Dysphotopsia and location of laser iridotomy: a systematic review

Abstract

This systematic review aimed to clarify the relationship between the location of laser peripheral iridotomy (LPI), a common procedure to prevent or treat angle-closure glaucoma, and the incidence of post-procedure visual disturbances known as dysphotopsias. Understanding this relationship is crucial due to the high frequency of LPIs performed and the significant impact dysphotopsia can have on vision and quality of life. Articles investigating the relationship between LPI location and dysphotopsia in at least five patients were identified via a literature search of OVID MEDLINE (1946-November 19, 2022) and EMBASE (1946-November 19, 2022). Non-comparative and non-English studies were excluded. Studies did not require a control group to be included. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system and Cochrane Risk of Bias 2 (RoB2) tool were used to appraise included studies. Our review included three studies encompassing 1756 eyes from 878 patients. The location of LPI was grouped into superior (604 patients, 889 eyes), inferior (150 patients, 150 eyes), and nasal/temporal (443 patients, 717 eyes). The analysis showed no significant difference in the incidence of any new dysphotopsia types among the location groups post-LPI. Overall, the incidence of lines, ghost images, and blurring significantly increased after LPI, while halos and glare significantly decreased. In conclusion, the current literature suggests that the location of LPI has no significant relationship to the types and rates of dysphotopsia experienced thereafter. While there is a 2–3% risk of linear dysphotopsia after LPI regardless of location, LPI may also resolve pre-existing halos and glare.

Introduction

Laser peripheral iridotomy (LPI) is a common first-line treatment option for patients with occludable angles or primary angle closure due to its ability to resolve pupillary block [1]. During the procedure, a neodymium:yttrium–aluminum–garnet (Nd:YAG) laser is used to create a small opening in the peripheral iris, thereby reducing the risk of intraocular pressure (IOP) buildup by providing an alternative outflow channel. Since this procedure is performed so frequently, it is important to fully characterize its side effect profile and determine which treatment parameters result in the best patient outcomes. One parameter in particular, the location of the LPI (typically described in clock-hours orquadrants: superior, inferior, nasal, temporal) has been implicated in the development of visual disturbances, or dysphotopsias [2, 3]. These dysphotopsias can cause significant reductions in visual quality and quality of life, especially when they occur secondary to an elective, preventative procedure.

Symptoms occur when light entering the iridotomy site is scattered, creating abnormal visual disturbances such as haloes or glare. Dypshotopsias may interfere with daily activities such as driving, reading, or using electronic devices, and they may also be associated with headaches, eyestrain, and difficulty adapting to low light conditions. The severity of dysphotopsia can vary between individuals, and in some cases, persist indefinitely, although most are mild and transient [4, 5]. Individuals with severe dysphotopsia have even been suggested to potentially experience associations with anxiety, depression, and social isolation, although these relationships may be influenced by various factors [6]. Thus, it is important to minimize the risk of dysphotopsia after LPI, which has a prevalence ranging from 2 to 16% among reports in the literature [2, 7–10].

The aim of this systematic review is to investigate the relationship between LPI location and patient-reported dysphotopsia, in addition to any other consistently reported outcomes. This may reveal an optimal location for the procedure and in turn inform clinical decision-making and ultimately lead to improved patient outcomes.

Methods

Eligibility criteria for considering studies for this review

Studies were included if they investigated the relationship between LPI location and dysphotopsia in at least five patients. Studies did not require a control group to be included. Non-English or non-original articles, abstracts, case reports, correspondences, letters, editorials, and reviews were excluded.

Search methods for identifying studies

Systematic literature searches were performed on OVID MEDLINE (1946-November 19, 2022) and EMBASE (1946-November 19, 2022) using keywords and subject headings to identify relevant published articles. The complete search strategy for MEDLINE is provided in Supplementary Table 1. This systematic review adhered to the Declaration of Helsinki, and institutional review board approval was not necessary given the design of the study. The protocol for this study was registered in PROSPERO (CRD42023393425).

Study selection

Two reviewers (M.B. and D.J.M.) independently screened all studies according to the selection criteria in a two-phase process: (i) title and abstract screening followed by (ii) full-text screening of the remaining eligible articles.

Data collection and risk of bias assessment

The following baseline study characteristics were collected: title, first author, year of publication, study design, treatment center, study period, outcome measures, and the number of patients and eyes undergoing LPI. Sample characteristics were also collected and included the following: age, sex, location of LPI, lid coverage of LPI, total laser energy applied, the number and types of dysphotopsia, and adverse events. To rate the quality of evidence for all outcomes in each study, we used the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) system [11]. This system assigns each outcome a rating of very low, low, moderate, or high quality of evidence. Furthermore, to critically appraise our included studies we also used the Cochrane Risk of Bias 2 (RoB2) assessment tool for randomized control trials [12]. For each domain, a rating of low risk, some concerns, or high risk was assigned. The domains included selection, performance, detection, attrition, and reporting bias, in addition to other biases (including conflicts of interest and industry sponsorship). Two reviewers (M.B. and D.J.M) independently assessed all included studies with the RoB2 and GRADE tool.

Data synthesis and analysis

The primary outcome was the frequency of new-onset linear dysphotopsia after LPI. Secondary outcomes included the number and types of all new dysphotopsias occurring after LPI, as well as the average total energy applied and any reported adverse events. Inconsistent reporting among studies precluded the analysis of changes in visual acuity or IOP. Study variables were stratified by LPI location, and their outcomes were reported narratively and quantitatively. Descriptive statistics were reported by means and standard deviations (SD) for continuous variables (weighted by sample size when possible) and by counts and percentages for categorical variables. The frequencies of dysphotopsias were compared between LPI locations using the chi-square test, while the McNemar test was used to compare correlated proportions within each LPI group (i.e., for comparing dysphotopsia frequencies before and after LPI). A p-value of less than 0.05 was used to denote statistical significance. Despite the paucity of available literature, we performed a meta-analysis using random-effects modeling and the Mantel–Haenszel method for categorical outcomes (RevMan 5.3; The Nordic Cochrane Center, The Cochrane Collaboration, Copenhagen, Denmark). Risk ratios (RR) and 95% confidence intervals (CI) were used to estimate the effect of LPI location on the risk of new linear dysphotopsia. The I² statistic (significance: >75%) and chi-squared test (significance: P < 0.05) were used to assess statistical heterogeneity.

Results

Screening process

The literature search identified 3277 articles. After excluding duplicates and screening titles and abstracts, 24 articles were selected. Full-text screening excluded another 21, leaving a total of three studies and 1756 eyes from 878 patients in this review (Fig. 1) [13–15].

Fig. 1. PRISMA flowchart.

Initial identification, screening and final number of included studies are shown.

Baseline study characteristics

The weighted average age was 53.2 ± 8.9 years, 26.9% of patients were male (n = 236), and all patients had undergone successful LPI (Table 1). All three articles were prospective, randomized trials [13–15]. Two of the three articles were paired-eye comparative studies [13, 14]. 559 patients (63.7%) came from one study in South India [15], 150 (17.1%) came from one study in Iran [14], and 169 (19.2%) came from one study in Canada [13]. They were all published between 2014–2018. Post-LPI follow-up visit times for each study were two weeks [15], one month [13], and two-, six- and twelve- month intervals [14]. Given the availability of reported data across studies, we categorized LPI location into three groups: superior, inferior, and nasal/temporal.

Table 1.

Baseline study characteristics.

Studya	Srinivasan (2018)		Ahmadi (2017)		Vera (2014)
Design	Prospective, Randomized Trial		Prospective, Randomized Paired-Eye Trial		Prospective, Randomized Paired-Eye Trial
Location	South India		Iran		Canada
LPI Location	Bilateral Superior LPI	Bilateral Nasal/Temporal LPI	Superior LPI	Inferior LPI	Superior LPI	Temporal LPI
Patients – n	285	274	150	150	169	169
Eyes – n	570	548	150	150	169	169
Age – mean (SD)	51.5 (8.8)	51.8 (8.7)	58.9 (6.4)	58.9 (6.4)	53.4 (11.5)	53.4 (11.5)
Males – n (%)	69 (24.2)	63 (23.0)	52 (34.7)	52 (34.7)	52 (30.8)	52 (30.8)

LPI Laser Peripheral Iridotomy.

^aFirst author.

Risk of bias

Quality assessment using the RoB2 tool (Supplementary Table 2) revealed that one study had an overall low risk of bias [15], while the other two had some concerns, particularly in the domains of allocation concealment and personnel and participant masking [13, 14]. The GRADE tool revealed that the overall quality of evidence for each outcome was moderate. Reports of linear and overall dysphotopsia had a higher quality of evidence while laser energy and adverse events were lower quality due to inconsistencies among the included studies (Supplementary Table 3).

LPI location characteristics and dysphotopsia

There were 604 patients (with 889 eyes) in the superior LPI group, 150 patients (with 150 eyes) in the inferior LPI group, and 443 patients (with 717 eyes) in the nasal/temporal LPI group (Table 2). The incidence of new linear dysphotopsia in superior, inferior, and nasal/temporal groups were 2.8% (n = 25), 2.7% (n = 4), and 2.0% (n = 14) respectively (χ2 p = 0.18). After pooling studies to compare superior to nasal/temporal LPI, there was no significant difference in the rate of new-onset linear dysphotopsia (RR: 1.71; 95% CI: 0.26–11.17; p-value: 0.57) (Fig. 2). However, there was significant statistical heterogeneity (I² > 75%, χ2 p < 0.05) given the limited number of available studies. Meta-analysis for inferior LPI was not feasible, as there was only a single study investigating this particular approach.

Table 2.

Aggregated comparison of LPI locations, demographics, and LPI characteristics.

Characteristics	Superior	Inferior	Nasal/Temporal
Patients – n (%)	604	150	443
Eyes – n (%)	889	150	717
Age – mean (SD)a	53.9 (9.0)	58.9 (6.4)	52.4 (9.8)
Males – n (%)	173 (28.6)	52 (34.7)	115 (26.0)
New linear dysphotopsia – n (%)	25 (2.8)	4 (2.7)	14 (2.0)
Total laser energy (mJ) – mean ± SD (range)a	48.6 ± 42.3 (16.8–59.1)	12.9 ± 1.4 (12.9–12.9)	45.6 ± 59.4 (45.1–47.1)
Lid coverage – n (%)
Covered fully	801 (90.1)	52 (34.7)	165 (23.0)
Partially exposed	50 (5.6)	23 (15.3)	0 (0.0)
Completely exposed	38 (4.3)	75 (50.0)	552 (77.0)

LPI laser peripheral iridotomy.

^aWeighted average by the number of patients in each study.

Fig. 2. Forest plot comparing new-onset linear dysphotopsia.

There was no significant difference in the rate of new-onset linear dysphotopsia for superior versus nasal/temporal laser peripheral iridotomy (LPI).

Only two of the three studies (inferior LPI not included) report data on the frequency of dysphotopsia symptoms before and after LPI, stratified by the different forms of visual disturbances (Table 3) [13, 15]. Overall, lines, ghost images, and blurring significantly increased in frequency after the LPI, while other forms of visual disturbances including halos and glare significantly decreased. Crescents and shadows did not significantly change. When comparing the absolute difference of before and after dysphotopsia rates, there were no significant differences for any of the dysphotopsia subtypes between the superior and nasal/temporal LPI groups (χ2 p = 0.28 for linear dysphotopsia).

Table 3.

Patient-reported dysphotopsia before and after LPI.

Variable	Superior (n = 454) – n (%) [% range]			Nasal/Temporal (n = 443) – n (%) [% range]			|After – Before|
	Before LPI	After LPI	P valuea	Before LPI	After LPI	P valuea	P valueb
Halos	35 (7.7) [4.2–13.6]	10 (2.2) [0.7–4.7]	<0.001	33 (7.4) [3.6–13.6]	19 (4.3) [3.3–5.9]	<0.001	0.09
Lines	13 (2.9) [0.6–4.2]	30 (6.6) [4.2–10.7]	<0.001	8 (1.8) [1.2–2.2]	19 (4.3) [3.0–5.1]	0.003	0.28
Crescent	4 (0.9) [0.0–2.4]	2 (0.4) [0.0–1.2]	0.48	2 (0.5) [0.0–1.2]	1 (0.2) [0.0–0.6]	1.00	0.58
Ghost Image	14 (3.1) [0.0–8.3]	25 (5.5) [0.7–13.6]	0.003	15 (3.4) [0.4–8.3]	24 (5.4) [0.7–13.0]	0.008	0.16
Glare	62 (13.7) [10.2–19.5]	17 (3.7) [2.4–4.6]	<0.001	59 (13.3) [9.5–19.5]	29 (6.5) [3.0–8.8]	<0.001	0.09
Shadows	13 (2.9) [1.8–4.7]	9 (2.0) [0.7–4.1]	0.13	13 (2.9) [1.8–4.7]	14 (3.2) [2.2–4.7]	1.00	0.19
Blurring	41 (9.0) [4.6–16.6]	50 (11.0) [6.0–19.5]	0.008	35 (7.9) [2.6–16.6]	49 (11.1) [5.1–20.7]	<0.001	0.26

LPI laser peripheral iridotomy.

^aMcNemar’s Test, Within-Groups comparison, boldface values indicate statistical significance at P < 0.05.

^bChi-Squared Test, Between-Groups comparison of the absolute difference between before and after dysphotopsia frequencies, boldface values indicate statistical significance at P < 0.05.

Although the majority of responses were collected only a few weeks after the LPI in these studies, Kavitha et al. subsequently conducted a six-month follow-up longitudinal study of their cohort [16]. There were 131 patients with superior LPI and 138 with nasal/temporal LPI that had 6-month data available, and the authors found significantly fewer patients (8.6%) reporting at least one dysphotopsia symptom compared to pre- (14.1%) and two weeks post-LPI (13.8%). At six months, the most common dysphotopsias were glare (7.1%) and blurring (2.6%), and patients were significantly less likely to report the presence of new linear dysphotopsia (0.4%) compared to two weeks post-LPI (2.6%). Furthermore, at both the two-week and six-month follow-ups, there were no significant differences in the proportion of patients with new overall or individual dysphotopsia symptoms between superior and nasal/temporal locations.

Superior and nasal/temporal groups had weighted averages of 48.6mJ and 45.6mJ of total laser energy applied, respectively. Inferior LPI had a total 12.9mJ applied on average. However, Ahmadi et al. were the only group among the studies in this review to investigate inferior LPIs and reported a total laser energy of only 16.8mJ for superior LPIs as well [14]. When comparing the degree of LPI lid coverage, patients receiving superior LPI had the highest proportion of complete lid coverage (90.1%), followed by inferior (34.6%) and nasal/temporal (23.0%) LPI (Table 2).

Kavitha et al. reported no serious complications in their cohort of 570 superior LPI and 548 nasal/temporal LPI patients [15]. The only complication reported by Vera et al. was intraoperative hemorrhage, which had similar rates between eyes receiving superior LPI (8.9%) versus temporal LPI (10.1%) [13]. The study by Ahmadi et al. reported various complications including: mild corneal edema (37.3% superior versus 20.6% inferior), iris bleeding (40.6% superior versus 30.0% inferior), posterior synechiae (1.3% superior versus 0.0% inferior), grade 2+ uveitis (74% superior versus 64% inferior), IOP spike >10 mmHg (72.3% superior LPI versus 55.3% inferior LPI), transient diplopia (1.3% superior versus 1.3% inferior), pigment release (62% superior versus 28% inferior), and retinal damage (0.6% superior versus 0.0% inferior). They also reported that the primary attempt was unsuccessful in 5% of superior LPIs and 0.6% of inferior LPIs.

Discussion

While LPI has been demonstrated to be a safe and effective procedure for the treatment and prevention of angle-closure glaucoma, the current body of evidence investigating the relationship between LPI location and dysphotopsia is limited [8, 17–19]. This systematic review found that there are no significant differences in the rates of dysphotopsia (overall and by subtype) between LPI locations. While larger and more robust studies are needed to make any well-founded conclusions, the current literature shows that LPI can be performed in any iris quadrant without having a major impact on the incidence or type of dysphotopsia.

Notwithstanding, it is crucial to place these findings in the context of evolving clinical practice. In recent years, there has been a shift in the utilization of LPI in the management of angle-closure diseases. Specifically, the emphasis on LPI as a prophylactic treatment for angle-closure glaucoma and more advanced primary angle-closure disease has been de-emphasized [20–23]. Instead, the primary focus is now more on early-stage primary angle-closure disease, especially in cases where intraocular pressure is between 21 and 29 mmHg. Thus, while the location of LPI appears not to significantly impact dysphotopsia rates, the overall incidence of LPI and consequently dysphotopsia may be influenced by these changing treatment strategies.

In keeping with previous studies, the onset of new visual disturbances after LPI were most commonly classified as linear dysphotopsia, while ghost images and blurring also significantly worsened post-procedure [7, 8, 13, 15]. Conversely, there was a significant reduction in the frequency of halos and glare after LPI. None of these changes remained significant between LPI locations, however. Previous studies suggested that pre-procedure dysphotopsias may occur as a result of intermittent IOP spikes or ocular surface disease, which in these cases may be relieved by the LPI, in addition to a possible procedural placebo effect [13, 15]. In fact, there were a total 347 overall dysphotopsias reported pre-procedure and 298 reported post-procedure, suggesting that LPIs may actually improve visual disturbances. These results highlight the importance of focusing on particular forms of dysphotopsia (i.e. linear dysphotopsia) when measuring the side-effect profile, as well as the possible limitations of existing patient-reported questionnaires and the need for more objective and reliable testing methods [2].

One such study that does employ objective testing methods by Congdon et al. applied a rigorous methodology to explore the influence of LPI on forward-scatter of light in addition to subjective visual symptoms [24]. Although this study did not explicitly report the types or numbers of dysphotopsia symptoms occurring at each LPI location, which was the focus of our systematic review and hence its exclusion from our analysis, it did report no significant association between the LPI parameters, including size and location, and changes in retinal straylight or subjective symptoms, even 18 months post-procedure [24]. These findings support the notion that the incidence of dysphotopsia is not significantly impacted by the location of LPI, and also illustrates the potential benefits of incorporating retinal straylight measurements in future investigations on post-LPI visual disturbances.

It is important to note that the studies included in this review had a range of limitations, including data availability, methods of comparison, and variable definitions. These limitations may have contributed to some inconsistencies in the results and the lack of a significant difference between LPI locations, and should be considered when interpreting the findings. For example, the largest study in this review reported no adverse events [15] while the smallest reported over 700 complications total in a sample size of 150 patients [14]. Moreover, one study reported approximately one-third the total laser energy applied on average [14] compared to the other two. The methods of comparison also differed, with two paired-eye trials evaluating dysphotopsia on a monocular-level [13, 14], while the third measured them binocularly at the patient-level [15]. Finally, the use of different questionnaires and the way in which they were administered might have contributed to the variability in the results.

Despite these limitations, the findings of this review suggest that the location of LPI has no major influence on the incidence of dysphotopsia. Clinicians should be aware that dysphotopsia is a relatively common side effect of LPI, regardless of the location of the procedure, and should educate patients about the potential for visual symptoms (and possible resolution) following LPI. Further research with larger, well-designed protocols should be conducted to confirm these findings and to establish stronger consensus on the link between LPI location and visual disturbance. Ideally, future studies should use a standardized questionnaire (in addition to other objective measurements such as retinal straylight or contrast sensitivity) to survey patients on the extent of their dysphotopsia before and after the procedure, at multiple follow-up intervals. If possible, studies should strive to follow patients longitudinally and record dysphotopsia symptoms at least six months post-LPI, given that many have been shown to resolve after this time period [16]. Additionally, it will be important to capture information including: ethnicity, iris color, subjective pain grade, visual acuity, degree of lid coverage, iridotomy size and distance from the pupil, limbus, and lid margin, and other ocular comorbidities including cataract with corresponding type and severity.

Conclusion

In conclusion, the results of this systematic review suggest that the location of LPI does not significantly affect dysphotopsia frequencies. Further research with standardized questionnaires and comprehensive reporting of visual disturbances preceding and following LPI is needed to establish a stronger consensus. Nevertheless, clinicians should be aware of the potential for different types of dysphotopsias following LPI and should inform patients about the possibility of experiencing visual disturbances, in particular a 2–3% risk of linear dysphotopsia, regardless of the location of the procedure. Clinicians may also counsel patients that in many cases, performing LPI can lead to the resolution of pre-existing dysphotopic symptoms, particularly halos and glare.

Summary

What is known about this topic

• Dysphotopsias can occur after laser peripheral iridotomy (LPI).

• The prevalence ranges from 2 to 16% in patients undergoing LPI.

• Limited evidence exists on the relationship between LPI location and dysphotopsia with studies show conflicting findings, contributing to uncertainty.

What this study adds

• LPI location does not significantly impact dysphotopsia frequencies.

• Further research with standardized tools and comprehensive reporting is needed for stronger consensus.

• Clinicians should inform patients of potential dysphotopsias, emphasizing a 2-3% risk of linear dysphotopsia, and possible resolution of pre-existing halos and glare after LPI.

Author contributions

MB was responsible for designing the review protocol, conducting the search, screening potentially eligible studies, extracting and analyzing data, interpreting results, updating reference lists and manuscript preparation. DJM was responsible for reviewing the protocol, screening potentially eligible studies, interpreting results, manuscript preparation, and overall supervision of the review process.

Funding

Glaucoma Research Society of Canada (GRSC).

Competing interests

The authors declare no competing interests.

Supplementary information

The online version contains supplementary material available at 10.1038/s41433-023-02913-1.