An eyepiece device for a surgical instrument, the eyepiece device including: an eyepiece frame； and at least one optical unit accommodated in the eyepiece frame, wherein the at least one optical unit comprises at least one first optical element and a second optical element connected with the at least one first optical element, wherein the second optical element is formed from a second material with abnormal dispersion and the first and the second optical elements together correct chromatic aberration； wherein the eyepiece frame comprises an expansion chamber for at least the second optical element, the expansion chamber forming an installation space for at least the second optical element in a radial direction.
