Earlier Intraocular Pressure Control After Ahmed Glaucoma Valve Implantation for Glaucoma

Tube shunt procedures are a popular surgery for the control of glaucoma. Tube shunt devices
are designed to drain eye fluid (aqueous humor) through a tube inserted into the front
chamber of the eye (anterior chamber) to a plate secured to the mid-posterior section of the
outer eyeball wall. The body then lays down collagen tissue and forms a capsule around the
plate. The fluid filters through the capsule of collagen tissue and is reabsorbed into the
ocular and systemic circulation. The collagen tissue continues to remodel itself over a long
period of time (up to years). However, a well characterized, yet poorly understood,
phenomenon occurs in many patients in the 4-8 weeks after the device's implantation, called
the hypertensive phase. The pressure of the eye can increase from a desirable level of about
10 immediately after the tube shunt implantation to much higher levels, in the range of 20
to 30's, and then it may gradually return to less than 20. Such a high pressure phase can
cause irreversible damage an eye with glaucoma. The usual management of a high pressure
phase is to start glaucoma medications as soon as it is detected. A previous study we
conducted showed that this high pressure phase resolves in about half of patients with
medical therapy, but the other half may continue to have higher than expected pressures. The
exact cause of this high pressure phase is unknown. However, it is postulated that the
mechanism may involve a compaction collagen tissue layers under the eye's own fluid pressure
while the collagen tissue is being laid down, which in turn creates a firm, dense capsule
that makes escape of fluid difficult. Therefore, it is argued that if the formation of eye
fluid is reduced by medication during this initial period when the collagen tissue is laid
down, the compaction of collagen, and subsequently the high pressure phase may be avoided.

The purpose of this study is to compare the occurrence rate of the high pressure phase and
the final pressure outcomes between patients treated with glaucoma medication prior to the
expected onset of the high pressure phase to those patients who have glaucoma medication
started at the onset of the high pressure phase. We hypothesize that if glaucoma medications
are started prior to the expected onset of high pressure phase, the high pressure phase will
not occur as frequently and the ultimate pressure level will be lower than if the glaucoma
medications are started at the onset of this phase.

We believe that this study will have a very significant impact on the management of glaucoma
with tube shut procedures. If it is true that the rate and pressure level of the
hypertensive phase can be reduced by simply starting glaucoma medications to reduce the
formation of eye fluid before the expected the high pressure phase begins, which is
generally 4 weeks after implantation of the tube shunt device, glaucoma patients can be
saved from exposure to the very high level of eye pressure, and the eventual pressure
control may be better.

Inclusion Criteria:

1. Patients requiring Ahmed glaucoma valve implantation to control intraocular pressure
between the ages of 18 and 85 years.

Exclusion Criteria:

1. Unwilling or unable to give consent or unwilling to accept randomization.

2. Patient out of area and potentially unavailable for follow-up visits.

3. Known allergic reaction to timolol, brimonidine, dorzolamide, brinzolamide, or sulfa
drugs.

4. Known medical contraindications to the use of beta-blockers, including congestive
heart failure, heart block, asthma, and chronic obstructive pulmonary disease.

5. Concurrent intraocular procedure with Ahmed glaucoma valve implantation

6. Previous Ahmed glaucoma valve implantation