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

**2. Epidemiology of blindness**

24 Causes and Coping with Visual Impairment and Blindness

tion of refractive errors and cataract surgery.

**3. Blindness from glaucoma**

almost 1 (subtotal excavation).

tion (5%).

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 correc-

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 degenera-

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

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.

the IOP. It should be performed at least every 5 years before the age of 40 years and every

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

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

27

To date, visual loss in glaucoma is irreversible because of the death of ganglion cells and their axons. The treatment is aimed to prevent continuous visual field loss and is divided into medical, laser, and surgical methods. To prevent visual field loss, the intraocular pressure should be at or below the target IOP, which is individual to each patient and related to the type of glaucoma, severity of the disease, patient's compliance, and allergy to medications. To date, there is no treatment addressing the different genetic defects and molecular mechanisms causing or related to glaucoma. The first line of treatment is usually medications. To enhance treatment, laser treatment may be applied. Some of the laser treatments such as selective laser trabeculoplasty have a short span of effectiveness, usually 1–1.5 years. If these fail, surgery is indicated. The number of medications, laser, and surgical procedures is wide and is deter-

Screening for glaucoma should include the entire population and should be composed of observation of the optic disc and documentation of the cup-disc ratio (C/D ratio) and other features of glaucomatous optic disc damage and intraocular pressure. Screening is usually performed every 5 years and over the age of 40 years twice a year. Patients with higher risk for glaucoma (e.g., family history of glaucoma, pseudoexfoliative syndrome, pigmentary dispersion syndrome, borderline IOP, etc.) may be routinely evaluated more often. Every patient who is diagnosed with glaucoma should be on appropriate medications permanently unless successful surgery has been performed, and even than the patient should be routinely followed. The follow-up is every 3–4 months for lifetime including after successful surgery. If aggravation occurs, the follow-up intervals may be more frequent. Examination should be performed at different hours of the day, and a diurnal curve is indicated for patients with controlled IOP under medications and continuous visual field damage. The diurnal curve is performed every 4 hours and may even be increased to every 2 hours under medications. Some types of glaucoma such as pseudoexfoliative and pigmentary have a high fluctuation rate that may be missed by routine IOP examination. It is imperative to perform surgery in a timely manner, before the glaucoma is too advanced and before splitting of the fixation on visual field testing. Patients with complete splitting of the fixation are at higher risk to lose their central vision after surgery. Except for glaucoma surgery, other procedures may be required and may result in decrease of IOP. Cataract surgery in presence of risk factors such as hard nucleus (brown, red or black cataract), pseudoexfoliation, phakodonesis, lens subluxation, small pupil, ocular surface disorders such as ocular cicatricial pemphigoid, and Fuch's corneal dystrophy should be performed early. As the number of risk factors increases, surgery should be performed earlier. Visual field should also be obtained for

these patients before surgery, if the glaucoma is advanced (C/D ratio of 0.9 or more).

Patients at high risk to lose their vision are those who do not take their medications regularly and/or do not follow-up with their ophthalmologist at regular intervals as indicated above.

6 months after the age of 40 years.

**5. Prevention of visual loss**

mined mainly by the type of glaucoma.

**Figure 3.** 24-2 and 10-2 Humphrey visual fields of a patient with advanced field damage. The damage encroaches on the fixation but does not split it. In this case, successful trabeculectomy with mitomycin-C was performed. The visual field remained unchanged. The best-corrected visual acuity remained 20/60, and the intraocular pressure decreased from 28 to 34 mmHg to 10–12 mmHg and remained at this level.

fiber loss, which usually begins in the arcuate bundles and the nasal fibers and ends with the papillomacular bundle.

When superior and inferior nasal steps coalescence with arcuate defects and spread centrally and peripherally, tunnel vision evolves. The visual acuity may remain intact (best-corrected visual acuity 20/20) in this situation. Eventually, central vision and/ or temporal peripheral island(s) may remain; when these are lost, the patient remains with no light perception. Occurrence in both eyes results in total blindness. In most types of glaucoma, the chronic ones, the patient may not be aware of the visual field loss, unless comparing each eye to the other. This is the reason that glaucoma is called the silent thief of vision. The patient may present only when the visual acuity in one eye is completely lost because the overlapping between the visual field of both eyes, micro-saccades, and most importantly, turning the head toward the area of interest. Therefore, screening of the population is the most crucial measure to detect glaucoma patients and treat them early.

The goal of treatment is to stabilize the visual field and prevent further deterioration in visual field and visual loss. Unfortunately, currently, the main treatment is aimed only at reducing the intraocular pressure (IOP) and achieving the ideal IOP (target IOP), which differs for each patient and is determined by the type of glaucoma, its severity, progression, patient compliance, and allergy to medications. In general, it should be as low as possible but not too low (hypotonia). Screening of the population includes observing the optic disc and checking the IOP. It should be performed at least every 5 years before the age of 40 years and every 6 months after the age of 40 years.
