Surgical treatment of glaucoma

Glaucoma surgery

Both laser and conventional surgeries are performed to treat glaucoma. Surgery is the primary therapy for those with congenital glaucoma. Generally, these operations are a temporary solution, as there is not yet a cure for glaucoma.

1-Canaloplasty

Canaloplasty is a nonpenetrating procedure using microcatheter technology. To perform a canaloplasty, an incision is made into the eye to gain access to the Schlemm’s canal, similarly to a viscocanalostomy. A microcatheter will circumnavigate the canal around the iris, enlarging the main drainage channel and its smaller collector channels through the injection of a sterile, gel-like material called viscoelastic. The catheter is then removed, and a suture is placed within the canal and tightened.

By opening the canal, the pressure inside the eye may be relieved, although the reason is unclear, since the canal (of Schlemm) does not have any significant fluid resistance in glaucoma or healthy eyes. Long-term results are not available.

2-Trabeculectomy

The most common conventional surgery performed for glaucoma is the trabeculectomy. Here, a partial thickness flap is made in the scleral wall of the eye, and a window opening is made under the flap to remove a portion of the trabecular meshwork. The scleral flap is then sutured loosely back in place to allow fluid to flow out of the eye through this opening, resulting in lowered intraocular pressure and the formation of a bleb or fluid bubble on the surface of the eye.

Scarring can occur around or over the flap opening, causing it to become less effective or lose effectiveness altogether. Traditionally, chemotherapeutic adjuvants, such as mitomycin C (MMC) or 5-fluorouracil (5-FU), are applied with soaked sponges on the wound bed to prevent filtering blebs from scarring by inhibiting fibroblast proliferation. Contemporary alternatives to prevent the scarring of the meshwork opening include the sole or combinative implementation of nonchemotherapeutic adjuvants such as the Ologen collagen matrix, which has been clinically shown to increase the success rates of surgical treatment.

Collagen matrix prevents scarring by randomizing and modulating fibroblast proliferation in addition to mechanically preventing wound contraction and adhesion.

3-Glaucoma drainage implants & Glaucoma valve

The first glaucoma drainage implant was developed in 1966. Since then, several types of implants have followed on from the original: the Baerveldt tube shunt, or the valved implants, such as the Ahmed glaucoma valve implant or the ExPress Mini Shunt and the later generation pressure ridge Molteno implants. These are indicated for glaucoma patients not responding to maximal medical therapy, with previous failed guarded filtering surgery (trabeculectomy). The flow tube is inserted into the anterior chamber of the eye, and the plate is implanted underneath the conjunctiva to allow a flow of aqueous fluid out of the eye into a chamber called a bleb.

The first-generation Molteno and other nonvalved implants sometimes require the ligation of the tube until the bleb formed is mildly fibrosed and water-tight. This is done to reduce postoperative hypotony—sudden drops in postoperative intraocular pressure.
Valved implants, such as the Ahmed glaucoma valve, attempt to control postoperative hypotony by using a mechanical valve.
Ab interno implants, such as the Xen Gel Stent, are transscleral implants by an ab interno procedure to channel aqueous humor into the non-dissected Tenon’s space, creating a subconjunctival drainage area similar to a bleb. The implants are transscleral and different from other ab interno implants that do not create a transscleral drainage, such as iStent, CyPass, or Hydrus.

The ongoing scarring over the conjunctival dissipation segment of the shunt may become too thick for the aqueous humor to filter through. This may require preventive measures using antifibrotic medications, such as 5-fluorouracil or mitomycin-C (during the procedure), or other nonantifibrotic medication methods, such as collagen matrix implant, or biodegradable spacer, or later on create a necessity for revision surgery with the sole or combinative use of donor patch grafts or collagen matrix implant.

4-Laser-assisted nonpenetrating deep sclerectomy

The most common surgical approach currently used for the treatment of glaucoma is trabeculectomy, in which the sclera is punctured to alleviate intraocular pressure.

Nonpenetrating deep sclerectomy (NPDS) surgery is a similar, but modified, procedure, in which instead of puncturing the scleral bed and trabecular meshwork under a scleral flap, a second deep scleral flap is created, excised, with further procedures of deroofing the Schlemm’s canal, upon which, percolation of liquid from the inner eye is achieved and thus alleviating intraocular pressure, without penetrating the eye. NPDS is demonstrated to have significantly fewer side effects than trabeculectomy. However, NPDS is performed manually and requires higher level of skills that may be assisted with instruments. In order to prevent wound adhesion after deep scleral excision and to maintain good filtering results, NPDS as with other non-penetrating procedures is sometimes performed with a variety of biocompatible spacers or devices, such as the Aquaflow collagen wick, ologen Collagen Matrix, or Xenoplast glaucoma implant.

Laser-assisted NPDS is performed with the use of a CO2 laser system. The laser-based system is self-terminating once the required scleral thickness and adequate drainage of the intraocular fluid have been achieved. This self-regulation effect is achieved as the CO2 laser essentially stops ablating as soon as it comes in contact with the intraocular percolated liquid, which occurs as soon as the laser reaches the optimal residual intact layer thickness.

5-Clear lens extraction

For people with chronic closed-angle glaucoma, lens extraction can relieve the block created by the pupil and help regulate the intraocular pressure. A study found that CLE is even more effective than laser peripheral iridotomy in patients with angle closure glaucoma. A systematic review comparing lens extraction and laser peripheral iridotomy for treating acute primary angle closure found that lens extraction potentially provides better intraocular pressure control and reduces medication needs over time. However, it remains uncertain if it significantly lowers the risk of recurrent episodes or reduces the need for additional operations.

Answer these questions according to the passage below.

1) According to the passage, what is the primary therapy for congenital glaucoma?
A) Topical beta-blockers
B) Laser therapy only
C) Surgery
D) Observation
E) Selective laser trabeculoplasty

2) In general, glaucoma operations are described in the passage as:
A) Curative for most patients
B) Preventive and permanent
C) Temporary solutions because there is not yet a cure
D) Primarily cosmetic
E) Unnecessary in closed-angle disease

3) Which of the following is NOT stated about canaloplasty?
A) It is a non-penetrating procedure using microcatheter technology.
B) Access to Schlemm’s canal is gained similarly to a viscocanalostomy.
C) Its long-term results are well established and widely available.
D) A suture is placed within the canal and tightened.
E) Viscoelastic is injected to enlarge drainage channels.

4) During canaloplasty, the injection of viscoelastic primarily aims to:
A) Seal the trabecular meshwork
B) Reduce aqueous production
C) Enlarge the main drainage and collector channels
D) Replace the aqueous humor
E) Induce scarring within the canal

5) The passage notes that lowering IOP after opening Schlemm’s canal is unclear because:
A) The iris blocks the canal in all glaucomas
B) Schlemm’s canal does not have significant fluid resistance in glaucoma or healthy eyes
C) The ciliary body immediately closes the canal
D) Viscocanalostomy always fails
E) Collector channels do not exist

6) In trabeculectomy, which step is correctly described?
A) Total scleral excision
B) Partial-thickness scleral flap with a window removing part of the trabecular meshwork, forming a bleb
C) Insertion of a valved tube into the vitreous
D) Laser iridotomy of the pupil
E) Full-thickness corneal trephination

7) To limit scarring after trabeculectomy, surgeons have traditionally applied:
A) Bevacizumab only
B) Hyaluronic acid alone
C) Mitomycin-C or 5-Fluorouracil on soaked sponges
D) Oral steroids
E) Only cautery of conjunctival vessels

8) The Ologen collagen matrix helps prevent scarring mainly by:
A) Killing fibroblasts outright
B) Sealing the scleral flap permanently
C) Randomizing/modulating fibroblast proliferation and mechanically preventing wound contraction/adhesion
D) Blocking aqueous flow
E) Stimulating angiogenesis

9) Glaucoma drainage implants are particularly indicated for patients who:
A) Have untreated mild ocular hypertension
B) Respond well to first-line medications
C) Fail maximal medical therapy and have a failed guarded filtering surgery (trabeculectomy)
D) Have conjunctivitis
E) Have open nasolacrimal ducts

10) Which is listed as a valved implant in the passage?
A) Baerveldt tube shunt
B) First-generation Molteno
C) Ahmed glaucoma valve
D) Xen Gel Stent
E) Hydrus

11) Which ab interno device creates transscleral drainage into non-dissected Tenon’s space, forming a subconjunctival bleb-like area?
A) iStent
B) CyPass
C) Hydrus
D) Xen Gel Stent
E) ExPress

12) With non-valved implants, postoperative hypotony may be reduced by:
A) Immediate bleb needling
B) Temporary ligation of the tube until the bleb mildly fibroses and becomes water-tight
C) Removing the plate
D) Cyclophotocoagulation
E) Pilocarpine infusion

13) Progressive scarring over the conjunctival dissipation segment of a shunt may necessitate:
A) Iridoplasty
B) Antifibrotics (5-FU or MMC) during surgery, or later revision with donor patch grafts and/or a collagen matrix implant
C) Bandage contact lens only
D) Prostaglandin analogs alone
E) Botulinum toxin injection

14) Regarding non-penetrating deep sclerectomy (NPDS), which statement is TRUE?
A) It punctures the scleral bed like trabeculectomy.
B) It has more side effects than trabeculectomy.
C) It deroofs Schlemm’s canal under a deep scleral flap, achieving percolation without penetrating the eye.
D) It never uses adjunctive spacers.
E) It requires less surgical skill than trabeculectomy.

15) In laser-assisted NPDS with a CO₂ laser, “self-termination” occurs because:
A) The laser is time-limited by software
B) CO₂ laser ablation stops on contact with percolated intraocular fluid once optimal residual layer thickness is reached
C) The sclera becomes opaque to CO₂ wavelengths
D) The pupil constricts
E) The conjunctiva absorbs all energy

16) The passage cites the most common surgical approach currently used for glaucoma as:
A) Canaloplasty
B) NPDS
C) Trabeculectomy
D) Iridoplasty
E) Cyclodestruction

17) The first glaucoma drainage implant was developed in:
A) 1950
B) 1966
C) 1978
D) 1989
E) 1996

18) In drainage-implant surgery, the flow tube is inserted into the:
A) Posterior chamber
B) Vitreous cavity
C) Anterior chamber
D) Sub-Tenon’s space
E) Suprachoroidal space

19) Regarding clear lens extraction (CLE), the passage reports that:
A) CLE is inferior to laser peripheral iridotomy (LPI) for angle-closure.
B) CLE eliminates the need for all medications in every patient.
C) CLE can be more effective than LPI in angle-closure glaucoma; in acute primary angle closure, it may better control IOP and reduce meds over time, but effects on recurrence or further surgery remain uncertain.
D) CLE has no role in chronic closed-angle glaucoma.
E) CLE guarantees no recurrent episodes.

20) CLE is specifically mentioned as helpful for:
A) Open-angle glaucoma only
B) Ocular hypertension without angle changes
C) Chronic closed-angle glaucoma
D) Neovascular glaucoma
E) Traumatic hyphema

Answer Key