A Randomized Clinical Trial Comparing Phacoemulsification and Goniosynechialysis With Phacoemulsification Alone in the Management of Primary Angle Closure

Study Background

Glaucoma is the worlds' leading cause of irreversible blindness with nearly 7 million bilaterally blind due to the disease, by some estimates, and as such, represents a disease with significant associated morbidity. Furthermore, as glaucoma is primarily a disease of old age, as the number of elderly people in the world continues to rise, the number of people with glaucoma blindness is likely to have increasing economic burden and public health costs.

Primary glaucoma is classified into 2 types, Primary Open Angle Glaucoma (POAG) and Primary Angle Closure Glaucoma (PACG). Classification depends on configuration of the anterior chamber drainage angle, specifically if it is open or if it shows evidence of closure. The proportions of people with POAG and PACG are approximately equal, with the latter disease more common in Asians and women. Although the result of both diseases is progressive cupping of the optic disc with corresponding visual fields loss, the mechanism by which this occurs is thought to be quite different in the two diseases. In POAG the mechanism is still to be established but in PACG it is thought that apposition of the peripheral iris to the drainage angle results in damage to the trabecular meshwork (TM) and the formation of peripheral anterior synaechiae (PAS) which act as a mechanical obstruction of aqueous outflow via the trabecular meshwork. This in turn results in raised intraocular pressure (IOP) and subsequent optic nerve damage. Apposition can occur in anatomically predisposed eyes, although a physiological dynamic element is likely to be involved also. Areas of the TM not obstructed by PAS are likely to retain some function, although it is not clear if this is at the same level as in normal subjects. The functioning of the TM posterior to the areas of PAS has also yet to be established and it is hope that this study will help to elucidate this matter.

Conventional initial management of PACG is to perform laser peripheral iridotomy (LPI) to allow flow of aqueous from the posterior chamber to the anterior chamber through the iatrogenically created iridotomy. This has two benefits - in those subjects where pupillary-block is thought to be the mechanism for angle closure, it can reduce the risks of an acute rise in IOP occurring (acute angle closure). In other subjects with PAC, LPI has been shown to increase the drainage angle and this has led to lowering of the IOP in some subjects. However, in a retrospective review of 65 subjects with PACG who had had LPI, after 5 years follow-up the vast majority required further interventions (medications and/or surgery) to lower the IOP. Furthermore, PAS formation has been show to still occur in the presence of a patent PI. Clearly, the current conventional management strategy for PAC/PACG is inadequate and likely to lead to further ocular morbidity.

The poor results of LPI in the long-term for subjects with PACG in terms of IOP control has led many clinicians to study the effect of cataract surgery on IOP control in these patients. It was thought that removing the lens would increase anterior chamber depth and increase the drainage angle and hence increase outflow. Cataract surgery does indeed seem to open the drainage angle and its effects on IOP control have been promising. However, opening of the drainage angle may be limited in subjects with significant PAS. This could compromise the IOP lowering effect of cataract surgery in this group of patients. In such cases, cataract surgery with mechanical breaking of PAS (i.e. goniosynechialysis) might lower IOP to a greater extent than cataract surgery alone. Phacoemulsification + intraocular lens + Goniosynechialysis (PEI-GSL) has been carried out in several published studies, with all studies reporting a reduction in post-operative IOP compared to pre-operative. The main complications associated with PEI-GSL are excessive post-operative anterior chamber fibrinous reaction and anterior chamber bleeding. Theoretically, excessive pressure to break PAS could also cause iridodialysis or cyclodialysis, with resultant ocular hypotony. In an effort to reduce these complication risks, Varma and Fraser described phacoemulsification + intraocular lens + viscogonioplasty (PEI-VGP) in which a viscoelastic is used to break PAS in a non-iris contact method, rather than using an instrument to push the iris back. The authors proposed that this procedure would reduce the complications of PEI-GSL but still open the angle sufficiently. It is not clear however, if PEI-VGP would provide sufficient force to open areas of PAS and therefore be as efficacious as PEI-GSL in lowering IOP. Furthermore, there is no evidence that either PEI-GSL or PEI-VGP are superior to phacoemulsification + intraocular lens (PEI) alone in reducing IOP. Most surgeons will perform cataract surgery in patients with PAC/PACG and uncontrolled IOP. By adding the relatively simple step of goniosynechialysis during the surgical procedure, it has been proposed that this will result in further IOP lowering and hence less risk of glaucoma development/progression. This has yet to be proven.