**3. Blindness from glaucoma**

Glaucoma is a distinctive group of optic nerve neuropathies characterized by specific optic disc and visual field changes, usually with an increase in intraocular pressure (IOP). In the past, a true IOP of up to 21 mmHg was considered normal in healthy individuals. Today, some consider an IOP between 18 and 22 as borderline. The term "true IOP" addresses the corrected IOP according to the thickness of the cornea and other parameters that influence the IOP. The main optic disc change is the increase of the cup (cupping) and decrease of the rim that contains the axons from the retinal ganglion layer (**Figure 1**). Early signs for this include disc notching, increased excavation, retinal nerve fiber defects, and papillary flame-shape hemorrhages. The early changes in visual field include Bjerrum defects (scotomata), paracentral scotoma, nasal step, and arcuate scotoma. As the disease progresses, visual field defects increase, first in depth and then in size. Arcuate scotoma may join nasal field, and when these increase toward the center and the periphery, tunnel vision and/or a temporal crescent or a

**Figure 1.** An advanced stage of glaucomatous optic disc damage showing thinning of the rim. The cup/disc ratio is almost 1 (subtotal excavation).

few visual islands remains. Eventually, these disappear too and the patient remains with no light perception. The changes in visual field correspond and follow closely with the changes in the optic disc. The chronic forms of this group are asymptomatic until advanced and irreversible visual loss occurs. Patients preserve normal visual acuity (even of 20/20) in one or both eyes until late in the disease. Such patients may not be aware of the small defects early in the course of the disease or even advanced concentric visual loss and tunnel vision, until they completely lose their vision in one or both eyes.

Two theories explain the neuronal loss in glaucoma. The first claims that mechanical force exerted on the optic disc causes direct destruction. The second claims that compromised blood flow causes damage. The damage may be caused also by a combination of these two processes. The end point is apoptosis of the ganglion cell layer.
