Glaucoma

What is glaucoma?

Glaucoma is a disease characterised by the progressive reduction of the visual field caused by an increase of internal pressure within the eye, which comes about through the accumulation of aqueous humour.

Aqueous humour is a liquid similar to water, produced by the anterior chamber of the eye to give the eyeball consistency. The relationship between the quantity of aqueous humour produced and the quantity that leaves should be such as to keep the internal eye pressure constant.

Left: normal vision; right: example of tubular vision

Any anomaly that causes a variation in this relationship may lead to a hypertony, i.e. an increase in eye pressure. Hypertony causes disruption in the nerve fibres that converge on the optic nerve. This results in a reduction of the visual field, generally initially affecting the visual field periphery, and then progressively the other parts.

Types of glaucoma

There are two types of glaucoma:

  • Primary glaucoma: this is caused by alterations in the areas through which the aqueous humour leaves the eye;
  • Secondary glaucoma: this is caused by factors pertaining to the eye or general factors outside the aqueous humour outflow system.

There are many clinical forms of glaucoma. The two main forms are open-angle glaucoma and closed-angle glaucoma:

  • Open-angle chronic glaucoma: this is the most frequent type of glaucoma. The aqueous humour reaches the iridocorneal angle inside the eye, but structural problems of this angle mean that it does not manage to pass through correctly; the pressure increases and leads to optic nerve damage.
  • Closed-angle glaucoma: this is less frequent than the other type. It is found more in elderly people and hypermetropes. In this case the access point to the aqueous humour is blocked by the fact that the angle formed by the iris and cornea is less wide than normal. Under certain conditions this may cause an acute attack of glaucoma. This is very serious and can lead to irreversible eyesight problems. The acute attack of glaucoma is characterised by a violent pain and marked reduction of eyesight.

    Closed angle between iris and cornea, blocking aqueous humour stream

Diagnosis

Glaucoma is often asymptomatic and prevention and early treatment are therefore essential, both in the general population (at least those over 40 years of age) and in the familial risk or predisposing factor categories.

If one suspects glaucoma, the principal diagnostic examinations are:

  • measurement of eye pressure (ocular tone)
  • measurement of eye pressure repeated several times over the same day (daily tonometric curve)
  • computerized examination of the visual field
  • gonioscopy

The frequency with which the examinations should be repeated depends on the severity of the illness: in glaucoma of a certain severity even every 2-3 months; in slight forms, once a year is sufficient.

Glaucoma can be treated with good results if diagnosed early. It is therefore important to have regular check-ups, even if there are no symptoms, especially when there is glaucoma in the family or when ocular tone is 21 mmHg and above (preventive screening).

Left: regular visual field; right: visual field in presence of glaucoma

Treatment

Laser treatment for glaucoma

Glaucoma may be treated:

  • Medically (eye drops)
  • Parasurgically (by laser technique)
  • Surgically (by procedures aimed at restoring the normal outflow of aqueous humour)

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