By Richard P. Wilson
A Brief Explanation of Glaucoma
Glaucoma is a general term used to describe a group of diseases of the eye, all of which have pressure within the eye greater than the eye can tolerate and still remain healthy. Where does this pressure come from? In the front of the eye, there is a watery fluid called aqueous which keeps the eyeball firm and its contents clear. This aqueous fluid is produced by a part of the eye called the ciliary body. In the normal eye, the fluid constantly flows into and out of the eye, and there is a perfect balance between the fluid made by the ciliary body and the fluid drained through the drain of the eye called the trabecular meshwork. In glaucoma, for a variety of reasons many of which are unknown, fluid does not flow out of the eye properly, often because the drain of the eye, the trabecular meshwork, becomes clogged. The eye continues to produce aqueous fluid normally but the fluid is not allowed to exit the eye at a normal rate, resulting in abnormally high intraocular pressure. When the pressure becomes too high (and this level varies from person to person), it causes damage to the delicate optic nerve in the back of the eye. The optic nerve transmits what the eye sees to the brain. Nerve fibers do not regenerate, therefore, damage to optic nerve is a serious matter. Unfortunately, the pressure may be very high without causing any pain or discomfort that would warn the patient. When glaucoma is diagnosed, the doctor determines what pressure level is safe for each individual and he or she varies the treatment accordingly. Treatment for glaucoma generally starts out with special drops which help to lower the pressure. If this is not successful, then alternate modes of treatment must be considered.
One way to combat the dangerously high pressure in an eye with one of the more difficult to control glaucomas is to cut down on the amount of fluid produced. This is how cyclocryotherapy works. Remember, the ciliary body produces the aqueous fluid in the eye. Applying a freezing probe to parts of the ciliary body literally freezes this part of the eye. The freezing stops the fluid production from that part of the ciliary body. Hopefully, with less fluid being made, medications can keep the amount of fluid produced equal to the amount of fluid drained – thus, the pressure remains controlled.
Cyclocryotherapy is considered surgery, even though no cut or incision is made in the eye. Therefore, it is associated with certain risks. The main risk is that it will not completely control the pressure. The success rate is 65%-70% with one treatment, 90% success after the second treatment, and 95% with the third treatment. However, 8% at 1 year and 12% by 4 years face cyclocryotherapy’s main complication, that not enough fluid will be produced after surgery, and the eye will become too soft. Eyes that end up with this complication are not painful, but the vision will not be better than the big “E” on the chart and may be much worse. While the explanation of this procedure may be alarming, glaucoma patients often find themselves in a situation where they cannot avoid risk. In many cases, there is less risk in having the procedure than in allowing the intraocular pressure to remain high. Glaucoma surgeons take all possible precautions and try to stay on the side of too little freezing rather than too much.
What to Expect?
This procedure is almost always performed as an outpatient in the office. Occasionally in some special situations, the patient must be admitted to the hospital before the procedure. The surgery is done under local anesthesia – so the patient is awake but the eye to be operated is asleep. The anesthesia lasts for about twelve hours, so there is no pain during and after the treatment. After the anesthesia wears off, there may be some discomfort which can be controlled with pain-relieving medication.
Another option to control pain is an injection which will numb the eye for about three months; this injection eliminates almost all discomfort. The drawbacks of this option are that the lid can be droopy during this period of numbness and the nerve that works the muscles to the eye can be affected. In about 20% of the cases, the eye does not move as well as it did before. Since the cornea is numbed also, it may dry out and form an ulcer. However, this happens very rarely, and only if the eye is not wet by blinking regularly. Any side-effects due to numbness from this injection disappear in two to three months.
After the treatment, patients continue to take most of the same medications as before surgery. The only exceptions are Pilocarpine (the green-top drop) and Xalatan (the clear top at bedtime) which should be discontinued after the treatment. A red-top drop to allow the eye to rest and a white-top drop for inflammation are added to the glaucoma medications. After the cyclocryotherapy, explicit instructions concerning post-operative care are given.
It is normal for patients to feel anxious and concerned about this procedure. Good communication with the treating ophthalmologist about the benefits and risks of cyclocryotherapy as well as alternative treatments are a must.