The term glaucome indicates the whole of the ocular diseases in which the intraocular pressure (PIO) is too high and involves a repercussion on the optical nerve.

Terminology

“Glaucome” is a vague term if one does not associate a precise qualifier with it. Indeed, the types of glaucome are numerous. More running of the glaucomes is the chronic glaucome with open angle.

One does not indicate a word of glaucome the Hypertonie S eyepieces (generally moderate) without repercussion on the optical nerve which are all the same to supervise because a certain number can evolve/move in glaucome.

It is known today that the level of hyperpression likely to generate a glaucome is specific to each individual, which returns the diagnosis of the difficult disease at its beginning. The border is sometimes difficult to establish between simple hypertonicity without consequence and hypertonicity with risk of glaucome. There exists a relation and a frequent but nonsystematic continuity between ocular hypertonicity and glaucome which represents in fact of the stages different from the same pathology.

The criteria of diagnosis extremely evolved/moved these last years. All the people presenting an ocular hyperpression will not develop a glaucome and certain people with a pressure considered according to the old criteria like normal (with being known between 10 and 21 mm Hg) will be reached by a glaucome.

Anatomical and physiological recall

Aqueous humor

The intraocular pressure (PIO) is function of the volume of aqueous Humor contained in the former room of the eye. This aqueous humor is secreted by the Corps ciliaire in space called posterior room, then passes through the Pupille (between the iris and the Cristallin) in the former room (space between the cornea and the iridal curtain). It is then reabsorbed in the irido-corneal Angle through the filter trabéculaire Trabéculum, then drained in the Canal of Schlemm. It is thrown finally in the veins sclérales to join general venous circulation.

Intraocular pressure

The usual intraocular (PIO) pressure in the adult lies between 10 and 21 mm of mercury (Hg) (average of 16). The PIO is measured nowadays using Tonomètre S automated with air blast. To define the normal PIO at a given person requires to know the rigidity of the cornea which depends its thickness primarily. Indeed, measurement is not done directly in the aqueous humor but through the cornea. Also, this last influence measurement. The people having a thick cornea have a measured ocular pressure higher than the people equipped with a fine cornea. In addition the ocular pressure increases naturally with the age.

In other words, the measurement of the ocular pressure is only one parameter which requires to be interpreted according to the corneal thickness and of the age of the person. This criterion given separately thus does not allow affirms that a person is carrying a glaucomateuse disease nor that it is unscathed.

Physiopathology of the glaucomes

Mechanisms of ocular hypertonicity

Ocular hypertonicity is not that a symptom like the east the fever for example. The ocular pressure can be found high in many different ocular affections which as many will define particular types of ocular hypertonicity or glaucomes.

The most current mechanisms are:

• a reduction in elimination by obstruction of the irido-corneal angle of origin congéniralt by an embryonic residual membrane (membrane of Barkan) congenital Glaucome or aquise with the age by Sclerosis of the Trabéculum. This second case orrespond with the chronic Glaucome with open angle (angle known as open because normal anatomically). It is about the cause of the ocular hypertonicity by far most frequent in practice.

• a pupillary blocking by the Crystalline secondary with ageing. This one increases volume and can cause a blocking of the pupillary opening. The aqueous humor accumulates then behind the iris and pushes this one ahead, which involves at certain predisposed people (people whose angle iridocornéen is already narrow, case that one especially meets at hypermétropes) a complete closing of the angle. It is the acute mechanism of the crises of glaucome called by closing of the angle. More rarely pupillary blocking is done by Synéchie S irido-cristalliniennes complicating an acute Uvéite former untreated. The Crystalline adhesive on the iridal edge and prevents the passage of the aqueous Humor.
• by increase in secretion ciliaire. It is traditional in the acute Uvéite S former (one speaks here about Uvéite hypertensive rather than of glaucome. It is about a rare cause.

Consequences

The consequences of a hyperpression intraoculaire are done primarily on the level of fiberoptics. These last correspond to the prolongations of the ganglionic cells of the retina which will leave the eye on the level of the optical papilla to constitute the Optical nerve. Ocular hypertonicity (or HTO) will cause an acceleration of the degeneration of these fibers. This hypertonicity will have all the more fast consequences as it is raised and prolonged.

The repercussion of the HTO, especially if it is chronic, will also depend on the quality of the Microcirculation of the subject, they are the “vascular factors of the chronic Glaucome with open angle”. Thus, the risk factors vascular, of Artériosclérose (arterial Hypertension, Diabetes sweetened, Nicotinism, Hypercholestérolémie) will be to also correct them when one treats a chronic Glaucome.

In practice, the ocular hyperpression is responsible for a degenerative optical neuropathy. A normal optical nerve contains more than one million fibers to the birth. Naturally, the number of fibers falls with the wire of time at a rate of approximately 5000 fibers per annum. The ocular hyperpression will involve an acceleration of this degeneration.

Another consequence of the ocular hyperpression, if it is major (higher than 40 or 50 mmHg, such as one observes it in the acute glaucomes) is a sideration of the acivity or a destruction of the corneal cells endothéliales which involves the appearance of a corneal edema describes like a " mist épithéliale".

See too

Various types of glaucome

• chronic Glaucome with open angle (GCAO): it is by far more frequent and when one says of a person that it is reached of a glaucome without more precision, it is often of this type of glaucome that he sagit.
• acute Glaucome with angle closed (GAAF)
• Glaucomes secondaries
• congenital Glaucome
• Alfred Vogt, inventor of the cyclodiathermy in the treatment of the glaucome (operation of Vogt).

External bonds

• Course of ophthalmology for the medical students
• Glaucome.net Public and professional, information and press review
• the glaucome Information on the glaucome, signs, gravity, mechanism, diagnosis, examinations, evolution, medical care and surgical.
• Committee of fight against Glaucome CLG Which is what the glaucome? How to consult and treat a glaucome?

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