What is secondary angle closure glaucoma (SACG)?
This is an angle closure type of glaucoma, i.e. the iris is physically obstructing the drainage angle of the eye. As its name suggests this is the name given to a group of glaucomas where there is another condition causing the raised intraocular pressure and thus the glaucoma.
Different conditions may cause secondary angle closure glaucoma, these include lens-induced glaucoma, neovascular glaucoma and glaucoma following other surgical interventions.
What is the cause of secondary angle closure glaucoma (SACG)?
In secondary angle closure glaucoma, the natural drainage angle is 'narrow' either because of the underlying condition or because of its formation. There are 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.
What are the symptoms of secondary angle closure glaucoma (SACG)?
In the early stages of secondary angle closure glaucoma, except from any symptoms that may arise from the condition causing the glaucoma, 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), or when the condition causing the glaucoma is identified. 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 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 secondary angle closure glaucoma, like other forms of symptomless glaucoma depends on regular routine 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, although the underlying condition may cause symptoms that require attention leading to the detection of the secondary angle closure glaucoma.
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. However, the precise diagnosis of all forms 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.
Treatment of secondary angle closure glaucoma (SACG)
In all forms of secondary glaucoma the underlying condition is addressed if possible and because the loss of vision in glaucoma is permanent glaucoma therapy is usually started without delay so that 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 treatments 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) may be used in some forms of secondary 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.