NTG Joint session with Japan Glaucoma Society
Imaging characteristics of NTG
Dr. Akagi Tadamichi shighlightes the heterogeneity of NTG. IOP is a significant contributor to the progression of most NTG patients. On the other hand, approximately 30% of NTG patients progressed despite well-controlled IOP. Possible risk factors are lower tolerance for mechanical damage, perfusion deficit and vascular dysregulation, translaminar pressure gradient, and oxidative stress. Imaging the deep optic nerve head structure might help in understanding the pathophysiology.
A recent study showed that NTG eyes with steep curved LC were strongly related to IOP. Ocular blood flow also contributes to the pathogenesis of NTG. Optical coherence tomography angiography (OCTA)-derived optic disc microvasculature was strongly related to the mechanical strain induced by IOP. He concludes that there still be a lot of outstanding issues in NTG.
IOP lowering therapy works for NTG
Dr. Keith Barton summarized Collaborative Normal Tension Glaucoma Study (CNTG) which is the only randomized study regarding the influence of IOP lowering therapy on NTG. Based on CNTG, reducing the mean IOP from 16 mmHg to 10.6 mmHg reduced the incidence of progression from 30% to 12% during the course of the study. This suggests that IOPs < 10 mmHg are likely to be required to eliminate progression if progression can be eliminated by lowering IOP. He concludes that this study provides incontrovertible evidence that IOP lowering is beneficial for NTG, and NTG is a part of the spectrum of POAG in which IOP plays a role.
Myopic optic neuropathy or GON?
Dr. Tae-Woo Kim suggests key points for differentiating myopic optic neuropathy from typical glaucomatous optic neuropathy. Myopic optic disc changes are mainly derived by tensile strength due to scleral expansion, not by IOP. Therefore, it generally progresses at the age between the late teens to 30s. He recommended starting IOP-lowering treatment for myopic eyes with damage when they are younger than 40 years. For those older than 40 years with a normal range of IOP, we may wait and see after careful discussion with the patient.
Characteristics of VF progression of NTG
Dr. Takuhei Shoji starts his talk by answering the question of whether there is a difference in visual field changes between NTG and HTG. Based on numerous publications on this issue, NTG tends to be associated with localized, deep visual field defects at the superior hemifield and parafoveal region. Given that disc morphology, axial length, and vasculature factors can be confounders in the differences in the pattern of VF defects between NTG and HTG, he points out that we need to be cautious in elucidating the characteristics of VF damage in NTG.
Epidemiology of NTG
Dr. Aiko Iwase summarizes studies on the epidemiology of NTG Especially, Tajimi, and Kumejima Studies are large epidemiology studies conducted in Japan. In these studies, the prevalence of NTG was high ranging between 3.3 to 3.6 %. Identified risk factors were IOP, myopia, and age. Interestingly, over 92 % of undiagnosed NTG were newly found in these studies. She emphasized that careful fundus examinations are important in detecting new NTG cases.
Monitoring of 24hr IOP in NTG
In this presentation, Dr. Takeshi Hara explains that night-time IOP rise is mainly derived from increased episcleral venous pressure in the supine position. Because of this, approximately 20 % of NTG patients had IOP ≥ 21 mmHg at night. Therefore, it is important to measure IOP at night, especially while the patient is sleeping. 24-hour IOP measurement devices such as Contact Lens Sensors, and IOP sensors implanted in the intraocular lens (IOL) are possible tools to enable this. Furthermore, he looks forward to IOP telemetry that enables IOP data to be shared across countries, thus providing big data for medical researchers.
