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Retinal Neurovascular Coupling in Patients with Glaucoma and Ocular Hypertension and Its Association with the Level of Glaucomatous Damage

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Retinal Neurovascular Coupling in Patients with Glaucoma and Ocular Hypertension and Its Association with the Level of Glaucomatous Damage Graefes Arch Clin Exp Ophthalmol (2013) 251:1577–1585 DOI 10.1007/s00417-013-2276-9 GLAUCOMA Retinal neurovascular coupling in patients with glaucoma and ocular hypertension and its association with the level of glaucomatous damage K. Gugleta & N. Waldmann & A. Polunina & A. Kochkorov & R. Katamay & J. Flammer & S. Orgul Received: 1 November 2012 /Revised: 1 January 2013 /Accepted: 22 January 2013 /Published online: 19 February 2013 # Springer-Verlag Berlin Heidelberg 2013 Abstract Correlation of flicker response of superior and inferior vessels Purpose To analyze neurovascular coupling in the retina of of the same eye was significant for the arteries (Pearson untreated primary open-angle glaucoma (POAG) and ocular r=0.23, p=0.004), as well as venules (r=0.52, p<0.001). hypertension (OHT) patients. Conclusion General vessel response to flicker light was de- Patients and methods Maximal vessel dilation in response to creased in POAG patients, compared to normal controls and flicker light was analyzed with Retinal Vessel Analyzer (RVA) OHT patients. In contrast to significant correlation between in temporal superior/inferior arterioles and veins in 51 POAG the two contralateral eyes of the flicker response itself, only its patients, 46 OHT and 59 control subjects. RVA parameters borderline correlation to IOP was seen. There was no correla- were compared between groups, between contralateral POAG tion to the level of damage, altogether indicating a systemic eyes, and correlated to intraocular pressure, visual field mean dysregulation phenomenon. defect and retinal nerve fiber layer thickness. Grants Results POAG eyes demonstrated generally smaller response Swiss National Foundation Grant 3200B0-113685, Velux of all vessels to flicker light than the other two groups Stiftung Grant, Freie Akademische Gesellschaft (FAG) (ANOVA p=0.026; mean arterial flicker response in percent Grant, Pfizer Inc. Grant of baseline, averaged superior and inferior was 3.48±2.22 % Clinical trial registration reference number ClinicalTrials.gov for controls , 2.35±2.06 % for POAG patients , and 2.97±2.35 NCT00430209 % for OHT patients; corresponding values for venules were 3.88±1.98 %, 2.89±1.72 %, 3.45±2.77 %). There was no Keywords Retinal vessels . Flicker . Glaucoma . Ocular difference in flicker response between the eye with more and hypertension less advanced damage in each patient of the POAG group (ANOVA p=0.79). Correlation of flicker response to intraoc- ular pressure (IOP) was borderline at best, correlations to the Introduction level of glaucomatous damage were not significant. Neurovascular coupling is a local, tissue-specific phenomenon and represents practically instant vascular reaction of the tissue Authors have full control of all primary data and agree to allow Graefes Archive for Clinical and Experimental Ophthalmology to review their to elevated functional activity [1, 2]. It has been explored in the data upon request. field of neurology, and in the last several years it has become subject of interest in glaucoma as well [3–6]. Blood flow K. Gugleta (*) : N. Waldmann : A. Polunina : A. Kochkorov : R. Katamay : J. Flammer : S. Orgul alterations, and in particular the variability of perfusion of optic Department of Ophthalmology, University Hospital Basel, nerve head, is believed to be one of the major risk factors for University Basel, glaucoma [7]. Capability of the vascular system to respond to Mittlerestrasse 91, CH-4031 Basel, Switzerland changing metabolic needs is essential for the functional and e-mail: [email protected] morphological integrity of the neural tissue. Analysis of vessel 1578 Graefes Arch Clin Exp Ophthalmol (2013) 251:1577–1585 response to challenge, rather than capturing a steady-state diagnosed based on glaucomatous optic disc cupping (in baseline flow, is essential for understanding the role of perfu- particular: thinning of the inferior and/or superior rim, sion in glaucomatous damage, in particular because ischemia- cup-to-disc ratio asymmetry of > 0.2 not due to optic disc reperfusion damage has been implicated in the pathogenesis of size asymmetry), and based on matching glaucomatous glaucoma [8]. The retina is an optically easily accessible ocular visual field defects (specifically, a cluster of three or more neural tissue, which makes the use of the Retinal Vessel test points with > 5 dB or two points with > 10 dB Analyzer (RVA; IMEDOS GmbH, Jena, Germany) suitable sensitivity reduction compared to age-eccentricity corrected for this purpose [9, 10]. Data on reproducibility of this device normal value) [16]. Importantly, untreated IOP was neither [11, 12], as well as protocols for specific use of the device, have exclusion nor inclusion criterion for POAG diagnosis; based been published recently [13]. Several studies have indicated a on this, patients from both the “high tension” and “normal disturbance of ocular neurovascular coupling in glaucoma, tension” sides of the IOP spectrum in POAG were included. using various techniques [4–6]. For this reason, we initiated a In contrast, narrow angle glaucoma, as well as patients with prospective project-study on retinal vessel response to flicker- any form of secondary glaucomas, including pigment dis- ing light in patients with open-angle glaucoma and ocular persion and pseudoexfoliation, were excluded. For ocular hypertensives. Parts of the project's database were used to hypertensives, at least two daily readings of untreated IOP analyze the dynamics of the vessel response to repeated flicker in the run-up to the study had to be equal or above stimulation, and results were recently published [14]. Based on 21 mmHg, in absence of disc or visual field damage. All the findings that some subjects may demonstrate alterations in participants with diabetes mellitus, untreated or unstable this regard [15], the focus of this partial analysis was on differ- essential hypertension, untreated or unstable hypercholester- ences in diameter vessel behaviour during the three entire olemia, drug or alcohol abuse, history of eye surgery except flicker periods (“area under the curve” of vessel diameter) in uneventful cataract surgery, high ametropia (spherical equiv- one retinal site. Herewith, we report final results of the cross- alent<−5 diopters or>+3 diopters), astigmatism above 2 sectional analysis of neurovascular coupling in untreated diopters, and significant cataract were excluded from the patients with glaucoma and ocular hypertension, with particular study. Smoking was an exclusion criterion [17]. In the emphasis on the association between the level of glaucomatous POAG group, both eyes were analyzed. In the OHT group damage and a maximal flicker-induced dilatory capacity of an eye with the higher mean diurnal IOP was selected, and retinal vessels. Comparisons of maximal vessel dilation were in healthy controls, one randomly selected eye per subject performed in various retinal sites (superior and inferior), as well entered the analysis. as between the two contralateral eyes in glaucoma patients. For retinal vascular examinations, we used RVA (IMEDOS GmbH, Jena, Germany). Details on the device and its flicker-light related application have been published Patients and methods previously [9, 10, 13–15, 18]. Briefly, an essential part of of the RVA device is the fundus camera (FF450, Zeiss Jena, Subjects and methods Germany), which allows the examination and recordings of the ocular fundus. It incorporates the illumination and the Local ethical committee approved the study, and after the study observation optical pathway. After being reflected from the registration at ClinicalTrials.gov, the recruitment was con- retina, the light is delivered through the observation path- ducted beginning in 2007 and lasted for 3 years. An informed way to the observation ocular and to the charge-coupled consent was obtained from each study subject, following the device (CCD) chip of the video camera simultaneously. tenets of the Declaration of Helsinki. Patients with primary The measuring principle of the RVA is as follows: inside open angle glaucoma (POAG) and ocular hypertension (OHT) the walls of the retinal blood vessels there is a column of red were consecutively recruited from the glaucoma consultations blood cells, separated from the walls by the plasma edge at the Ophthalmology Department of the University Hospital stream. Red blood cells absorb one part of the light. RVA Basel. As subjects of the cross-sectional analysis per protocol measures the diameter of the column of the red blood cells. needed to be therapy-free, newly diagnosed and untreated The fundus camera was adjusted to the dilated pupil POAG and OHT patients meeting study criteria underwent and a clear fundus image with good contrast and no study examinations, patients on intraocular pressure (IOP)- reflections was obtained on the monitor. There are 25 lowering therapy were first subjected to a 4-week wash-out captured full video frames per second. Flicker stimula- phase. Healthy controls were recruited through ads in local tion is achieved by the optoelectronic shutter with newspapers. A detailed medical and ophthalmic history was 12.5 Hz frequency, which darkens each second frame, recorded. As detailed previously [14], ophthalmological leaving every other one normally exposed. These still examinations included the IOP readings with Goldmann pictures were analyzed by the RVA software. RVA pro- applanation tonometry at 8 h, 11 h and 16 h. POAG was duces one vessel width measurement, expressed in units Graefes Arch Clin Exp Ophthalmol (2013) 251:1577–1585 1579 of measurement (UM), for each segment length of 12.5 of morphologic glaucomatous damage. Details on this de- UM. In an emmetropic person, 1 UM=1 micrometer. vice and its previous use in glaucoma have been published Four major temporal vessel segments were selected for elsewhere [18, 20, 21]. Fast RNFL thickness protocol was our measurements: one vein and one artery, one of each applied, scans with signal strength (as a measure of scan inferior and superior. Vascular geometry governed the exact quality) of less than 6/10 were repeated and if no higher location of the measurement (Fig.
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