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Editors Selection IGR 8-1

Clinical Examination Methods: Ocular Hemodynamics

Comment by Makoto Araie on:

80085 Ocular Hemodynamics in Acute Nonarteritic Anterior Ischemic Optic Neuropathy Compared With Normal Tension Glaucoma, Kuerten D; Fuest M; Bienert M et al., Journal of Glaucoma, 2019; 28: 334-340

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It has been assumed that blood velocity of retrobulbar vessels {ophthalmic artery (OA), posterior ciliary artery (PCA) and central retinal artery (CRA)} and resistance indexes (RI), a parameter indicating down-stream resistance of the questioned vessel, could be estimated in vivo using color Doppler imaging (CDI). However, a formula for calculating RI which has more clinical implications in evaluating peripheral circulatory conditions was rheologically over-simplified and could be affected by factors other than mere peripheral vascular resistance. In spite of these limitations, previous prospective or retrospective longitudinal studies reported that higher RI values in the OA and/or PCA or slower blood velocity in the OA, CRA and/or PCA were associated with progression of primary open-angle glaucoma (POAG).

PCA hemodynamics of NTG eyes were already similarly affected as in the NAION eyes

The results of the authors' study to characterize retrobulbar hemodynamics in eyes shortly after the onset of non-arteritic anterior ischemic optic neuropathy (NAION) in comparison with that of chronic POAG with normal pressure (normal-tension glaucoma, NTG) are of clinical interest. In spite of a clear inter-group difference in the frequency of cardiovascular risk factors and time period the onset, no significant difference was seen in the PCA CDI parameters between the NAION and NTG group. The authors' second explanation for this rather unexpected finding that PCA hemodynamics of NTG eyes were already similarly affected as in the NAION eyes seems more reasonable than other explanations provided. On the other hand, significantly worse CDI parameter values, i.e., higher OA RI and slower CRA blood velocities in the NAION eyes than in the NTG eyes, are rather easier to understand. The NAION eyes had much worse overall visual field damage and had a significantly higher systemic blood pressure which is well known to be associated with a smaller central retinal arteriole equivalent (CRAE) value, i.e., more constricted retinal arteries. These factors would result in worse CRA CDI parameters and thus OA (= CRA+PCA) CDI parameter. Because of a large user dependency of CDI measurements and lack of an age-matched normal control group, however, it would be difficult to draw any conclusions regarding CRA or OA CDI parameter values in NTG eyes. The authors' result showed that in eyes with NAION shortly after the onset, central retinal arterial hemodynamics were thought to be significantly disturbed in spite of the supposed pathogenesis of NAION that disturbance of PCA perfusion was mainly responsible for its onset.

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