Glaucoma is a condition in which the eye pressure, also known as intra-ocular pressure (IOP), is too high for a given eye and thus causes damage to the optic nerve of that eye. Damage to the optic nerve results in progressive loss of peripheral or side vision. Central or straight ahead vision is preserved until the end of the disease (tunnel vision). Pressure is measured in mm of Hg (mercury). Normal pressure is between 10 – 21 mm Hg with 14 being the average.
Only 10-20% of the patients having an eye pressure between 21-24 mm Hg go on to develop loss of the peripheral vision or loss of side vision over a ten-year period of time. Fifty percent loose peripheral vision if their pressure is consistently between 25-27 mm Hg, and 90% loose vision if the pressure is 30 mm Hg. The natural history of patients that have non-treated glaucoma is slow progression. Glaucoma is usually a slow disease.
Untreated glaucoma takes on an average of 15 years to progress from early damage to blindness with an IOP of 21 to 25 mmHg, 7 years with 25 to 30 mmHg, and 3 years with a pressure more than 30 mmHg. Thus, most eye doctors will treat a pressure over 30 without signs of damage. We tend to treat a little earlier.
Like blood pressure, the eye pressure (intra-ocular pressure) will vary from day to day and time of day, usually higher in the morning and lower in the early evening. Therefore, it is important to measure the pressure at different times of the day. Patients without glaucoma may vary 4 mm Hg while patients with glaucoma tend to vary more. This variability necessitates multiple readings at different times of the day before making any decision. Unless the pressure is very high, one reading is meaningless. In addition, it takes years for the pressure to damage the eyes, thus, time is on our side. One should use the time to make an appropriate decision without panicking.
Causes for Increase in Eye Pressure
The truth is that we are not sure. Either we make too much fluid, have restricted drainage or the (“thermostat”) control system does not maintain a proper pressure. Treatment is directed at either decreasing production of the aqueous (the fluid in the front part of the inside of the eye) or increasing the out flow. This is analogous to your sink, to maintain a constant level of water in the sink one must control the amount of water going into the sink or increase the size of the holes in the drain. Whichever mechanism is causing the increase in pressure, treatment today is directed towards reducing pressure. Newer thoughts suggest that blood flow to the nerve may be as important as pressure. Also, newer drugs may provide neuro-protection (slow down the death process). The only thing that has shown to slow the progression of glaucoma is control of eye pressure.
Types of Glaucoma
Testing for Glaucoma
Those at risk for glaucoma are advised to have a dilated eye exam at least once a year.
Screening for glaucoma is usually performed as part of a standard eye exam by our optometrist. Testing for glaucoma include measurements of the intraocular pressure via tonometry, examination of the optic nerve head to look for any visible damage to it and visual field assessment. How frequently these tests are performed depend on the severity of the progression of glaucoma..
If you have a family history of glaucoma or high eye pressure, contact our office to schedule a vision test today at (512) 260-0405.