Open AccessOptical properties of the eye, including the refractive compensation, for example, may change if there are changes in any of the components that make up the eye. The sensitivity to such changes isquantified via the derivative. This paper employs the reduced eye and Gaussian optics to illustrate a general method for the analysis of sensitivity in eyes. The method requires a clear statement of the dependent variable as a function of independent variables. A symbolism is offered that makes the function unambiguous. Sensitivities are determined for the fundamental optical properties,the transference and the corneal-plane refractivecompensation of a reduced eye to change in corneal power, curvature and radius of curvature and to change in axial length and index of refraction. Emsley’s reduced eye is examined in particular. Its corneal-plane refractive compensation has a sensitivity of 135 −135 D to change in refractive index, 1 − 2.7 D/mm to change in length and 135 −1/3 to change in corneal curvature when the other two independent variables are held fixed. The method has the potential to develop guidelines that are useful clini- cally.