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Editors Selection IGR 17-4

Clinical Forms of Glaucoma: Blood pressure dips and ONH hemorrage in NPG

Comment by Ki Ho Park on:

71290 Association between Nocturnal Blood Pressure Dips and Optic Disc Hemorrhage in Patients with Normal-Tension Glaucoma, Kwon J; Lee J; Choi J et al., American Journal of Ophthalmology, 2017; 176: 87-101

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There is still debate on the pathogenic mechanism of optic disc hemorrhage (ODH), specifically on the question of whether mechanical or vascular factors predominate. The current study by Kwon et al. supports the hypothesis that ODH is a manifestation of vascular dysregulation in patients with normal-tension glaucoma (NTG). It is the strength of their study that it enrolled a large number of consecutive 349 NTG patients (698 eyes) who were ≥ 40 years old and had undergone 24-hour intraocular pressure and ambulatory blood pressure (BP) monitoring in the habitual position. The patients were classified into two groups: 'non-physiologic' dippers, including nondippers and overdippers, and 'physiologic' dippers. Nocturnal BP overdipping was defined as nighttime BP reduction > 20%, as calculated by the following formula: [(daytime mean MAP - nighttime mean MAP)/daytime mean MAP] X 100. Nighttime BP overdippers showed a significantly greater frequency of ODH than did nondippers or dippers. Being an overdipper was a significant as well as an independent risk factor for ODH occurrence during follow-up.

Additionally, in a multivariate analysis, the standard deviation of daytime MAP was shown to be one of the risk factors associated with ODH, which means that MAP fluctuation is associated with ODH. Further, daytime MAP was higher in overdippers (95.1 mmHg) than in physiologic dippers (92.7 mmHg) or nondippers (87.5 mmHg). In other words, the nighttime BP overdippers in this study were also daytime BP overpeakers. For example, if a patient had a daytime MAP of 150 and a nighttime MAP of 100, the nighttime BP reduction would be (150-100/150) x 100 = 33%. And for the same patient, the daytime BP elevation could be calculated, by the same formula, as (150-100/100) x 100 = 50%.

There is a possibility that ODH is associated not only with nighttime BP reduction but also with daytime BP elevation

So, there is a possibility that ODH is associated not only with nighttime BP reduction but also with daytime BP elevation. Given that individuals on antihypertensive agents were not excluded from the study, there remains the possibility that patients with systemic hypertension were enrolled, over-treated, and, thus showed low nighttime BP subsequently. It should be noted, in this respect, that systemic hypertension has been reported as an ODH risk factor among Korean NTG patients.¹

The current study supports an IOP-independent mechanism of ODH in some proportion of NTG eyes; however, it should be emphasized that in order to understand the pathogenesis of ODH, the systemic vascular mechanism cannot be considered independently of localized structural vascular susceptibility and the pressure balance among IOP, cerebrospinal fluid pressure and arterial/venous pressure around the optic nerve head.²

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