In terms of instruments. The intraocular pressure gauge has not been adjusted to standardization, zero deviation, friction between mechanical structures, etc;
On the patient side. Mental tension, inability to relax the eyelids, inability to fix one eye, small eyelids, changes in corneal curvature, corneal leukoplakia, and other corneal surface irregularities;
In terms of operation. There is compression when exposing the eyeball, incorrect support of the tonometer handle, and insufficient alignment between the base and corneal curvature.