As compared to multicomponent optical glasses, when fused silica optical glass (pure SiO2) is ground or polished, it exhibits unique features, such as low surface microroughness and subsurface damage, low grinding-induced residual stresses, and low removal rates. On the other hand, fused silica glass is known to densify permanently when subjected to sufficiently large compressive stresses. Such densification, manifested as a permanent increase in the index of refraction, is facilitated by shear stresses. We discuss a simple constitutive model describing the densification of fused silica, under large applied model to interpret nanoidentification tests of fused silica over loads in the range 1 - 100 mN (about 0.1 - 10 gf) via finite element simulations of indentation of an axisymmetric half- space by a conical indenter with a spherical tip. Such geometry resembles the action of polishing and microgrinding abrasives used in optics manufacturing. The fused silica nanoindentation data are compared to other optical glasses such as BK7 and LHG8.