessed further elevation. Hence, it becomes of paramount importance to explore strategies for preventing and intervening in postoperative dry eye conditions.

In 2008, Nagy et al. first introduced and applied femtosecond lasers in key phacoemulsification steps, such as corneal incision, cataract fragmentation, and capsulorhexis.^6,7 Since then, many studies have favored femtosecond laser–assisted cataract surgery (FLACS) for cataracts.^8–10 Its advantages include efficient continuous circular capsulorhexis, reduced phacoemulsification time, and better IOL positioning.^11–13 During FLACS, the femtosecond laser emitter is attached to the ocular through a patient interface (PI). Then, anterior segment optical coherence tomography uses image data, including but not limited to corneal thickness measurements, to create a clear corneal incision, centered capsulorhexis, prefragment the nucleus, and even perform astigmatic keratotomy. The 2018 Chinese Expert Consensus on FLACS standardization noted “For functional IOLs, FLACS is recommended. A perfect anterior capsulotomy ensures lens centering and stability, likely leading to better results.”¹⁴ Studies indicate that FLACS has facilitated advancements in refractive outcomes, such as improved IOL centration and astigmatic keratotomy precision, positioning the technique as a key component in modern refractive cataract surgery protocols.^9,11,13,14

Post-FLACS dry eye etiology involves more than ocular surface damage, including tear film layer deficits impairing stability and increasing tear osmolarity.¹⁵ Corneal injury from surgery compression disrupts tear reflexes and repair. FLACS exacerbates inflammation through elevation of interleukin (IL)-6 or IL-8. In addition, to avoid intraoperative inflammatory miosis, the perioperative use of nonsteroidal anti-inflammatory drugs increases the chances of epithelial damage from preservative-laden formulations. In addition, studies have found that the development of dry eye may be associated with the concentration of vascular endothelial growth factor (VEGF) on the ocular surface.¹⁶ Hence, FLACS offers incision precision and reduced phacoemulsification energy but causes greater goblet cell injury and may lead to clinically significant dry eye.¹⁷

Previous studies show mixed results in comparing dry eye outcomes between FLACS and conventional phacoemulsification surgery (CPS), with both procedures known to be associated with postoperative dry eye. Two studies reported that dry eye symptoms after FLACS were less severe than those after CPS.^18,19 However, other retrieved articles suggested that FLACS may lead to more pronounced dry eye compared with CPS.^20–23 A careful review of these studies revealed that both procedures led to postoperative dry eye, with the difference only in the severity. Notably, previous studies have not explored the impact of PI suction attempts on dry eye. The unique PI-ocular surface interaction in FLACS remains uninvestigated regarding suction attempts in inflammation or tear dynamics, creating a critical knowledge gap.

The PI attachment, unique to FLACS, directly contacts the ocular surface. Evidence suggests it is a crucial factor in inducing dry eye.^15,23,24 Although most patients achieve successful PI attachment in a single attempt during FLACS, occasional suboptimal initial placement may require adjustments—such as readministering topical anesthesia to ensure patient comfort and conducting brief rehearsals of suction cooperation to guide patients in maintaining stable eye position—followed by a secondary suction procedure (referred to as “secondary suction”). Postoperative dry eye may relate to multiple factors. However, clinical observations of conjunctival hyperemia or subconjunctival hemorrhage after secondary suction—potential indicators of ocular surface trauma—suggest it may contribute to dry eye development through the damage of ocular structure.

In this study, we aim to explore whether the secondary suction group has more severe dry eyes and identify related risk factors. Based on previous studies, fluctuations in tear cytokine concentrations, as well as changes in key ocular surface indicators before and after surgery, will be analyzed.^15,16,25 This will clarify whether dry eye after FLACS correlates with negative pressure suction and its underlying mechanisms, providing a theoretical basis for the prevention and treatment of clinical dry eye.

METHODS

Research Participants and Grouping Criteria

A prospective cohort study was conducted. Patients with cataract visiting Xiamen Eye Center of Xiamen University from December 2023 to May 2024 and opting for femtosecond laser–assisted cataract surgery were enrolled. Groups were split based on the suction attempts at the procedure: the conventional suction group which proceeded with routine surgery and single suction and the secondary suction group which required reapplication after suction loss.

Inclusion criteria were (1) clinically diagnosed age-related cataracts, (2) voluntary acceptance of FLACS, (3) no prior ocular surgery or trauma history, and (4) normal pupils dilating more than 7 mm.

Exclusion criteria were (1) 3 or more suction attempts during surgery; (2) lens dislocation/subluxation needs extra steps such as iris hooks; (3) participants diagnosed with glaucoma; (4) individuals with preexisting ocular surface diseases, including but not limited to conjunctivitis, keratitis, and corneal leukoma; (5) participants diagnosed with autoimmune or systemic connective tissue disorders, such as lupus erythematosus, multiple sclerosis, rheumatoid arthritis, and ankylosing spondylitis; (6) pregnant women and individuals with psychiatric disorders defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, such as schizophrenia, bipolar disorder, and major depressive disorder requiring active treatment; (7) patients failing to attend scheduled postoperative follow-up visits at 1 week and 1 month; and (8) surgery complications such as posterior capsule rupture.

In this study, all patients participated voluntarily. This study adhered to the tenets of the Declaration of Helsinki, reviewed by the Ethics Committee of Xiamen Eye Center (Registration No.: XMYKZX-KY-2024-027; ChiCTR2400094804).

Specialist Examinations

All patients in this study underwent cataract-related ophthalmic specialist examinations. Their comprehensive basic information was collected, including age, sex, hypertension history, and smoking and drinking habits. The duration of femtosecond laser use during surgery and the occurrence of secondary suction were carefully recorded.

According to research requirements, patients had a series of evaluations and tests: ocular surface disease index (OSDI) assessment, Schirmer I test, tear film breakup time (TBUT), tear meniscus height (TMH), meibomian gland dropout area ratio determination, surface regularity index (SRI) measurement, lipid layer thickness (LLT) quantification, and inflammatory factor quantitative analysis by flow cytometry after tear sampling. These were performed at different times: before surgery, 1 day, 1 week, and 1 month postoperatively.

TBUT, TMH, and LLT were measured with the Oculus Keratograph 5M Ocular Surface Analyzer (Oculus Optikgeräte GmbH). The SRI was measured using the OPD-Scan III (Nidek Co., Ltd.). For the meibomian gland dropout area ratio, infrared images were exported to a PC and calculated through ImageJ software (v. 1.8.0_345).²⁶ Importantly, as the OSDI is a questionnaire for patients' dry eye symptoms in the past week, it was only statistically analyzed at 3 timepoints: preoperatively, 1 week, and 1 month postoperatively.

Intraoperative Ocular Movement Monitoring

The degree of ocular movement of patients was monitored with the assistance of the Catalys femtosecond laser system. As illustrated in Figure 1, when the patient's ocular had a slight movement, the yellow warning on the monitor would not be triggered. However, when the patient had a relatively obvious ocular movement under the negative pressure suction state, the yellow warning would be activated, alerting the surgeon that negative pressure loss might occur imminently. The incidence of flagged movement, as indicated by the yellow light, was counted for each procedure and included in analysis.

Figure 1.

It shows the ocular movement monitoring system of the Catalys femtosecond laser. According to the schematic diagrams of simulated human faces in the upper right corners of sections A and B, the surgical eye in the legend is the right eye. Among them, section A presents the ocular movement monitoring situation when the patient's right eye had a slight movement toward the temporal-superior direction. When the patient's right eye had an obvious movement toward the temporal-superior direction, the ocular movement monitoring system in the upper left corner of section B would trigger the yellow warning, notifying the surgeon that negative pressure loss might occur in this patient.

Tear Sampling and Flow Cytometry Detection

Tear sampling was conducted by gently inserting sterile 5 × 35 mm filter paper strips into the inferior fornix. Three samples per eye were placed into a modified 0.5 mL Eppendorf tube (bottom opening 1 mm), which was then nested in a 1.5 mL centrifuge tube and spun at 13 000 rpm for 1 minute. Fifteen microliters of the resultant tear fluid were analyzed through flow cytometry to quantify cytokines, including IL-1β, IL-5, IL-6, interferon, and VEGF, to analyze and reflect ocular surface inflammation.

Surgical Method

An experienced chief physician performed the surgery under topical anesthesia using the Catalys femtosecond laser (capsulorhexis diameter 5.2 mm, fragmentation diameter adaptive, 6–equal part mode). Subsequently, clear corneal incisions were made with a main and side incision scalpel. Then, a ophthalmic viscosurgical device agent was injected through the main incision using an ultrasonic emulsification instrument. After completing capsulorhexis, hydrodissection, nucleus fragmentation and aspiration, and cortex removal, an IOL was implanted, and the incision was hydrated and closed.

Of note, the femtosecond laser system used a ring-shaped PI, which exclusively engaged the conjunctiva, ensuring no direct contact with the corneal surface. This design feature minimizes the risk of iatrogenic corneal abrasions during the suction process.

Statistical Analysis

A power analysis was performed using G*Power 3.1.9.6 to determine sample size adequacy. Based on the observed incidence rate of secondary suction in our patient population (conventional suction group: 73%, secondary suction group: 22%), the study achieved a statistical power exceeding the conventional threshold of 80%.²⁷ It is important to note that the group-specific incidence rates reflect real-world clinical data because the universal prevalence of secondary suction remains unestablished. Despite sample size and incidence heterogeneity, this discrepancy represents natural real-world data fluctuations, with statistical power verified adequately by G*Power.

Data were processed using SPSS Statistics 26.0. Measurement data were described as mean ± SD. The independent-sample t test was used for between-group comparisons of measurement data. The self-matching control method was used to conduct intergroup comparisons using intraindividual changes from preoperation to postoperation in each group. Univariate regression analyzed risk factors, with P < .05 indicating significance. Multivariate regression was performed when risk factors were comparable and confounding. Some count data were presented as n1: n2 and tested by the 2 × 2 contingency table chi-square test; the Fisher exact test was used when the 2 × 2 contingency table sample size was <5. A P value less than 0.05 denoted a statistically significant difference.

RESULTS

Impact of Secondary Suction During FLACS on the Postoperative Ocular Surface

General Information

Of the initially recruited 50 patients, 2 individuals had pupils that failed to dilate beyond 7 mm before the surgery. One patient was diagnosed with Sjogren syndrome, another was detected to have subluxation of the lens during the surgical procedure, and 5 patients did not show up for the scheduled follow-up after the operation. Consequently, these 9 patients were excluded from the study. It is emphasized that all 9 excluded patients underwent successful single-attempt suction. Eventually, data from a total of 41 patients were gathered, with 21 patients constituting the secondary suction group and 20 patients making up the conventional suction group. Preoperative baseline data of both groups were collected, and the sociodemographic baseline values of the 2 groups are presented in Table 1.

Table 1.

Sociodemographic baseline values of the 2 groups

Index	Total sample (n = 41)	Secondary suction group (n = 21)	Conventional FS group (n = 20)	P value
Patient characteristics
Age (y)	66.68 ± 7.82	67.86 ± 6.89	65.45 ± 8.70	.331
Sex (M)	12 (29)	4 (19)	8 (40)	.141
Hypertension	16 (39)	8 (38)	8 (40)	.901
Smoking status	11 (27)	4 (19)	7 (35)	.249
Alcohol consumption status	11 (27)	4 (19)	7 (35)	.249
Ocular characteristics
Axial length (mm)	22.76 ± 1.30	22.58 ± 0.79	22.96 ± 1.68	.349
Corneal diameter (mm)	11.48 ± 0.45	11.32 ± 0.41	11.64 ± 0.44	.025*
Corneal flat axis K value	44.03 ± 1.83	44.57 ± 1.46	43.46 ± 2.04	.052
Corneal steep axis K value	44.75 ± 2.34	44.95 ± 2.56	44.54 ± 2.13	.586
OSDI	12.27 ± 9.92	12.62 ± 10.37	11.90 ± 9.67	.820
TBUT (s)	7.80 ± 2.51	8.06 ± 2.91	7.56 ± 2.09	.524
TMH (mm)	0.22 ± 0.75	0.21 ± 0.05	0.23 ± 0.09	.434
SIt (mm)	12.20 ± 6.40	12.43 ± 7.01	11.95 ± 5.85	.814
SRI	0.68 ± 0.45	0.70 ± 0.49	0.67 ± 0.43	.801
LLT (μm)	66.07 ± 27.73	67.85 ± 28.66	64.38 ± 27.40	.694
Meibomian gland deficiency area ratio	0.29 ± 0.12	0.33 ± 0.14	0.26 ± 0.08	.066
Tear cytokine concentration
log(Tear IL-6 concentration)	1.87 ± 0.77	1.71 ± 0.74	2.04 ± 0.78	.178
log(Tear VEGF concentration)	2.86 ± 0.52	2.91 ± 0.41	2.81 ± 0.62	.569

FS = femtosecond; IL = interleukin; LLT = lipid layer thickness; OSDI = ocular surface disease index; SIT = Schirmer I test; SRI = surface regularity index; TBUT = tear film breakup time; TMH = tear meniscus height; VEGF = vascular endothelial growth factor

Data are expressed as mean ± SD or n (%)

^*Statistically significant

Relevant data, including obvious ocular movement, femtosecond laser operation time, negative pressure duration, and total surgical time, were retrieved from the Catalys femtosecond laser platform system and the CENTURION phacoemulsification instrument system. The statistics of FLACS-related data for the 2 groups is shown in Table 2.

Table 2.

Statistics of FLACS-related data of the 2 groups

Index	Total sample (n = 41)	Secondary suction group (n = 21)	Conventional FS group (n = 20)	P value
Obvious ocular movement	18 (44)	15 (71)	3 (15)	<.001*
Femtosecond duration (s)	18.27 ± 5.95	15.64 ± 3.13	21.03 ± 6.97	.004*
Negative pressure duration (s)	99.68 ± 18.68	102.71 ± 23.81	96.50 ± 10.80	.287
Total surgical duration (min)	13.51 ± 1.43	14.05 ± 1.40	12.95 ± 1.28	.012*

FS = femtosecond.

Data are expressed as mean ± SD or n (%)

^*Statistically significant

Changes in Ocular Surface Indicators and Tear Cytokine Concentrations at Different Postoperative Periods in the 2 Groups

As demonstrated in Table 3, in the first week after the surgery, the OSDI score (P = .045) and TMH (P = .020) in the secondary suction group were markedly higher than those in the conventional suction group. At 1 month after the surgery, the TMH in the secondary suction group was significantly greater than that in the conventional suction group (P = .023). The alterations in tear cytokine concentrations at different postoperative periods for the 2 groups exhibited the following principal characteristics: On the first day after the surgery (P = .042) and during the first week after the surgery (P = .045), the concentration of IL-6 in the tears of the secondary suction group was considerably higher than that in the conventional suction group; however, at 1 month after the surgery, there was no statistically significant difference in the concentration of IL-6 in the tears between the 2 groups. No other significant differences were observed in the remaining indicators between the 2 groups. For detailed information regarding the forest plot, refer to Figure 2.

Table 3.

Changes in ocular surface indicators and tear cytokine concentrations at different postoperative periods in the 2 groups

Time and index	Groups
	Total sample (n = 41)	Secondary suction group (n = 21)	Conventional FS group (n = 20)	P value
1 d postoperatively
OSDI	N/A	N/A	N/A	N/A
TBUT (s)	0.38 ± 3.84	0.34 ± 3.25	0.41 ± 4.47	.955
TMH (mm)	0.04 ± 0.14	0.07 ± 0.16	0.01 ± 0.09	.153
SIt (mm)	−0.34 ± 6.10	0.48 ± 7.12	−1.20 ± 4.84	.386
SRI	0.15 ± 0.35	0.15 ± 0.44	0.15 ± 0.24	.988
LLT (μm)	20.24 ± 26.38	22.00 ± 23.61	18.40 ± 29.52	.668
log(Tear IL-6 concentration)	0.21 ± 0.76	0.44 ± 0.68	−0.04 ± 0.78	.042*
log(Tear VEGF concentration)	−0.18 ± 0.54	−0.20 ± 0.60	−0.16 ± 0.48	.778
1 wk postoperatively
OSDI	4.22 ± 7.29	6.43 ± 7.96	1.90 ± 5.85	.045*
TBUT (s)	−0.95 ± 3.09	−0.92 ± 2.30	−0.98 ± 3.81	.947
TMH (mm)	0.02 ± 0.08	0.04 ± 0.09	0.01 ± 0.07	.020*
SIt (mm)	−1.22 ± 5.83	−0.95 ± 6.60	−1.50 ± 5.06	.768
SRI	0.03 ± 0.33	0.01 ± 0.37	0.04 ± 0.28	.726
LLT (μm)	15.07 ± 31.49	16.86 ± 26.66	13.20 ± 36.49	.715
log(Tear IL-6 concentration)	−0.24 ± 0.80	0.01 ± 0.64	−0.49 ± 0.89	.045*
log(Tear VEGF concentration)	0.00 ± 0.48	−0.03 ± 0.50	0.03 ± 0.47	.705
1 mo postoperatively
OSDI	−1.00 ± 3.79	−1.00 ± 4.18	−1.00 ± 3.43	1.000
TBUT (s)	−0.81 ± 2.99	−0.37 ± 2.74	−1.27 ± 3.25	.342
TMH (mm)	0.02 ± 0.14	0.07 ± 0.17	0.03 ± 0.07	.023*
SIt (mm)	−1.78 ± 5.43	−1.86 ± 6.17	−1.70 ± 4.69	.928
SRI	−0.07 ± 0.34	−0.06 ± 0.41	−0.08 ± 0.27	.874
LLT (μm)	5.68 ± 27.75	3.57 ± 21.04	7.90 ± 33.84	.628
log(Tear IL-6 concentration)	−0.40 ± 0.75	−0.31 ± 0.70	−0.50 ± 0.81	.432
log(Tear VEGF concentration)	−0.35 ± 0.67	−0.26 ± 0.54	−0.44 ± 0.79	.419

FS = femtosecond; IL = interleukin; K = keratometry; LLT = lipid layer thickness; N/A = not applicable; OSDI = ocular surface disease index; SIT = Schirmer I test; SRI = surface regularity index; TBUT = tear film breakup time; TMH = tear meniscus height; VEGF = vascular endothelial growth factor.

Data are expressed as mean ± SD

^*Statistically significant

Figure 2.

Forest plot presents the results with statistical differences. In this figure, Group 1 denotes the secondary suction group, while Group 2 represents the conventional femtosecond group. IL = interleukin; OSDI = ocular surface disease index; TMH = tear meniscus height

Univariate Analysis of the Occurrence of Secondary Suction During FLACS

As indicated in Table 4, through univariate regression analysis, it was discovered that there were statistically significant differences between the 2 groups in corneal diameter (P = .025) and obvious ocular movement (P < .001). Specifically, the patients in the secondary suction group had a smaller corneal diameter and more significant ocular movement. Given the substantial impact of the ocular movement factor in this study, multivariate regression analysis was not performed.

Table 4.

Univariate regression analysis of the occurrence of secondary suction during FLACS

Index	Standardized coefficient	P value
Corneal diameter	0.350	.025*
Corneal flat axis K value	−0.306	.052
Obvious ocular movement	−0.568	<.001*
OSDI	−0.037	.820
TBUT	0.102	.524
TMH	0.128	.426
SIt	−0.038	.814
SRI	0.041	.801
LLT	0.063	.694
Meibomian gland deficiency area ratio	0.295	.061
log(Tear IL-6 concentration)	0.215	.178
log(Tear VEGF concentration)	−0.092	.569

IL = interleukin; K = keratometry; LLT = lipid layer thickness; OSDI = ocular surface disease index; SIT = Schirmer I test; SRI = surface regularity index; TBUT = tear film breakup time; TMH = tear meniscus height; VEGF = vascular endothelial growth factor

All factors involved in the analysis are presurgical indicators

^*Statistically significant

DISCUSSION

In ophthalmic surgery, FLACS is widely used for its precision and safety.²⁸ However, postoperative dry eye in some patients affects visual rehabilitation.²⁹ Dry eye pathogenesis is complex, involving tear dynamics and inflammation. With femtosecond technology progress, researchers note the PI's impact, yet few studies investigate the mechanism of FLACS-induced dry eye.²³ In the refractive cataract surgery, visual quality demands rise.^30,31 FLACS evolves, but postoperative dry eye from PI draws attention. This study used a prospective cohort design to investigate the impact of secondary suction on post-FLACS dry eye because the secondary suction procedure involves applying negative pressure to the ocular surface twice through the PI. Data were collected from 41 patients who underwent FLACS, with 21 assigned to the secondary suction group and 20 to the conventional suction. Although no literature defines FLACS secondary suction incidence, ours might be high due to center volume and patient traits. As a specialty clinic focusing on combined cataract and glaucoma cases, our patient population features a higher prevalence of anatomical variations such as smaller corneal diameters. Although this study excluded patients with glaucoma, the increased proportion of Asian patients with smaller corneal diameters still likely contributed to unstable negative pressure and subsequent need for secondary suction attempts.³² Notably, although clinical experience suggests that corneal diameters as small as 10 mm are encountered in Asian populations, the corneal diameters of participants in this study ranged from 10.8 mm to 12.4 mm.¹⁴ None of the participants had such extreme measurements as 10 mm. These findings underscore the importance of considering anatomical variability when interpreting the generalizability of our results.

Although baseline characteristics did not differ significantly between groups, subtle numerical variations in preoperative OSDI scores were noted. To mitigate potential confounding from these differences, priority was given to using intraindividual changes from preoperation to postoperation for all variables in intergroup comparisons. This approach aligns with best practices for longitudinal studies, replacing simple absolute value comparisons to reduce the impact of interindividual variability. For subjective measures such as OSDI, which are prone to interindividual variability, focusing on difference value rather than absolute values provides a more robust assessment of clinical relevance. Although the initial between-group baseline comparisons were nonsignificant, this analytical adjustment enhances the validity of our findings by accounting for real-world biological variation. Future studies with larger samples may clarify the impact of minor baseline discrepancies on treatment responses.

Postsurgery, OSDI scores rose in both secondary suction and conventional femtosecond groups, likely due to PI-induced ocular surface damage in FLACS worsening short-term dry eye.¹⁵ The secondary suction group's OSDI increase was more prominent 1-week postsurgery (P = .045) because the secondary suction might have further damaged the ocular surface, affecting the tear film and conjunctival goblet cells. By 1 month, scores in both groups declined with no significant difference (P = 1.000), perhaps because of corneal epithelial cell regeneration, conjunctival goblet cell function recovery, and ocular surface microenvironment stabilization. Corneal epithelial regeneration, driven by limbal stem cells, typically renews the epithelium within 4 to 7 days.³³ Previous studies found that conjunctival goblet cells, critical for mucin secretion, gradually restore density postsurgery, improving tear film stability and reducing OSDI scores.³⁴

In both groups, TMH increased postoperatively compared with baseline, potentially due to surgical trauma-induced ocular surface edema and inflammation leading to more tear accumulation.³⁵ The secondary suction group had a higher TMH rise at 1 week (P = .020) and 1 month (P = .023) postoperatively, possibly because of more severe ocular surface edema, greater impact on tear dynamics, or imbalance in tissue fluid exudation and reflux.³⁶ However, no statistical differences in TBUT, SRI, and Schirmer I test were found between the groups. Previous studies have reported conclusions similar to ours.²¹ We hypothesize that the transient increase in TMH at 1 day postoperatively may be attributed to pain and irritation from surgical manipulation, leading to artificially elevated tear lakes. The changes in TBUT suggest compromised tear film stability, potentially due to alterations in corneal surface curvature from the procedure or postoperative hyperemia and inflammatory edema. These factors may disrupt normal mucin secretion and reduce mucin adhesiveness, ultimately destabilizing the tear film.¹⁵

Comparing tear cytokine concentrations and ocular surface indicators, the secondary suction group had significantly higher IL-6 levels in tears 1-day and 1-week postsurgery, suggesting it exacerbated the short-term inflammatory response and potentially contributed to the OSDI and TMH changes at 1 week.³⁷ By 1 month, no IL-6 difference was noted, reflecting resolution of the inflammatory response or postoperative recovery. For VEGF in tears, no statistical differences were seen at any timepoint, implying a limited or complex relationship with ocular surface changes. This study mainly focused on IL-6 and VEGF fluctuations, while other cytokines such as IL-1β, IL-5, IL-8, and interferon, with no significant changes, were not further analyzed.

Previous studies suggest ocular surface immune disruption causes dry eye, related to cytokine changes such as IL-6 and VEGF.^38–49 Abnormal cytokine levels trigger inflammation, worsening dry eye.^50,51 Consistent with previous research, postoperation, OSDI scores of both groups aligned with tear IL-6 levels. In week 1, the secondary suction group's OSDI was higher, matching its day 1 higher IL-6. IL-6 declined by week 1 and stabilized at month 1, paralleling OSDI return to preoperative levels. Tear VEGF was higher at week 1 than on day 1, with no statistical difference between groups and similar changes from preoperation, indicating VEGF poorly reflects dry eye.

The use of VEGF as an observational marker in this study was inspired by its reported associations with dry eye in non-FLACS contexts, where altered VEGF concentrations have been tentatively linked to ocular surface inflammation. Although trend-level changes in VEGF were observed between preoperative and postoperative timepoints, the lack of statistical significance may reflect several possibilities: (1) VEGF may not be a primary contributor to dry eye pathogenesis after FLACS; (2) its role in dry eye could be more complex than mere concentration changes, involving spatiotemporal dynamics or interaction with other angiogenic or neurotrophic factors; and (3) early postoperative wound healing processes may have confounded VEGF expression patterns. Given the absence of previous studies investigating VEGF in FLACS-related dry eye, these findings should be interpreted cautiously. Future research involving larger cohorts, longitudinal sampling, or calibrating cytokine concentrations against tear volume collected per patient may clarify whether VEGF plays a nuanced role in FLACS-induced ocular surface dysfunction.

Through previous research and discussion, we know that secondary suction can exacerbate early postoperative dry eye symptoms after FLACS; thus, it is crucial to avoid secondary suction as much as possible. This study used univariate regression analysis identified smaller corneal diameter (P = .025) and significant ocular movement (P < .001) as independent risk factors for secondary suction. Although the corneal flat keratometry value approached statistical significance (P = .052), we observed a strong inverse correlation between corneal diameter and curvature (r = −0.592, P < .001), consistent with previous biomechanical studies.⁵² This relationship underscores that smaller corneas exhibit steeper curvatures, compromising PI stability by reducing surface contact area and increasing pressure gradients during negative pressure application.^53,54 Aligning with regression analysis, the findings highlight that preoperative discussion about the importance of patient fixation and stability during the procedure remain paramount. This may be more impactful in patients with smaller corneas.^55,56

It is noteworthy that the reason for not conducting a multivariate regression analysis is that the factor of “significant ocular movement during the surgical procedure” is overly significant in the univariate regression. If a multivariate regression analysis were performed, it might dilute the importance of other risk factors.

Nevertheless, this study was not without its limitations. One prominent constraint we encountered was the relatively limited sample size ultimately obtained. This factor potentially precluded the derivation of more precise conclusions in diverse aspects of data analysis. Second, during the experimental design phase, the significance of quantifying the volume of centrifuged tears was overlooked. This omission also exerted a certain degree of influence on the overall accuracy of the study results. Finally, a limitation is the lack of detailed corneal microscopy or slitlamp assessments to evaluate corneal abrasions, potentially affecting injury mechanism interpretation. Although a ring-shaped PI avoided direct corneal contact, corneal injury risk may still exist. Future research should use larger samples, quantify centrifuged tear volume, and conduct detailed corneal assessments to enhance accuracy and mechanistic understanding.

In summary, the secondary application of negative pressure suction with the PI during FLACS has been shown to aggravate dry eye symptoms in the early postoperative stage. It has been observed that the occurrence of postoperative dry eye is significantly influenced by the concentration of IL-6 in tears. Moreover, the key risk factors identified for the development of this condition are relatively smaller corneal diameter and pronounced ocular movement during the surgical procedure. Consequently, it is of utmost importance to enhance preoperative patient education to mitigate these risks.

WHAT WAS KNOWN

• Cataracts are a leading cause of blindness globally, and FLACS has become an important treatment option. FLACS offers advantages such as efficient capsulorhexis and better IOL positioning.

• Postoperative dry eye is a common issue after cataract surgery, and the patient interface used in FLACS may be a factor contributing to dry eye. Some patients require secondary suction during FLACS, but the impact of this on the ocular surface and tear factors is not well understood.

• Previous studies have delved into dry eye after FLACS. To date, no empirical investigation has specifically investigated the role of secondary suction and its related risk factors. Given that secondary suction is a real-world occurrence in clinical practice, this has led to a knowledge gap in effectively preventing and managing dry eye in FLACS patients who experience secondary suction.

WHAT THIS PAPER ADDS

• This study demonstrates that although both secondary suction and conventional suction in FLACS can exacerbate early postoperative dry eye, secondary suction significantly worsens symptoms, as shown by higher ocular surface disease index scores and tear meniscus height changes and is associated with increased tear interleukin-6 levels in the short term.

• Identifies key risk factors for secondary suction, namely, small corneal diameter and obvious eye movement during the operation. This knowledge can help surgeons identify high-risk patients in advance.

• Provides a basis for developing preventive strategies. By understanding these factors, preoperative patient education can be enhanced to reduce the risk of secondary suction and subsequent dry eye, potentially improving the overall surgical experience and visual outcomes for FLACS patients.