What is glaucoma?
Glaucoma means that the eye pressures are raised. The front of the eye is filled with a fluid called aqueous. This fluid is produced in the eye by a structure called the ciliary body and flows out of the eye from a structure called the trabecular meshwork or the drainage angle of the eye.
If there is an imbalance between the production and drainage of aqueous then the pressure of the eye goes up. This high pressure damages the delicate optic nerve fibres which are responsible for vision. This damage of the nerve fibers results in gradual vision loss and this vision loss is irreversible.
Who are more likely to develop glaucoma?
What is open angle glaucoma?
Open angle glaucoma is that type of glaucoma in which the drainage angle of the eye (trabecular meshwork – area of drainage of aqueous) is not obstructed, thus open. The problem here is that over the years the trabecular meshwork has gradually lost its efficiency thus leading to rise in pressure. This rise of pressure if untreated leads to vision loss. Finally after considerable vision loss the patient is left with what is known as tunnel vision.
What is narrow / closed angle glaucoma?
Narrow / closed angle glaucoma is that type of glaucoma in which the drainage angle of the eye (trabecular meshwork – area of drainage of aqueous) is obstructed, thus closed. Sometimes this obstruction occurs suddenly and leads to an rapid rise of pressure. More commonly this obstruction is caused by the iris (part of the eye from which the eye derives its colour).
This rapid rise in pressure is called acute angle closure glaucoma. The various symptoms are:
What is normal tension glaucoma?
As described previously due to raised eye pressures there is damage to the optic nerve fibers at the back of the eye and this is called as glaucoma. Normal tension glaucoma is different because the eye pressures are not raised but there is still damage to the optic nerve fibers in a manner similar to that seen in patients with raised pressures.
This condition is treated by medications to further lower the eye pressures.
What is ocular hypertension?
Ocular hypertension is the other end of the spectrum of normal tension glaucoma. In this condition the eye pressures are above normal range however the patient does not have optic nerve damage, the kind that is usually seen with raised pressures.
As there is no damage to the optic nerve fibers, no treatment is required. However, a close follow-up is required to detect early damage to the optic nerve fibers.
How is glaucoma diagnosed?
Glaucoma is diagnosed based on 4 factors
1. Eye pressure
2. The depth of the drainage angle
3. The shape and contour of the optic nerve
4. The status of the peripheral vision
This is checked by your eye doctor with an instrument called as the tonometer. The normal range of eye pressure is 10-21mm of mercury.
Depth of the drainage angle
This is checked by your eye doctor with an instrument called the gonioscope. Grading the depth of the drainage angle will help your eye doctor decide on how to treat your glaucoma.
The shape and contour of the optic nerve
This is examined by your eye doctor by a process called ophthalmoscopy. Your doctor will decide on how severe is the optic nerve damage if at all and then institute treatment accordingly.
The status of the peripheral vision
The peripheral vision is checked by an instrument which is called a perimeter. In glaucoma when the optic nerve fibers are damaged the peripheral vision is the first aspect of vision which is lost. This test which is known as perimetry will detect that loss of peripheral vision and help your eye doctor decide on the course of management.
How is glaucoma treated?
Glaucoma is treated by one of the following methods
Both eye drops and oral medications can be used. Eye drops can be used in most types of glaucoma. Over the past few years the number of eye drops that have become available for use in glaucoma has increased tremendously. The schedule for applying these drops has to be stuck to very strictly. Over a period of time your eye doctor may change the eye drops that you are using. These eye drops are usually changed or the dosage of the same eye drop changed because over the years the body develops a kind of tolerance to the eye drops and thus the efficacy of these drops reduces.
Laser is used only in some types of glaucoma. Two modalities of laser are commonly used.
1. Peripheral iridotomy,
This also known as yag iridotomy mainly because the yag laser is used. It is used in narrow angle glaucoma to make a hole in the iris. This is done to deepen the drainage angle. To read more about this please read the brochure on ‘Yag – Iridotomy.’
2. Argon laser trabeculoplasty (ALT)
Here the Argon laser is used and thus the name. This is used in chronic open angle glaucoma.
One must keep in mind that in spite of laser, eye drops may be required to control the eye pressure.
Surgery is the last option that is used to control the pressures if medicines or laser fail to do so. Here a small opening is made in the eye so that the aqueous flows out and the pressure is reduced.
How often do I need to come to the clinic if I have glaucoma?
Your eye doctor will tell you as to when he or she would like to see you again in the clinic. A glaucoma patient needs to come to the clinic often for eye pressure checkups. Also you may require to get the field test done repeatedly to see the status of your peripheral vision.
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