Abstract
Aim
To compare the risk of early intraocular pressure (IOP) spikes following micropulse (MP) vs continuous wave (CW) transscleral cyclophotocoagulation (CPC).
Methods
Single-center, prospective, nonrandomized study that included glaucoma patients planned for MP- or CW-CPC at Wills Eye Hospital (2020–2021). IOP was measured using rebound tonometry (iCare) immediately before, immediately after, and 1 hour after the CPC, then on postoperative day 1. The primary outcome measure was the incidence of IOP spikes, defined as IOP elevation ≥10 mm Hg vs baseline. Patients with severe IOP spikes received IOP-lowering agents (topical or oral).
Results
Twenty-six eyes (15 CW and 11 MP) of 26 patients were included, with a mean age of 64.4 ± 15.1 years. At the baseline visit, IOP was 29.5 ± 11.3 mm Hg, and the medication number was 3.8 ± 1.4, with no difference between groups. IOPs (CW vs MP, mm Hg) were 31.9 ± 10.5 vs 24.1 ± 7.3 immediately before CPC (p = 0.044), 22.9 ± 10.8 vs 16.1 ± 6.3 immediately after CPC (p = 0.760), 24.6 ± 11.9 vs 23.2 ± 9.5 at 1 hour after CPC (p = 0.757), and 18.0 ± 6.1 vs 20.8 ± 6.9 at 1 day later (p = 0.335). Three eyes (11.5%; 1 CW, 2 MP) experienced IOP spikes (p = 0.556) at 1 hour post-CPC; IOP responded to topical and/or oral medications. At day 1 and month 1, mean IOP reduction compared to baseline was significant in CW eyes (p < 0.001) and insignificant in MP eyes (p > 0.05).
Conclusion
MP- and CW-CPC have similar risks of early postoperative IOP spikes. Significant early IOP reduction was better achieved following CW-CPC. Early postoperative IOP spikes may be detrimental; there may be a role for IOP monitoring in such cases.
Clinical significance
Understanding the early postoperative outcomes of MP- and CW-CPC is critical for optimizing glaucoma management. This study highlights that while both procedures carry a similar risk of early IOP spikes, CW-CPC demonstrates superior early IOP reduction. These insights help clinicians tailor CPC strategies to individual patient requirements.
How to cite this article
Shalaby WS, Arbabi A, Wong J, et al. Early Postoperative Intraocular Pressure Profile Following Micropulse vs Continuous Wave Transscleral Cyclophotocoagulation: Cohort Study. J Curr Glaucoma Pract 2025;19(1):8–14.
Keywords: Cohort study, Continuous wave cyclophotocoagulation, Glaucoma surgery, Intraocular pressure spikes, Micropulse cyclophotocoagulation
Introduction
The treatment of glaucoma is focused on lowering the intraocular pressure (IOP) with topical medications, laser techniques, and surgical procedures.1 Transscleral cyclophotocoagulation (CPC) is a procedure that targets the ciliary body processes, leading to decreased aqueous humor production.2 Owing to the risk of serious complications, CPC has generally been reserved for advanced, refractory glaucoma patients.3,5
Diode CPC in both micropulse (MP) and continuous wave (CW) modes is effective in lowering IOP in refractory glaucoma.6 In contrast to the traditionally used CW-CPC, where a continuous train of high-intensity energy is delivered, MP-CPC uses repetitive MPs of active diode laser with rest periods in between pulses.7 MP-CPC has been shown to demonstrate effectiveness as a method of lowering IOP in refractory glaucoma, comparable with conventional CW-CPC.7,8
Transient IOP spikes in the immediate postoperative period may occur following many glaucoma laser and surgical procedures, which could inflict further damage to the already compromised optic nerve, leading to vision loss.9 In one study, almost all eyes had significant IOP elevation immediately after CW-CPC.10 Another study reported that 34% of eyes undergoing CW-CPC had an IOP elevation ≥3 mm Hg during the first 3 hours postoperatively, with a mean increase of 10.3 mm Hg.11 Additionally, another cohort observed IOP spikes ≥5 mm Hg in 10.8% of patients 1 hour following CW-CPC.12 While the previous studies reported the IOP spike rates following CW-CPC, there is a lack of comparative research examining the incidence of this event between MP- and CW-CPC. Thus, the purpose of this study was to compare the immediate and short-term risk of IOP spikes following MP- vs CW-CPC.
Methods
Study Design
This was a prospective, comparative, nonrandomized study at a single tertiary care center and included patients with refractory glaucoma planned for MP- or CW-CPC. Written informed consent was obtained from all participants before enrolling.
Inclusion and Exclusion Criteria
Patients aged ≥18 years with refractory glaucoma and preoperative IOP >21 mm Hg planned for CW- or MP-CPC were included. Patients with no light perception (NLP) vision preoperatively or those with prior CPC or significant corneal opacity interfering with accurate IOP measurement were excluded.
Procedure
The choice of CPC type was based on the preferences of the six surgeons who contributed patients to this study. All surgeons were fellowship-trained glaucoma specialists. The procedures were performed in the operating room under topical ocular anesthesia, and intravenous sedation with propofol and cardiopulmonary monitoring were given by the anesthesia team. The starting laser parameters for MP-CPC were a treating time of 40–80 seconds per quadrant and a preset power of 2000–2500 mW, including four quadrants while sparing the 3 o'clock and 9 o'clock positions and any prior surgical sites (e.g., tube shunts, trabeculectomy, or vitrectomy). Both slow coagulation and titration methods were allowed for CW-CPC according to the surgeon's preferences. The parameters for the slow coagulation technique, based on the degree of iris pigmentation, were a preset power of 1250–1500 mW, a treating time of 3500–4500 ms, and 14–21 spots. The parameters for the titration method were a power of 2000 mW, a treating time of 2000 ms, and 14–21 spots. On the basis of the pop sound, power was titrated down or up until 250 mW less than when pops were heard.
Intraocular pressure was measured in the sitting position using the iCare tonometer immediately before, immediately after, and 1 hour after the procedure. The average of three consecutive IOP measurements at each time point was used for analysis. IOP was measured on postoperative day one using both iCare and Goldmann applanation tonometers (GAT). Postoperatively, all patients were instructed to use topical 1% prednisolone acetate four times daily (tapered over a 6-week period), and glaucoma medications were adjusted as required.
Outcome Measures
The primary outcome measure was the rate of IOP spikes following MP- and CW-CPC, defined as an IOP elevation of ≥10 mm Hg immediately after, 1 hour after, or 1 day after the CPC compared to baseline. Eyes with an IOP elevation of ≥5 mm Hg were also included in a secondary analysis; this allowed us to compare our results with those of other studies. A severe IOP spike prompting treatment was defined as a 30% IOP elevation with preoperative IOP ≥30 mm Hg, or a 40% IOP elevation with preoperative IOP <30 mm Hg immediately after or 1 hour after the CPC. Those with severe IOP spikes received topical IOP-lowering medications or oral acetazolamide at the discretion of the attending surgeon. Changes in visual acuity (VA), IOP, and glaucoma medications at postoperative day 1, month 1, and the final visit were secondary outcome measures. For patients who underwent glaucoma reoperation, including repeat CPC, IOP and medication number were censored from the analysis after these events.
Results
Baseline Characteristics
A total of 26 eyes of 26 patients were included. Fifteen eyes underwent CW-CPC, and 11 eyes underwent MP-CPC. Table 1 shows baseline patient characteristics. Patient demographics, as well as baseline ocular characteristics including glaucoma type and severity, medication number, cup-to-disk ratio, and lens status, were comparable in both groups. Baseline VA was significantly worse in the CW vs MP groups (1.56 ± 0.92 vs 0.87 ± 0.7, respectively; p = 0.050). Likewise, baseline IOP measured with GAT was significantly higher in the CW vs MP groups (34.5 ± 9.3 vs 25.4 ± 8.9 mm Hg, respectively; p = 0.020). Neovascular glaucoma was the most common glaucoma type in the CW group (46.7%). In the MP group, neovascular glaucoma (27.3%) along with primary open-angle glaucoma (27.3%) were the most common glaucoma types. A total of 76.9% of patients had undergone glaucoma surgery prior to the CPC, with no difference between groups (p = 0.389). In the CW group, the titration method was used in 12 eyes, employing a mean power of 1850 ± 443 mW with an average total duration of 34 ± 7 seconds (2000 mS/spot) and application of 13–21 spots, while three eyes had the slow coagulation method, employing a mean power of 1462 ± 102 mW with an average total duration of 75 ± 9 seconds (4000 mS/spot) and application of 16–20 spots. For the MP group, a mean power of 2164 ± 172 mW was used on the MP setting for an average total duration of 221 ± 58 seconds (40–80 seconds/quadrant).
Table 1:
Baseline characteristics in the CW- and MP-CPC groups
| CW | MP | Total | p-value | ||
|---|---|---|---|---|---|
| Eyes # | 15 | 11 | 26 | ||
| Patients # | 15 | 11 | 26 | ||
| Age: years | 64.5 ± 10.0 | 64.3 ± 20.7 | 64.4 ± 15.1 | 0.966 | |
| Female sex: N (%) | 7 (46.7) | 6 (54.5) | 13 (50.0) | 1.000 | |
| Race: N (%) | White | 3 (20.0) | 4 (36.4) | 7 (26.9) | 0.241 |
| Black | 1 (6.7) | 3 (27.3) | 4 (15.4) | ||
| Hispanics | 1 (6.7) | 0 (0.0) | 1 (3.8) | ||
| Other | 10 (66.7) | 4 (36.4) | 14 (53.8) | ||
| Glaucoma type: N (%) | POAG | 2 (13.3) | 3 (27.3) | 5 (19.2) | 0.565 |
| PACG | 2 (13.3) | 1 (9.1) | 3 (11.5) | ||
| PXG | 0 (0.0) | 1 (9.1) | 1 (3.8) | ||
| NVG | 7 (46.7) | 3 (27.3) | 10 (38.5) | ||
| Traumatic | 0 (0.0) | 1 (9.1) | 1 (3.8) | ||
| Malignant | 1 (6.7) | 0 (0.0) | 1 (3.8) | ||
| Axenfeld-Rieger | 1 (6.7) | 1 (9.1) | 2 (7.7) | ||
| Silicone oil induced | 1 (6.7) | 0 (0.0) | 1 (3.8) | ||
| Postinjection | 0 (0.0) | 1 (9.1) | 1 (3.8) | ||
| Melanoma | 1 (6.7) | 0 (0.0) | 1 (3.8) | ||
| Glaucoma severity: N (%) | Mild | 2 (13.3) | 1 (9.1) | 3 (11.5) | 0.811 |
| Moderate | 5 (33.3) | 5 (45.5) | 10 (38.5) | ||
| Severe | 8 (53.3) | 5 (45.5) | 13 (50.0) | ||
| Prior glaucoma surgery: N (%) | 11 (73.3) | 9 (81.8) | 20 (76.9) | 0.389 | |
| Prior vitrectomy: N (%) | 2 (13.3) | 1 (9.1) | 3 (11.5) | 1.000 | |
| VA: LogMAR | 1.6 ± 0.9 | 0.9 ± 0.7 | 1.3 ± 0.9 | 0.050 | |
| IOP: mm Hg | 34.5 ± 9.3 | 25.4 ± 8.9 | 30.6 ± 10.1 | 0.020 | |
| Glaucoma medications: # | 3.9 ± 1.4 | 4.3 ± 0.8 | 4.0 ± 1.1 | 0.384 | |
| Oral diamox: N (%) | 6 (40.0) | 6 (54.5) | 12 (46.2) | 0.692 | |
| Cup-to-disk ratio | 0.8 ± 0.2 | 0.7 ± 0.2 | 0.7 ± 0.2 | 0.147 | |
| Lens status: N (%) | Phakic | 7 (46.7) | 6 (54.5) | 13 (50.0) | 0.399 |
| Pseudophakic | 8 (53.3) | 5 (45.5) | 13 (50.0) | ||
| Gonioscopy: N (%) | Open-angle | 2 (13.3) | 7 (63.6) | 9 (34.6) | 0.059 |
| Narrow angle | 10 (66.7) | 3 (27.3) | 13 (50.0) | ||
| Silicone oil | 1 (6.7) | 0 (0.0) | 1 (3.8) | ||
| Hazy view | 2 (13.3) | 1 (9.1) | 3 (11.5) | ||
NVG, neovascular glaucoma; PACG, primary angle closure glaucoma; POAG, primary open-angle glaucoma; PXG, pseudoexfoliation glaucoma
Outcome Measures
Table 2 shows the main outcome measures in the CW and MP groups. A total of three eyes (11.5%) experienced an IOP increase of at least 10 mm Hg at 1 hour after the CPC (1 CW, 2 MP) with no difference between groups (p = 0.556). All three eyes also met the criteria for a severe IOP spike at 1 hour post-CPC as defined in the study protocol, which warranted treatment. Following treatment with topical and/or oral pressure-lowering medications, all three eyes showed a reduction in IOP of at least 5 mm Hg by the 2nd hour. Characteristics of patients who developed IOP spikes are highlighted in Table 3. In the CW eye that developed an IOP spike, the IOP was 12.0 mm Hg at month 1, then was elevated to 57.0 mm Hg by the final visit (16.3 months). Among the patients with IOP spikes in the MP group, one patient required reoperation for glaucoma (tube shunt) by month 1 due to persistent IOP elevation (33.0 mm Hg). The other patient had a final IOP of 20 mm Hg (29.2 months) without additional glaucoma surgery. When considering IOP elevation ≥5 mm Hg, two additional eyes were observed: one CW eye (immediately after and 1 hour after the CPC) and one MP eye (at day 1).
Table 2:
Main outcome measures in the CW- and MP-CPC groups
| CW | MP | Total | p-value | ||
|---|---|---|---|---|---|
| IOP spikes ≥10 mm Hg: N (%) | 1 (6.7) | 2 (18.2) | 3 (11.5) | 0.556 | |
| IOP spikes ≥5 mm Hg: N (%) | 2 (13.3) | 3 (27.3) | 5 (19.2) | 0.620 | |
| IOP: iCare-mm Hg | Immediately before | 31.9 ± 10.5 | 24.1 ± 7.3 | 28.6 ± 9.9 | 0.044 |
| Immediately after | 22.9 ± 10.8 | 16.1 ± 6.3 | 20.0 ± 9.6 | 0.760 | |
| 1-hour after | 24.6 ± 11.9 | 23.2 ± 9.5 | 24.0 ± 10.8 | 0.757 | |
| Postoperative day 1 | 18.0 ± 6.1 | 20.8 ± 6.9 | 19.4 ± 6.5 | 0.335 | |
IOP, intraocular pressure
Table 3:
Characteristics of patients who developed postoperative IOP spikes ≥10 mm Hg
| Patient 1 | Patient 2 | Patient 3 | |
|---|---|---|---|
| Age: years | 83 | 89 | 59 |
| Sex | Female | Female | Male |
| Race | Other | Black | Other |
| Glaucoma type | PXG | POAG | NVG |
| Glaucoma severity | Moderate | Severe | Moderate |
| Prior glaucoma surgery | Trabeculectomy | None | None |
| CPC type | MP | MP | CW |
| Average power: mW | 2000 | 2000 | 1550 (1100–2000) |
| Total duration: seconds | 180 | 320 | 32 |
| Other parameters | – | – | Titration method 16 spots 2000 ms/spot 4 audible pops |
| IOP immediately before: mm Hg | 16.7 | 34.7 | 20.0 |
| IOP immediately after: mm Hg | 23.0 | 42.7 | 24.0 |
| IOP 1-hour after: mm Hg | 35.0 | 47.3 | 31.0 |
| Baseline IOP: mm Hg | 28.0 | 24.0 | 47.0 |
| Day 1 IOP: mm Hg | 35.0 | 18.0 | 13.0 |
| Month 1: mm Hg | 33.0 | NA | 12.0 |
| Final visit IOP: mm Hg | 18.0 | 20.0 | 57.0 |
| Follow-up duration: months | 2.3 | 29.2 | 16.3 |
| Reoperation | Tube shunt (at month 1) |
None | None (NLP from LP) |
CPC, cyclophotocoagulation; CW, continuous wave; IOP, intraocular pressure; LP, light perception; MP, micropulse; NLP, no light perception; NVG, neovascular glaucoma; POAG, primary open-angle glaucoma; PXG, pseudoexfoliation glaucoma
The mean IOP in the CW and MP groups was 31.9 ± 10.5 vs 24.1 ± 7.3 immediately before CPC (p = 0.044), 22.9 ± 10.8 vs 16.1 ± 6.3 immediately after CPC (p = 0.760), 24.6 ± 11.9 vs 23.2 ± 9.5 1 hour after CPC (p = 0.757), and 18.0 ± 6.1 vs 20.8 ± 6.9 1 day later (p = 0.335), respectively (Fig. 1, changes in IOP observed in each group at different time points, and Fig. 2, changes in IOP observed in each patient at different time points).
Fig. 1:
Immediate and early IOP changes in the CW- and MP-CPC groups using iCare. *Error bars represent 95% confidence intervals
Fig. 2:
IOP changes over time following CPC in each study patient
Table 4 highlights the changes in VA, IOP, and medication number in each group at postoperative day 1, month 1, and final visit compared to the baseline. The average follow-up duration was 25.6 ± 12.18 months in the CW group (N = 11) and 20.6 ± 13.5 months in the MP group (N = 11), with no difference between groups (p = 0.387). Using GAT, the IOP was significantly reduced from 34.5 ± 9.3 mm Hg at baseline to 16.8 ± 6.4 mm Hg at postoperative day 1 (p < 0.001), 12.1 ± 4.4 mm Hg at month 1 (p < 0.0001), and 22.0 ± 16.4 mm Hg at the final visit (p = 0.062) in the CW group, while in the MP group, the IOP was reduced from 25.4 ± 8.9 mm Hg at baseline to 21.0 ± 7.6 mm Hg at postoperative day 1 (p = 0.103), 21.4 ± 8.1 mm Hg at month 1 (p = 0.329), and 17.6 ± 5.3 mm Hg at the final visit (p = 0.206). IOP changes over time are demonstrated in Figure 3. The VA and mean number of glaucoma medications remained stable in both groups at all visits compared to baseline. Reoperation for glaucoma was required in seven (31.8%) eyes, three (27.3%) in the CW group and four (36.4%) in the MP group (p = 0.999). Types of reoperations included repeat CPC for all CW eyes (N = 3) and tube shunt (N = 3) or CW-CPC (N = 1) for the MP eyes.
Table 4:
Postoperative outcomes in the CW- and MP-CPC groups
| Baseline | Day 1 | Month 1 | Final visit | |
|---|---|---|---|---|
| CW | ||||
| VA: LogMAR | 1.6 ± 0.9 | 1.9 ± 0.8 | 1.7 ± 1.0 | 1.8 ± 1.2 |
| Number of patients | 15 | 15 | 11 | 11 |
| p-value | 0.053 | 0.359 | 0.592 | |
| IOP: mm Hg | 34.5 ± 9.3 | 16.8 ± 6.4 | 12.1 ± 4.4 | 22.0 ± 16.4 |
| Number of patients | 15 | 15 | 11 | 8 |
| p-value | <0.001 | <0.001 | 0.062 | |
| Glaucoma medications: # | 3.9 ± 1.4 | 3.7 ± 1.7 | 3.5 ± 1.6 | 3.0 ± 1.7 |
| Number of patients | 15 | 15 | 11 | 8 |
| p-value | 0.610 | 0.341 | 0.316 | |
| MP | ||||
| VA: LogMAR | 0.9 ± 0.7 | 0.8 ± 0.6 | 0.9 ± 0.9 | 0.8 ± 0.8 |
| Number of patients | 11 | 11 | 9 | 11 |
| p-value | 0.443 | 0.247 | 0.908 | |
| IOP: mm Hg | 25.4 ± 8.9 | 21.0 ± 7.6 | 21.4 ± 8.1 | 17.6 ± 5.3 |
| Number of patients | 11 | 11 | 9 | 7 |
| p-value | 0.103 | 0.329 | 0.206 | |
| Glaucoma medications: # | 4.3 ± 0.8 | 4.0 ± 1.2 | 4.2 ± 1.0 | 4.4 ± 1.1 |
| Number of patients | 11 | 11 | 9 | 7 |
| p-value | 0.192 | 0.347 | 0.999 | |
Fig. 3:
IOP changes over time in the CW- and MP-CPC groups using Goldmann applanation tonometer. *Error bars represent 95% confidence intervals
Discussion
In this prospective study, we examined the incidence of early postoperative IOP spikes following CW- and MP-CPC. Among 26 eyes of 26 patients, significant IOP spikes were noted in three eyes (11.5%) at 1 hour following the CPC. All eyes exhibited a favorable response to topical and/or oral medications. By day 1 and month 1, the CW group displayed a significant reduction in IOP, whereas the MP group demonstrated a more modest reduction.
The clinical relevance of IOP spikes following CPC procedures necessitates thorough postoperative examination. These spikes can impact the surgical outcomes in glaucoma patients and their visual function. While most IOP spikes in healthy eyes, such as those developing following cataract surgery, are probably benign and do not result in permanent optic nerve damage or visual field defects,13,14 there is evidence suggesting that comparable transient elevations of IOP might be harmful in patients with compromised optic disks, leading to irreversible visual impairment if left untrea-ted.9,15,16 Additionally, sustained high IOP levels may increase the risk of corneal decompensation, exacerbating preexisting corneal conditions and impeding visual rehabilitation. Moreover, anterior ischemic optic neuropathy (AION) may rarely complicate IOP spikes as a result of reduced ocular perfusion pressure, significantly compromising blood supply to the optic disk.17,18 In our study, we implemented a follow-up protocol of at least 1 hour for all patients to detect immediate IOP spikes, subsequently providing appropriate treatment to those who experienced significant IOP elevation. An alternative approach involves administering prophylactic oral acetazolamide to all patients before the procedure, a method reported to notably reduce the incidence of IOP spikes following cataract surgery.19 However, it should be noted that almost half of the patients in this study of CPC were already taking oral CAIs. Prior studies have reported the rates of IOP spikes following CW-CPC,10,12 but no studies have compared the spike rates between CW- and MP-CPC.
Uppal et al.11 investigated the rates of immediate and short-term IOP spikes following CW-CPC in a prospective case series that included 53 eyes of 41 patients. The IOP measurements were taken immediately prior to the CPC and hourly for 3 hours afterward. IOP spikes were defined at two levels: ≥3 and ≥10 mm Hg from the baseline. Out of 49 eyes that completed the study protocol, 17 eyes (34%) had IOP elevation ≥3 mm Hg during the first 3 hours postoperatively (with a mean increase of 10.3 mm Hg), and 9 eyes (18%) had IOP elevation ≥10 mm Hg (with a mean increase of 13.8 mm Hg). When comparing these results to the rates of IOP spikes in our overall sample, including both CW and MP, their findings were comparable to ours (18 vs 11.5% for IOP elevation ≥10 mm Hg). However, when comparing the spike rates for the CW group alone, the difference became more pronounced (18 vs 6.7%). Potential reasons for this difference include several factors. In Uppal's study, both eyes from the same patient were included in some cases, eyes with prior CPC were not excluded (N = 16), and they used fixed power (2000 mW) and duration (2 seconds) even if “pops” were heard during the treatment. In contrast, in our study, we included only one eye per patient, excluded eyes with prior CPC, and used the titration or slow coagulation methods for CW eyes. Additionally, we had a relatively smaller sample size compared to their study, and we measured the IOP at two time points following the CPC (immediately after and 1 hour after) compared to three measurements for 3 hours in their study.
Contreras et al.12 retrospectively evaluated the incidence of IOP spikes, defined as IOP elevation ≥5 mm Hg at 1 hour after CW-CPC, in 116 eyes of 110 patients. The study reported a spike rate of 10.8%, which is comparable to our rates for the CW cohort (13.3%) considering IOP elevation ≥5 mm Hg. Similar to Uppal's study, eyes with prior CPC were included, and a higher spike rate was observed in eyes with retreatment, as well as eyes with neovascular glaucoma, but the difference did not reach statistical significance for either.
Razeghinejad et al.10 included 10 eyes of 10 patients in a prospective case series evaluating IOP spikes following CW-CPC. IOP was measured immediately before, immediately after, and 3 hours after the CPC. The titration method was used for all patients, with starting laser parameters of 2000 mW power and 2000 mS duration/spot, then power was adjusted in steps of 250 mW based on the pop-sound response. The power used ranged between 1500 and 3000 mW, and the duration/spot ranged between 2000 and 4000 mS. Those with immediately high IOP post-CPC received intravenous 20% mannitol (1 gm/kg). Out of 10 eyes, nine showed a significant increase in IOP immediately after the CPC (IOP of 31.4 ± 9.8 immediately before vs 44.3 ± 14.3 mm Hg immediately after the CPC; p = 0.012). Despite receiving the intravenous mannitol, six patients had IOP ≥30 mm Hg and two had IOP ≥50 mm Hg 3 hours after the procedure. However, on the first postoperative day, no patients had IOP ≥30 mm Hg. The rates of immediate IOP spikes in this study are significantly high (90%) compared to our results and the aforementioned studies. Similar to ours, the study is limited by its relatively small sample size. Additionally, their inclusion of pediatric patients aged <18 years (N = 4, range 1–12 years) introduces a potential factor of different responses compared to adults. There was no specific set definition of “significant IOP elevation.” However, upon examining the IOP readings they provided for each patient, two out of nine had IOP increase of 8 mm Hg, and seven out of nine had IOP increase ≥10 mm Hg (range 8–38 mm Hg).
The definition of an IOP spike can significantly influence its reported incidence. However, there is currently no universally accepted formal definition of a clinically significant spike. To address this, we included two different definitions of IOP spikes. The first definition utilized a fixed cutoff point of 10 mm Hg, irrespective of the baseline IOP values. The second definition considered the percentage increase of IOP compared to the baseline, with two grading criteria: a 30% increase for preoperative IOP ≥30 mm Hg, or a 40% increase for preoperative IOP <30 mm Hg. This approach allows for a lower threshold when the baseline IOP is already elevated (baseline IOP was significantly higher in the CW group), as spikes could potentially cause greater harm in such scenarios. However, the rates of IOP spikes were similar using both definitions. With only three eyes experiencing IOP spikes in our study, we were unable to conduct a regression analysis to reliably identify predictors or risk factors associated with this complication. We also analyzed a lower cutoff point of 5 mm Hg increase of IOP, and the rates of IOP spikes remained low (five eyes or 19.2%) and similar in both groups (p = 0.620).
Prior studies have compared the surgical success and safety of MP- vs CW-CPC over variable follow-up durations (12–24 months).6,20,21 While the surgical success of both modalities was comparable, the overall complication rates (including prolonged inflammation, hypotony, choroidal/retinal detachment, phthisis, vision decline, and scleral thinning) were consistently reported to be significantly higher in the CW group.6,20,21 Comparing the long-term success was outside the scope of our study, but we observed significant IOP reduction at postoperative day 1 and month 1 in the CW group (p < 0.001 for all), compared to modest reduction in the MP group (p > 0.05 for all). These findings do not necessarily reflect better efficacy of the CW-CPC for two reasons. Firstly, early IOP reduction is not always associated with better long-term control. Secondly, the baseline IOP was significantly higher in the CW group, and this relationship between the higher baseline IOP and the better IOP reduction is consistently observed across various IOP-lowering procedures, such as cataract surgery,22 SLT,23,24 microshunt,25 aqueous shunts,26 and trabeculectomy.27 However, our study's findings in the early postoperative period can guide clinicians in selecting the appropriate CPC modality when rapid IOP reduction is required.
This study has several potential limitations. The relatively small sample size of 26 eyes may restrict the generalizability of the results to broader populations. Additionally, the lack of randomization in assigning patients to the CW- or MP-CPC groups could introduce selection bias, especially considering that we observed a significantly higher baseline IOP in the CW group compared to the MP group. Similarly, there was no standard protocol for the use of postoperative glaucoma medications, and variations in the number of medications may have affected IOP measurement on day 1 and at later visits. Furthermore, the relatively short follow-up duration employed in this study may not have provided sufficient time to capture the effect of early IOP spikes on final outcomes. Moreover, we excluded patients with prior CPC, who may exhibit different response patterns and potentially more refractory glaucoma. Future larger-scale prospective randomized studies with longer follow-up duration may be necessary to address these limitations. Despite these limitations, our study still offers important insights into the short-term IOP spike rate following two CPC techniques, particularly considering the lack of similar comparative studies. In certain patients, early postoperative IOP spikes could have potential damaging effects; thus, there may be a role for IOP monitoring and/or prophylactic IOP lowering in such cases.
Conclusion
To our knowledge, this is the first study to prospectively report the rate of early postoperative IOP spikes in MP- vs CW-CPC. Both groups showed similar risk of IOP spikes, while significant early IOP reduction was better achieved with CW-CPC in this sample.
Clinical Significance
Understanding the early postoperative outcomes of MP- and CW-CPC is critical for optimizing glaucoma management. This study highlights that while both procedures carry a similar risk of early IOP spikes, CW-CPC demonstrates superior early IOP reduction. These findings can guide clinicians in selecting the most appropriate CPC approach based on individual patient needs.
Footnotes
Source of support: Nil
Conflict of interest: None
References
- 1.Schuster AK, Erb C, Hoffmann EM, et al. The diagnosis and treatment of glaucoma. Dtsch Arztebl Int. 2020;117(13):225–234. doi: 10.3238/arztebl.2020.0225. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Pastor SA, Singh K, Lee DA, et al. Cyclophotocoagulation: a report by the American Academy of Ophthalmology. Ophthalmology. 2001;108(11):2130–2138. doi: 10.1016/s0161-6420(01)00889-2. [DOI] [PubMed] [Google Scholar]
- 3.Chen MF, Kim CH, Coleman AL. Cyclodestructive procedures for refractory glaucoma. Cochrane Database Syst Rev. 2019;3:CD012223. doi: 10.1002/14651858.CD012223.pub2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4.Schlote T, Derse M, Rassmann K, et al. Efficacy and safety of contact transscleral diode laser cyclophotocoagulation for advanced glaucoma. J Glaucoma. 2001;10(4):294–301. doi: 10.1097/00061198-200108000-00009. [DOI] [PubMed] [Google Scholar]
- 5.Ramli N, Htoon HM, Ho CL, et al. Risk factors for hypotony after transscleral diode cyclophotocoagulation. J Glaucoma. 2012;21(3):169–173. doi: 10.1097/IJG.0b013e318207091a. [DOI] [PubMed] [Google Scholar]
- 6.Aquino MCD, Barton K, Tan AMWT, et al. Micropulse versus continuous wave transscleral diode cyclophotocoagulation in refractory glaucoma: a randomized exploratory study. Clin Exp Ophthalmol. 2015;43(1):40–46. doi: 10.1111/ceo.12360. [DOI] [PubMed] [Google Scholar]
- 7.Sanchez FG, Peirano-Bonomi JC, Grippo TM. Micropulse transscleral cyclophotocoagulation: a hypothesis the ideal parametersfor. Med Hypothesis Discov Innov Ophthalmol. 2018;7(3):94–100. 30386797 [PMC free article] [PubMed] [Google Scholar]
- 8.Tan AM, Chockalingam M, Aquino MC, et al. Micropulse transscleral diode laser cyclophotocoagulation in the treatment of refractory glaucoma. Clin Exp Ophthalmol. 2010;38(3):266–272. doi: 10.1111/j.1442-9071.2010.02238.x. [DOI] [PubMed] [Google Scholar]
- 9.Tranos P, Bhar G, Little B. Postoperative intraocular pressure spikes: the need to treat. Eye (Lond) 2004;18(7):673–679. doi: 10.1038/sj.eye.6701319. [DOI] [PubMed] [Google Scholar]
- 10.Razeghinejad MR, Hamid A, Nowroozzadeh MH. Immediate IOP elevation after transscleral cyclophotocoagulation. Eye (Lond) 2017;31(8):1249–1250. doi: 10.1038/eye.2017.59. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11.Uppal S, Stead RE, Patil BB, et al. Short-term effect of diode laser cyclophotocoagulation on intraocular pressure: a prospective study. Clin Exp Ophthalmol. 2015;43(9):796–802. doi: 10.1111/ceo.12558. [DOI] [PubMed] [Google Scholar]
- 12.Contreras I, Noval S, Gonzalez Martin-Moro J, et al. [IOP spikes following contact transscleral diode laser cyclophotocoagulation] Arch Soc Esp Oftalmol. 2004;79(3):105–109. doi: 10.4321/s0365-66912004000300003. [DOI] [PubMed] [Google Scholar]
- 13.Radius RL, Maumenee AE. Visual field changes following acute elevation of intraocular pressure. Trans Sect Ophthalmol Am Acad Ophthalmol Otolaryngol. 1977;83(1):61–68. 898476 [PubMed] [Google Scholar]
- 14.Sanborn GE, Friberg TR, Allen R. Optic nerve dysfunction during gravity inversion. Visual field abnormalities. Arch Ophthalmol. 1987;105(6):774–776. doi: 10.1001/archopht.1987.01060060060033. [DOI] [PubMed] [Google Scholar]
- 15.Kolker AE. Visual prognosis in advanced glaucoma: a comparison of medical and surgical therapy for retention of vision in 101 eyes with advanced glaucoma. Trans Am Ophthalmol Soc. 1977;75:539–555. 613530 [PMC free article] [PubMed] [Google Scholar]
- 16.Savage JA, Thomas JV, Belcher CD, 3rd,, et al. Extracapsular cataract extraction and posterior chamber intraocular lens implantation in glaucomatous eyes. Ophthalmology. 1985;92(11):1506–1516. doi: 10.1016/s0161-6420(85)33828-9. [DOI] [PubMed] [Google Scholar]
- 17.Hayreh SS. Anterior ischemic optic neuropathy. IV. Occurrence after cataract extraction. Arch Ophthalmol. 1980;98(8):1410–1416. doi: 10.1001/archopht.1980.01020040262010. [DOI] [PubMed] [Google Scholar]
- 18.McCulley TJ. Ischemic optic neuropathy and cataract extraction: what do I need to know? Oman J Ophthalmol. 2012;5(3):141–143. doi: 10.4103/0974-620X.106090. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19.Hayashi K, Yoshida M, Manabe SI, et al. Prophylactic effect of oral acetazolamide against intraocular pressure elevation after cataract surgery in eyes with glaucoma. Ophthalmology. 2017;124(5):701–708. doi: 10.1016/j.ophtha.2016.12.027. [DOI] [PubMed] [Google Scholar]
- 20.Kelada M, Normando EM, Cordeiro FM, et al. Cyclodiode vs micropulse transscleral laser treatment. Eye (Lond) 2024;38:1477–1484. doi: 10.1038/s41433-024-02929-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 21.Zemba M, Dumitrescu OM, Vaida F, et al. Micropulse vs. continuous wave transscleral cyclophotocoagulation in neovascular glaucoma. Exp Ther Med. 2022;23(4):278. doi: 10.3892/etm.2022.11207. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 22.Poley BJ, Lindstrom RL, Samuelson TW, et al. Intraocular pressure reduction after phacoemulsification with intraocular lens implantation in glaucomatous and nonglaucomatous eyes: evaluation of a causal relationship between the natural lens and open-angle glaucoma. J Cataract Refract Surg. 2009;35(11):1946–1955. doi: 10.1016/j.jcrs.2009.05.061. [DOI] [PubMed] [Google Scholar]
- 23.Alaghband P, Galvis EA, Daas A, et al. Predictors of selective laser trabeculoplasty success in open-angle glaucoma or ocular hypertension: does baseline tonography have a predictive role? Br J Ophthalmol. 2020;104(10):1390–1393. doi: 10.1136/bjophthalmol-2019-315489. [DOI] [PubMed] [Google Scholar]
- 24.Khawaja AP, Campbell JH, Kirby N, et al. Real-world outcomes of selective laser trabeculoplasty in the United Kingdom. Ophthalmology. 2020;127(6):748–757. doi: 10.1016/j.ophtha.2019.11.017. [DOI] [PubMed] [Google Scholar]
- 25.Rabiolo A, Toscani R, Sacchi M, et al. Risk factors for failure in glaucoma patients undergoing microshunt implantation. Am J Ophthalmol. 2024;259:117–130. doi: 10.1016/j.ajo.2023.11.011. [DOI] [PubMed] [Google Scholar]
- 26.Bowden EC, Choudhury A, Gedde SJ, et al. Risk factors for failure of tube shunt surgery: a pooled data analysis. Am J Ophthalmol. 2022;240:217–224. doi: 10.1016/j.ajo.2022.02.027. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 27.Song BJ, Ramanathan M, Morales E, et al. Trabeculectomy and combined phacoemulsification-trabeculectomy: outcomes and risk factors for failure in primary angle closure glaucoma. J Glaucoma. 2016;25(9):763–769. doi: 10.1097/IJG.0000000000000493. [DOI] [PMC free article] [PubMed] [Google Scholar]