Glaucoma

Glaucoma is the leading cause of irreversible blindness in the world.

It is characterised by progressive loss of the visual field, due to a progressive atrophy of the optic nerve, by unidentified nerve cell loss and, without treatment, can end in blindness.

The changes caused by glaucoma can be prevented by early diagnosis and subsequent close follow-up. All vision loss in glaucoma is completely irreversible.

Glaucomatous lesions are related to increased intraocular pressure and other factors. However, as ocular pressure is the element on which we can act, it is on this that we focus our attention.

The eye continuously produces (in the ciliary body, an organ located behind the iris in the periphery) aqueous humour liquid which passes through the pupil into the anterior part of the eye and is eliminated into the circulation through holes in the angle between the cornea and iris, called the trabecular meshwork. When there is a balance between production and elimination, the eye pressure remains stable. If there is more production than elimination, or elimination is hindered by resistance to the passage of aqueous humour through the trabecular meshwork, the pressure inside the eye rises, exceeding the perfusion pressure of the blood vessels irrigating the optic nerve. As a result, the irrigation of the optic nerve decreases, the nerve fibres die, with progressive loss of vision.

The progressive destruction of the optic nerve initially causes a slow loss of the peripheral visual field, which goes unnoticed by the vast majority of people. If it is not detected, the field closes further and further, until a tubular field remains, through which clear vision can still be seen. The patient has great difficulty in orienting himself, because he sees as if through a spyglass. This later leads to a total loss of vision.

In most cases of glaucoma we find an increase in intraocular pressure, some degree of optic nerve atrophy and characteristic visual field losses.

Types of Glaucoma

Usually when making the diagnosis we find only bilateral high eye pressure with no other signs, or one eye with more advanced glaucoma and the other at the beginning with no symptoms. Later, if left untreated it becomes bilateral. Painless initially, later if the pressure is very high with deafening pain around the eye and in the head on the same side.

The loss of vision is initially limited, of the peripheral visual field not identifiable in everyday life. As it gets worse the patient realises that something is wrong. He knocks on someone else's shoulder, cannot see the doorframe and eventually consults the ophthalmologist.

The visual field narrows until it reaches a tubular vision, in which case he can distinguish objects, but at a distance, without seeing what is around him, as if he were looking through a spyglass. Later he ends up losing his vision completely.

There is also low-tension glaucoma, in which the eye pressure is normal, but all the signs described in the previous case are present.

In acute or closed angle glaucoma there is an abrupt increase in intraocular pressure due to the closure of the angle of the anterior chamber by dilation of the pupil. As the angle is sufficiently narrow, the iris tissue ends up closing the trabecular meshwork, which, as already mentioned, is situated at the vertex of this angle, thus acutely increasing the ocular pressure enormously, due to the impossibility of draining the aqueous humour. The patient has severe pain which is almost impossible to bear, the eye is very red due to congestion of the superficial blood vessels and the pupil is dilated. Typically this type of glaucoma occurs in eyes with a small anterior segment (hypermetropes) and large crystallines (increased volume as may happen with age-related opacification of the lens in cases with a small anterior chamber).

Secondary glaucoma results from eye diseases that end up in one way or another causing glaucoma. It is the case we talked about earlier of the increase in volume of the crystalline lens by cataract, the prolonged use of steroids causing in a glaucoma similar to the simple chronic one.

When iris pigment disperses and is deposited in the trabecular meshwork region, it can lead to pigmentary glaucoma, similar in its evolution to simple chronic glaucoma.

Neovascular glaucoma results from the formation of new blood vessels in the iris reaching the trabecular meshwork, preventing the elimination of aqueous humour. It is usually associated with retinal vascular diseases such as diabetic retinopathy and venous occlusions. Secondary glaucoma is generally very difficult to treat because the anatomical alterations are very marked.

Congenital glaucoma is a special case, detected at birth, as babies are born with very large eyes (buftalmos).

In the early stages of glaucoma, symptoms are almost non-existent or unnoticeable. The progression of the disease is "silent".

Symptoms and signs such as red eyes, watering eyes, photophobia (sensitivity to light), eye pain and headache are frequent in patients with glaucoma. As mentioned above, glaucoma can go undiagnosed even in advanced stages, if you have never consulted the ophthalmologist, being initially the loss of partial vision in one eye, it is not detected by the patient. It is therefore very important to consult the ophthalmologist from the age of forty, especially if there is a family history.

Age, individuals over 40 with a family history of glaucoma, severe myopia and hyperopia, diabetes associated or not with diabetic retinopathy, uveitis (inflammatory disease of the uvea, the dark part of the middle layer of the eye and 90% of the time of unknown cause) and prolonged treatment with local or oral corticosteroids are known risk factors.

As already mentioned, early diagnosis in glaucoma is very important.

When presenting a clinical picture of glaucoma, it is important to evaluate not only the intraocular pressure, but also the optic nerve alterations and to check for campimetric alterations, i.e. the visual field.

There are several factors that may influence the intraocular pressure levels. In the presence of a high central corneal thickness, the pressure value may be falsely increased, on the other hand a decreased thickness may lead to an underestimation of the pressure. It is important to know the pachymetry (corneal thickness measurement) of the patient's cornea to be considered when measuring the ocular pressure (tonometry).

It is very important to carry out a functional and structural assessment because in these patients, before changes in the visual field are detected, there is already a considerable loss of ganglion cells (cells connecting photoreceptors to the brain and whose axons form the optic nerve), that is, structural changes precede functional changes.

In order to evaluate structural changes, the optic disc (circular area of the ocular fundus where the aforementioned axons come together to form the optic nerve) is observed, specifically the excavation and staining, through ophthalmoscopy (direct observation) or retinography.

The study of the thickness of the retinal nerve fibre layer and of the papilla (the optic disc) and its cupping (the degree of loss is directly related to the cupping of the papilla) is performed using optical coherence tomography (OCT). This examination allows for a precise study of the relative loss of nerve fibres and their location. It is then compared with the study of the visual field to be certain of the real loss, as both are subject to false results.

Visual field alterations should be regularly studied by means of computerised static perimetry or by kinetic campimetry (or Goldman campimetry). Either of these can be used to assess the initial defects and allow comparative follow-up over time.

It should be understood that any type of glaucoma treatment, even surgical, has the sole aim of controlling eye pressure, as it is the only factor that we can try to control.

In open angle glaucoma, the treatment is initially medical, with the application of hypotensive eye drops, assisted or not, by laser treatment, SLT (laser trabeculoplasty) performed with YAG laser. This treatment allows the trabecular meshwork or trabecule to be opened, which in chronic glaucoma offers resistance to the elimination of the aqueous humour, causing the pressure to increase. This technique is used when hypotensive eye drops are not sufficient to lower the ocular pressure to acceptable values or when the local reaction to them makes them impossible to tolerate. It is also used in some cases as an initial treatment. In more difficult to control eye pressure, surgery is used and in other cases photocoagulation of the ciliary body may be used.

The treatment of closed angle glaucoma is either surgical or by YAG Laserwhich is, nowadays, the preferred technique. Iridotomy consists of opening a hole in the iris, creating a bypass for the aqueous humour which returns the pressure to normal in acute cases. In a prophylactic way, it can also be performed in suspected cases of a closed (or narrow) angle, likely to have an acute episode.

The classic surgery for the treatment of glaucoma is trabeculectomy. This surgery creates a bypass for the elimination of the aqueous humour by recession of a small part of the trabecular meshwork, for easier elimination of the aqueous humour and a significant lowering of the ocular pressure. Modernly, in order to simplify the surgery and with fewer complications, small implants (small tubes) are placed through the eye wall, through the trabecular meshwork. This simplifies the creation of the bypass.

There is another non-invasive treatment that allows part of the ciliary body to atrophy, thus lowering the ocular pressure (because there is less production of aqueous humour), the ultrasound cyclopast. It is not without complications, a third of patients have no response to treatment but it seems to achieve a 30% reduction in intraocular pressure in the remaining patients.

In glaucoma, in cases where medical treatment with eye drops or laser cannot lower the eye pressure to acceptable values, or when the patient does not follow treatment properly, for any acceptable reason, surgery is indicated to control it.