General examination in open angle glaucoma
 

Cystic bleb indicating a functioning  trabeculectomy Adrenochrome pigments on the tarsal  conjunctiva seen with topical adrenaline use

In the examination, the examiner may ask you to examine a patient with known open angle glaucoma. You need to look for : physical signs indicating the treatment that the patient is receiving physical signs indicating the possible causes such as pigment dispersion syndrome and pseudoexfoliation syndrome physical signs indicating the severity of the lesion The most common sign is trabeculectomy. This is usually performed at the superior limbus. However, if there was previous  operation the second trabeculectomy may be found more temporally. Iridectomy is usually present. Poor drainage is  suggested by an absence of bleb or a dome-shaped vascularized bleb caused by subconjunctival fibrosis. Occasionally, you may encounter patients who had Scheie procedure for aqueous drainage. This full-thickness filtering surgery. The  anterior chamber is opened to the subconjunctival space. Uveal tissue is visible at the sclerotomy site. This procedure  is now out-dated. Other physical signs associated with glaucoma treatment include: constricted pupil with pilocarpine heterochromia iridis with latanoprost especially if the application is unilateral adrenochrome with topical adrenaline application, the conjunctiva is usually hyperaemic from the use of adrenaline. This can be easily missed unless you evert the lower lid which it is most commonly seen. Molteno's tube in the anterior chamber The most common cases of secondary open angle glaucoma with anterior physical signs are pigment dispersion syndrome,  pseudoexfoliation syndrome, iridocorneal endothelial (ICE) syndrome and Fuch's heterochromic cyclitis. The severity of the glaucoma is graded according to the loss of neural tissue best seen at the optic disc.

Questions:

1. What are the advantages and disadvantages between limbal based and fornix based conjunctival flap in trabeculectomy?

Answer
The advantages for limbal based conjunctival flap are reduced post-operative leakage and less trauma to the cornea. The disadvantages are smaller bleb, poorer scleral exposure and higher chance of button holes.
The fornix based flap has the advantages of better exposure of the limbus, more diffuse bleb due to the lack of a posterior scar line to limit the extension of the bleb. In addition, the technique is easier and requires less time. The disadvantages are frequent wound leaks, and risk of corneal trauma.

2. How would you manage a flat anterior chamber post-trabeculectomy?

Answer
The management depends on the underlying cause. The causes may be:
Low intraocular pressure in the presence of wound leakage. The treatment is usually patching. If leakage fails to respond after 24 to 48 hours, res-suturing is needed. Absence of leakage may suggest excessive drainage, again patching may be use. Persistent marked shallowing of the anterior chamber chamber with hypotony is often seen with choroidal effusion. If the large choroidal effusion persists for 10 to 14 days postoperatively, surgical drainage would be needed along with anterior chamber reformation.
High intraocular pressure. It may be due to angle closure glaucoma which is suggested by a non-patent iridectomy. In this case, YAG iridotomy is needed. If the iridectomy is patent, malignant glaucoma is an important diagnosis to consider. This is caused by misdirection of the aqueous into the vitreous. The majority responds to medical treatment with cycloplegic, beta-blockers and systemic acetazolamide. Those who fails to respond medically may be treated with Nd:YAG laser to disrupt the posterior or anterior hyaloid if the eye is phakic or aphakic. Alternatively, par plana vitrectomy is useful. In phakic eye, pars plana vitrectomy and lensectomy may be needed.

3. What factors increase the risk of failure in trabeculectomy?

Answer
Age of the patient: young more than old
Race of the patient: black more than other races
Type of glaucoma: traumatic, neovascular and uveitic are more likely to fail
Previous failed surgery
Use of certain topical medication such as topical adrenaline
 

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