COMPARISON OF METHODS TO MEASURE RETINAL VESSEL DIAMETERS

Title COMPARISON OF METHODS TO MEASURE RETINAL VESSEL DIAMETERS
Author, Co-Author John Lovasik, Catherina Ieraci, Marc Melillo
Topic
Year
1992
Day
Monday
Program Number
Poster 36
Room
Great Hall
Affiliation
Abstract Absolute measurements of volumetric blood flow are required when correlating retinal vascular autoregulation with retinal function. Blood flow, Q, equals S*Vmean[subscript], where S is the cross sectional area (piD2/4)[ pi d squared on 4] of a vessel, and Vmean[subscript]=mean blood velocity. Thus the accuracy of Q depends on D2 and is twice as sensitive to the accuracy to which the vessel diameter 'D' can be measured (Riva & Petrig, 1990). Here we compared the ease and accuracy of 4 methods (M1, M2, M3, M4) for measuring 'D' of 6 calibrated micropipettes, and slides of retinal vessels during altered ocular perfusion pressure (OPP): For M1 and M2, each target was magnified, digitized and a density plot profile generated. The pixel distance between the half-height of either side of the profile above background noise was taken as 'D'. This distance was determined subjectively in M1, and objectively in M2 via a customized algorithm. In M3 and M4, an electro-optical system (Imagen 1024/DS) displayed magnified images on a hi-res monitor, and edges were found manually by electronic cursors in M3, and semi-automatically in M4 using its internal edge detection feature. All measurements were done 10 times for each method. All methods calibrated linearly for the pipettes. All methods showed an underestimation, of less than 3% for M1 & M2 and of less than 1% for M3 & M4. The SEM value for data sets across each method was less than 0.80. Vessel diameters were more variable than the diameters for sharply defined pipettes. During decreasing OPP, infero-nasal arteries increased slowly while veins decreased. On normalizing the OPP the arteries and veins enlarged quickly, and returned to near baseline size in 4 min. These trends were clearest for M2. The response profile for M4 deviated the most from all other profiles. Technical and theoretical aspects of our procedures are discussed.
Affiliation of Co-Authors
Outline