At the completion of this article, the reader should be able to improve their detection of glaucoma using gonioscopy, including:
- Understand the role of the Primary Angle Closure Glaucoma (PACG) continuum in diagnosis and management of glaucoma
- Understand the consequences of unintended indentation of the cornea with a gonioscope
- Be familiar with the ‘Gonio Game’ technique and how it can increase the possibility of detection of angle closure.
Dr Jeremiah Lim
BOptom, MPhil, PhD (Melb)
Senior Lecturer, School of Allied Health, Optometry
The University of Western Australia, Perth WA
Lisa Jansen
BOptom(Hons), CertOcTher
Lecturer, School of Allied Health, Optometry
The University of Western Australia, Perth WA
Pauline Xu
M.Optom, CertOcTher, BOptom
Senior Lecturer, School of Allied Health, Optometry
The University of Western Australia, Perth WA
In the first instalment of Insight’s CPD gonioscopy primer, the authors offered key insights from educational gonioscopy workshops at the University of Western Australia optometry school in 2023. Now, they bust two lingering myths: that IOP measurement alone can suffice for monitoring glaucoma suspects and that Van Herick angle assessments are dependable alternatives to gonioscopy.
In the Part 1 of our ‘Gonioscopy Primer’ we showed how and why skilled gonioscopy remains indispensable for precise anterior chamber assessment. While technology can assist, it does not supplant the art of gonioscopy.
In this, the second part of our ‘Gonioscopy Primer,’ we explain why dynamic gonioscopy is such an important skill and we address the myths that intraocular pressure (IOP) and Van Herick (VH) angle measurements alone are reliable substitutes for gonioscopy.
Myth: For glaucoma suspects, routine IOP measurements are an adequate substitute for primary angle closure monitoring.
It surprises many eyecare professionals to learn that IOP elevation is often missed on routine clinical testing. But it’s not so surprising once you understand the intermittent nature of angle closure.
In a comprehensive review, Sun and his co-authors beautifully summarised the primary angle closure glaucoma (PACG) continuum as “starting from a pre-clinical stage, which remains clinically undetectable using IOP, visual fields (VF) or optical coherence tomography (OCT). Then progressing to an attack stage, which may be composed of a series of intermittent mild or acute attacks, ultimately giving rise to optic nerve head (ONH) damage and the formation of peripheral anterior synechiae (PAS). With the formation of PAS, the increase in IOP becomes more consistent, eventually leading to chronic- or end-stage PACG”. 1
The majority of patients with angle closure disease i.e. PAC and PACG do not present with acute angle closure crisis – where IOPs can often present above 30 mmHg. Clinically, these patients may be virtually indistinguishable from open angle forms of glaucoma in terms of IOP, ONH appearance, OCT and VF. In this regard, the only distinguishable difference between two fundamentally different forms of glaucoma is gonioscopy.
In other words, there is a risk that PACG is misclassified as primary open angle glaucoma (POAG). Unfortunately, this means a number of PACG patients currently on standard POAG medical or laser therapy will continue to progress and develop chronic PAS formation if one is not thorough in their glaucoma assessment.
Growing emphasis on monitoring PACS with gonioscopy
Let’s say I have just performed gonioscopy and detected at least two quadrants of iridotrabecular touch (ITC) without other signs and diagnosed PACS (primary angle-closure suspect). So what do I do now – observe or refer for prophylactic laser peripheral iridotomy (LPI) treatment?
There have been quite a few developments in this space over the past two decades. The Vellore Eye Study conducted in Southern India in the early 2000s showed that up to 22% of PACS progressed to PAC over a five-year period2 and up to 30% of PAC progressed to PACG,3 which supports prophylactic treatment.
However, more recently, the Zhongshan Angle Closure Prevention (ZAP) trial4 involving a large Chinese population showed that only 8% of untreated PACS progress to PAC over a five-year period, reaffirming that acute angle closure is less common in at-risk eyes than previously thought and that the rate of developing peripheral anterior synechiae (PAS) and elevated IOP is relatively slow.
In a similar vein, the Singapore Asymptomatic Narrow Angles Laser Iridotomy Study (ANALIS) trial involving a multi-ethnic, but predominantly Chinese population, showed untreated rates of progression closer to 10%5 over a five-year period.
Consequently, there has been a shift away from prophylactic LPI to increased monitoring of PACS.* For practitioners, this means that there will be an increased emphasis on regular monitoring of PACS using gonioscopy.
Clinical recommendations
In our clinic, we recommend monitoring asymptomatic PACS six monthly, provided that the patient is not on medications that are likely to provoke an angle closure attack. We also consider the individual’s location (e.g. rural) and occupations (like fly-in/fly-out workers) which may affect access to care. Another indication for prophylactic LPI is if they need frequent dilation (as with diabetes).
In the presence of PAC or PACG, referral to an ophthalmologist is recommended for LPI or lens extraction.
Laser Peripheral Iridotomy
When referring patients off for treatment, it’s important to set the right expectations. The standard of care includes LPI which mitigates future angle closure attacks but, as seen from the ZAP or ANALIS, it only reduces the risk of progression.4 This means up to 50% of your patients still progress further along the primary angle closure disease spectrum despite treatment. It is also important to note that the aim of LPI or lens extraction is not to lower IOP but rather to modify the angle in a way that prevents further attacks. Indeed, up to 59% of patients maintain some form of ITC after LPI treatment.6
Peripheral Anterior Synechiae
In the presence of extensive PAS, standard glaucoma medical therapy or surgery may be used to reduce the IOP. To the eyecare practitioner, this means continued regular gonioscopy after LPI to look for future – or further – PAS development. In addition, continued monitoring of the patency of the LPI which, in our experience, is best viewed using fundus retroillumination, preferably under dilation with the upper lids lifted. Under high magnification, it’s also possible to view aqueous movement through the iridotomy.
Dynamic gonioscopy: A skill you already possess
Currently, the best way to look for PAS is the use of dynamic gonioscopy. Also known as ‘corneal indentation gonioscopy’, this is an important skill for the optometrist to have, depending on the demographic they serve, as well their comfort level with the technique.
In order to perform corneal indentation, you need to have a contact diameter smaller than the horizontal visible iris diameter (HVID) (typically ≤9 mm) to allow for central corneal displacement without moving the globe posteriorly (Figure 1).
In our experience, one of the most common mistakes made by novice gonioscopists is the assumption that all anatomical structures from Schwalbe’s line (SL) to the ciliary body (CB) band should be visible.
This may be akin to how we assume a patient should be able to read 6/6 on the vision chart. This assumption is counterintuitive – unlike visual acuity, one is not able to ‘improve’ the grade of the angle. What often happens is the unintended indentation of the cornea by the practitioner, revealing structures that are appositionally closed under normal conditions. The danger in doing so is that patients with narrow angles may be incorrectly classified as having ‘open angles.
Figures 2A-2C. Summary of three common situations where dynamic gonioscopy is useful in the assessment of the anterior chamber angle.
The ’Gonio Game’
One of the ways to prevent unintentional indentation is to encourage novices to first get a stable view of the angle (with or without indentation) and, once a comfortable view is obtained, to slowly ease the pressure off the cornea and carefully observe as structures recede away from view.
Colloquially known as the ‘Gonio Game’ by author Dr Jeremiah Lim, the assumption behind this technique is 1) if you can manipulate the angle ‘open’ through indentation, then the opposite must be true; and 2) if an angle is truly anatomically wide open (CB visible), no matter how much you ease off the eye, this will not artificially result in the ‘closing’ of the angle.
The aim of the ‘Gonio Game’ is to ‘make’ the angle as narrow as possible, recording one’s narrowest assessment of the angle. This flips the assumption that ‘angles should be open’ on its head, incentivising clinicians to increase their sensitivity towards the detection of angle closure.
When to indent
There are numerous scenarios where dynamic gonioscopy is indicated, such as acute angle closure first aid. However, this article will focus on three specific indications for the technique (summarised in Table 1): differentiating appositional from synechial closure and plateau iris.
Appositional vs synechial closure
Appositional closure occurs when angles are anatomically narrow or are occludable in the absence of pathology. In practice, what this means is during gonioscopy, only the Schwalbe’s line (SL) and anterior trabecular meshwork (ATM) are visible. But upon indentation, deeper structures such as the posterior trabecular meshwork (PTM), scleral spur (SS) or ciliary body (CB) are revealed.
As one might recall from Part 1 of this article, the appearance of two or more appositionally closed quadrants would lead to a diagnosis of PACS. In the event that indentation does not reveal more structures, then one can assume the presence of PAS, hence changing the diagnosis from PACS to PAC even in the absence of elevated IOP.
Unlike posterior synechia, which appear around the pupil margin and may occasionally be broken with dilating drops such as atropine, PAS does not break with indentation. Often laser or surgical treatments are required to prevent further progression. Occasionally a form of surgery known as goniosynechialysis,7 where the surgeon inserts a spatula or microforceps into the anterior chamber in order to break the PAS, is performed.
Plateau iris
Dynamic gonioscopy may also be useful in troubleshooting narrow angles arising from the anterior insertion of the iris root as seen in plateau iris. In this case, the angle is narrow because of the anatomical crowding of the angle by the iris. Another tell-tale sign of the presence of plateau iris is when a patent LPI fails to relieve the block mechanism.
Using indentation gonioscopy, instead of revealing more structures, the increased pressure within the AC is unable to open the angle due to the forward position of the iris root. The increased force moves more centrally, causing a temporary ‘dip’ in the region between the iris root and the pupil margin, resulting in a ‘double hump’ or sine-wave sign. The practitioner can choose to intermittently indent to appreciate the sine wave movement of the iris using this technique.
Myth: Van Herick angle measurements are adequate substitutes for gonioscopy or at the very least, provide indication on the need to perform gonioscopy.
Sensitivity of VH technique alone is insufficient for detecting angle closure.
One barrier to gonioscopy that we encountered through our workshops is frequent over-estimation of the VH angle. Similar to unintended indentation on gonioscopy, one can overestimate the width of the VH angle by accidentally moving the light away from the limbus and closer to the central cornea. In a similar vein to the ‘Gonio Game’ introduced above, practitioners should aim to ‘make’ the VH angle as small as possible, on the same premise that a truly wide angle cannot close. Interestingly, a study performed at the Wilmer Eye Institute, showed that even with specialised VH training, up to 40% of angle closures are still missed.8
Given the degree of skill involved in performing a good VH assessment and the poor sensitivity and specificity of the technique, we recommend performing gonioscopy in all glaucoma suspects, regardless of their VH status or IOP. As one might recall from Part 1 of the primer, IOP elevation is not the only indicator of PAC. As the VH classification does not detect PAS, it is incapable of detecting progression to PAC hence not used in primary angle closure disease classification.
Another point to note is that gonioscopy is also a key tool used to identify secondary causes of glaucoma such as pseudoexfoliation or pigment dispersion. In the absence of secondary causes, gonioscopy serves as an equally important tool to diagnose POAG or PACG by exclusion.
Gonioscopy indications, setup, and grading
We hope that the knowledge shared in this article has provided the motivation for clinicians to pick up their gonio lenses more often. In our experience, gonioscopy has minimal impact on chair time once practitioners progress from the novice into the adept stages. This last section serves as a quick refresher on the technique.
Indications
Gonioscopy should be performed on all glaucoma suspects, and routinely on those with a VH angle of ≤0.25, asymmetrical anterior chamber (AC) depths or clinical signs suggestive of previous angle closure (e.g. glaucomflecken or pigment in the AC).
Although the absence of symptoms does not rule out angle closure, practitioners should look out for patients who complain of intermittent blur, red eyes, headaches, haloes around light—all of which may occur especially at night when pupils are larger.
Setup
When setting up for gonioscopy, it’s important to have the room lights dimmed to prevent unnecessary pupil constriction which pulls the iris away from the angle, giving the false impression that the angle is physiologically open. This includes avoiding shining light into the pupil when viewing through the central mirror. Upon mounting the gonio lens, it is useful to allow for a 10 second rest period to increase your likelihood of detecting a pupil block. Another useful modification to the technique is the use of a shorter beam height (1 mm) to ensure that light does not spill into the central mirror when viewing the angle.
Grading
When it comes to recording gonioscopy findings, several grading systems are available (Table 1). It’s worth noting that the two most commonly-used grading scales, the Shaffer and the Scheie, are opposite to each other. The Shaffer grades how ‘wide’ the angle is whereas the Scheie grades how narrow the angle is. In the Australian context, the Shaffer system appears to be the preferred grading scale used by specialists. To avoid ambiguity, clinicians should state the grading system used. Our preference is to name the most posterior anatomical layer seen in each quadrant.
Conclusion
While imaging devices, VH angle measurements and IOP assessments are, of course, still valuable tools in optometric practice, as we have shown they cannot replace the art and science of gonioscopy.
Mastering gonioscopy remains essential for precise anterior chamber assessment and the early detection of glaucoma. Optometrists should prioritise learning and practicsing this skill; it plays a pivotal role in comprehensive eyecare today and will continue to play a pivotal role in the future.
*In both studies, it was shown that prophylactic Laser Peripheral Iridotomy (LPI) halved the risk of progression from PACS to PAC.
More reading
Gonioscopy primer: Insights from a gonioscopy workshop (Part 1)
Keeping the ocular surface healthy in the glaucoma patient
Pearls for expanding use of OCT-A in optometric practice
References
1. Sun X, Dai Y, Chen Y, Yu D-Y, Cringle SJ, Chen J, et al. Primary angle closure glaucoma: What we know and what we don’t know. Progress in Retinal and Eye Research. 2017; 57: 26-45.
2. Thomas R, George R, Parikh R, Muliyil J, Jacob A. Five year risk of progression of primary angle closure suspects to primary angle closure: a population based study. The British journal of ophthalmology. 2003; 87 (4): 450.
3. Thomas R, Parikh R, Muliyil J, Kumar RS. Five–year risk of progression of primary angle closure to primary angle closure glaucoma: a population–based study. Acta ophthalmologica Scandinavica. 2003; 81 (5): 480-5.
4. He M, Jiang Y, Huang S, Chang DS, Munoz B, Aung T, et al. Laser peripheral iridotomy for the prevention of angle closure: a single-centre, randomised controlled trial. Lancet. 2019; 393 (10181): 1609-18.
5. Baskaran M, Kumar RS, Friedman DS, Lu QS, Wong HT, Chew PTK, et al. The Singapore Asymptomatic Narrow Angles Laser Iridotomy Study: Five-Year Results of a Randomized Controlled Trial. Ophthalmology. 2022; 129 (2): 147-58.
6. He M, Friedman DS, Ge J, Huang W, Jin C, Cai X, et al. Laser peripheral iridotomy in eyes with narrow drainage angles: ultrasound biomicroscopy outcomes. The Liwan Eye Study. Ophthalmology. 2007;114 (8): 1513-9.
7. Campbell DG, Vela A. Modern goniosynechialysis for the treatment of synechial angle-closure glaucoma. Ophthalmology. 1984; 91 (9): 1052-60.
8. Johnson TV, Ramulu PY, Quigley HA, Singman EL. Low Sensitivity of the Van Herick Method for Detecting Gonioscopic Angle Closure Independent of Observer Expertise. Am J Ophthalmol. 2018; 195: 63-71.
