Traditional tonometers are mainly divided into two types: indentation and flattening.
Compression type: It uses a certain weight of intraocular pressure measuring rod to compress the cornea into a depression. Under the condition that the weight of the intraocular pressure gauge remains unchanged, the deeper the compression, the lower the intraocular pressure, and its measurement value is affected by the hardness of the eyeball wall. Schiotz tonometer belongs to this category.
Flattening type: It uses a certain amount of force to flatten the convex surface of the cornea without sinking, and the volume of the eyeball changes very little, so it is less affected by the hardness of the eyeball wall.
According to the area or pressure of corneal flattening, it can be divided into two types.
One type is fixed flattening integrability, which depends on the amount of force required to flatten the area. Those with lower force also have lower intraocular pressure, such as the Goldmann flattening intraocular pressure gauge;
Another method is to fix the pressure (with the weight of the tonometer unchanged) and observe the flattened area. The larger the flattened area, the lower the intraocular pressure, such as the Maklakov flattened tonometer