Updated April 17, 2024 Author: Manuel Domingues Glaucoma is a silent and progressive vision disease. When a patient realizes it, the disease has already limited their visual field. The visual field is the space in which we can observe objects when our gaze is fixed on a point. While driving, for example, when we look at a car in front of us, we can still see sidewalks, the sky, trees, and the rear-view mirrors. A person with glaucoma will not be able to perceive, for example, the presence of the rear-view mirror. As the visual field is the stage for visual function, screening and early detection of glaucoma is very important. Glaucoma is a disease of the optic nerve, usually due to increased intraocular pressure. Aqueous humor is the clear fluid that fills the space between the cornea and iris, and drains the eye to maintain healthy pressure. In glaucoma, this drainage is impeded resulting in increased pressure that will damage the optic nerve. The death of ganglion cells prevents the transmission of images from the eye to the brain, resulting in visual field loss. This disease is characterised by: Reduction of the retinal nerve fibre layer; Changes in the appearance of the optic disc; Loss of visual field. Intraocular pressure is one of the most important causes of glaucoma, and is the factor that can be most effectively controlled. However, there is a type of glaucoma that is not associated with high intraocular pressure; this is known as normal tension glaucoma. Glaucoma is a common and often undiagnosed disease. In these circumstances, and when it is not treated, it is one of the main causes of blindness. Most cases of glaucoma can be treated and controlled with medical or surgical treatment. Glaucoma: the optic nerve The optic nerve is made up of nerve fibres from all the ganglion cells in the retina. It transports the sensory information captured by the retina and transmits it to the brain. Besides small vessels and nerves, the optic nerve is the only structure that crosses the wall of the eye. The starting point of the optic nerve inside the eye is directly visible, and is known as the optic nerve papilla or optic disc. The nerve fibres forming the optic nerve are supported by structures on the wall of the eye (the lamina cribrosa), and outside the eye by a fibrous sheath and by septa of this sheath. Irrigation of the optic disc depends upon intraocular circulation. Glaucoma: Ocular pressure The eye is a roughly spherical structure with a flexible consisting of the cornea and the sclera. The shape of the eye is maintained by means of internal pressure , created by a liquid known as the aqueous humour . Aqueous humour is produced behind the iris and comes out of the eye through the angle of the anterior chamber. The wall of the eye keeps the intraocular volume consistent. Therefore, intraocular pressure depends on the balance between the amount of aqueous humour produced and the amount of aqueous humour leaving the eyeball. When the eye pressure is greater than 22 mmHg, ocular hypertension exists. The higher this is, the greater the probability that the optic nerve will lose nerve fibres: in other words, the more likely it is that glaucoma will occur. Most cases of ocular hypertension occur as the result of increased resistance to the drainage of aqueous humour from the eye. What are the main types of glaucoma? In adults, there are 2 main groups of glaucoma: Angle closure glaucoma (also known as acute glaucoma); Open-angle glaucoma (also known as chronic glaucoma). Angle closure glaucoma In angle closure glaucoma , or acute glaucoma, the iris occludes the angle of the anterior chamber and prevents the draining of aqueous humour. Intraocular pressure rises within a few hours and clinical symptoms are dramatic ; these include: Pain; Sickness; Nausea; Reddening of the eye; Irregular dilation of the pupil; Acute reduction in vision. Open-angle glaucoma In open-angle glaucoma , or chronic glaucoma, obstruction to the drainage of aqueous humour develops over years and intraocular pressure rises slowly. This type of glaucoma has no symptoms until the stage at which the central visual field changes. Open-angle glaucoma is the most frequent type, and is divided into various sub-types. Normal tension glaucoma evolves in the same way as open-angle glaucoma, but without ocular hypertension. It is thought that changes in the structure or irrigation of the optic nerve occur in these cases, making it incapable of withstanding normal intraocular pressure without undergoing glaucomatous changes. How is glaucoma diagnosed? Open-angle glaucoma is the most common form of glaucoma and has no symptoms until late and irreversible stages of the disease are reached. Diagnosis can only be made upon examination by an ophthalmologist , using the following methods: Direct examination of the optic nerve; Study of visual fields; Measurement of intraocular pressure. Intraocular pressure measurement on its own is not enough to diagnose glaucoma. As mentioned above, there are also types of glaucoma in which the intraocular pressure is normal and the ocular pressure is elevated without the optic nerve undergoing glaucomatous changes. What is the treatment for glaucoma? Intraocular pressure can be controlled with various types of topical medicines (drops) used alone or in combination. There are also 2 types of laser that can be used in the treatment of acute (angle closure) glaucoma and in simple chronic glaucoma. Finally, there are various surgical techniques that make it possible to increase the drainage of aqueous humour and reduce intraocular pressure. In any case, the patient must be regularly monitored by the ophthalmologist. In the hospitals and clinics of the Hospital da Luz network, there are ophthalmologists who specialise in the diagnosis and treatment of eye diseases and who can perform the necessary examinations for your condition. This article was written with the support of physicians and other clinical professionals from the Hospital da Luz network. The content published in the Health Guide is intended for the general public and is provided for informational and educational purposes only. It does not replace individual medical assessment, diagnosis, or personalized clinical advice from a qualified healthcare professional. The content is produced or reviewed by physicians and other healthcare professionals at Hospital da Luz and is based on the knowledge available at the time of publication or the most recent update, as indicated at the beginning of each item.
