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Glaucoma |
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Glaucoma is a group of eye diseases that gradually cause loss of vision without us realising the loss of vision. It is the leading cause of irreversible blindness in India. It is estimated that approximately 12million people will be affected by 2010 in India increasing to 16 million by 2020 due to increasing life expectancy. More than 90% of glaucomas remained undiagnosed in India compared to 40-60% cases in developed countries. In the early stages of the disease, there may be no symptoms.
Vision loss is caused as a result of damage to the optic nerve which connects the eye ball to the brain and carries electrical stimuli to the brain where the stimuli are processed and perceived as image.
Glaucoma can’t be cured completely, but can be treated by medication or surgery to prevent further visual loss. The appropriate treatment depends upon the type of glaucoma among other factors. Early detection is vital to stopping the progress of the disease.
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Family History, Risk – importance of frequent eye examinations
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Close blood relatives of patients with POAG have at least a four times increased risk of glaucoma compared with those without a family history of glaucoma. People with family history of glaucoma should be tested for glaucoma from 35 years of age onwards regularly, at least once a year, tests include ophthalmoscopy, tonometry and perimetry. Some times at an earlier age if they are subject to other risk factors, such as being of African-Caribbean origin, or having diabetes or myopia (short sight ).
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Causes
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Increased pressure within the eye, known as intraocular pressure or IOP, is the main factor in the optic nerve damage. Although IOP is clearly a risk factor, we now know that other factors must also be involved because even people with “normal” levels of pressure can experience vision loss from glaucoma. Adult glaucoma falls into two categories, Open angle glaucoma and closed angle or angle closure glaucoma.
These categories are subdivided, according to whether the cause is unknown (primary glaucoma) or known i.e. the high eye pressure is caused by other conditions of the eye (secondary glaucoma).
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Primary Open Angle Glaucoma
In open angle types of glaucoma, there is no physical obstruction of the drainage angle of the eye. As its name suggests, there is no identifiable cause. The drainage angle is open, and the pressure is higher than normal because of the restriction to the flow of the aqueous humour through the trabecular meshwork which is sieve like structure in the drainage angle.
 This high pressure causes damage to nerve fibers at the optic nerve head.
Normal Tension/Pressure glaucoma: In about one third of eyes with glaucoma, the pressure is not high and the condition is called normal tension glaucoma or low tension glaucoma. In these cases, it is thought that a poor blood supply or a weakness in the optic nerve structure may make the nerve susceptible to damage by eye pressures which are not abnormally high.
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Primary Angle Closure Glaucoma (PACG)
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Common in people with long-sightedness(plus glasses, hypermetropia).In this type, the iris (diaphragm of muscle which forms the pupil) blocks the drainage of the eye through the trabecular meshwork. Two types include chronic angle type and acute angle closure type.
In this type, the drainage angle is narrow and iris is pressed against the meshwork in the angle and closes the angle, sometime it is even stuck to 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.
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Secondary Glaucoma
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Numerous diseases, injuries, surgeries of the eye, as well as even medical treatment, can lead to increased or, less frequently, low IOP.
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Symptoms and diagnosis
Early detection of glaucoma is very important because treatment is much more likely to succeed when started early than when damage has already progressed to an advanced stage.
- Diagnosis of glaucoma is possible only if the patient is seen by the ophthalmologist as it may not produce any symptoms.
- Changes in the early stage of the disease are sometimes not easily differentiated from normal variations and may delay happen in diagnosis.
- Unaffected eye can compensate for the affected eye and patient may not notice the damage to the affected eye.
- Patients assume that the vision loss is simply due to age.
- ) Detail central vision is not affected until late in the disease
There is often a period of uncertainty as to whether or not the patient will develop glaucomatous damage. Hence, frequent eye examinations are very much necessary to diagnose it.
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Tests
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Optic disc assessments for cupping, visual field assessment, pressure assessment are very essential for diagnosis and detection of glaucoma.
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Treatment
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All treatments are aimed to reduce the level of intraocular pressure to a point at which no further damage to the optic nerve happens. Treatments include eye drops, tablets, laser treatments and surgery.
Eye drops usually form the first stage of treatment for glaucoma. There are now a wide variety of eye drops which work in a number of different ways. The only tablet commonly used in the treatment of glaucoma is Diamox, which is a very powerful type of water tablet. It is most commonly used in the short term treatment of acute angle closure glaucoma prior to laser iridotomy and is rarely prescribed for long term use due to its side effect profile.
Lasers are used to treat both open and closed angle glaucomas with different lasers and different techniques used according to need. There are also a variety of types of surgery for glaucoma depending on the individual needs of the patient.
Treatment for glaucoma is effective and in the vast majority of cases useful sight can be retained for life.
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Babies and Children (Developmental and Congenital Glaucoma)
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Glaucoma in infants is a rare condition (about 1 in 10,000 births). There have been tremendous advances in the treatment of this condition in recent years, it is now reasonable to expect a prognosis that is considerably better than was the case even one generation ago.
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Signs and Symptoms
- Large eyes: The outer coat (sclera) of a child’s eye is much softer and more flexible than that of an adult. It gets stretched and results in a large eye due to high intraocular pressure. Reducing the pressure does not usually bring the eye back to its normal size but may reduce the size of the eye very slightly.
- Sensitivity to Light: Children with raised intraocular pressure often become very sensitive to light. Even after the pressure is lowered, some degree of sensitivity to light may persist in the long term.
- Cloudy Eyes: The cornea, clear dome shaped structure becomes due to damage to the structure as a result of increased pressure.
- Watering Eyes: due to high pressure, resultant corneal swelling leadings to increased glare and watering.
- Poor Vision and Jerky Eyes (Nystagmus):Poor vision from the childhood results in jerky eyes . After treatment, most of these symptoms improve.
- Squint (strabismus):In some children the eye with poorer vision may be seen to turn inwards, towards the nose, or outwards.
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Treatment
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Most babies and children initially need to be examined under anaesthetic. If their eye pressure is found to be raised, then surgery will usually be carried out at the same time to save a further anaesthetic. Every time a child is examined under anaesthetic, there is a chance that a further procedure may be required and parents should be aware of this. Generally speaking, a child can be examined without anaesthetic after the age of 5 years, but this can vary. There are several types of surgeries, like goniotomy, trabeculotomy, drainage tubes, trabeculectomy etc.
Children with glaucoma should have regular refraction done and need frequent change of glasses to maintain good vision and prevent lazy eye.
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