  The perihelion precession of planetary orbits and the bending angle of null
geodesics are estimated for different gravity theories in string-inspired
models. It is shown that, for dilaton coupled gravity, the leading order
measure in the angle of bending of light comes purely from vacuum expectation
value of the dilaton field which may be interpreted as an indicator of a
dominant stringy effect over the curvature effect. We arrive at similar results
for spherically symmetric solution in quadratic gravity. We also present the
perihelion shift and bending of light in the Einstein-Maxwell-Gauss-Bonnet
theory with special reference to the Casimir effect and Damour-Polyakov
mechanism. Numerical bounds to different coupling parameters in these models
are estimated.
