There are various types of glaucoma but the main type that your optician screens for using a tonometer is primary open angle glaucoma or chronic glaucoma. This type is characterised by a gradual increase in the intra-ocular pressure.

Other types of glaucoma include acute glaucoma, which occurs when there is a sudden blockage to flow of the intra-ocular fluid, secondary glaucoma which is a rise in the pressure of the fluid in the eye as a consequence of another eye condition, and developmental glaucoma. This is extremely rare and occurs when a baby’s eyes are not formed correctly within the womb.

To learn more about glaucoma, see our dedicated guide.