Glaucoma can cause irreversible vision loss without any obvious symptoms at the start. It happens when our nerve fibres that transmits signals from the eye to the brain (to produce the image that we see) gets damaged.

When a significant part of the nerve is affected, you will start losing your peripheral field of vision - this vision loss would gradually spread towards your central vision, until all sight is lost. Vision loss caused by glaucoma is permanent and there are 2 primary types of Glaucoma: Open-angle Glaucoma and Closed-angle Glaucoma (Angle-closure Glaucoma /Narrow-angle Glaucoma)