Limited vitrectomy in phacomorphic glaucoma.

One of the challenging situations for a cataract surgeon is phacoemulsification in the shallow anterior chamber like cases of phacomorphic glaucoma. Some of the main concerns of operating in a narrow space include endothelial decompensation, descemet's detachment, and posterior capsular rents. High vitreous pressure predisposes to posterior capsular rents owing to a reduced concavity of the posterior capsule and increasing the proximity of phaco-tip to the posterior capsule. We describe a technique of limited vitrectomy in such cases. A small gauge 23-G/25-G trocar cannula is passed transconjunctivally, and the liquefied vitreous is allowed to egress. Vitrectomy is done extraocularly till the vitreous pressure lowers down. This technique helps to debulk the vitreous and decompress the globe in a controlled manner. The resultant posterior displacement of iris-lens diaphragm causes a deepening of the anterior chamber to facilitate phacoemulsification.

Phacoemulsification in a crowded anterior chamber is one of the most challenging situations that a cataract surgeon faces. Shallow anterior chamber is commonly encountered in cases of intumescent cataract, phacomorphic glaucoma, hypermetropia, and cataract in an eye with preexisting glaucoma or a combination of these. Some of the main concerns of operating in a narrow space include endothelial compromise, descemet's detachment, capsulorhexis extension, and zonular dialysis. In addition to these, the presence of high vitreous pressure increases the risk of posterior capsular rent, repeated iris prolapse, suprachoroidal hemorrhage, and expulsive choroidal hemorrhage as well.[1]

Multiple techniques have been described to lower the intraocular pressure (IOP) in such eyes to facilitate phacoemulsification. These include controlled anterior chamber paracentesis, vitreous tap, and limited anterior vitrectomy that help in reducing the vitreous pressure and deepen the anterior chamber.[234]

We describe a novel technique of limited anterior vitrectomy in eyes with high vitreous pressure and a shallow anterior chamber.

Technique

Surgery is performed under peribulbar anaesthesia. A small gauge (23-G/25-G), nonvalved trocar cannula is passed transconjunctivally through the pars plana 3.5–4 mm posterior to the limbus in a quadrant opposite to the site of corneal incision [Fig. 1]. This allows an egress of the vitreous in the presence of increased vitreous pressure leading to a controlled and slow decompression of the globe. An automated vitrectomy hand-piece is used without infusion. A high cutting rate (3500–5000 cps) and a low vacuum (150–200 mmHg) are used to remove the oozing vitreous extraocularly [Fig. 2]. This allows the iris-lens diaphragm to move posteriorly creating more space in the anterior chamber and facilitates phacoemulsification. The trocar cannula is plugged in place and lens extraction is done using a standard phacoemulsification technique of nucleotomy [Fig. 3] and a foldable intraocular lens is inserted in the capsular bag. The vitrectomy can be repeated if required during the cataract surgery [Fig. 4]. After the cataract surgery, the trocar cannula is removed, and the wound is allowed to self-seal [Video 1].

Figure 1

Insertion of small (23-G) gauge trocar cannula 3.5 mm posterior to the limbus in the inferotemporal quadrant

Figure 2

Vitrectomy done extraocularly to remove the egressing liquified vitreous

Figure 3

Phacoemulsification using standard procedure

Figure 4

Repeat vitrectomy when intraoperative vitreous upthrust is noted

Discussion

Phacomorphic glaucoma causing a shallow anterior chamber with high IOP is commonly seen in developing countries. Performing a phacoemulsification in these cases poses multiple challenges. Construction of a clear corneal incision may be difficult owing to iridocorneal apposition in the periphery. Iris-instrument touch may lead to intraoperative miosis, and there is increased iris prolapse owing to a more anterior positioning of the iris. Increased anterior capsular convexity leads to a greater risk of capsular extension, and capsulorhexis is difficult to control. There is increased proximity of the phaco-tip and the endothelial cells thereby leading to increased endothelial cell loss in a cornea that already has less endothelial cell reserve. Injection of viscoelastic substance to deepen the anterior chamber may lead to a further elevation in IOP and increased iris prolapse. The presence of positive vitreous pressure leads to a reduced concavity of the posterior capsule increasing the risk of posterior capsular rent owing to the proximity of the posterior capsule with the phaco tip.

Various techniques have been described earlier to deepen the anterior chamber in the presence of phacomorphic glaucoma to facilitate phacoemulsification.

Vitreous tap with needle aspiration has been described, however, it carries a greater risk of vitreous hemorrhage, retinal traction, retinal tears, and consequent retinal detachment.[5] Another technique that has been suggested is vitreous tap without the use of plunger. This allows a passive removal of the vitreous thereby avoiding vitreous traction. However, unless a liquefied vitreous lacuna is reached, the egress of vitreous does not occur. A searching movement with the needle to find the lacuna may prove to be hazardous.[6]

Pars plana partial-core vitrectomy has also been described earlier in the management of shallow anterior chamber in phacomorphic glaucoma. In this technique, a sutureless, small gauge vitrectomy is done to achieve a controlled debulking of the anterior vitreous. The drawback of this technique is that in the presence of dense cataracts, direct visualization is often not possible.[4]

In our technique, the 23-G/25-G trocar cannula is passed transconjunctivally in a quadrant opposite to the site of the clear corneal incision. In the presence of positive vitreous pressure, egress of vitreous is allowed, and removal is done using vitrectomy cutter at the hub of the cannula. This precludes the need of an intraocular blind procedure in cases of dense or mature cataracts. Furthermore, most patients of phacomorphic glaucoma and dense cataracts have a liquefied vitreous, which makes the egress of vitreous easier. The cannula is plugged in place, and phacoemulsification is carried out in the usual manner. The presence of the trocar cannula during the phacoemulsification procedure allows the vitreous to be removed multiple times during the surgery in cases of repeated vitreous upthrusts. The resultant vitreous debulking allows a slow posterior displacement of the lens and deepens the anterior chamber. As opposed to the sudden decompression seen in anterior chamber paracentesis, this controlled decompression of the globe reduces the chances of expulsive choroidal hemorrhage. The convexity of the anterior capsule reduces allowing for a controlled capsulorhexis. At the same time, the posterior capsular concavity increases owing to the loss of positive vitreous pressure, which allows the aspiration of the liquefied cortex easily from a depressurized capsular bag. The decreased proximity of the posterior capsule to the phaco-tip also helps to reduce the chances of posterior capsular rent.

Conclusion

This technique allows a controlled anterior chamber deepening and also provides the ease of repeating the vitrectomy, if required, more than once.

It is also worth mentioning that with the newer advances, clear lens extraction being done in angle closure glaucoma and refractive lens exchange being done in hyperopia, the need for facilitating phacoemulsification in crowded anterior chamber increases.[78]

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Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.