TY - JOUR
T1 - A novel method for computerized measurement of episcleral venous pressure in humans
AU - Sit, Arthur J.
AU - Ekdawi, Noha S.
AU - Malihi, Mehrdad
AU - McLaren, Jay W.
N1 - Funding Information:
Supported in part by the American Glaucoma Society Physician–Scientist Award (AJS), the Research to Prevent Blindness Robert and Helen Schaub Special Scholar Award (AJS), the American Health Assistance Foundation, an unrestricted departmental grant from Research to Prevent Blindness, and the Mayo Foundation for Medical Education and Research.
Copyright:
Copyright 2011 Elsevier B.V., All rights reserved.
PY - 2011/6
Y1 - 2011/6
N2 - Episcleral venous pressure (EVP) is an important determinant of intraocular pressure (IOP) and can be estimated by the pressure required to compress an episcleral vein. However, the lack of objective measurement endpoints makes EVP measurements in humans uncertain. To address this issue, we developed a new method to measure EVP objectively and reproducibly, and demonstrated its utility on a group of normal subjects. Our system for pressure chamber based venomanometry included a computer-controlled motor drive to increase pressure automatically, a transducer to record pressure, and a high-definition video camera to record vein collapse. Pressure measurements were synchronized with the video stream to determine the pressure required to collapse the vein to a specific pre-determined degree. This system was used to measure EVP in 10 eyes from 5 young healthy volunteers. Episcleral veins were selected in each of 4 quadrants. EVP was calculated to be the pressure in the chamber that compressed the vein by 0% (by back-projection), 10% or 50% as determined by using image analysis of the video stream. For this group of subjects, mean EVP was 6.3 ± 2.8 mmHg (mean ± SD, n = 40 measurements), 7.0 ± 2.6 mmHg, and 9.6 ± 2.6 mmHg using the 0%, 10% and 50% reduction endpoints, respectively. Pressures and standard deviations determined from these endpoints were significantly different from each other (p < 0.001). Coefficients of variation between right and left eyes were12.7%, 10.2%, and 6.8% using the 0%, 10% and 50% endpoints, respectively. Based on previous research and theoretical considerations, the 0% endpoint is assumed to provide the most accurate estimate of baseline EVP, and can only be estimated by analyzing the brightness profiles of the vessels in the video stream. Objective measurement of EVP is important for understanding normal aqueous humor dynamics and its changes in disease states and with therapies. EVP has typically been assumed to be constant because of the lack of a convenient means of its measurement. This new method provides a precise means to assess EVP based on specific endpoints of vessel collapse, and enables, for the first time, objective and non-invasive measurements of EVP changes.
AB - Episcleral venous pressure (EVP) is an important determinant of intraocular pressure (IOP) and can be estimated by the pressure required to compress an episcleral vein. However, the lack of objective measurement endpoints makes EVP measurements in humans uncertain. To address this issue, we developed a new method to measure EVP objectively and reproducibly, and demonstrated its utility on a group of normal subjects. Our system for pressure chamber based venomanometry included a computer-controlled motor drive to increase pressure automatically, a transducer to record pressure, and a high-definition video camera to record vein collapse. Pressure measurements were synchronized with the video stream to determine the pressure required to collapse the vein to a specific pre-determined degree. This system was used to measure EVP in 10 eyes from 5 young healthy volunteers. Episcleral veins were selected in each of 4 quadrants. EVP was calculated to be the pressure in the chamber that compressed the vein by 0% (by back-projection), 10% or 50% as determined by using image analysis of the video stream. For this group of subjects, mean EVP was 6.3 ± 2.8 mmHg (mean ± SD, n = 40 measurements), 7.0 ± 2.6 mmHg, and 9.6 ± 2.6 mmHg using the 0%, 10% and 50% reduction endpoints, respectively. Pressures and standard deviations determined from these endpoints were significantly different from each other (p < 0.001). Coefficients of variation between right and left eyes were12.7%, 10.2%, and 6.8% using the 0%, 10% and 50% endpoints, respectively. Based on previous research and theoretical considerations, the 0% endpoint is assumed to provide the most accurate estimate of baseline EVP, and can only be estimated by analyzing the brightness profiles of the vessels in the video stream. Objective measurement of EVP is important for understanding normal aqueous humor dynamics and its changes in disease states and with therapies. EVP has typically been assumed to be constant because of the lack of a convenient means of its measurement. This new method provides a precise means to assess EVP based on specific endpoints of vessel collapse, and enables, for the first time, objective and non-invasive measurements of EVP changes.
KW - Aqueous humor dynamics
KW - Aqueous veins
KW - Episcleral venous pressure
KW - Glaucoma
KW - Intraocular pressure
KW - Uveoscleral flow
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U2 - 10.1016/j.exer.2011.03.018
DO - 10.1016/j.exer.2011.03.018
M3 - Short survey
C2 - 21463627
AN - SCOPUS:79956349600
SN - 0014-4835
VL - 92
SP - 537
EP - 544
JO - Experimental Eye Research
JF - Experimental Eye Research
IS - 6
ER -