Video 4.1: Intraocular pressure
Physiology of Intraocular Pressure (IOP)
- Circulation of the aqueous humour, the physiological fluid of the eye:
- Secreted by the ciliary body in the posterior chamber,
- Passes through the pupil (between the iris and the lens),
- Then fills the anterior chamber,
- Is reabsorbed by the irido-corneal angle,
- Is filtered by the trabeculum and joins Schlemm’s canal.
- Mechanism that is at the origin of regulation of intraocular pressure (IOP).
- The optic nerve:
- Connects the retina to the brain and ensures transmission of images as nerve impulses.
- The value of the IOP determines the proper perfusion of the optic nerve.
A disease characterised by a progressive lesion of the optic nerve caused in large part by increased Intraocular Pressure. The excess pressure inside the eye compresses the nerve fibres of the retina and of the optic nerve, resulting in slow deterioration of the visual field which can progress to loss of vision.
The following are differentiated:
- Primary types of glaucoma:
- open angle
- closed angle
- Glaucoma secondary to another disease (1).
- On a world-wide scale:
- One of the primary causes of decreased visual acuity: 2%. (2).
- Accounts for 12.3% of cases of blindness world-wide, i.e. about 4.5 million blind persons because of primary glaucoma (3).
- The leading cause of blindness in the industrialised countries.
- In France, glaucoma may be responsible for 10 to 15% of cases of blindness and/or decreased vision, i.e. about 15,000 cases. (4)
Elevated IOP increases the risk of glaucoma, but does not always result in a lesion to the optic nerve.
- A very low risk before 45 years of age (age of presbyopia).
- Average risk between 55 and 75 years of age.
- High risk after 80 years of age.
- Existence of congenital types of glaucoma.
- Family history
- Non-systematic heredity
- In case of family context: increased monitoring
- Ethnic background
- Higher risk in melanodermia patients
- Risk of Open angle primary glaucoma in Hispanic patients
- Risk of Angle closure primary glaucoma in Asian patients.
- Sudden trauma to the eye and complex surgeries.
- Patients with severe myopia have a specific risk of glaucoma. (1)