Abstract
Abstract: :
Purpose: The Retinal Vessel Analyzer (RVA) is able to measure retinal vessel reactions in response to stimuli in real time. Whether the reaction to short term IOP increase in retinal branch arteries differs between healthy subjects, untreated and treated glaucoma patients is investigated. Methods: 9 untreated primary open angle glaucoma (POAG) patients (age 55,7+8,5 years, IOP 23,3+1,9 mmHg) and 9 age matched normal volunteers (age 55,7+8,5 years, IOP 13,7+1,6 mmHg) were examined. The 9 POAG patients were treated for 4 weeks with tid dorzolamide eye drops (IOP 17,6 +2,2 mm Hg). Baseline RVA measurement was performed for 2 minutes. IOP was increased for 3 sec to suprasystolic levels and released. The RVA measurements were continued for further 10 minutes. Changes in vessel diameter of branch retinal arteries were assessed along a 1 mm segment. The characteristic parameters of local vessel behavior were analyzed by non–parametric tests and Fourier analysis. Results: No statistically significant difference was found in spectral edge frequency of the power spectrum (SEF) between baseline measurements in normal volunteers (0,102+0,03 MU–1), untreated (0,115+0,035 MU–1) or treated (0,115+0,045 MU–1) POAG patients (p>0,1). After IOP provocation a vessel dilation was observed in all cases. In the dilation phase a statistically significant difference in SEF between normals (0,112+0,03 MU–1) and untreated POAG patients (0,153+0,141 MU–1; p=0,023; 1–ß =0,5) was found in arteries, however not between SEF of normals and treated glaucoma patients (0,141+0,053 MU–1). Conclusions:Anatomically neighboring vessel segments demonstrate varying vessel widths during baseline assessment and behave differently after IOP provocation. As a characteristic description for this fact we employed the SEF of the power spectrum of local vessel diameters. It is an expression for the frequency in amplitude change of vessel width which we termed "vessel thickness change frequency". In arteries we found a significant difference in this characteristic after IOP provocation between normals and untreated glaucoma patients (p<0,05), however not between normals and treated glaucoma patients (p=0,85). Assessment of the functional dynamic response to increased IOP could represent a new method to characterize retinal autoregulation in healthy subjects and glaucoma patients.
Keywords: retina • clinical research methodology • imaging/image analysis: clinical