This article is more than 5 years old. Information may no longer be current.
At Issue: Setting the target pressure
At Issue posed the following question to a panel of experts: "How do you determine your postoperative target IOP when planning glaucoma surgery?"
Click Here to Manage Email Alerts
Alain Bèchetoille, MD: Decreasing IOP is the
main, if not the only way to prevent further deterioration of visual function
in glaucoma patients. This goal is achieved with the use of medications, laser
surgery and trabeculectomy or other close filtration procedures, which can be
performed with or without the use of antimetabolites.
Some studies provide evidence that glaucoma surgery is the best way to control IOP and thus preserve visual field in the long term. Despite a concern about complications, surgery is considered when a significant threat to quality of life is observed, as in a relatively young patient or when medications are not providing the adequate target IOP.
Postoperative target pressure is the level of IOP that one wishes to obtain in the long term or, better, for the lifetime of the patient, to prevent further deterioration of visual field. It is dependent on preoperative pressure but also on the stage and severity of glaucoma. Many glaucoma surgery studies give results only on the basis of a target pressure of 21 mm Hg, which is not low enough, in most cases requiring surgery to secure visual field.
Conversely, a decrease of 30% in IOP was shown to be effective in many normal pressure glaucoma patients, and the same decrease of 30% could be an adequate target pressure for any glaucoma patient, including high pressure and refractory glaucoma.
From a practical point of view, adequate target pressure is the lowest IOP one can obtain with an acceptable rate of complications — including possible permanent ocular hypotony. This has to be considered when choosing a surgical procedure. Selecting between conventional trabeculectomy and safer viscocanalostomy or deep sclerectomy is an issue, unless you manage through technical improvements or the use of adequate devices to obtain the equivalent long-term results. The same choice has to be made when considering the use of antimetabolites with any kind of glaucoma surgery and when considering the use of tubes or valves in refractory glaucoma patients.
 |
|
Eve J. Higginbotham, MD: First of all, I prefer the
term “goal” versus “target.” I teach a number of young
residents, and using the former term rather than the latter suggests a range of
pressures rather than one specific number. Sometimes a student may ask why we
are not changing the course of therapy when the patient’s IOP is 16 mm Hg
rather than 14 mm Hg, without considering that there has been already a 40%
reduction in IOP.
Once the decision is made that the current range of IOP is too high for the health of the patient’s optic nerve, then one should aim for at least a 20% reduction in IOP. The patient’s optic nerve examination and the associated functional loss that may be documented by perimetry are the primary “drivers” for setting the postoperative goal. However, if the office pressures are low, such as 12 mm Hg or lower, then I will ask the patient to come in for a diurnal curve. One usually finds that the patient may be peaking to 16 mm Hg or 17 mm Hg; thus a goal of 12 mm Hg would be appropriate. Of course, the concern if one is setting a goal in the single digits is the risk of hypotony maculopathy.
The concept of setting a goal is very useful. However, it is important to continually assess the patient’s structure (through optic nerve examination) and function (through perimetry) to determine the appropriate management strategy over time.
 |
|
Enrique Malbran Jr., MD: Trabeculectomy, both by
itself and in combination with phacoemulsification, not only consists in
reducing the IOP but also in determining the target pressure point and in
maintaining IOP at that point as long as possible. Resistance to outflow is
determined by the tension that exists between the dried flap and the scleral
wall. Target postoperative IOP is obtained by adjusting the scleral flap by
means of three or more interrupted 10-0 nylon stitches spaced enough to allow
continuous but slight outflow. Fluid must be instilled through a paracentesis.
Loosening and tightening are performed until the right IOP is achieved.
In the first few days, digital message performed by the doctor or the patient is of great value. Once a good anterior chamber is achieved, stitches must be removed one by one (especially if antimetabolites have been used) by means of suture lysis with the argon laser. In case there is bleeding, a krypton or diode laser is recommended. We use a Mandelkorn lens (Ocular Instruments, Bellevue, Wash.), trying to move the conjunctiva as little as possible. Our most frequent values with the argon laser are 0.1 sec, 100 mm and 400 to 700 mW. Generally two or three shots are necessary. Another alternative is releasable sutures. The advantage of using this alternative is that no laser is needed postoperatively.
The trabeculectomy itself is made with the Kelly 0.75 mm punch, and we always refill the anterior chamber with viscoelastic material once the trabeculectomy is completed.
In the combined procedure (phacotrabeculectomy) we use a scleral incision 2.5 mm behind the limbus. When cataract surgery is completed the Kelly punch performs the sclerectomy. Two releasable sutures are placed.
 |
|
Kensaku Miyake, MD: Postoperative target pressure
when planning glaucoma surgery is established from two factors: visual
function, particularly visual field, and preoperative IOP. I set an IOP in the
low teens as the target pressure for patients with advanced disturbance of
their visual fields, and the middle teens as the target pressure in other
cases.
Operative procedures also differ depending upon the height of the target pressure. I use trabeculectomy with mitomycin-C treatment in cases when aiming for the low teens as a target pressure and non-penetrating trabeculotomy or viscocanalostomy when aiming for the middle teens as a target pressure.
In most cases I evaluate the IOP between 1 and 2 months postoperatively as an indicator of whether or not the target pressure has been achieved. If the target pressure is not achieved, my routine is to use additional medical treatments.
 |
|
Bo Philipson, MD, PhD, and Örjan Wallin, MD:
At St. Erik Eye Hospital we perform 450 to 500 glaucoma surgery operations
each year. About 250 of them are combined with phacoemulsification and around
150 are “pure” trabeculectomies. Mitomycin is used in about 15% of
the trabeculectomies, only in eyes with prior eye surgery. We do not use
mitomycin routinely even in combined cases.
Our proportion of deep sclerectomies is rising, especially since the lower incidence of postoperative complications makes us more confident to perform earlier surgery. The number of deep sclerectomies with implants was 42 last year. Furthermore, we do around 80 transscleral diode laser cyclocoagulations and 5 to 10 glaucoma shunts.
This rather heterogeneous group of patients and operations makes the issue of a target pressure rather complex. Sometimes we operate on an eye with mostly cataract and only little glaucoma damage to the disc or visual field and moderately high pressure; sometimes we have an eye with only a central island left and a high pressure. Naturally we aim for different target pressures in such different patients. What we do is look at the degree of visual field defect and optic disc cupping and try to determine at what level of IOP progression of the disease occurred. In most cases we aim for a pressure of 10 to 15 mm Hg, avoiding hypotonous complications in each eye.
Glaucoma with high pressure (more than 40 mm Hg) is not so uncommon for us, as we have a high frequency of pseudoexfoliative glaucomas. In these cases we think that a 50% reduction of pressure to 20 mm Hg could be enough, even in severely damaged eyes. This means that we also regard the percentage of IOP-lowering to be important to prevent further progression.
Unfortunately we do not always reach the level of IOP that we aim for even if we do revisions of surgery. If not, we most often start with medications again before considering re-operation.
 |
|
Theo Seiler, MD, PhD: The target pressure after
glaucoma surgery is very much dependent on the type of glaucoma. If the patient
is suffering from normal tension or increased tension glaucoma we intend a
postoperative pressure of 15 mm Hg or less. In cases of a low tension glaucoma
the target pressure is 10 mm Hg.
Also, the intended pressure decrease is dependent on the state of the glaucoma, as defined by the extent of visual field defects and the excavation of the optic disc. In cases of advanced glaucoma a lower IOP is intended to prevent further damage. This decision, however, is sometimes difficult because a pressure decrease that is too large may induce complications such as hypotony syndrome and even progression of the field defect.
Although not the desired outcome, in some cases the final target pressure can be obtained only with additional medication. Especially in advanced glaucoma such medication has to be selected carefully because of the side effects of some drugs, for example on the perfusion of the eye.
 |
|