Transscleral cyclophotocoagulation followed by cataract surgery: a novel protocol to treat refractory acute primary angle closure

Acute primary angle closure (APAC) is a common ophthalmic emergency with the rising rapidly to extremely high levels because of a sudden obstruction of the anterior chamber angle [1]. APAC patients often have typical symptoms, including blurred vision, ocular pain, headache, nausea, and vomiting. Immediate aggressive management is required to prevent irreversible damage to the eye and optic nerve and to relieve the excruciating symptoms of the patient [2]. However, the current treatment options for APAC do not always timely result in a sufficiently lowered IOP.

The current treatment strategy for APAC is to lower IOP by both topical and systemic medications followed by laser peripheral iridoplasty or iridotomy, and finally removal of the lens. However, this strategy has several limitations. The IOP of a significant proportion of APAC eyes cannot be controlled successfully by medical treatment, while laser application is often limited by corneal edema [3]. If the conventional treatment fails to reduce the IOP, surgical procedures in the acute phase have to be considered. However, performing acute surgery on APAC eyes is technically challenging and may increase the risk of complications because of the presence of corneal edema, inflammation, shallow anterior chamber, floppy iris and unstable lens [3].

In our previous study [4], and some other reports [5‐7], diode laser transscleral cyclophotocoagulation (TCP) showed its IOP-lowering effects in eyes with APAC. However, the underlying mechanism remains unclear. In this study, we aimed to evaluate the safety and efficacy of TCP followed by cataract surgery on treating APAC. We also compared several ultrasound biomicroscopy (UBM) parameters to explore the underlying mechanisms.

Thirteen APAC eyes of 13 consecutive patients refractory to medical treatment (including 1% pilocarpine, 2% carteolol, 0.2% brimonidine, 1% brinzolamide, oral methazolamide and intravenous 20% mannitol, if there were no contraindications) were prospectively enrolled in this study. All patients presented with typical APAC symptoms and signs, including blurred vision, severe ocular pain, headache, nausea, vomiting, corneal edema, unresponsive dilated pupil, shallow anterior chamber, and elevated IOP. All these patients underwent emergency TCP followed by scheduled cataract surgery (interval time: 5–10 days, median: 7 days). Table 1 presents the characteristics of the study group and control group.

In the study group, the IOP decreased significantly from 51.5 ± 7.0 mmHg (mean ± standard deviation) before TCP to 16.4 ± 5.4 mmHg at day 1 after TCP (P < 0.001). At day 1 after the TCP, the excruciating symptoms had disappeared and the corneal edema had been resolved in all patients (Fig. 2). The IOP of the study group before cataract surgery (17.2 ± 4.8 mmHg) was significantly lower than that of the control group before emergency phacotrabeculectomy (40.1 ± 5.7 mmHg; P < 0.001). At 6 months after surgery, the IOP was 14.0 ± 3.4 mmHg and 16.7 ± 4.3 mmHg in the study group and control group, respectively (P = 0.090). At 6 months after surgery, there were no patients in the study group and 2 patients in the control group who needed anti-glaucoma medications to control the IOP (P = 0.48).

Table 2 shows the effect of TCP on the 8 UBM parameters studied. A significant increase was found for ACD, AOD500, and CBTmax; a significant decrease was found for ICPD. Figure 3 shows the effect per quadrant for the 6 parameters that were studied for each quadrant separately. As can be seen in this figure, the global changes (as depicted in Table 2) in especially AOD500 and to a lesser extent also in ICPD were mainly due to changes in the, treated, inferior quadrant (Fig. 4) whereas the global change in CBTmax was due to changes in all quadrants.

There were no complications during the TCP procedure. After the TCP, anterior chamber cells were present in all the patients, which could be part of the APAC attack itself or it could be due to the TCP. A self-limiting ciliochoroidal detachment was found in 5 patients (39%) by UBM, mostly in the superior and temporal quadrant (Fig. 4). There were no complications during the subsequent cataract surgery or post-cataract surgery. For the control group, there was 1 patient having a posterior lens capsule rupture during phacotrabeculectomy. After surgery, there were 5 patients with a fibrinous membrane in the anterior chamber in the control group, which needed YAG laser to resolve.

In this study, we explored the safety and efficacy of emergency TCP followed by scheduled cataract surgery on treating refractory APAC and described the anterior segment morphological changes of APAC eyes after TCP by UBM, aiming to explore the IOP-lowering mechanism of TCP. The acute attack resolved in all included patients with a major lowering of the IOP. The observed anatomical changes were an increase in ACD, inferior AOD500, and CBTmax, and a decrease in ICPD. Outcomes after 6 months regarding BCVA and IOP control were similar for emergency TCP followed by cataract surgery versus emergency phacotrabeculectomy.

After two reports on TCP in chronic angle closure glaucoma eyes [16, 17], the use of TCP on acute angle closure (AAC) eyes was first reported in 5 AAC cases from two ophthalmic units in the United Kingdom, in which conventional management, including topical and systemic medical treatment, laser iridotomy, and laser iridoplasty, had been unsuccesful [6]. All of their 5 cases achieved a successful control of the IOP and resolution of the acute attack after TCP. TCP was also shown to be safe and effective in reducing IOP in AAC patients secondary to intumescent cataract [5, 7]. The only published paper of TCP on APAC eyes was from our previous study [4], in which the IOP of medically unresponsive APAC eyes decreased but remained over 21 mmHg after TCP in all eyes. In the present study, however, the IOP of all the patients was well controlled. This difference might be the result of different laser settings and/or treatment location (20 × 2000 ms × 2000 mW in the inferior quadrant in the current study versus 20–40 × 1000 ms × 1700–2200 mW in the inferior 180 degrees in our previous study).

In this study, we tried to uncover the mechanism underlying the observed decrease in IOP after TCP in APAC. One possible mechanism explaining the decrease in IOP is shrinkage of the ciliary body. Histologically, TCP can cause coagulation necrosis, tissue contraction, and focal atrophy of ciliary body [18, 19], and clinically shrinkage can be observed during endocyclophotocoagulation treatment. Shrinkage will lead to a backward movement of the lens-iris diaphragm, deepening of the anterior chamber, and re-opening of an appositionally closed angle. Another possible mechanism is a sudden decrease in aqueous humor production, which may also contribute to the resolution of the pupillary block [1]. We found significant changes in four parameters: ACD (increase), AOD500 (increase), ICPD (decrease), and CBTmax (increase). The first three are ‘in between structures’ measures; CBTmax is a ‘structure’ measure. Both shrinkage and a sudden decrease in aqueous humor production will change the ‘in between structures’ measures (ACD, AOD500, and ICPD) in the observed direction. These changes describe the disappearance of the block and support the clinical observation: a huge decrease in IOP and clearance of the cornea. At first sight, the observed increase in CBTmax seems to falsify the shrinkage hypothesis, thus favoring a sudden decrease in aqueous humor production as the primary mechanism. However, we only treated inferiorly and the effect of this treatment was at least as effective as the treatment we performed over a larger area in our earlier study [4], arguing against a sudden decrease in aqueous humor production as the primary mechanism. One possibility is an initial shrinkage resolving the pupillary block followed by swelling due to edema formation. UBM observations performed more frequently than a single observation one day after the treatment, as we did, should be able to further our understanding of the exact mechanism of the beneficial effect of TCP in APAC.

The BCVA of all the APAC eyes improved and there was no vision loss after TCP. The main reason of the improvement might be the disappearance of corneal edema after TCP. TCP was initially introduced for IOP reduction in eyes with little or no visual potential. Nowadays, however, TCP is being used widely in eyes with good vision, although the results vary [16, 17, 20, 21]. Four studies presenting data on visual acuity changes due to TCP [22‐25] reported amounts of vision loss after TCP of 2 lines or more in 24% [22], 2 lines or more in 31% [23], unspecified loss in 13% [24], and 3 lines or more in 14% [25]. These values are in line with values reported after trabeculectomy or tube surgery [26]. The absence of vision loss in our series suggests that there was no excessive transient IOP rise directly after TCP (we did not measure IOP directly after the procedure; the first measurement was at day 1 after TCP).

Although there were 2 patients in the control group who needed medications to control IOP, there was no significant difference in IOP and BCVA at 6 months after surgery between the two groups. However, the complications of the control group were more severe than study group. This might be resulted from the cloudy cornea and high IOP during phacotrabeculectomy. The poor visibility would increase the risk of intra-operative complications and the dramatic sudden decrease of IOP during surgery would facilitate the occurrence of post-operative fibrinous membrane. Moreover, even without a difference in final BCVA and IOP, the TCP approach has a major logistic advantage as no emergency surgery has to be performed.

We acknowledge the limitations of our study. First, this was not a randomized clinical trial and the sample size was relatively small. Second, IOP was measured by noncontact tonometry. Although a good inter-device agreement between Goldmann tonometry and noncontact tonometry has been reported, [27, 28] Goldmann tonometry is still the gold standard in IOP assessment. However, Goldmann readings also have their limitations with cloudy, edematous corneas, and given that the treatment-induced IOP changes were very large, the type of tonometer is also less critical. Third, the duration of the IOP-lowering effect of TCP was not evaluated, because TCP was considered a temporary measure to allow for further, final cataract surgery. However, to the best of our knowledge, this is the first study to evaluate the safety and efficacy of TCP followed by cataract surgery on treating APAC and our UBM results can help to better understand the IOP-lowering mechanism of TCP on APAC eyes.

Our findings suggest that TCP can effectively lower the IOP, deepen the ACD, and widen the inferior angle in APAC. The presumed mechanism is an initial shrinkage of the involved tissues; UBM more frequently performed early after treatment is needed to further our understanding regarding the exact mechanism. However, even without the mechanism being fully uncovered, TCP could be considered a viable option for the initial treatment of APAC and can facilitate the following cataract surgery. Obviously, a further randomized two-armed clinical trial (TCP followed by cataract extraction versus cataract extraction alone) with larger sample size is needed to confirm the promising results in the present study.