Visual pathologies


"What is Glaucoma ?
It's a disease that affects the eye, characterized by an attack on the optical nerve, altering the visual field, often accompanied by high intraocular pressure.
In other words :
Ocular tension is maintained by the continuous production within the eye of a fluid called aqueous humor.
This aqueous humor is permanently evacuated to the blood vessels through a meshed zone called trabecular meshwork.
This trabecular meshwork is situated in the cornea next to the iridocorneal angle - the angle between the iris and the cornea. This angle is normally of 60°.

What are the different types of glaucoma ?
We can define 3 types of glaucoma depending on the opening and filling of the iridocorneal angle.

- Chronic glaucoma or open-angle glaucoma, in which the iridocorneal angle is normal but in which the evacuation of aqueous humor is slowed down at the trabecular meshwork.
 - Acute angle-closure glaucoma or “closed-angle glaucoma”, in which the iridocorneal angle is very thin. This permits the iris to close the angle and to stop the aqueous humor going through the trabecular meshwork.
 - Congenital glaucoma, resulting from the presence of embryonic remnants in the iridocorneal angle, prevents the aqueous humor from going through the trabecular meshwork.
There also exist secondary glaucomas linked to ocular conditions (venous thromboses) or some forms of medication such as corticosteroids.

What symptoms for the different types of glaucoma ?

- For chronic glaucoma
There is no forewarning : it's a ""silent"" disease.
Chronic glaucoma evolves slowly, without any pain or loss in eyesight at the very beginning. The eyesight slowly deteriorates over the years, starting with peripheral vision.
The damage is irreversible and the subject only realizes the loss of vision when their vision straight ahead is affected.

- For acute angle-closure glaucoma:
* Very strong ocular pain,
* Headaches with nausea, sometimes vomiting,
* Blurred vision,
* Red eyes.

- For congenital glaucoma : the infant is tearful, reacts to light (photophobic) and often has enlarged eyes.
- For secondary glaucomas, depending on the condition, the symptoms can resemble those of chronic and acute angle-closure glaucoma.

What are the risk factors of the different glaucomas ?
- For chronic glaucoma :
* Hereditary : presence of the disease in family history
* Vascular problems : hyper or hypo-tension.
* Age : starting from 45 years.
* Ethnic background : 4 times more frequent for black people.

* For acute angle-closure glaucoma:
- Anatomical non-conformation of the eye with a bulging crystalline and prolapsed iris.
- Hyperopic eye.
- More frequent for women around the age of fifty.

* For congenital glaucoma : hereditary with recessive transmission.

Glaucoma detection
The systematic eye exam is often undertaken at the first signs of presbyopia, which goes to show the importance of a full eye examination at that period in life.
- Normal eyestrain is 17mm/hg (millimeters of mercury). This amount varies from one person to another but remains under 20mm/hg.
- The ophthalmologist and the patient are alerted for values superior to this norm.
- Most commonly, the condition is bilateral.

Which examinations can give more precision to the initial diagnostic?
- In the case of chronic glaucoma, they are painless because they are performed after the instillation of anesthetic eye drops in both eyes.
 - Pachymetry measures the thickness of the cornea. A value greater than normal means an excessive eyestrain.
The ""3-mirror"" examination. It consists in placing a contact lens on the eye through which the iridocorneal angle and whole retina are visible. In the retina, the shape and color of the optic disk are criteria of evolution.
 - The automated examination of the field of vision looks for zones called scotomas, where the eyesight or contrast are weaker.
 - Blue light images of the back of the eye and the OCT (tomography of the retina under coherent light) permit the analysis of the state of the retinal nerve fiber layers.
 - The perception of colours is only affected in the final stages of the disease.

- In the case of acute angle-closure glaucoma, the examination is performed in emergency. It defines the level of eyestrain, the transparency of the cornea and the state of the iridocorneal angle.
- In the case of congenital glaucoma, the examination is performed under general anaesthesia and measures eyestrain, the diameter of the cornea, its transparency and sometimes also the opalescence.

How to treat glaucoma ?
- For chronic glaucoma :
- Medication :
* The treatment, which aims to reduce intraocular pressure, consists in administering eye drops. The drops can be classified into different categories according to their effect :
- Those that lower the production of aqueous humor (beta-blockers, alpha-adrenergic agonists, carbonic anhydrase inhibitors).
- Those that help its evacuation (prostaglandins, miotics).

It should be noted that carbonic anhydrase inhibitor based treatments are also available in tablets and have the same action as eye-drops.

* Eye drops can be prescribed alone or associated with another treatment depending on how the patient reacts to them. The potentially high frequency of instillations requires immaculate hygiene measures.
* Once started, the treatment is lifelong. It consists in daily instillations, once or twice a day. This is something the family GP must be aware of.

- Surgery :
* It is suggested when medical treatment alone cannot contain eye pressure. It is an ambulatory procedure, performed under local anaesthesia.
* It aims to assist the flow of aqueous humor under the conjunctiva by opening or relieving the trabecular meshwork.

- Treatment monitoring :
* Verification of its effectiveness by measuring the intraocular pressure and, depending on the situation, a yearly or biannual study of the field of vision.

* Between two ophthalmic consultations, the GP may prescribe eye drops.

* Glaucoma doesn't require stopping any particular activity - work, driving, hobbies.

* There are no dietary recommendations.

* The family GP is required to follow the patient's general condition, which includes blood pressure.

- In the case of acute angle-closure glaucoma, the treatment must be performed in emergency :
- Medically :
* Local treatment: repeated instillation of eye drops.
* Systematic or intravenous administration: treatments that aim to relieve eye tension, reduce the size of the pupil and fight the inflammation.

- Surgically :

* Often required, it's an ambulatory procedure performed under local anaesthesia which consists in creating a small opening in the iris with a laser beam or other surgical procedure.

- Evolution :

* Excellent if the treatment has been followed.
* If no treatment has been undertaken, the glaucoma becomes chronic.

- For congenital glaucoma: treatment should be performed in emergency and consists in incising the embryonic remnant - called the Barkan membrane - to allow the aqueous humor to flow freely through the trabecular meshwork.

How many people are affected by chronic glaucoma ?
It's a common condition: 2 to 4% of the population are affected, representing 1 million people in France.

How to prevent glaucoma ?
There exists no preventive treatment against glaucoma.
The regulation of blood pressure is beneficial." 

Date: 12/24/2012
Author: Sylvie Ervé
Organization: Centich, France
Only for Members: No
Content type: Good practises
Tags: glaucoma
Categories: Medical & Functions, Eye - Vision impairment