Professor Gerd U. Auffarth and collegues have found that ophthalmic viscoelastic devices that combine both dispersive and cohesive properties, so that they can be used in sequence and at the appropriate phases of cataract surgery, can result in decreased complications, low adverse events, improved visibility and good space management.
In order to create a safe anterior chamber environment that protects the eye and maintains the intraocular space during cataract surgery, surgeons have been using ophthalmic viscoelastic devices (OVDs) for more than 20 years. For many of those years, they have had only one option: a cohesive ophthalmic viscoelastic containing sodium hyaluronate (NaHA).
While a cohesive OVD contains a high-viscosity material with intramolecular adhesion and entanglement that is suitable for creating and maintaining space during capsulorhexis and IOL insertion, it does not protect corneal endothelium well, which makes it unsuitable for phacoemulsification.
However, dispersive OVDs contain a low-viscosity solution that adheres easily to intraocular structures and instruments, which protects corneal endothelium during phacoemulsification, although, given that dispersive solutions are difficult to remove, they are not ideal for use at the end of surgery.
My colleague and I have conducted research comparing the safety and efficacy of two OVDs that combine dispersive and cohesive solutions in a single device. We found that OVDs that combine both categories, so that they can be used in sequence and at the appropriate phases of cataract surgery, can result in decreased complications, low adverse events, improved visibility and good space management, which all enhance safety.
My colleagues and I compared the performance and safety of two similar OVDs that combine a dispersive and cohesive viscoelastic in a single device (Twinvisc, Carl Zeiss Meditec AG and Duovisc, Alcon Laboratories).1 These OVDs both contain hyaluronic acid, and Duovisc also includes chondroitin sulfate.
Duovisc has two syringes in one package, one with a dispersive viscoelastic (Viscoat [sodium hyaluronate 3%– chondroitin sulfate 4%]) and the other with a cohesive viscoelastic (Provisc [sodium hyaluronate 1%]) OVD. The other OVD (Twinvisc) also includes both a dispersive and cohesive OVD, but instead of two separate syringes, the solution is in a single syringe that is separated by a bypass stopper system.
A total of 200 cataract patients underwent phacoemulsification and IOL implantation in one eye. They were randomly assigned to receive one of the two OVDs. Preoperative and 3-month postoperative examinations included mean IOP, incidence of IOP peaks (≥30 mm Hg and ≥24 mm Hg), endothelial cell count (ECC), corneal thickness and intraocular inflammation.
During both procedures, surgeons made self-sealing clear corneal incisions for capsulorhexis and phacoemulsification. The OVDs were injected according to the manufacturers’ recommendations.
The dispersive OVD was injected straight after the main corneal incision and just before completing continuous curvilinear capsulorhexis (CCC), which was followed by phacoemulsification of the nucleus and aspiration of the residual cortex. Next, surgeons injected the cohesive solution and implanted a monofocal IOL in the capsular bag.
Residual OVD was then removed by bimanual irrigation/aspiration followed by anterior chamber rinsing. After each procedure, surgeons completed a survey to assess maintenance of the anterior chamber during CCC and IOL implantation, retention during phacoemulsification, ease of use, ergonomics, facilitation of CCC, transparency during surgery and ease of removal.
We found that both OVDs had similar performance and safety profiles.
All surgeons know that up to 7 hours after surgery, IOP can rise due the surgical trauma of the procedure. However, pressure can also rise due to remnants of viscoelastic remaining after the procedure is complete.
We found that incidences of IOP peaks and mean IOP were not statistically significantly different between the groups. At 6 hours, the incidence of IOP spikes of 30 mm Hg or higher was 6.5% and 7.2% in Twinvisc and Duovisc groups, respectively (P = 0.846). The incidence of IOP spikes of 24 mm Hg or higher was 16.8% and 25.2%, respectively (P = 0.128).
In the Twinvisc group, the mean postoperative ECC showed a mean cell density loss of 11.7% when compared with baseline measurements. In the Duovisc group, the mean postoperative ECC at 3 months revealed a 9.6% reduction from baseline measurements.
In both groups, endothelial cell loss was statistically significant when compared with baseline value, which is normal. However, there was no statistically significant difference in the mean endothelial cell reduction between the two groups.
Corneal endothelium protection
There was a good protection of the corneal endothelium. On the first postoperative day, there was a slight increase in pachymetry by 9.8%, which went away after a couple of days, which is insignificant. After 90 days, the increase of pachymetry was below 1%.
Inflammatory reactions were mild and reported in both groups at 6 hours, 24 hours and 7 days postoperatively. However, at 30 and 90 days postoperatively, inflammation reduced to baseline levels.
Although no serious adverse events related to the OVDs were reported, the Duovisc group had 20 (17.6%) cases of ocular hypertension, one case of corneal oedema (0.9%), one case (0.9%) of capsule break, and one of bubbles from the cohesive solution. The Twinvisc group had 14 (12.6%) cases of ocular hypertension, one case (0.9%) of corneal oedema, and one patient had (0.9%) cystoid macular oedema.
Our findings show that, although they employ different techniques, both OVDs are equally efficient and safe to use during cataract surgery. Although Duovisc was reported as being easier to use, Twinvisc was reported for better maintenance of the anterior chamber during IOL plantation.
Most importantly, there were no clinically relevant differences between the devices. The topic of viscoelastics may not be as attractive to discuss as a shiny, new technology; however, it is a topic that should not be neglected because we use viscoelastic during every single cataract procedure to ensure safety.
1. Auffarth GU, et al. Comparison of the performance and safety of 2 ophthalmic viscosurgical devices in cataract surgery. J Cataract Refract Surg. 2017;43:87-94.
Professor Gerd U. Auffarth, MD, FEBO
Prof. Auffarth is chairman of the Department of Ophthalmology, University of Heidelberg, Germany, director of the International Vision Correction Research Centre, and director of the David J. Apple International Laboratory for Ocular Pathology. Prof. Auffarth reports that he receives research grants, lecture fees and travel grants from Carl Zeiss and research grants, lecture fees, travel grants and consulting fees from Alcon. Prof. Auffarth can be contacted via his assistant, at: Raquel.WillrichAmroussi@med.uni-heidelberg.de