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Editors Selection IGR 8-4

Angle closure glaucoma: Cataract extraction for ACG

Comment by Erik Greve on:

13368 To compare argon laser peripheral iridoplasty (ALPI) against systemic medications in treatment of acute primary angle-closure: mid-term results, Lai JS; Tham CC; Chua JK et al., Eye, 2006; 20: 309-314

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13378 Visual acuity after acute primary angle closure and considerations for primary lens extraction, Tan GS; Hoh ST; Husain R et al., British Journal of Ophthalmology, 2006; 90: 14-16

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The AIGS organized its third Consensus meeting on the topic of Angle Closure Glaucoma. Of course cataract extraction for ACG was among the topics for discussion. A host of papers have been published over the past twenty years on this topic. It is clear that the relative size and position of the lens plays an important role in the pathogenesis of ACG. Eyes with a thin artificial lens do not develop ACG. All papers point in the direction of a benefit of cataract extraction for both acute and chronic ACG, at least for the majority of patients.

The AIGS Global Consensus Statements on lens extraction in PACG (May 2006) are:

• There is insufficient evidence for deciding which cases with PACG should undergo lens extraction alone (without trabeculectomy).
• Lens extraction alone may be considered in eyes with a mild degree of residual angle closure (less than 180 degrees) after laser iridotomy, mild optic nerve/visual field damage or those that are not on maximal tolerated medical therapy. There is lack of evidence for recommending lens extraction alone in eyes with more advanced PACG. Published studies to date have been non-randomized with small sample sizes and short follow-up.
• Combined cataract and glaucoma surgery in certain eyes may be useful to control IOP and restore vision. There is limited published evidence about the effectiveness of combined cataract extraction and trabeculectomy in eyes with PACG. There is need for studies comparing this form of surgery with separately staged cataract extraction and trabeculectomy.

In the recent literature, Lai et al. (156) published a prospective study on phacoemulsification through a corneal incision in a consecutive series of patients with primary ACG. The follow-up period was at least one year (13-26 months). Unfortunately, the study is small: 21 patients of which nine with a history of acute ACG. The IOP was decreased from 19.7 mmHg to 15.5 mmHg, the number of medications was decreased from 1.9 to 0.5.

Table 2 states that 5 patients had higher IOP (in three the increase was minimal) after the operation and 16 a decreased (15) or unchanged (one) IOP, although with less medication. The mean result is influenced by one outlyer whose IOP decreased from 40 mmHg preoperatively to 12 mmHg postoperatively.

The authors describe that visual acuity improved in ten eyes, was unchanged in nine eyes and deteriorated in two eyes (one with preoperatively advanced visual field defects and one with diabetic retinopathy). Unchanged visual acuity was thought to be due to advanced visual field defects (five), corneal decompensation (two), and retinal disease (two). The angle opened postoperatively in 75% of the cases. This study is an example of the many that have shown a benefit of lens extraction in PACG. It shares the limitations and particularly the lack of comparison with other modalities.

In a second study, Tan et al. (157) examined visual acuity after acute ACG in 135 consecutive subjects. They concluded that "within days after acute ACG more than half of the affected eyes had a good visual acuity. This means that the other half had a reduced visual acuity which is presumably due to cataract in most cases. I would suggest that in the presence of - even early - cataract there is a good reason for cataract extraction as a primary procedure particularly in APACG where angle closure is recent and the effect on IOP large. That leaves to be discussed those patients where the lens is assumed to be clear. Here the results of a prospective randomized study - after pi - should decide.

The effect of cataract extraction in ACG is thought to depend on the elimination of pupillary block and most importantly on the remaining function of the trabecular meshwork. The function of the trabecular meshwork depends on the presence of permanent synechial blockage of the trabecular meshwork, on the extend of damage to the trabecular meshwork by temporary apposition of the iris, and on the direct effect of high IOP on the outflow system.

The more synechiae and the longer the apposition the less the chance of reduction of IOP presumably will be.

So why does it make sense to consider cataract extraction for ACG:

• The relative thickening lens plays a prominent role in the mechanism;
• Improvement of visual acuity is not a necessary precondition;
• Reduction of IOP is likely to occur in a majority of patients;
• The procedure will prevent further rise of IOP through deepening of the anterior chamber;
• Pseudophakia is safe basis for trabeculectomy.

Cataract extraction in ACG may not always be easy. In experienced hands this should not influence the final result. Furthermore the increased surgical difficulty is off-set by the increased safety of subsequent trabeculectomy if needed.