**5. Prevention of visual loss**

**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

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

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

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

to 34 mmHg to 10–12 mmHg and remained at this level.

26 Causes and Coping with Visual Impairment and Blindness

to detect glaucoma patients and treat them early.

papillomacular bundle.

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 determined mainly by the type of glaucoma.

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. Other major factors for visual loss are late diagnosis that may occur with all types of chronic glaucomas and slow decision making. Aggressive glaucoma and poor surgical outcomes may contribute to visual loss.

with high and large fluctuations that are on full medical treatment may benefit from early glaucoma surgery, either trabeculectomy with mitomycin C or shunt procedure. Still, patients without IOP fluctuations may progress to blindness from other reasons as stated below.

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

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

29

People spend about one third of the day (6–8 hours) sleeping. The resting time may increase after retirement. The IOP increases at supine position compared with standing or sitting in healthy subjects by 2.47 ± 2.12 mmHg (mean ± standard deviation) (p < 0.001) when measured by non-contact tonometer Keeler, Pulsair EasyEye [2]. In another study, the IOP in sitting position was found to be 13.5 ± 2.0 mmHg in the right eye and 13.2 ± 2.3 mmHg in the left eye in healthy individuals [3]. The IOP increased in supine position to 16.8 ± 2.3 mmHg and 17.0 ± 2.3 mmHg, respectively (p = 0.001). This may result in deterioration of the optic disc and visual fields. Diurnal curve has probably no meaning if the patient is awakened at bedtime,

The intracranial pressure (ICP) may also influence the progression of glaucoma [4, 5]. The ICP is directed through the subarachnoid space opposite to the IOP through the lamina cribrosa, and the difference between them is the translaminar pressure gradient. Theoretically, if this is low, the progression may be slower than if it is high but this may not be true. A high ICP and IOP with a low gradient may be sufficient to cause increased optic disc damage because of the increased shearing force in the lamina cribrosa and decrease in axonal plasma flow. This may

Most ophthalmologists do not live with their glaucoma patients and have no idea about their behavior in daily life. The patients may sleep on their affected eye(s), and this causes further increase of the IOP in addition to the increase caused by supine position. When the eye leans against the bed or pillow or when the entire mass of the head is over all or part of the globe, IOP is increased by 33%. Thus, the physician should inquire about the sleeping habits of the glaucoma patients. Actually, increase in IOP measurement can be seen in patients who squeeze their eyes during evaluation with Goldmann tonometer, as well as with some other instruments. It can also be seen if the examiner presses the globe during IOP measurement.

Glaucoma patients are usually older and have many associated aging and pathologic conditions, including atherosclerosis and systemic hypertension. Other ischemic diseases such as diabetes mellitus may also be encountered. Taking antihypertensive drugs before sleeping increases the risk for anterior ischemic optic neuropathy (AION) [6]. Antihypertensive medications decrease the perfusion into the optic disc, and this may join atherosclerotic changes in the blood vessels. AION may be difficult to diagnose in patients with advanced glaucoma. In advanced glaucoma, the cup may be large (cup/disc ratio of 0.8 or more), and the rim is thin enough not to distinguish pallor of the rim following additional AION. In addition, AION field defects may be superimposed on the glaucoma visual field defects. In advanced glaucoma, the visual field scotomata may be large enough (e.g., tubular vision) to prevent detection of the additional scotomata caused by AION. According to the vascular theory, damage to the optic nerve may be caused

**8.2. Increased IOP in supine position (at bedtime)**

and the pressure is measured while sitting.

initiate or facilitate axonal apoptosis.

**8.4. Antihypertensive drugs at bedtime**

**8.3. Increased IOP when sleeping on the affected eye(s)**
