Primary angle-closure glaucoma is a common cause of permanent blindness worldwide. The disease spectrum is classified into 3 groups based on gonioscopic and clinical features:
- Primary angle-closure suspect (PACS): ≥180° of iridotrabecular contact (ITC).
- Primary angle closure (PAC): Peripheral anterior synechiae (PAS) or elevated intraocular pressure (IOP) in addition to the features of PACS.
- Primary angle-closure glaucoma (PACG): Signs of glaucomatous optic neuropathy (visual field or structural changes) in addition to features of PAC.
The Effectiveness of Early Lens Extraction for the Treatment of Primary Angle-closure Glaucoma (EAGLE) study provided evidence for the first-line use of clear lens exchange over laser peripheral iridotomy (LPI) for patients with PAC or PACG.1 However, there is more ambiguity regarding optimal management and treatment for PACS.
Management of PACS often involves either observation or a prophylactic LPI. The 14-year outcomes of the Zhongshan Angle-closure Prevention (ZAP) study demonstrated that the risk of conversion of PACS to PAC or PACG was 3 times lower in eyes receiving a prophylactic LPI.2 Similarly, the Singapore Asymptomatic Narrow Angle Laser Iridotomy Study (ANA-LIS) showed that LPI decreased the incidence of PAS formation over 5 years from 4.9% in the non-treated group compared to 1.3% in the LPI group.3 These studies suggest that although prophylactic LPI produces a notable relative risk reduction, the absolute risk reduction in the conversion of PACS to PAC or PACG remains small.
In our clinical practice, we routinely perform LPIs, particularly in patients who are high risk (higher IOPs or significant narrowing and ITC on gonioscopy). Laser peripheral iridotomy is a safe and effective intervention that can help reduce the risk of a catastrophic acute event (acute angle-closure attack) as well as a more progressive decline (chronic angle-closure glaucoma). That being said, LPI is not without its risks. Potential complications include dysphotopsia, postprocedural inflammation, intraocular pressure spikes, hyphema, cataract formation, and the possibility of needing repeat procedures.4,5
Despite these risks, treatment of PACS with LPI may be favored over observation in many circumstances. Observation of PACS requires careful monitoring and routine gonioscopy to evaluate for progressive narrowing and PAS formation. Several studies have shown that routine gonioscopy is not commonly or accurately performed, with many angle-closure patients often being misclassified as open-angle glaucoma.6,7 Definitions of the PAC disease spectrum and monitoring for disease progression depend on precise gonioscopy grading. However, this can be challenging, as factors such as clinic conditions, technique, and clinician experience can all influence the accuracy of angle assessment.
Given the potential variability in gonioscopy, efforts have been made to use anterior segment ocular coherence tomography (AS-OCT) to better risk stratify patients who require laser peripheral iridotomy. A growing body of evidence suggests that several metrics on AS-OCT (angle opening distance [AOD]; trabecular iris space area [TISA]; and angle recession area [ARA]) can aid in the diagnosis and monitoring of PACS.8,9 However, the measurements can be prone to some variability, particularly with differing lighting conditions. Furthermore, the lack of longitudinal studies evaluating the predictive power of AS-OCT limits its widespread use in risk stratifying PACS.
The decision to treat a PACS eye with a prophylactic LPI remains nuanced and requires careful consideration of individual patient factors. In this article, we present 3 case examples to illustrate our approach to managing patients with PACS.
Case 1
A 56-year-old female presents for annual follow-up. She was referred by optometry for concern for narrow angles in both eyes. She is not currently taking any topical medications. Visual acuity is 20/20 in both eyes. Her IOP is 13 in the right eye and 14 in the left eye. Gonioscopy is open to nonpigmented trabecular meshwork, but with compression the angle deepens to scleral spur and no PAS is present. Slit lamp exam shows clear lenses bilaterally. Optic nerves show a cup-to-disc ratio of 0.25 in both eyes. OCT imaging of the retinal nerve fiber layer (RNFL) and 24-2 HVF have been stable over the past 4 years (Figure 1).
Figure 1. Ocular coherence tomography (OCT) imaging of the retinal nerve fiber layer (RNFL) for this 56-year-old female was stable over the course of 4 years. Image courtesy James C. Liu, MD.
Discussion: This patient has been followed for the past 4 years with normal IOP and normal testing. Serial gonioscopy exams have not demonstrated notable changes or PAS formation. Given the stability of her disease and consistency of follow-up, observation with annual gonioscopy is a reasonable approach here. Reviewing the signs and symptoms of an angle-closure attack is important. We also recommend personally screening for any medications (antidepressants, allergy medications, cold medications, or neurologic medications) that may put the patient at risk for an acute angle-closure event. If PAS begins to develop, lens extraction or LPI may be considered, depending on the patient’s accommodative status and cataract symptoms.
Case 2
A 69-year-old female presents for cataract evaluation of the left eye. The patient was noted to have primary open-angle glaucoma of both eyes by the referring provider. On exam, visual acuity is 20/25 in the right eye and 20/50 in the left eye. Her IOP is 15 mmHg in the right eye and 16 mmHg in the left eye, while on 1 IOP-lowering agent in both eyes. On gonioscopy, both eyes show no visible angle structures, deepen to bare scleral spur with compression, but the right eye has no visible PAS while the left eye has 2 to 3 clock hours of scattered PAS. Slit lamp exam shows a mixed cataract in both eyes, left eye worse than right. OCT RNFL is normal on the right eye but with severe polar thinning in the left eye (Figure 2). Humphrey visual field of the right eye is normal; the left eye showed a superior arcuate (Figure 3).
Figure 2. OCT imaging of a 69-year-old female patent shows a healthy RNFL in the right eye and polar thinning in the left eye. Image courtesy James C. Liu, MD.
Discussion: The patient was initially referred with a diagnosis of POAG in both eyes. However, on presentation to our clinic, it was determined that she had signs of angle closure on gonioscopy. The patient presented as PACS in the right eye and PACG in the left eye. Given the severity of the glaucoma in the left eye, the patient agreed to phacoemulsification and goniotomy in that eye.
Figure 3. Humphrey visual field (HVF) of the left eye of a 69-year-old female patient shows a superior arcuate that corresponds to the polar thinning shown on RNFL images (A); HVF of the right eye (B) is normal. Image courtesy James C. Liu, MD.
This case highlights the potential for severe and rapid progression that can occur in this disease process. Although the 2 eyes are anatomically similar, progression into PACG in the left eye was quite rapid and led to significant asymmetry compared to the right eye. Often in these patients with severe unilateral PAC/PACG, the course of the first eye should inform the management of the second eye. In this case, an LPI was performed in the right eye given the severity of the disease of the left eye. It is also important to counsel the patient that despite treatment with the LPI, regular follow-up is still important, because the angle may continue to narrow in LPI-treated eyes as the crystalline lens grows with age and causes phacomorphic changes.10
Case 3
A 54-year-old male presents for evaluation of narrow angles. LPI was performed in both eyes at outside clinic, but the iridotomies did not result in any visible change to the angle anatomy. On presentation to our clinic, visual acuity is 20/20 in both eyes. IOP is 15 mmHg in the right eye and 14 mmHg in the left eye without topical agents. There is no afferent pupillary defect. Gonioscopy demonstrates iridotrabecular contact with occlusion of the pigmented trabecular meshwork 360° in both eyes without PAS formation. OCT RNFL is within normal limits and HVF is full in both eyes as well. Ultrasound biomicroscopy (UBM) is conducted (Figure 4) to further investigate the etiology of the narrow angle configuration, given the poor response to LPI.
Figure 4. Ultrasound biomicroscopy (UBM) of the right (A) and left (B) eyes shows anterior rotation of the ciliary body consistent with a plateau iris configuration in both eyes. Images courtesy James C. Liu, MD.
Discussion: This patient presented from an outside clinic for evaluation after LPI. Given the angle configuration, an LPI was certainly justifiable. However, the lack of angle opening angle after LPI suggests a non-pupillary block mechanism. UBM shows anterior rotation of the ciliary body consistent with a plateau iris configuration in both eyes, explaining the lack of efficacy with LPI.
This case illustrates that although LPI is effective in treating pupillary block, it does not address other mechanisms of angle closure, including phacomorphic lens rise and plateau iris configuration. Performing an LPI also does not necessarily preclude the need for serial gonioscopy or glaucoma screening tests. Plateau iris syndrome can sometimes be treated with argon laser peripheral iridoplasty. However, if this patient progressed to PACG, our preferred approach would be to offer cataract surgery and endoscopic cyclophotocoagulation to shrink and rotate the ciliary bodies away from the angles. Given the patient’s age, lack of family history of glaucoma or angle-closure events, normal testing, and normal IOP, the decision was made to observe this patient.
Conclusions
In patients who follow up reliably, have not shown changes in their IOP or gonioscopy findings, and are hesitant to undergo a procedural intervention, close observation is a reasonable approach if they are well informed of the potential risks of angle closure. However, in higher risk patients (higher IOPs, significant ITC on gonioscopy, or more notable disease on the PAC spectrum in the fellow eye), we typically recommend LPI or lens extraction depending on the patient’s accommodative status and cataract symptoms. It is important to keep in mind the different mechanisms of angle closure. If the angle does not open as expected after an LPI, further thought must be given to other potential mechanisms, such as lens rise or plateau iris. UBM can be a helpful tool in better elucidating the mechanism of angle closure in these patients.
The cases highlighted here demonstrate several scenarios one may encounter when approaching a primary angle-closure suspect. As illustrated here, the decision to observe, perform an LPI, or consider early cataract surgery often depend on the individual nuances of the patient and careful examination. GP
References
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