The Education Committee carefully selects presentations from the World Glaucoma Congress 2017 in Helsinki for your benefit. This edition Monisha Nongpiur gives the introductions for the sessions Normal tension glaucoma: pathogenesis, progression and treatment and OCT angiography in glaucoma.
Normal Tension Glaucoma: Pathogenesis, Progression and Treatment
Ocular blood flow: How does ocular blood flow influence the course of glaucoma?
Professor Alon Harris
Prof Harris spoke about the role of vascular risk factors in glaucoma. He highlighted the associations of disc haemorrhage (DH) and ocular blood flow with disease progression in NTG, and described the presumed vascular and mechanical theories for the pathogenesis of DH. He also talked about the non-ocular vascular abnormalities in subjects with glaucoma. Prof Harris then presented a physically-based mathematical model that incorporated biomechanics and blood flow parameters, to better explain the vascular role in glaucoma and predict blood flow changes.
The Low-Pressure Glaucoma Treatment Study (LOGTS) Revisited
Professor Robert Ritch
Prof Robert Ritch provided an update on the LOGTS trial, which was conducted 18 years ago comparing 0.2% brimonidine with 0.5% timolol. The primary goals of the study was to identify risk factors associated with progression in NTG. One of the significant outcomes from the study was the possibility of a neuroprotective action of brimonidine; and the prospects for IOP-independent treatment options for glaucoma. Prof Ritch also talked about the importance of monitoring blood pressure (BP) in patients with glaucoma, and specifically discussed the effects of nocturnal BP on ocular blood flow.
Ocular Perfusion Pressure (OPP) and Glaucoma
Professor Michael S. Kook
In the first part of his talk, Prof Michael Kook described the basic concepts of ocular perfusion pressure (OPP) and the important role that OPP may play in the pathogenesis of glaucoma, and also the possible associations of disease progression with nocturnal dips in blood pressure. In the second part of his talk, Prof Kook presented several clinical scenarios that entail the assessment of OPP in clinical practice. He highlighted the importance of clinical interventions to improve OPP including working closely with physicians/cardiologists to modify antihypertensive medications.
The role of Cerebrospinal Fluid in Glaucoma
Dr Yaxing Wang presented on behalf of Professor Ningli Wang
Dr Yaxing talked about the possible mechanisms by which low CSF pressure and trans-laminar pressure difference (TLPD) may be involved in the development/pathogenesis of glaucoma especially in NTG. She then discussed findings from their experimental longitudinal study on monkeys where they found that lowering the CSF pressure by lumbar-peritoneal shunt induced optic neuropathy. She described the complex associations of the CSF pressures measured in the 3 cavities namely orbital, intracranial and lumbar and emphasized that TCPD estimation is more complex than just a difference between IOP and intracranial pressure.
Lamina Cribrosa Configuration in Normal Tension Glaucoma
Professor Tae-Woo Kim
Prof Kim spoke about the importance of stratifying glaucoma based on the predominant disease mechanism(s) as this can lead to tailored treatment approaches. He discussed the effects of IOP on lamina cribrosa deformation and configuration specifically in NTG patients; and suggested that stratification based on lamina cribrosa morphology may be an option for personalized disease management.
Risk Factors for Progression under treatments/without treatment
Professor Catherine J. Liu
Prof Catherine Liu talked about the importance of risk factors, natural history of the disease, and the need to rule out other conditions before confirming a diagnosis of NTG. She exquisitely summarized findings from the different large scale studies such as CNTGS and EMGT describing the natural history, factors associated with progression in both treated and untreated patients, and the effects of IOP reduction.
OCT Angiography in Glaucoma
Evidence for a vascular component and the impact of ocular perfusion pressure on glaucoma
Professor Vital P. Costa
Prof Costa discussed the challenges and limitations of different studies (experimental, cross-sectional, and longitudinal) and current techniques employed in the evaluation of ocular blood flow. Whilst OPP is considered a surrogate for ocular blood flow; its estimation is however influenced by several factors that affect the measurements of IOP, blood pressure, blood viscosity and vessel diameter. He reckons that OCTA imaging modality may better demonstrate the associations between ocular blood flow and glaucoma.
Principles and scanning protocols of OCT angiography
Dr Kaweh Mansouri
Dr Kaweh Mansouri reiterated the poorly understood vascular theory of glaucoma that is mainly due to the limitations of the available tools and techniques to evaluate ocular blood flow. Dr Mansouri then discussed the principles and advantages of the OCTA including an ability to visualize the different layers of vasculature from the superficial retinal layers to the choroid, and to perform quantitative estimations of the areas occupied by vessels. He ended the talk by illustrating potential applications of OCTA in glaucoma management.
OCT angiography versus structural assessment findings
Professor Gabor Hollo
Professor Gabor Hollo compared the diagnostic value of OCTA and OCT imaging modalities, and highlighted that the two provide complimentary information. He stressed upon the importance of correcting for artifacts and image quality. He then showed that OCTA might be useful in detecting glaucoma and progression. Prof Hollo emphasized that OCTA findings are not disease specific and clinical assessments are mandatory.
OCT angiography and glaucomatous optic nerve damage
Professor Tae-Woo Kim
Prof Tae talked about the application of OCTA in glaucoma for diagnosis as well as for the assessment of disease pathophysiology. He discussed the relevance and possible implications of microvascular dropouts (MVD) of the parapapillary area and deeper retinal layers. Alludes to the fact that it is not clear whether RNFL defect precedes vessel dropout or whether it is a secondary by-product.
The Role of Microvasculature in the Pathophysiology of Glaucoma: Evidence from OCT Angiography
Professor Linda M Zangwill
Mirroring Prof Kim’s view of the uncertainty in the sequences of events of microvascular changes in glaucoma pathogenesis, Prof Zangwill suggested that in some individuals, vascular changes are the primary event, whereas in others, mechanical damage may be the primary event. She then described the relationship between vascular and mechanical factors in the pathophysiology of glaucoma, which was assessed by evaluating vessel density in glaucomatous eyes with and without lamina cribrosa defect. She ended her talk by suggesting the need for longitudinal OCTA studies that would provide valuable information that may help improve our understanding of the pathophysiology of glaucoma.
Present and Future of OCTA in glaucoma management
Dr Harsha Rao
Dr Rao summarized the current status of OCTA in the diagnosis of glaucoma, confounders of measurements, and in the detection of progression. In terms of disease diagnosis, he showed that whilst OCTA can differentiate glaucomatous eyes from normal, however it was not superior to traditional structural measurements. In terms of the future of OCTA, Dr Rao emphasized on the need for advancements in technology before it can become a part of routine glaucoma workup in the clinics. He also stated that in the future, it is likely that glaucoma phenotype may be defined based on OCTA features.
Projection-resolve reflectance compensated OCTA in glaucoma
Professor David Huang
Prof Huang talked about the technological improvements in OCTA that would help improve the evaluation of glaucoma. He explained about the effects of projection artifacts in OCTA images and the processes to eliminate them resulting in Projection-resolved (PR) images. Based on the evaluation of PR-OCTA images, Prof Huang showed that the superior vascular complex (SVC) in the macula region was primarily affected in glaucoma, whereas the radial peripapillary capillary plexus (RPCP) was primarily involved in the parapapillary region. Furthermore, reflectance compensated measurements of vessel density improved the diagnostic accuracy of OCTA in glaucoma.