Glaucoma is one of the leading causes of preventable blindness worldwide. Because the damage caused by glaucoma is not reversible, treatment is naturally targeted to prevent damage to the optic nerve and increased optic nerve cupping, which will ultimately become manifest as scotoma typical of nerve fibre layer tracts, such as nasal stepping and Bjerrum scotoma. As our knowledge of the mechanism and natural history of glaucoma becomes more advanced, testing for glaucoma becomes more sophisticated and target IOP values become lower, the pool of patients diagnosed as early glaucoma or prone to developing glaucoma continues to swell.

Table 1: Side effects of commonly used glaucoma medications.

Although there have been giant steps in the advancement of pharmacologic treatment of glaucoma, we have reduced but still not solved many of the difficulties associated with medical control. These problems include common side effects from medication usage (see Table 1), longterm preservative exposure to the eye, lack of control of the diurnal curve and the costs of the newer medications. Of course, no discussion of the medical control of glaucoma would be complete without the pervasive problem of patient non-compliance. Because of the asymptomatic nature of glaucoma in the early stages, patients notice no benefit from medication usage. As a result, numerous studies have reported that non-compliance rates of 50% are common, and these non-compliance rates increase as patients are asked to use more and more medications for glaucoma and for other medical conditions.

One of the reasons surgical control of glaucoma has been advocated by the American Academy of Ophthalmology, with the publication of their preferred practice pattern treatment guidelines since 2003, is because of the non-compliance issues. The penetrating trabeculectomy — with or without the use of anti-metabolites — is used as the 'gold standard' to measure all glaucoma surgical procedures against. The problems of this intraocular filtering procedure have long been known, including hypotony, scarring and failure of the bleb, bleb leakage and infection. Numerous other alternatives are now available or in the pipeline and attempting to ameliorate these issues, but all continue to have the same problems of any penetrating procedure aimed at controlling the outflow of aqueous over the long-term. Each has its own 'Goldilocks' approach, of not enough filtration or too much in an effort to reach just the right amount of filtration.

Novel treatment approach

We have found a novel approach to the treatment of glaucoma known as the scleral spacing procedure (SSP) using PresView Scleral Implants (PSI, Refocus-Group, Dallas, Texas, USA). These implants are being studied as a treatment for presbyopia in an FDA monitored investigational device exemption (IDE) clinical trial currently underway in the US. During the initial phase of that study, it was found that the implants also appeared to have an IOP lowering effect on the normotensive presbyopic emmetropes in whom they were implanted. Although not clinically significant in this group of patients without glaucoma, a statistically significant reduction in IOP of approximately 20% was found in patients with baseline IOP of ?16 mmHg. Our interpretation of these results — and the similarity in age of onset for presbyopia and POAG — led to an interest in conducting a study regarding the use of SSP for early POAG and OHT patients as an alternative to medical and or penetrating surgical treatment. By removing patient compliance issues, side effects of medication usage, risk of hypotony, and variability of penetrating surgery, the SSP may become a first line treatment in glaucoma care.

Figure 1: The PresView Scleral implant, its locking design and the size in comparison with a 5 Euro cent piece.

The first step in SSP involves delineation of the position of the vertical recti muscles and careful marking of the four oblique quadrants to avoid compression of the anterior ciliary arteries that travel in the cardinal quadrants arising from the recti muscles. Under direct visualization, careful measurements are made to ensure the position of the PSI will be just posterior to the lens equator using algorithms based on high resolution UBM and OCT data. After the position of the implant is determined, an automated scleratome is used to create a lamellar scleral tunnel (LST) that is 4 mm long, 1.5 mm wide and 400 microns deep. The implant (Figure 1) is then threaded through this tunnel and locked into place to avoid slipping out of the tunnel. The shape of the PSI and tight fit in the LST stretches and lifts the sclera anterior to the implant. As there is no penetration into the anterior or posterior chamber, there is no risk of hypotony common to other penetrating surgical solutions to managing elevated IOP and glaucoma.