New Ways of Looking
In the past, ophthalmologists who suspected glaucoma had to rely on a visual field-testing machine, a tonometer, and an ophthalmoscope. Those were simpler times, but these are better ones.
With Ike Ahmed, Earl Randy Craven, Marlene Moster, Constance Okeke, Paul I. Singh, and Robert N. Weinreb
At a Glance
- The Advanced Glaucoma Technologies Forum took place in New York, USA, in October 2018
- An invited panel of glaucoma experts, chaired by Ike Ahmed, discussed many topics, including aqueous outflow and patient selection
This article explores the topic of advanced diagnostic technologies used to identify and stage glaucoma.
Today, our diagnostic tools do much more than simply rule glaucoma in or out: they help us stage the disease, estimate risk of progression, and measure any progression that does occur. In particular, data provided by modern tools helps us identify patients at highest risk – information which is key to glaucoma management and good clinical decisions. But, as is often the case, better information raises more questions than it answers; as Paul Singh says: “The more we learn, the more we realize how far we have to go.” So where have we got to on this journey?
Identifying and staging
At present, identifying and staging glaucoma still requires both structural and functional information: today, these are mainly provided by optical coherence tomography (OCT) and visual field (VF) testing, respectively. In combination, these types of data help surgeons identify patients as early as possible in the course of the disease. Elucidation of the underlying disease mechanisms in a given patient, says Singh, can also guide management; for example, it can suggest a “watch and wait” strategy, thus saving aggressive therapy for those who really need it. “Understanding the relationship between structural and functional change,” adds Marlene Moster, “helps us choose the right treatment for each individual patient.” Only a minority of patients, she continues, are serious enough to justify a trabeculectomy; most can be classified into various categories that are more suited to one or another of the alternative approaches now available. “Glaucoma therapy can be personalized more than ever before,” she says.
Constance Okeke has firm views on the diagnostic benefits of gonioscopy. “It’s a key tool to guide MIGS selection – the angle helps you decide which procedure to use.” She gives an example: a patient with a narrow angle and appositional closure. “Here, I would probably use a Trabectome procedure, because the hand piece tip allows me to not only open up the angle by goniosynechialysis, but also to follow up by removing the trabecular meshwork with a partial goniotomy so as to open up the outflow system.” By revealing ocular pathology, such as pseudo exfoliation, pigment dispersion, or synechia, says Okeke, gonioscopy helps guide the surgeon regarding the choice of MIGS (e.g. goniotomy, stents or canaloplasty).
Progression risk and progression measurement
Estimations of progression risk, by contrast, rely on assessment of risk factors such as family history, disc hemorrhage, intraocular pressure (IOP), central corneal thickness (CCT), and corneal hysteresis (CH). All agree on the importance of IOP (See box: IOP), but Okeke emphasizes the utility of CH in determining how aggressively to treat a given patient, and Bob Weinreb agrees: “Corneal hysteresis is powerfully associated with risk of glaucoma progression – and is often overlooked.” He suggests that, absent CH, the association between CCT and glaucoma progression actually may not exist.
Measuring glaucoma progression, however, requires both structural (OCT) and functional (VF) information. In the former context, Okeke suggests that OCT-mediated analysis helps indicate speed of glaucomatous change, and Weinreb notes that OCT angiography may be highly useful in monitoring patients with advanced disease. Regarding structural and functional analysis, the importance of testing macular OCT and VF is increasingly clear – Weinreb reminds us of work by Don Hood, Gus DeMoraes and Jeff Liebmann (1).
In conclusion
Ultimately, Randy Craven says, glaucoma diagnostics has benefited from a process of evolution: as problems arise, the ophthalmology community has addressed them, and so the field has advanced. “But we are still on the quest to find the magic number – the precise risk factor for each individual patient.” Population-based studies, better OCT systems and other tools are helping us move towards this goal; ophthalmologists can now – with more confidence than ever before – judge how aggressively to treat a given patient. And this is unequivocally good; as Craven concludes: “We are no longer automatically opting for trabeculectomy – with all its downsides, including hypotony – rather, we are trying to do the right thing for each patient. That’s personalized therapy, in a way.”
IOP: How can it guide treatment? Some expert views
Randy Craven: “There are several ways of measuring IOP, which all work in different ways: for example, ORA, rebound tonometry, Goldmann tonometry, pneumotonometry. In each case, patient variations can interfere with the measurements – you end up adjusting Goldmann numbers in cases of thick corneas, for example. My habit now is to take measurements with three different instruments – when you see big differences between techniques, it actually tells you a bit more about the eye, such as how compliant or viscoelastic it is. Therefore, I rely on a group of pressure measurements from different machines – I don’t know if I’m unique in that.”
Marlene Moster: “We need 24/7 IOP measurements to really understand whether our treatments are effective or not. Moving towards implanting sensors in the eye will enable us to better understand how the individual is responding, and will help us make better surgical decisions for that patient.”
Paul Singh: “We have to remember that IOP is just a number, a risk factor – it is not directly related to glaucoma. In fact, it’s a moving target, which is why I find it’s helpful to have other measurements. In particular, hysteresis provides information about the quality of the IOP measurements: for example, I’d be more concerned about low hysteresis and high IOP than about high hysteresis and higher IOP. So we shouldn’t look at IOP in isolation – we need to take account of many other variables, including age, magnitude of pressure fluctuations, and rate of progression.”
Ike Ahmed: “The incorporation of ocular biomechanics, specifically hysteresis measurements, assists risk analysis and helps us understand how the eye can handle a head of pressure. The ability to monitor pressure during out-of-office hours has been very revealing – when you see self-monitored IOP spiking in the patient’s home, it is another indication that proactive, aggressive treatment may be required.”
The Advanced Glaucoma Technologies Forum was hosted by The Ophthalmologist and supported by Ellex, Santen, Heidelberg Engineering, Reichert Ametek and Aerie Pharmaceuticals Inc.
Ike Ahmed is Assistant Professor at University of Toronto, Canada.
Earl Randy Craven is Associate Professor of Ophthalmology at Johns Hopkins University, Maryland, USA.
Marlene Moster is Professor of Ophthalmology, Wills Eye Hospital, Philadelphia, USA.
Constance Okeke is a glaucoma and cataract surgery specialist at Virginia Eye Consultants, and also an Assistant Professor of Ophthalmology at Eastern Virginia Medical School, Virginia, USA.
Paul I. Singh is an ophthalmic surgeon at Eye Centers of Racine and Kenosha, Wisconsin, USA.
Robert N. Weinreb is Distinguished Professor and Chair, Ophthalmology, University of California, USA.
- DC Hood et al., “Glaucomatous damage of the macula”, Prog Retin Eye Res, 32, 1 (2013). PMID: 22995953.
