Glaucoma
For the eye to maintain its external shape, there must be a certain amount intraocular pressure. Otherwise, the eye would shrink. The intraocular pressure is measured in milimeters of mercury (mm Hg). The blood pressure is also measured in the same unit. Normaly, the intraocular pressure ranges between 10 and 21 mm Hg. It changes approximately 4 mm Hg throughout the day and is higher in the morning compared to the evening. The intraocular pressure is regulated by the aqueous humor. The aqueous humor passes beside the lens and reaches to the anterior chamber of the eye through the pupil where it drains back into the the canal of Schlemm via the trabecular meshwork which functions as a filter.
Glaucoma leads to a damaged optic nerve and the narrowing of the visual field. Glaucoma has different types. It is not possible to treat damages that have already been caused by any type of glaucoma. Especially two types are very important: chronic (open-angle) glaucoma and narrow-angle glaucoma.
In open-angle glaucoma, the values of increased intraocular pressure may be 30 mmHg or above, and this arises from the structure called the trabecular meshwork. At advanced ages, the pores in the trabecular meshwork may be obstructed or the structure may get thick spontaneously. Therefore, flow of the aqueous humor is prevented and the intraocular pressure is increased. These changes that occur on both sides are normally hidden processes. Chronic (open-angle) glaucoma is the most common type of glaucoma. After the age of 40 years approximately 2% of the population is compromised by this disease. Approximately 12% of the cases of blindness in industrialized countries are related with glaucoma. Especially relatives of glaucoma patients, diabetes patients and patients with advanced myopia have a high risk in terms of glaucoma.
Another type of open-angle glaucoma is normal pressure glaucoma. Here, the optic nerve is damaged and the visual field narrows. However, the intraocular pressure is always normal.
Narrow-angle glaucoma occurs especially in eyes with congenital narrow chamber angle. This is observed especially frequently in hypermetropia. In these eyes, the chamber angle may be shifted by the iris, and the aqueous humor can not flow any more. Most of the time, thickening of the lens in advanced ages causes to this angle to narrow. The iris is forced anteriorly because of this thickening and applies pressure towards the chamber angle. When sudden obtructions occur, glaucoma crisis occurs and the intraocular pressure values may be above 60 mmHg. Chronic processes may also cause to angle narrowing. Narrow-angle glaucoma occurs in one of 1000 individuals after the age of 40 years and is observed in both eyes.
In chronic (open-angle) glaucoma, increased intraocular pressure rarely causes eye pain or headache. Generally, no complaints are observed, especially in the beginning of the disease. The visual field narrows in an unnoticable way. Early symptoms are not observed because of the latent process of the disease, and chronic (open-angle) glaucoma cannot be diagnosed in the early stage. Sometimes, narrowing in the visual field is found in both eyes in advanced cases. Damage that has once occured can not be treated. Early warning symptoms are not observed in chronic narrow-angle glaucoma either. Only glaucoma crisis leads to severe eye pain, headache and sometimes nausea occurs. In addition, blurred vision, lacrimation and hyperemia in the eye may occur. If glaucoma crisis is not treated rapidly, there is a possibility of blindness.
The most important measurement in glaucoma is measurement of the intraocular pressure. Firstly, an anesthetic eye drop applied to the eye. Afterwards, a small measurement cap is placed on the cornea and the intraocular pressure is measured. This examination is completely painless.
Mostly computarized devices are used currently for examination of the visual field (Perimeter). Light points with different sizes and brightness are projected automatically in a hemisphere. The patient looks at the middle of the hemisphere and presses a button, if he/she sees a light point. The opthalmologist also checks the chamber angle and the head of the optic nerve. If the optic nerve is damaged because of glaucoma, the head of the optic nerve is recessed and pale.
Most of the time, the intraocular pressure can be reduced by related eye drops. These eye drops should be used regularly. If the intraocular pressure can not be reduced with eye drops, laser treatment of the chamber angle may be performed. If the intraocular pressure can not be reduced with this procedure either, operation is inevitable.
According to the type of glaucoma, an artificial passage should be formed for the aqueous humor to flow outside. This passage is formed by way of trephination (outward) or trabeculectomy (for secretion from the iris inward). If operations have been performed in the eyeball before or a second glaucoma is forming because of neovascularization in the chamber angle, the intraocular pressure should be reduced by decreasing production of the aqueous humor. Here, the ciliary body is destructed partially. This procedure is performed by a special laser method which is called cyclophotocoagulation. Other operations may be required in rare cases.