Normal fluid consumption does not pose a threat to a patient s intraocular pressure. These daily fluctuations are normal and should not affect your glaucoma on a long-term basis. These tonometers involve measurements taken on the cornea, the clear surface of the eye that covers the iris and lets light enter the eye. The applanation tonometer is considered the most accurate of all the instruments, but the patient must have a clear, regularly shaped cornea for it to give an accurate reading. Before a reading is taken with an applanation tonometer, the patient receives a drop that contains a numbing agent and a colored stain called fluorescein.
Fluorescein is a yellow coloring agent that glows when a blue light is shone on it.
The tonometer is placed on the cornea and a very small amount of pressure is applied to the cornea by a tiny instrument that checks the pressure. The numbing effect of the drops usually disappears within 20-30 minutes. The Schiotz tonometer is an example of indentation tonometry. The Schiotz tonometer works with weights connected to a plunger-type device. The weights help determine how far the plunger will indent an eye with a given pressure.