Invented by Schiotz in 1905, it is still widely used in our country because of its cheap, durable and easy to operate: it is composed of a metal pointer, foot plate, movable press needle, scale, handle and weight (Figure 1), the movable press needle and pointer weight are 5.5g, 7.5g, 10g and 15g respectively. The scale of the tonometer depends on the degree to which the tonometer pressure needle presses the cornea downward, so the measurement value is affected by the hardness of the ball wall. When the hardness of the ocular wall is high (such as high farsightedness and long-lived glaucoma), the iOP values are high. When the ocular wall hardness is low (such as high myopia, after retinal detachment surgery), the IOP value is low. The error caused by the hardness of the ball wall can be eliminated by checking the table after measuring with two different weights.