The crossed cylindrical mirror is made by superimposing and grinding two cylindrical mirrors with the same degree, opposite signs and mutually perpendicular axes. Commonly used specifications are ±0.25 and ±0.50. Hand-held cross cylindrical mirror, where the red scale line represents the axis of negative astigmatism, the black scale line represents the axis of positive astigmatism, the two axes are perpendicular to each other, and there is a handle in the middle of the positive and negative axes. The crossed cylindrical mirror attached to the comprehensive refractometer, the red dot represents the axis of negative astigmatism, the white dot represents the axis of positive astigmatism, and there are two flip handwheels in the middle of the positive and negative axes. The crossed cylindrical mirror is mainly used to precisely adjust the axis and degree of astigmatism. When the subject's best corrected visual acuity can reach 0.7 or above, use a ±0.25 crossed cylindrical lens to adjust the astigmatism. The following mainly introduces how to use the cross cylindrical mirror in the comprehensive refractometer to accurately adjust the axis and degree of negative astigmatism.