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15
Modern Glaucoma Surgery
vitreous biopsy is performed after treatment with antibiotics, the culture will likely be negative
because the antibiotics in the biopsy sample will kill the germs before they can grow on the
culture plate. A vitrectomy may be needed to clear the bulk of the infection from the eye.
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Tenon cyst.
There is a fibrocellular layer between the conjunctiva and the sclera called Tenon’s
layer. It is typically treated like a second layer of conjunctiva during glaucoma surgery.
Approximately three to six weeks postoperatively, the cells of Tenon’s layer can form what is
called a Tenon cyst, in which the inside walls of the bleb become lined with a thick capsule that
aqueous cannot penetrate. As a result, aqueous cannot escape the bleb, so it stops exiting the
eye into the bleb, and the operation essentially fails. This can be reversed by making the cyst go
away. Many times, Tenon cysts resolve on their own in six to eight weeks. During that time, the
use of medications that suppress aqueous production can be used to manage IOP until the bleb
resumes functioning. Alternatively, a needling procedure as previously described can be
employed. This is technically challenging as the goal is to cut through the Tenon cyst but not the
overlying conjunctiva (which would cause bleb leaks) but can be performed at the slit-lamp in
most patients. Again, subconjunctival 5-FU is useful to prevent recurrence.
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Hypotony maculopathy.
If the IOP is chronically low after surgery (<5 mmHg), the eye can start to
collapse in on itself like a balloon with not enough air in it. This causes the retina to wrinkle,
particularly the macula. Signs of hypotony maculopathy are a hyperopic shift as the eye becomes
smaller, decreased vision, and metamorphopsia (distorted vision). This condition typically arises
from overfiltration and may require surgical revision to tighten the sutures holding down the
scleral flap to increase resistance to aqueous outflow.
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Long-term complications.
The operation is successful only as long as the bleb remains, and blebs
can fail at any time postoperatively, from the first day to years later. Because blebs are both
perilimbal and raised, they can cause dellen (smaller divots in the cornea) at the base of the bleb
due to incomplete spreading of tears with each blink (the bleb gets in the way). Lubrication alone
can address most of these. Blebs can also cause irritation because they are somewhat raised
and the eyelid rubs against them. Over time, this can erode through the bleb, causing a bleb leak
(which typically presents with low IOP and an incessantly watering eye). These leaks let aqueous
out but can also let bacteria in, so patients are at risk for blebitis/endophthalmitis for as long as
the operation continues to be successful. All glaucoma surgery patients should be made to
understand that any red eye is an emergency until proven otherwise, as time is of the essence in
preventing blebitis from progressing to potentially blinding endophthalmitis.
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Complications unique to Ex-PRESS.
In addition to all of the previously described issues, eyes
with an Ex-PRESS device can have device-related complications. The device can come
unanchored from its trans-scleral location and fall into the eye or retract out of the eye into the
subconjunctival space, requiring an operation to retrieve it and another to address the glaucoma
using a different procedure. The flange can also erode through the scleral flap and conjunctiva,
causing a bleb leak.
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Complications unique to tube-shunts.
In addition to the possibility of previously described issues
arising, the occurrence of diplopia can occur in surgeries involving tube-shunts. This is because
the reservoir for tube-shunts is large and occupies space within the orbit, usually near the point
where the extraocular muscles insert onto the sclera. The tube itself can erode through the
conjunctiva (and the donor sclera/pericardium if used) to create a bleb leak. The tube can
become obstructed with debris (such as lens fragments after cataract surgery or inflammatory
debris in uveitic glaucoma), or it can retract from the eye. The tube tip can rub against the iris,
causing iritis, or against the endothelial surface of the cornea, causing corneal decompensation.
Returning the Patient to the Referring Doctor
In a glaucoma referral practice, patients are typically returned to the care of their referring doctor once the
postoperative period is complete. This should only occur once the patient is completely stable, IOP is at
target, and any complications have been addressed and have resolved. The surgeon should
communicate to the referring doctor in writing, reporting the type and date of surgery, any complications,