I'd try to zero out the bright stuff, then threshold and call regionprops() and compute the circularity. Here's a start:
mask = grayImage > 200;
grayImage(mask) = 0;
binaryImage = grayImage < 50; % or whatever works.
labeledImage = bwlabel(binaryImage);
props = regionprops(labeledImage, 'Area', 'Perimeter');
allAreas = [props.Area];
allPerims = [props.Perimeter];
circularities = allPerimeters .^ 2 ./ (4 * pi * allAreas);
roundBlobIndexes = find(circularities < 2);
roundBlobs = ismember(labeledImage, roundBlobIndexes);
imshow(roundBlobs);

