The laser interferometry is a frequently used diagnostics for plasma density measurements. The measurements in plasmas with no density gradients allow direct correspondence of the fringe shift and plasma density along the laser line of sight. The change of the interferometer contrast due to scene beam deflection in plasmas with density gradients reduces the fidelity of interferometer measurements due to the change in the contrast of the fringe. The analytic expression for the maximum acceptable deflection angle is derived, analyzed, and compared to the experiment. Ways to improve the accuracy of interferometer measurements are proposed. ©1998 American Institute of Physics.