Hydrogel bandages for cataract wound stability

Hydrogel bandages, which have been shown to reduce fluid ingress and egress ex vivo and to stop microleaks in vivo, should be further studied as a way to enhance cataract wound stability and reduce the risk of endophthalmitis, John Hovanesian MD, UCLA Jules Stein Eye Institute, told the XXIX Congress of the ESCRS.

“For many years the association has been made between wound leakage and endophthalmitis, with an increase in incidence with clear corneal incisions,†Dr Hovanesian noted.

He cited a 2005 study of 27 cases of endophthalmitis that found leaky wounds to be the leading risk factor, increasing the chances of infection 44-fold (Wallin T et al. J Cataract Refract Surg 2005; 31:735-741).

Studies also suggest that intraocular pressure fluctuations in the early postoperative period may challenge the integrity of clear corneal incisions, leading to wound leaks (McDonnell PJ et al. Ophthalmology 2003; 110:2342-8), Dr Hovanesian said. Eye rubbing, sneezing and even eye blinking have been shown to cause significant pressure spikes.

Dr Hovanesian conducted a study with Dr Samuel Masket that set out to assess clear corneal incisions for leakage due to pressure spikes. Working with Ocular Therapeutix, Inc., they used a recently developed calibrated force gauge that can apply measurable amounts of force to the eye. The foot of the applicator was placed near the clear corneal incision on the scleral side of the wound, and up to 28 grams of force was applied.

The researchers examined the response to external pressure of 30 eyes with temporal clear corneal incisions sealed with stromal hydration. Mean incision width was 2.5mm; 14 were single plane and 16 biplane, constructed using a grooved technique. All main and paracentesis incisions were confirmed to be closed before pressure was applied using the Seidel test to detect leakage.

After 28 grams of pressure was applied for two to three seconds about a half millimeter from the main incisions on the scleral side, 22 out of 30, or 73.3 per cent, leaked. Nearly 90 per cent of single plane and approximately 60 per cent of biplane incisions leaked. Also, 11 of 20, or 55 per cent of paracentesis ports leaked. No adverse events were reported.

“One ounce of pressure is adequate to simulate eye rubbing,†Dr Hovanesian noted.

In a test of 21 eyes with clear corneal incisions with a mean width of 2.54mm closed with sutures, the overall leak rate was much lower at 23.8 per cent. Here again, single plane incisions were more likely to fail, with four, or 36 per cent, of 11 single plane incisions leaking compared with one, or 10 per cent, of 10 biplane incisions. No adverse events were reported.

He noted an earlier study that found light and firm digital pressure caused average IOP to fluctuate between 27 and 58 mmHg respectively (McMonnies CW et al. Eye & Contact Lens 33(3):124-129, 2007). A test of the Ocular Therapeutix calibrated force gauge involving 30 eyes by Daniel Wee MD and Michael B Raizman MD of Boston, US, fell in the middle of that range. In this trial, applying 28 grams of pressure raised mean IOP by nearly 26 mmHg, from 17.5 mmHg to 43.5 mmHg, an increase of nearly 150 per cent.

Bandage a solution?

The results suggest that clear corneal incisions may still place patients at risk because they often leak due to changes in IOP.

“The study demonstrated to us that wounds closed by either stromal hydration or sutures are prone to leakage, and the forces leading to leakage are similar to those exerted by a patient in the postoperative period,†Dr Hovanesian said.

“Biplanes were less likely to leak than single planes, and sutures represented an improvement as expected, but were still faced with a challenge. Nearly 24 per cent of sutured incisions could leak when force is applied.â€

This raises the question of how surgeons can do a better job of ensuring that cataract wounds stay closed. Dr Hovanesian believes that hydrogel bandages may be the answer.

In his own ex vivo study, Dr Hovanesian has shown that cataract wounds closed with polymerizing hydrogel bandages can prevent both ingress and egress of fluids (Hovanesian JA. J Cataract Refract Surg 2009; 35(5):912-916). At least one recent study also has shown that that hydrogel bandages can stop microleaks of cataract incision in vivo, he noted (Calladine D et al. J Cataract Refract Surg 2010; 36:1839-1848).

“We know that forces on the wound after surgery can cause the wound to become incompetent,†Dr Hovanesian said. “Hydrogel bandages may enhance wound stability. We look forward to further studies to show what the role of these bandages might be.â€