**2. Epidemiology of blindness**

The World Health Organization (WHO) estimated that in 2014, 285 million people (4%) out of the 7.2 billion world population had either low vision (246 million) or blindness (49 million) [1]. Ninety percent of these live in low-economic settings and 82% are aged over 50 years. Eighty percent of visual impairment can be prevented or cured. The best examples are correction of refractive errors and cataract surgery.

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

Why Do Patients with Controlled Glaucoma Continue to Lose Their Vision?

http://dx.doi.org/10.5772/intechopen.79764

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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

The visual field loss (scotoma) in glaucoma has a distinctive pattern that differs from visual loss due to other causes (**Figures 2** and **3**). The visual field defects include Bjerrum scotoma, paracentral scotoma, nasal step, and arcuate defect. These defects correspond to retinal nerve

**Figure 2.** Advanced visual field loss of the right eye in a glaucoma patient. On the left, a 24-2 Humphrey visual field demonstrating a concentric visual field loss with only a small para-central island remained. The fixation point is split. This is also demonstrated in the same patient on the right with a 10-2 visual field. Glaucoma surgery at this point can

cause the loss of the fixation and a decrease in best-corrected visual acuity to counting fingers.

completely lose their vision in one or both eyes.

**4. Pattern of visual loss in glaucoma**

processes. The end point is apoptosis of the ganglion cell layer.

The most common cause for blindness worldwide is cataract (47%), and it is reversible upon surgery. The second common cause for blindness is glaucoma (12%), and it is the most common cause for irreversible blindness. This is followed by age-related macular degeneration (5%).
