What is primary angle closure glaucoma (PACG)?
This is a closed angle type of glaucoma, i.e. the iris is found to be blocking the drainage of the eye through the trabecular meshwork. It is a primary glaucoma because there is no known cause relating to another condition, although the problem itself is clearly visible and related to the depth of the drainage angle of the eye (which is shallow).
It includes chronic angle closure glaucoma and acute angle closure glaucoma (previously called acute glaucoma).
What is the cause of primary angle closure glaucoma (PACG)?
In PACG, the drainage angle is 'narrow', with signs that the iris has pressed against the trabecular meshwork and damaged it, or the drainage angle is 'closed', with the iris stuck to the surface of the trabecular meshwork.
In most eyes with this sort of glaucoma, the pressure in the eye is constantly higher than 'normal' because there is a blockage of, or damage to, the trabecular meshwork. In some eyes, the pressure is intermittently higher than normal because the iris blocks the trabecular meshwork only some of the time.
Sometimes angle closure results in an episode of very severe pain in the eye with short-term loss of vision. This is called acute angle closure glaucoma (previously called acute glaucoma).
Intermittent or acute angle closure typically occurs during activities such as reading or sewing and may be precipitated by low light levels, such as those experienced during a visit to the cinema. Symptoms are more common in individuals with a European ethnic background.
Chronic or acute angle closure is termed angle closure glaucoma when damage to the vision or optic nerve has occurred as a result of high pressure in the eye.
Who is at risk of primary angle closure glaucoma (PACG)?
Some people are more at risk of developing primary angle closure glaucoma than others:
Age: Acute and chronic angle closure becomes much more common with increasing age. It is uncommon below the age of 40.
Sex: Women suffer from acute and chronic angle closure more frequently than men.
Race: If you are of Asian origin you are more at risk of angle closure glaucoma than someone of European origin. It may also come on at a younger age and be more severe.
Family History: If you have glaucoma, your close relatives have an increased chance of developing the condition.You should advise members of your family to have regular eye tests by an optometrist (optician).
Long sight: People with a high degree of long sight are more prone to angle closure glaucoma.
What are the symptoms of primary angle closure glaucoma (PACG)?
In the early stages of PACG, there may be no symptoms – your vision may seem perfectly normal and there is no pain. The condition is usually first picked up when your eyes are examined by your optometrist (optician).
For this reason, regular visits every year or two are essential if glaucoma is to be detected early. In the later stages of glaucoma, when a considerable amount of the field of vision has been lost, getting about and using stairs becomes difficult, although reading vision and vision for recognising people is usually still good. However, if the glaucoma is untreated, even the centre of the field of vision may be damaged so that reading vision becomes affected and sight may be lost.
In eyes that develop high pressure without symptoms, the condition is called chronic angle closure. This form is more common in individuals with an Asian ethnic background.
In some eyes, there may be intermittent symptoms of eye ache with cloudy vision, where the vision becomes milky or hazy, like looking through smoke.
Detection and diagnosis
The detection of chronic angle closure glaucoma, like other forms of symptomless glaucoma depends on regular routing eye examinations which include all three glaucoma tests.
This is because an unaffected eye can 'fill in' for the other, the detailed central vision is not affected until a late stage and because people wrongly assume that the reduction in their vision is simply due to age.
Everyone over 40 years of age should ensure that they have regular sight tests every two years to discover if their eyesight has deteriorated. These tests are a good opportunity to check for any signs of glaucoma.
During these visits, make sure you ask the optometrist (optician) to carry out the three glaucoma tests.
The three glaucoma tests are:
1. Eye pressure (tonometry):- Tonometry is the measurement of intraocular pressure (the pressure inside the eye) and can be carried out with several different instruments. In general, Goldmann applanation tonometry (with the blue light) is used in hospitals and non-contact (air puff) tonometry is used in optometric (optician) practices.
Goldmann applanation tonometry involves local anaesthetic drops (with yellow dye called fluorescein) being given to allow the instrument to touch the front of the eye.
The drops sting a little, but the procedure itself is completely painless. It is generally considered to be the most accurate method of measuring the pressure.
In non-contact tonometry, a puff of air is blown at the eye from the instrument. This does not require any form of anaesthetic and is generally considered to be somewhat less accurate.
2. Optic disc appearance (ophthalmoscopy):- The appearance of the optic disc can be examined using an ophthalmoscope (a special sort of torch) or by the use of a slit lamp. This allows the examiner to assess the degree of cupping of the optic disc and the health of the retina.
3. Visual field (perimetry):- Perimetry is the technique of mapping out the blank or less sensitive areas in the field of vision, so that the presence of optic nerve damage can be assessed.
These three tests together increase the likelihood of glaucoma detection by four times when compared with ophthalmoscopy alone.
The three tests are quick and painless and, depending on the instruments used, should only take around 15 minutes in addition to the normal eye examination but they will only establish that there is glaucoma present.
The precise diagnosis of angle closure glaucoma is dependent on gonioscopy, which is where the examiner uses a special type of contact lens to view the drainage angle of the eye.
Acute angle closure glaucoma
As has already been described, this is a painful event and people suffering an attack of acute angle closure glaucoma are certain to seek medical attention urgently.
If there is an increased likelihood of a person suffering an attack, because of family history, then gonioscopy can be carried out in order to assess the depth of the anterior chamber and the condition of the drainage angle and if necessary treatment can be given to prevent an attack.
Treatment of Primary Angle Closure Glaucoma (PACG)
The loss of vision in glaucoma is permanent, but with early treatment, the damage to vision can be minimised. In some patients, the loss of vision occurs very slowly and treatment may not be necessary. However, most patients do require treatment. This prevents or slows further loss of vision in most patients. Taking the treatment is important, even though the vision may seem normal, because the loss of vision may get worse without the patient noticing.
All treatment for glaucoma is designed to reduce the level of intraocular pressure to a point at which further damage to the optic nerve is prevented. This reduction in the level of intraocular pressure is achieved by a variety of means including eye drops, tablets, laser treatment for glaucoma and surgery for glaucoma.
Each has advantages and disadvantages and the choice of the glaucoma management regime best suited to an individual patient should be made as a collaborative decision involving the patient and the ophthalmologist.
Eye drops usually form the first stage of treatment for primary angle closure glaucoma but Diamox, (which is a very powerful type of water tablet) is often used in cases of acute angle closure glaucoma as a short term measure to bring the intraocular pressure to a sufficiently low level for laser iridotomy or surgical iridectomy to be performed. These procedures provide a bypass of the blockage caused by the iris and let the aqueous humour pass through to the trabecular meshwork thereby controlling the intraocular pressure.
Treatment for glaucoma is effective and in the vast majority of cases useful sight can be retained for life providing the treatments are used properly and the agreed management regime followed.