Doubt in the function estimateFu​ndamentalM​atrix

In the function estimateFundamentalMatrix, my doubt is regarding the output 'inliersIndex'. Can I compute 'inliersIndex' manually if I have a fundamental matrix, matchedPoints1 and matchedPoints2? How does the inbuilt function compute it? Does it make use of the parameter 'DistanceThreshold' to find out which matchedPoints are inliers? If yes, can someone tell me exactly how?

Thanks in advance!!