Efficiency and safety of argon laser in trichiasis: A systematic review and meta-analysis

Abstract

To conduct a systematic review and meta-analysis evaluating the efficacy and safety outcomes of argon laser treatment for trichiasis, a common eye condition that can lead to blindness. We conducted a systematic review and meta-analysis. PubMed, Cochrane Library, Science Direct, Embase, and ClinicalTrials.gov databases were searched for studies on argon laser treatment of trichiasis, without language restriction, up to March 2025. We computed random-effect meta-analysis and meta-regressions on putative influencing factors. The PRISMA guidelines were followed. The meta-analysis was registered on PROSPERO (ID: CRD42024546074). Twenty-seven articles were included in the systematic review, and 20 in the meta-analysis, for a total of 1044 patients. The prevalence of trichiasis recurrence at the end of follow-up was 4.1% (95% CI 2.7 to 5.5%), ranging from 0% to 37.7%, reflecting substantial heterogeneity between studies (I2 91.5%). After only one session, the prevalence of trichiasis recurrence was 35.8% (25.9 to 45.7%, I2 91.5%). The prevalence of lid complications was 0.1% (-0.2 to 0.5%). Reported complications included notching (0.1%; 95% CI, -0.2% to 0.5%), hypopigmentation (0.0%; 95% CI, -0.1% to 0.2%), and rash (0.0%; 95% CI, -0.3% to 0.3%). The prevalence of pain was 0.0% (-0.1 to 0.2%). The certainty of the evidence was assessed using the GRADE approach, and most outcomes were rated as low certainty due to limitations in study design and heterogeneity. Argon laser for trichiasis is an effective procedure, but several sessions may be necessary. The safety profile of this technique is very good with few and mild complications.

Trichiasis is a common pathology in ophthalmology,[1] characterized by misdirected eyelashes, leading to their distal ends abrading the ocular surface. Persistent mechanical irritation from aberrant lashes can lead to corneal epithelial damage, ulceration, and stromal opacification over time,[2] leading to significant visual loss.[3] Various etiologies can induce trichiasis, in particular chronic blepharoconjunctivitis, ocular pemphigoid, trauma, and trachoma, especially in developing countries.[4] Surgical intervention is the primary approach for managing trichiasis in patients with numerous misaligned lashes or advanced disease stages, a strategy widely accepted in clinical practice.[5,6,7,8] However, for patients with a limited number of pathological eyelashes, an array of treatment modalities has been proposed, including radiofrequency, cryotherapy, electrocoagulation, mechanical epilation, and photocoagulation.[8,9] Radiofrequency and cryotherapy may result in scarring,[10,11] whereas electrocoagulation has a lower success rate.[12] Mechanical epilation provides temporary relief but requires frequent follow-up due to the high recurrence rates.[13] Therefore, photocoagulation using an argon laser is a common and favored approach that can be easily implemented in conventional clinical settings. Photocoagulation targets the affected lash and its follicle using a series of laser pulses to obliterate them effectively.[14] Despite its widespread adoption since the 1970s, the efficacy and safety profile of argon laser photocoagulation for trichiasis management remain subjects of ongoing discussion, particularly regarding recurrence rates and potential adverse effects.[15] While the influence of factors such as age, sex, and anesthesia on argon laser photocoagulation outcomes for trichiasis remains unclear, existing evidence suggests optimal treatment parameters include high power settings and depths around 3 millimeters.[16,17] Furthermore, etiologies associated with herpes group viruses and chemical burns, as well as prior invasive treatments such as surgery and cryotherapy, appear to be associated with an increased risk of recurrence.[18] Therefore, the primary characterized objective of this study was to conduct a systematic review and meta-analysis to determine the recurrence rate following argon laser treatment for trichiasis. Secondary aims were to evaluate the recurrence rate based on the number of argon laser sessions, potential adverse effects, and factors that may influence the efficacy and safety of argon laser treatment for trichiasis.

Methods

Literature search

The meta-analysis was registered on PROSPERO (ID: CRD42024546074). All prospective and retrospective studies involving patients with trichiasis undergoing argon laser procedure were included if they reported recurrence rate of trichiasis or number of patients who had a recurrence of trichiasis. We searched PubMed, ScienceDirect, Cochrane Library, Embase, and ClinicalTrials.gov until March 15, 2025, with the following keywords: trichias* AND (argon OR laser OR photocoagulation). No language, date, or publication status restrictions were applied [details of the search strategy are available in Appendix 1]. We included any type of study with original data reporting at least our main outcome, that is, recurrence of trichiasis. More specifically, we included retrospective and prospective cohorts as well as randomized controlled trials (RCTs) but not case reports. We did not limit our search to specific languages, dates, or minimal sample of patients. Reference lists of all included publications were manually searched to identify any further studies that were not found using the electronic search. The search strategy is presented in Fig. 1. Two authors (Louis Escassut and Adrien Franceschino) conducted all literature searches, independently reviewed abstracts, and determined article suitability based on selection criteria. A third author (Frédéric Dutheil) reviewed articles where consensus on suitability was debated. Then, all authors reviewed eligible articles. We followed the guidelines outlined by Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Figure 1.

Search strategy. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for the search strategy

Data extraction

The collected data included first author’s name, publication year and dates of study conduction, country, continent, study design, aims and outcomes of included articles, age, sex, sample size (number of patients, eyes, lids, and lashes), comorbidities (general and ophthalmic), etiologies and preceding treatment of trichiasis, parameters of photocoagulation (spot size, number of shots, duration and power of shot, crater depth, with or without anesthesia), recurrence of trichiasis after one and all sessions, maximum number of interventions, complications (notching, rash, hypopigmentation, pain, etc.), postprocedure treatment, and duration of follow-up.

Definition of recurrence

Given the variability in recurrence definitions across studies, we adopted a standardized approach where recurrence was defined as the reappearance of any misdirected eyelashes in previously treated areas at follow-up examination. Studies reporting “success rates” were included with recurrence calculated as the inverse proportion.

Quality assessment

We used the Scottish Intercollegiate Guidelines Network (SIGN) checklist to assess the quality of included studies. The SIGN checklist has 17 questions for cohort studies and 13 questions for RCT, with 3 or 4 answers possible: Yes, No, Can’t say, or Does not apply [Fig. 2].[19] We further used the Newcastle-Ottawa Scale (NOS) for observational studies,[20] and the Risk of Bias 2 (RoB 2) scale for RCT [Appendix 2].[20] To calculate overall scores on these scales, we determined the percentage of acceptable values for each item. Only items relevant to each study were considered, and items not applicable to some studies were excluded from the calculation. The evidence synthesis for this review was conducted in accordance with the Grading of Recommendations Assessment, Development and Evaluation (GRADE) guidelines[21] [Appendix 3].

Figure 2.

Methodological quality of included articles using the Scottish Intercollegiate Guidelines Network (SIGN) checklists. The SIGN grid for cohort studies consists of 14 items, and the SIGN grid for randomized controlled trials consists of 9 items, evaluating the main causes of bias through 4 possible answers (yes, no, can’t say, or not applicable)

Statistical considerations

Statistical analysis was conducted using Stata software (v16, StataCorp, College Station, US). Data were summarized as mean ± standard deviation for continuous variables and as number (%) for categorical variables. The prevalence of trichiasis recurrence after all treatment sessions and 95% confidence intervals (95% CI) were estimated using random-effects models to address study variability. We also performed a meta-analysis on recurrence after one session and on prevalence of complications (notching, hypopigmentation, rash, and pain). Heterogeneity was assessed using forest plots, 95% CI, and the I-squared (I²) statistic, categorized as low (I² <25%), moderate (25–50%), or high (>50%). For rigor, we also computed metafunnels to search for potential publication bias. Sensitivity analyses excluded unevenly distributed studies and studies outside the base of the metafunnels. Meta-regressions were conducted to investigate factors affecting the prevalence of recurrence: age, sex, sample size (number of patients, eyes, eyelids, and lashes), comorbidities (general and ophthalmic), etiologies and preceding treatment of trichiasis, parameters of photocoagulation (spot size, number of shots, duration and power of shot, crater depth, with or without anesthesia), recurrence of trichiasis after one and all sessions, maximum number of interventions, complications (notching, rash, hypopigmentation, pain, etc.), postprocedure treatment, and duration of follow-up. Results were expressed as regression coefficients with 95% CI, and a Type I error rate was set at α = 0.05.

Results

The initial search yielded 902 articles. After applying the inclusion criteria, and after removing redundant data or full-text not available, 20 studies were included in the meta-analysis [Fig. 1].[4,9,14,16,18,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36] All articles were written in English, except three in French[18,34,35] and one in Portuguese.[36] Main characteristics of studies included are presented in Table 1.

Table 1.

Characteristics of included studies

Study		Design		Control Group		Country		Follow-up, months		Characteristics of patients						Laser procedure
										n patients		Age		Sex		Spot size (µm)		Power (mW)		Duration (s)		n shots		Postoperative		Anesthesia
								Mean (min-max)		(n lids)		Mean (min-max)		(% men)		Mean (min-max)		Mean (min-max)		Mean (min-max)		Mean (min-max)		treatment*
Al-Bdour 2007		Prospective		-		Jordan		8		54 (68)		53 (-)		44.0		? (50-100)		500		0.3		? (30-40)		Antibiotics/Corticosteroids – 7 days		Topical + Local
Awan 1988		Prospective		-		USA		? (3-24)		31		? (-81)		64.3		? (50-200)		? (1000-1200)		? (0.1-0.2)		? (12-50)		?		Topical
Bartley 1991		Prospective		-		USA		13 (1-48)		44		63 (30-86)		38.6		? (50-100)		1000		0.2		? (20-30)		Antibiotics/Corticosteroids – 7 days		Local
Basar 2000		Prospective		-		Turkey		6 (4-12)		45 (60)		55 (35-82)		31.1		? (100-200)		? (1000-1200)		0.2		20		Antibiotics – 7 days		Topical
Bellamine 2022		Retrospective		-		Morocco		? (?-9)		201 (230)		59		?		? (50-100)		? (500-1000)		? (0.1-0.2)		? (10-30)		Antibiotics/Corticosteroids – 10–20 days		Local
Berry 1979		Prospective		-		USA		6		8		?		?		? (50-100)		?		?		?		?		Local
Campbell 1990		Retrospective		-		New Zealand		? (3-6)		12 (15)		? (56-87)		?		? (50-100)		? (1200-2000)		? (0.05-0.1)		? (15-60)		Antibiotic – At the end of the procedure		Topical
Gossman 1992		Prospective		-		USA		7.9		54 (60)		?		?		? (100-200)		1500		0.5		?		Erythromycin ointment – 4 days		Topical + Local
Hata 1999		Prospective		-		Brasil		4		68 (77)		68 (42-87)		39.0		50		? (600-1000)		0.2		31		Chloramphenicol – 5 days		Topical
Huneke 1992		Retrospective		-		USA		1		77		76.3 (22-94)		53.2		50		300		0.5		39.4 (2-77)		Warm compresses – 5 days		Topical + Local
Ladas 1993		Prospective		-		Greece		18 (12-36)		78		66.2 (58-83)		57.7		? (50-100)		? (800-1200)		? (0.1-0.2)		?		Antibiotics/Corticosteroids – 7 days		None
Oshry 1994		Prospective		-		Israel		5.875		17		?		?		50		? (800-1400)		0.2		? (15-20)		Chloramphenicol/Polymixin B – 3 days		Topical
Reck 1993		Prospective		-		UK		?		30		?		?		50		1000		0.1		31		None		None
Salour 2011		RCT		X		Iran		3		52		54.8		44.2		50		760		?		?		Tetracycline – 6 hours		Topical
Schapiro 2007		Retrospective		-		France		?		60 (85)		?		?						?		?		?		?
Sharif 1991		Prospective		-		UK		6.57 (2-12)		21 (28)		67.3 (50-86)		52.4		? (50-200)		? (1000-1200)		0.2		20		Antibiotics – 7 days		None
Unlü 2000		Prospective		-		Turkey		10.6 (6-22)		22 (36)		64.9 (49-71)		36.4		? (50-200)		? (1000-1200)		0.2		17.3		Antibiotics/Corticosteroids – 5 days		Local
Yeung 1995		Prospective		-		Hong Kong				? (107)		?		?		100		? (1000-1200)		0.2		?		?		Topical + Local
Yung 1994		Prospective		-		USA		3		8 (8)		57.1 (31-79)		?		? (100-200)		1000		0.5		?		Antibiotics – 7 days		Topical + Local
Zenjouri 2015		Prospective		-		Morocco		6		55 (75)		53		56.0		? (50-100)		? (500-1200)		0.2		? (10-30)		Antibiotics/Corticosteroids – 7 days		Local

*All topicals were ointment, except in Oshry 1994 that also used chloramphenicol drops

Risk of bias assessment

Using the SIGN checklists, the overall quality of the 19 cohort studies was moderate, with a mean score of 55.5 ± 11.6%, ranging from 41.6%[14,31] to 72.7%,[36] and the RCT scored 81.8%.[22] The main limitation noted was the lack of control cases [Fig. 2 and Appendix 2]. Using the NOS checklist, cohort studies had a mean score of 93.9 ± 10.0% ranging from 66.7[31] to 100%.[4,9,18,24,26,27,28,29,30,32,33,34,35] Using the ROB scale, the RCT had a mean score of 83%[22] [Appendix 2]. The certainty of the evidence (GRADE) was rated as low for our main outcome and for most secondary outcomes [Appendix 3].

Study designs, geographic zones, and follow-up

All were either prospective[4,9,14,18,24,25,26,27,28,29,30,31,32,33,36] or retrospective[16,23,34,35] without controls, except for one double-blind randomized clinical trial.[22] Six of the included studies were from North America[14,16,24,25,30,32] (all from the United States), one from South America (Brazil),[36] six from Europe (France, United Kingdom, Turkey, and Greece),[4,26,28,29,33,34] two from Africa (Morocco),[18,35] one from Oceania (New Zealand),[23] and four from Asia (Jordan, Iran, Hong Kong, and Israel).[9,22,27,31] The follow-up duration ranged from 1[16,25] to 48 months [Table 1].[25]

Inclusion and exclusion criteria of the included studies

The common inclusion criteria were recurrent trichiasis without further details, except two studies that included only trachomatous trichiasis,[27,29] and two studies including patients after epilation[28,32] or electrolysis[28] failure. Most studies also did not give any exclusion criteria, except studies that excluded patients with entropion[4,27,28,29,32,34] or those with an excessive number of lashes (10[22,28,29,31,34] or 12 lashes[32]). Four studies also excluded patients with palpebral deformities,[22] eyelid inflammation,[22,32] a history of prior palpebral surgery,[22] patients with mucous membrane diseases,[31] those under 18 years old[31] or who did not complete the entirety of the follow-up appointments,[18] and those with challenging treatment circumstances such as nervousness,[32] mental retardation,[22,32] or head tremor.[22,32]

Population studied

The sample size ranged from 8[14,30] to 201[35] within each included study for a total of 1044 patients with recurrent trichiasis included. Only one study had a control group.

The age was in average age 59.1 years (95CI 46.0 to 72.1 years), varying from 53 years[9,18] to 76.3 years.[16] Eight studies did not specify age.[14,23,24,27,31,32,33,34]

Sex was not reported in nine studies.[14,23,24,27,29,30,33,34,35] The mean percentage of male was 47.0% (95CI 41.0% to 53.1%), varying from 31.1%[4] to 64.3%.[32]

Etiologies were diverse: postoperative,[4,16,23,24,28] traumatic,[24,25,30,36] ocular pemphigoid,[4,24,25,28] Stevens–Johnson,[24,25] blepharitis,[4,9,18,24,28,30,33,35,36] herpes group viruses,[9,18,28,33] trachoma,[4,9,18,23,27,29,35] chemical burn,[9,18,25,35] trachomatous trichiasis,[4,14,18,27,29,35,36] or idiopathic.[4,9,18,23,24,25,28,30,31,33,35] Only three distichiasis[25] were included.

Previous treatments for trichiasis varied, including epilation,[4,9,18,25] electrolysis,[4,9,18,32,33] surgery,[4,9,16,18,33] and cryotherapy.[4,9,18,25,32]

No other descriptive characteristics were given.

Argon laser and procedure management

The number of sessions of treatment by argon laser varied from one[22,31] to two,[14,18,25] three,[4,9,23,26,29,32] four,[27,28] and five.[36] Eight studies gave the percentage of patients by number of sessions.[4,14,16,23,26,28,32,36]

Parameters of Argon laser treatment were described in most studies. The minimum spot size was reported in all studies, ranging from 50[9,14,18,23,25,26,28,29,32,35] to 200 µm.[4,24,28,29,30,32] The number of shots per lash was reported in 13 studies[4,9,16,18,23,25,27,28,29,32,33,35,36] and varied from 2[16] to 77.[16] The duration of spot was reported in all studies but two,[14,22] ranging from 0.05[23] to 0.5 s.[16,24,30] Most studies reported a duration of 0.2s.[4,18,25,27,28,29,31,36] The power used was reported in all studies but one[14] and varied from 300[16] to 1500 mW.[24] The depth of the pit dug was reported in 12 studies and was mostly around 2 mm,[4,9,16,18,23,24,27,29,30,32,33] with a range from 1[27] to 3 mm.[4,9,16,23,33] To note, one study[30] used the bevel of a 27G needle (measuring 2 mm) to evaluate the depth of the pit dug.

Anesthesia methods were described in all but one study.[34] Except in two studies,[28,33] topical anesthesia was used in all studies – mostly tetracaine[16,22,32] and oxybuprocaine[4,31,35] – and local infiltration was used in ten studies.[9,14,16,18,24,25,29,30,31,35]

Postprocedure treatments often included antibiotic-corticosteroid ointment,[4,9,18,25,26,29,35] antibiotic ointment alone (tetracycline,[22] erythromycin,[24] chloramphenicol,[36] or unprecised antibiotic),[4,23,28,30] antibiotic drops (chloramphenicol,[27] polymyxin B),[27] or warm compresses.[16] Five studies did not mention any treatment after the laser procedure.[14,31,32,33,34]

Meta-analysis on recurrence

All studies were included in the analysis of recurrence after all treatments, and 15 studies in the analysis after one session [Fig. 3].[4,9,14,16,18,23,24,25,26,28,29,31,34,35,36] The overall recurrence was 4.1% (95CI 2.7 to 5.5%), ranging from 0%[14,24,28,30,35] to 37.7%,[16] highlighting a high heterogeneity (I2 = 91.5%) [Fig. 4]. After one session, the recurrence was 35.8% (25.9 to 45.7%, I2 = 91.5%), ranging from 11.6%[24] to 66.6%,[23] with four studies reporting recurrence over 50%[23,26,28,36] [Appendix 4].

Figure 3.

Summary of meta-analysis on efficiency (recurrence of trichiasis) and safety (lids complications and pain) of argon laser treatment. Blue lozenges represent the overall prevalence for recurrence of trichiasis (after the 1^st session of Argon laser and after all sessions of Argon laser), lids complication, and pain. Gray lozenges represent the overall lids complication for each type of complications (notching, hypopigmentation, rash). The length of each horizontal line around the lozenges represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis

Figure 4.

Meta-analysis of recurrence of trichiasis following all sessions of Argon laser. Blue lozenge represents the overall prevalence of trichiasis recurrence following all sessions of Argon laser. Dots represent the prevalence of trichiasis recurrence for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis; Weight (%): weight of each study for each meta-analysis

Meta-analysis on complications

Seventeen studies were included in the analysis of overall lids complications,[4,9,13,14,16,18,22,23,24,26,27,28,29,30,32,33,36] 16 for notching,[4,9,14,16,18,22,23,24,25,26,27,28,29,30,32,36] 15 for hypopigmentation,[4,9,14,16,18,23,24,25,26,27,28,29,30,32,36] 11 for pain,[16,18,22,23,26,27,28,29,30,32,36] and 2 for rash.[33,36] The prevalence of lids complications was 0.1% (95CI -0.2 to 0.5%, I2 = 62.1%) [Fig. 5], including notching (0.1%, -0.2 to 0.5%), hypopigmentation (0.0%, -0.1 to 0.2%), and rash (0.0%, -0.3 to 0.3%). The prevalence of pain was 0.0% (-0.1 to 0.2%) [Fig. 3 and Appendix 5].

Figure 5.

Meta-analysis of lids complications following Argon laser for trichiasis. The blue lozenge represents the overall prevalence of lids complications following Argon laser for trichiasis. Dots represent the prevalence of lids complications for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis; Weight (%): weight of each study for each meta-analysis

Meta-regressions and sensitivity analyses

The recurrence of trichiasis decreased by 20.9% (95% CI 10.5 to 31.4%, P = 0.002) with a maximum depth <3 mm, by 19.1% (35.8 to -2.45, P = 0.027) with spot sizes set at 200 µm vs 50 µm, by 17.8% (-35.4 to -0.32%, P = 0.046) for power between 1000 and 1500 mW vs <1000 mW, and by 26.4% (-47.2 to -5.6%, P = 0.017) for postoperative antibiotics as well as for antibiotics associated with steroids (-22.5%, -43.6 to -1.5%; P = 0.038) vs no postoperative treatments. Minimum depth, other spot sizes, local anesthesia, and postoperative complications had no effect on recurrence, nor sociodemographic, etiologies, and prior treatments [Fig. 6]. As many studies were outside the basis of the meta funnels, further sensitivity analyses were deemed impossible [Appendix 6].

Figure 6.

Metaregressions, i.e., variables influencing the risk of trichiasis recurrence. The effect of each variable on the risk of trichiasis recurrence is represented by a dot on a horizontal line in the forest plot. The dots represent the coefficient for each variable, and the length of each line around the dots represents their 95% confidence interval (95CI). The black solid vertical line represents the null estimate (with a value of 0). Horizontal lines that cross the null vertical line represent nonsignificant variables on the risk of trichiasis recurrence

Discussion

Our meta-analysis highlights that argon laser photocoagulation is an effective treatment for trichiasis, with a recurrence rate of 4.1% after multiple sessions. However, the high heterogeneity in recurrence rate highlights the putative benefits of optimizing laser parameters such as using a wider spot size, higher power levels, and a maximum depth under 3 mm, as well as adding postoperative antibiotics or antibiotic–corticosteroid combinations. There was no effect of sociodemographic nor etiology.

Efficacy and safety

Trichiasis, an ocular pathology characterized by the misdirection of eyelashes toward the ocular surface, leads to a substantial burden on affected individuals, often resulting in corneal abrasions, ulcers, and visual impairment, impacting the patient’s quality of life.[1] Argon laser photocoagulation has emerged as a widely utilized therapeutic intervention aimed at limiting aberrant eyelashes and improving associated symptoms.[11] Our exhaustive meta-analysis, synthesizing data from 20 studies including a cohort of over 1000 patients, allows us to better understand the efficacy and safety profile of argon laser photocoagulation in the management of trichiasis. Our main objective was first to evaluate recurrence rate following argon laser photocoagulation sessions, which we found as low as 4.1%. It highlights the effectiveness of the intervention in reducing trichiasis recurrence, ensuring long-lasting relief from symptoms. The significant difference in recurrence rates between single-session (35.8%) and multiple-session treatments (2.8%) represents a critical finding with direct clinical implications. This supports the practice of planning sequential treatments rather than expecting permanent resolution from initial intervention. The superior outcomes with multiple sessions likely reflect more complete follicle destruction achieved through repeated applications. We know that other trichiasis treatments can cause significant complications such as pain or eyelid deformities.[37] Throughout the range of included studies, the lack of major complications directly linked to the procedure suggests its safety.[4,9,14,16,18,22,23,24,25,26,27,28,29,30,32,33,36] Furthermore, the observation of common adverse events, such as hypopigmentation and notching, was predominantly mild, with low clinical significance.[4,9,18,24,30] In total, the complications rates were low, at 0.1%, in comparison to the heavy burden of trichiasis.[38] The findings extrapolated from our meta-analysis affirm argon laser photocoagulation as a safe and effective treatment option for trichiasis, offering long-lasting symptomatic improvement and a minimized risk of recurrence. However, it is important to note that the definition of recurrence may vary between studies, which can influence the results. Moreover, we should be mindful of potential variations in reporting practices among studies, as well as the importance of minimizing adverse events in real-world clinical settings, particularly considering factors such as laser procedure, etiologies, or sociodemographic.[18]

Management of the laser procedure

The key of the treatment for the ophthalmologists could be the laser parameters. Among these, spot size and power use seem to be determinant of treatment efficacy.[24] We can describe the most common values used. The spot size typically ranges from 50 to 100 µm,[9,14,16,18,22,23,25,26,27,32,33,35,36] and the power mostly used is around 1 W.[4,18,25,26,27,28,29,30,31,32,33,35,36] The duration of the spot is often of 0.2 s.[4,18,25,26,27,28,29,31,32,35,36] These parameters are interdependent; for example, a smaller spot size requires lower power and vice versa. Our meta-regressions suggest that using a wider spot size and higher power levels may be associated with reduced trichiasis recurrence post-laser treatment, in line with histological studies.[17] Surprisingly, a maximum pit depth exceeding 3 mm appears to worsen outcomes, although in theory, there is a greater chance to destroy the follicle by going deeper.[14,16,17] The number of shots is highly variable (2 to 77),[16] but there should be enough to dig a pit of 2 mm.[17] Regarding anesthesia, opinions diverge: local infiltration anesthesia[14,18,25,29,35] topical anesthesia,[4,22,23,27,32,36] both,[9,16,24,30,31] or no anesthesia at all according to some authors.[28,33] As pain rates are low in our analysis, topical anesthesia alone might be a better compromise as it is quick, cheap, and without adverse effects. It does not seem necessary to propose an invasive anesthesia method. Finally, regarding postprocedure treatment, antibiotic–corticosteroid ointments were the most commonly used, while antibiotics alone, though less frequently reported, were also associated with a reduction in recurrence rates compared to no treatment.[9,18,25,26,29,35] However, inconsistencies in reporting durations and dosages across studies limit the ability to draw definitive conclusions.

Patients’ variables influencing treatment outcomes

It is established that patient-specific variables play a pivotal role in determining treatment outcomes.[6,39] It is known that a large number of trichiasis eyelashes[40] are associated with a higher risk of recurrence.[26] Our meta-analysis aimed to elucidate nuanced patient conditions that could significantly influence treatment efficacy. Age, sex, etiology, and prior treatment history of trichiasis were examined as potential influencers.[18] The current clinical evidence lacks consensus on age or sex’s influence on trichiasis treatment success, not described in any study. Our findings are in agreement with the observed absence of significant associations depending on those variables, but possibly due to limited statistical power. Similarly, while there are suspicions of an impact depending on the etiology, particularly between healthy eyelids and those affected by trauma or infection,[18] the absence of statistically significant findings may benefit from a meta-analysis of individual data. The lack of detailed recurrence data across distinct patient subgroups within the reviewed literature may limit the precision of our observed associations. The included studies were from various continents, which strengthens the potential for generalizing the findings across diverse ethnic groups. However, further analysis could be conducted to assess the role of ethnic or geographic factors in treatment outcomes. Furthermore, our results may not be generalizable to certain patient populations, particularly those excluded from the studies included in our analysis.

Sources of heterogeneity

The substantial heterogeneity observed in our meta-analysis (I² = 91.5%) can be attributed to several key factors. First, methodological diversity was evident across studies, including variations in study design (prospective vs retrospective), sample sizes ranging from 8 to 201 patients, and different follow-up durations (1 to 48 months). Second, clinical heterogeneity stemmed from differences in patient populations, including diverse etiologies of trichiasis (trachomatous, postoperative, idiopathic, etc.), varying numbers of aberrant lashes treated, and different previous treatment histories. Third, technical heterogeneity was substantial, with variations in laser parameters (spot size: 50–200 µm, power: 300–1500 mW, depth: 1–3 mm), anesthesia methods, and postprocedure treatments. Fourth, outcome heterogeneity resulted from differences in recurrence definitions and reporting practices across studies. This comprehensive heterogeneity analysis provides important context for interpreting our pooled estimates and highlights the need for standardized protocols in future research.

Limitations

The main limitation of this meta-analysis is the high heterogeneity among included studies, which likely reflects several factors, including variations in patient populations, trichiasis etiologies, laser parameters, treatment protocols, and outcome definitions across studies. This heterogeneity limits the generalizability of our pooled estimates and suggests that treatment outcomes may vary considerably depending on specific clinical contexts and technical approaches. Also, the inclusion of both retrospective and prospective observational studies may introduce bias and confounding factors. The limited number of RCTs (only one)[22] reduces the strength of the evidence. Additionally, publication bias is a concern as studies with significant findings are more likely to be published, potentially overestimating treatment efficacy. Despite extensive literature searches, residual publication bias cannot be avoided. Some studies were excluded due to the unavailability of full texts or redundant data.[41] Furthermore, the limited long-term follow-up data in many studies prevent a comprehensive evaluation of recurrence over time. The lack of standardized reporting on adverse events further complicates the assessment of the safety profile of argon laser photocoagulation. Last, meta-analytic techniques are inherently constrained by the quality and availability of primary data, limiting the strength of our conclusions. The distribution of studies in meta-funnels prevented meaningful sensitivity analyses, further constraining our ability to assess the robustness of our findings.[42] Finally, the need for multiple sessions may pose challenges in resource-limited or trachoma-endemic settings; consequently, this approach may be less effective in a general scenario, reflecting the substantial heterogeneity in recurrence rates observed.

Clinical implications

Our findings have several clinical implications. Argon laser photocoagulation appears to be a safe and effective treatment for trichiasis, but clinicians and patients should expect that multiple treatment sessions may be necessary to achieve optimal outcomes. The very low complication rate supports its use as a first-line treatment for patients with limited numbers of aberrant lashes. However, for patients with extensive trichiasis, surgical approaches may be more appropriate.

Conclusion

In conclusion, argon laser photocoagulation demonstrates efficacy and safety for trichiasis management, particularly when multiple sessions are employed. The procedure shows a favorable safety profile with minimal complications, supporting its use as a first-line treatment for limited trichiasis. However, the low certainty of evidence due to methodological limitations and substantial heterogeneity necessitates cautious application of these findings in clinical decision-making. Future research should focus on standardized protocols, randomized controlled trials, and long-term follow-up to strengthen the evidence base for this treatment modality.

Author contributions

LE and AF contributed equally to this work and should be considered co-first authors. LE, AF and FD were responsible for the design and conception of the study. AF and LE searched and collected studies and data. AF, LE, FC, and FD analysed and interpreted data. AF, LE, FD were in charge of statistical analyses. AF, LE, FC and FD wrote the manuscript. All authors made critical revisions to the article. All authors gave their final approval of the article.

Data availability statement

All relevant data are within the paper.

Conflicts of interest

There are no conflicts of interest.

Electronic

Supplementary Material

Supplementary materials

Appendix 1. Details for the search strategy used within each database.

Appendix 2. Details of checklists (using the SIGN and NOS / Rob2), and associated evaluation of quality of included studies.

The Scottish Intercollegiate Guidelines Network (SIGN) checklist for cohort studies

The Scottish Intercollegiate Guidelines Network (SIGN) checklist for randomized controlled trials

The Newcastle-Ottawa Scale (NOS) for cohort studies

The Rob checklists for randomized controlled trials

Appendix 3. Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) instrument - Certainty of the evidence for our main outcome and secondary outcomes.

Appendix 4. Meta-analysis of trichiasis recurrence following the 1^st session of Argon laser.

The blue lozenge represents the overall prevalence of trichiasis recurrence following the 1st session of Argon laser. Dots represent the prevalence of trichiasis recurrence for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis; Weight (%): weight of each study for each meta-analysis.

Appendix 5. Meta-analysis on each complications following session of Argon laser.

The blue lozenge represents the overall prevalence of each complication following all the sessions of Argon laser. Dots represent the prevalence of trichiasis recurrence for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis; Weight (%): weight of each study for each meta-analysis.

Appendix 6. Metafunnels for each meta-analysis: recurrence of trichiasis, lids complication, and pain.

Each dot represents a single study, with its corresponding effect size (x axis) and its associated standard error of the effect estimate (y-axis). Large high-powered studies are placed towards the top, and smaller low-powered studies towards the bottom. The plot should ideally resemble a pyramid or inverted funnel, with scatter due to sampling variation. Studies outside funnel plot are likely to present bias ⁴³.

Appendix 1. Details for the search strategy used within each database

Pubmed

trichias* AND (argon OR laser OR photocoagulation)

Cochrane

trichias* AND (argon OR laser OR photocoagulation)

ScienceDirect

(trichiasis) AND ((argon) OR (laser) OR (photocoagulation))

Embase

trichias* AND ('argon'/exp OR argon OR 'laser'/exp OR laser OR photocoagularion)

ClinicalTrials

trichiasis AND (argon OR laser OR photocoagulation)

Appendix 2. Details of quality of included studies (using the SIGN and NOS / Rob2), and associated checklists.

Methodological quality of included studies using the Scottish Intercollegiate Guidelines Network (SIGN) (cohort studies, n=19)

Methodological quality of included studies using the New-Ottawa Scale (NOS) (cohort studies, n=19)

Methodological quality of included studies using the Risk of Bias 2 (RoB 2) scale for randomized controlled trial (n=1)

Newcastle-Ottawa Scale (NOS) for cohort studies

Selection (Maximum 4 stars)

1) Representativeness of the exposed cohort

a) truly representative of the average_________________ (describe) in the community *

b) somewhat representative of the average________________________________________________ in the community*

c) selected group of users eg nurses, volunteers

d) no description of the derivation of the cohort

2) Selection of the non exposed cohort

a) drawn from the same community as the exposed cohort *

b) drawn from a different source

c) no description of the derivation of the non exposed cohort

3) Ascertainment of exposure

a) secure record (eg surgical records) *

b) structured interview *

c) written self report

d) no description

4) Demonstration that outcome of interest was not present at start of study

a) yes *

b) no

Comparability (Maximum 2 stars)

1) Comparability of cohorts on the basis of the design or analysis

a) study controls for ______________ (select the most important factor) *

b) study controls for any additional factor * (This criteria could be modified to indicate specific control for a second important factor.)

Outcome (Maximum 3 stars)

1) Assessment of outcome

a) independent blind assessment *

b) record linkage *

c) self report

d) no description

2) Was follow-up long enough for outcomes to occur

a) yes (select an adequate follow up period for outcome of interest) *

b) no

3) Adequacy of follow up of cohorts

a) complete follow up - all subjects accounted for *

b) subjects lost to follow up unlikely to introduce bias - small number lost - > _______ % (select an

adequate %) follow up, or description provided of those lost) *

c) follow up rate <____ % (select an adequate %) and no description of those lost

d) no statement

SIGN Scale for cohort studies

Methodology Checklist 3: Cohort studies

Study identification (Include author, title, year of publication, journal title, pages)

Guideline topic:	Key Question No:	Reviewer:
Before completing this checklist, consider:
1. Is the paper really a cohort study? If in doubt, check the study design algorithm available from SIGN and make sure you have the correct checklist.
2. Is the paper relevant to key question? Analyse using PICO (Patient or Population Intervention Comparison Outcome). IF NO REJECT (give reason below). IF YES complete the checklist..

Reason for rejection: 1. Paper not relevant to key question □ 2. Other reason □ (please specify):

Please note that a retrospective study (ie a database or chart study) cannot be rated higher than +.

SECTION 1: INTERNAL VALIDITY

In a well conducted cohort study:		Does this study do it?
1.1	The study addresses an appropriate and clearly focused question.!	Yes □ No □ Can't say □
SELECTION OF SUBJECTS
1.2	The two groups being studied are selected from source populations that are comparable in all respects other than the factor under investigation. ii	Yes □ No □ Can't say □ Does not apply □
1.3	The study indicates how many of the people asked to take part did so, in each of the groups being studied.iii	Yes □ No □ Does not apply □
1.4	The likelihood that some eligible subjects might have the outcome at the time of enrolment is assessed and taken into account in the analysis. iv	Yes □ No □ Can't say □ Does not apply □
1.5	What percentage of individuals or clusters recruited into each arm of the study dropped out before the study was completed.v
1.6	Comparison is made between full participants and those lost to follow up, by exposure status. vi	Yes □ No □ Can't say □ Does not apply □
ASSESSMENT
1.7	The outcomes are clearly defined. i	Yes □ No □ Can't say □
1.8	The assessment of outcome is made blind to exposure status. If the study is retrospective this may not be applicable.ii	Yes □ No □ Can't say □ Does not apply □
1.9	Where blinding was not possible, there is some recognition that knowledge of exposure status could have influenced the assessment of outcome.iii	Yes □ No □ Can't say □ □
1.10	The method of assessment of exposure is reliable.iv	Yes □ No □ Can't say □
1.11	Evidence from other sources is used to demonstrate that the method of outcome assessment is valid and reliable.v	Yes □ No □ Can't say □ Does not apply□
1.12	Exposure level or prognostic factor is assessed more than once.vi	Yes □ No □ Can't say □ Does not apply □
CONFOUNDING
1.13	The main potential confounders are identified and taken into account in the design and analysis.vii	Yes □ No □ Can't say □
STATISTICAL ANALYSIS
1.14	Have confidence intervals been provided?viii	Yes □ No □
SECTION 2: OVERALL ASSESSMENT OF THE STUDY
2.1	How well was the study done to minimise the risk of bias or confounding?ix	High quality (++) □ Acceptable (+) □ Unacceptable - reject 0
2.2	Taking into account clinical considerations, your evaluation of the methodology used, and the statistical power of the study, do you think there is clear evidence of an association between exposure and outcome?	Yes □ Can't say □	No □
2.3	Are the results of this study directly applicable to the patient group targeted in this guideline?	Yes □ No □
2.4	Notes. Summarise the authors conclusions. Add any comments on your own assessment of the study, and the extent to which it answers your question and mention any areas of uncertainty raised above.

SIGN Scale for clinical trials studies

Methodology Checklist 2: Controlled Trials

Study identification (Include author, title, year of publication, journal title, pages)

Guideline topic:	Key Question No:	Reviewer:
Before completing this checklist, consider:
1. Is the paper a randomised controlled trial or a controlled clinical trial? If in doubt, check the study design algorithm available from SIGN and make sure you have the correct checklist. If it is a controlled clinical trial questions 1.2, 1.3, and 1.4 are not relevant, and the study cannot be rated higher than 1 +
2. Is the paper relevant to key question? Analyse using PICO (Patient or Population Intervention Comparison Outcome). IF NO REJECT (give reason below). IF YES complete the checklist.

Reason for rejection: 1. Paper not relevant to key question □ 2. Other reason □ (please specify):

SECTION 1: INTERNAL VALIDITY

In a well conducted RCT study...			Does this study do it?
1.1	The study addresses an appropriate and clearly focused question.		Yes □ No □ Can't say □
1.2	The assignment of subjects to treatment groups is randomised.		Yes □ No □ Can't say □
1.3	An adequate concealment method is used.		Yes □ No □ Can't say □
1.4	The design keeps subjects and investigators ‘blind' about treatment allocation.		Yes □ No □ Can't say □
1.5	The treatment and control groups are similar at the start of the trial.		Yes □ No □ Can't say □
1.6	The only difference between groups is the treatment under investigation.		Yes □ No □ Can't say □
1.7	All relevant outcomes are measured in a standard, valid and reliable way.		Yes □ No □ Can't say □
1.8	What percentage of the individuals or clusters recruited into each treatment arm of the study dropped out before the study was completed?
1.9	All the subjects are analysed in the groups to which they were randomly allocated (often referred to as intention to treat analysis).		Yes □ No □ Can't say □ Does not apply □
1.10	Where the study is carried out at more than one site, results are comparable for all sites.		Yes □ No □ Can't say □ Does not apply □
SECTION 2: OVERALL ASSESSMENT OF THE STUDY
2.1	How well was the study done to minimise bias?		High quality (++)□

RoB 2 Scale for clinical trials studies

Signalling questions	Comments	Response options
1.1 Was the allocation sequence random?		Y / PY / PN / N / NI
1.2 Was the allocation sequence concealed until participants were enrolled and assigned to interventions?		Y / PY / PN / N / NI
1.3 Did baseline differences between intervention groups suggest a problem with the randomization process?		Y / PY / PN / N / NI
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the predicted direction of bias arising from the randomization process?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable
Signalling questions	Comments	Response options
2.1. Were participants aware of their assigned intervention during the trial?		Y / PY / PN / N / NI
2.2. Were carers and people delivering the interventions aware of participants' assigned intervention during the trial?		Y / PY / PN / N / NI
2.3. If Y/PY/NI to 2.1 or 2.2: Were there deviations from the intended intervention that arose because of the trial context?		NA / Y / PY / PN / N / NI
2.4 If Y/PY to 2.3: Were these deviations likely to have affected the outcome?		NA / Y / PY / PN / N / NI
2.5. If Y/PY/NI to 2.4: Were these deviations from intended intervention balanced between groups?		NA / Y / PY / PN / N / NI
2.6 Was an appropriate analysis used to estimate the effect of assignment to intervention?		Y / PY / PN / N / NI
2.7 If N/PN/NI to 2.6: Was there potential for a substantial impact (on the result) of the failure to analyse participants in the group to which they were randomized?		NA / Y / PY / PN / N / NI
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the predicted direction of bias due to deviations from intended interventions?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable
Signalling questions	Comments	Response options
3.1 Were data for this outcome available for all, or nearly all, participants randomized?		Y / PY / PN / N / NI
3.2 If N/PN/NI to 3.1: Is there evidence that the result was not biased by missing outcome data?		NA/Y / PY/PN/N
3.3 If N/PN to 3.2: Could missingness in the outcome depend on its true value?		NA / Y / PY / PN / N / NI
3.4 If Y/PY/NI to 3.3: Is it likely that missingness in the outcome depended on its true value?		NA / Y / PY / PN / N / NI
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the predicted direction of bias due to missing outcome data?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable
Signalling questions	Comments	Response options
4.1 Was the method of measuring the outcome inappropriate?		Y / PY / PN / N / NI
4.2 Could measurement or ascertainment of the outcome have differed between intervention groups?		Y / PY / PN / N / NI
4.3 If N/PN/NI to 4.1 and 4.2: Were outcome assessors aware of the intervention received by study participants?		NA / Y / PY / PN / N / NI
4.4 If Y/PY/NI to 4.3: Could assessment of the outcome have been influenced by knowledge of intervention received?		NA / Y / PY / PN / N / NI
4.5 If Y/PY/NI to 4.4: Is it likely that assessment of the outcome was influenced by knowledge of intervention received?		NA / Y / PY / PN / N / NI
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the predicted direction of bias in measurement of the outcome?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable
Signalling questions	Comments	Response options
5.1 Were the data that produced this result analysed in accordance with a pre-specified analysis plan that was finalized before unblinded outcome data were available for analysis?		Y / PY / PN / N / NI
Is the numerical result being assessed likely to have been selected, on the basis of the results, from...
5.2.... multiple eligible outcome measurements (e.g. scales, definitions, time points) within the outcome domain?		Y / PY / PN / N / NI
5.3 ... multiple eligible analyses of the data?		Y / PY / PN / N / NI
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the predicted direction of bias due to selection of the reported result?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable
Risk-of-bias judgement		Low / High / Some concerns
Optional: What is the overall predicted direction of bias for this outcome?		NA / Favours experimental / Favours comparator / Towards null /Away from null / Unpredictable

Appendix 3. Grading of Recommendation, Assessment, Development, and Evaluation (GRADE) instrument - Certainty of the evidence for our main outcome and secondary outcomes.

Outcomes	Study design	n studies	Certainty of evidence				Number of patients	Prevalence (95CI)	Quality of evidence	Importance of ouctome
			Risk of bias	Risk of inconsistency	Risk of indirectness	Risk of imprecision
Recurrence of trichiasis following...
the 1st session of Argon laser	Observational	15	Moderate	Significant	Low	Low	883	35.8% (25.9 to 45.7%)	⮾◯◯◯	Important
all sessions of Argon laser	Observational and 1 RCT	20	Moderate	Significant	Low	Low	1044	4.1% (25.9 to 45.7%)	⮾◯◯◯	Important
Lids complications	Observational and 1 RCT	17	Moderate	Significant	Low	Moderate	676	0.1% (-00.2 to 00.5%)	⮾◯◯◯	Important

Appendix 4. Meta-analysis of trichiasis recurrence following the 1^st session of Argon laser.

The blue lozenge represents the overall prevalence of trichiasis recurrence following the 1st session of Argon laser. Dots represent the prevalence of trichiasis recurrence for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each metaanalysis; Weight (%): weight of each study for each meta-analysis.

Appendix 5. Meta-analysis on each complications following session of Argon laser.

The blue lozenge represents the overall prevalence of each complication following all the sessions of Argon laser. Dots represent the prevalence of trichiasis recurrence for each included study. The length of each horizontal line around the lozenge represents their 95% confidence interval (95CI). I-squared (%): percentage of heterogeneity between studies for each meta-analysis; Weight (%): weight of each study for each meta-analysis.

Appendix 6. Metafunnels for each meta-analysis: recurrence of trichiasis, lids complication, and pain

Each dot represents a single study, with its corresponding effect size (x axis) and its associated standard error of the effect estimate (y-axis). Large high-powered studies are placed towards the top, and smaller low-powered studies towards the bottom. The plot should ideally resemble a pyramid or inverted funnel, with scatter due to sampling variation. Studies outside funnel plot are likely to present bias⁴².

Funding Statement

Nil.