Views: 338 Author: Site Editor Publish Time: 2026-06-15 Origin: Site
The human eye is one of the most delicate and complex organs in the body, requiring extraordinary precision during surgical intervention. Within the confined space of the anterior chamber—just millimeters deep—surgeons must navigate around irreplaceable tissues: the corneal endothelium with its precious population of approximately 2,500 cells per square millimeter, the iris with its sensitive sphincter muscles, and the crystalline lens capsule that holds the intraocular lens in place.
Since the introduction of sodium hyaluronate in 1979, ophthalmic viscoelastic devices (OVDs) have transformed ocular surgery from a high-risk endeavor into a predictable, controlled procedure. These remarkable substances—often called "liquid cushion" or "biological lubricant"—serve as indispensable protective barriers during virtually every intraocular operation.
This article explores the multifaceted mechanisms through which viscoelastic materials safeguard ocular tissues during surgery, examining both their physical protective properties and emerging evidence for their biochemical protective effects.
Viscoelastic materials possess unique properties that combine characteristics of both solids and fluids. In ophthalmic surgery, these properties are not incidental—they are precisely engineered to provide optimal tissue protection.
Viscosity determines an OVD's resistance to flow and is directly related to molecular weight and concentration. High-viscosity OVDs create effective space and resist displacement, making them ideal for maintaining surgical fields.
Pseudoplasticity describes how viscosity changes under shear stress. At rest (zero shear rate), OVDs maintain high viscosity and coat tissues effectively. Under surgical manipulation (high shear rate), they become more fluid, allowing easy injection through small cannulas while retaining their protective properties when placed.
Elasticity enables OVDs to return to their original shape after deformation. This property allows them to cushion instruments, absorb mechanical energy, and maintain the corneal dome shape throughout the procedure.
Coatability—determined by surface tension and contact angle—governs how well an OVD spreads across tissue surfaces. Low surface tension enables complete, uniform coverage that creates an effective protective film over vulnerable structures.
The protection mechanism originates at the molecular level. Sodium hyaluronate, the primary component of most modern OVDs, consists of long-chain polysaccharides that form three-dimensional networks when concentrated. These networks create a physical barrier that:
· Prevents direct instrument-to-tissue contact
· Dissipates mechanical energy across a larger surface area
· Maintains hydration of delicate cell layers
· Creates separation between adjacent structures
The corneal endothelium is perhaps the most vulnerable and irreplaceable tissue encountered during anterior segment surgery. Unlike the skin or liver, the cornea cannot regenerate functional endothelial cells—those lost through surgical trauma are permanently gone.
Mechanical trauma from surgical instruments accounts for direct cell loss. Even the most skilled surgeon cannot entirely prevent some instrument contact with the endothelium during complex maneuvers.
Ultrasound energy during phacoemulsification generates heat through cavitation—the rapid formation and collapse of microbubbles. This thermal energy can denature proteins and damage cell membranes.
Free radical formation represents a particularly insidious threat. Phacoemulsification causes water molecules to disintegrate, releasing reactive oxygen species that attack corneal endothelial cells through oxidative stress. Research published in the BMC Ophthalmology journal demonstrated that dispersive OVDs significantly reduce free radical formation during phacoemulsification compared to no protection.
Vitreous loss and capsular rupture can lead to direct contact between the corneal endothelium and vitreous humor or lens fragments, causing immediate and severe cell loss.
When properly injected into the anterior chamber, OVDs form a continuous layer over the corneal endothelium. The protection mechanism works through several simultaneous actions:
Physical Separation: The OVD layer physically separates the endothelium from surgical instruments, nuclear fragments, and irrigation currents. Even if instruments touch down, they contact the OVD rather than cells.
Energy Dissipation: The elastic properties of OVDs absorb and distribute mechanical energy. Instead of focused pressure points, instruments encounter distributed resistance across the entire OVD layer.
Surface Coating: OVD molecules adhere to the negatively charged cell membranes of the corneal endothelium, creating a stable coating that persists even under irrigation turbulence.
The choice between dispersive and cohesive OVDs significantly impacts endothelial protection:
Dispersive OVDs contain shorter molecular chains with lower viscosity but superior coating ability. Their molecules behave independently, forming a solution with low pseudoplasticity and high surface adhesion. Like honey coating a surface, they remain in place longer under irrigation stress, providing extended protection during prolonged procedures. Examples include Viscoat (Alcon) and Healon D (Johnson & Johnson).
Cohesive OVDs feature long-chain molecules with high viscosity that tend to stay together as a mass. They excel at maintaining space and creating surgical pressure but can be displaced more easily under turbulent conditions. Healon and ProVisc represent classic cohesive formulations.
Combination Systems: Many surgeons employ dual approaches, using dispersive OVDs to coat and protect the endothelium while using cohesive OVDs to create and maintain surgical space. The "soft-shell technique," described by Dr. Steve Arshinoff, involves first injecting a dispersive OVD directly over the endothelium, then placing a cohesive OVD beneath to deepen the anterior chamber while pushing the dispersive layer even closer to the corneal surface.
The iris with its pupillary margin and sphincter muscle is particularly susceptible to trauma during surgical maneuvers. Viscoelastic materials protect the iris through:
· Mechanical cushioning during instrument passage through the pupil
· Mydriasis maintenance by physically dilating and holding the pupil open
· Tissue separation preventing iris incarceration in wound incisions or suture sites
· Hemostasis through gentle pressure and coating of vascular structures
The crystalline lens capsule must remain intact to support the intraocular lens throughout the patient's life. OVDs contribute to capsular protection by:
· Creating space during capsulorhexis, allowing controlled circular tearing
· Cushioning the capsule during nuclear rotation and phacoemulsification
· Separating the capsule from the vitreous face during cortex removal
· Protecting the posterior capsule from instrument trauma during lens implantation
In combined anterior-posterior segment procedures, OVDs extend their protective effects posteriorly. Viscoelastic materials help:
· Maintain the architecture of the anterior vitreous face
· Prevent vitreous herniation into the anterior chamber
· Create a barrier between surgical instruments and the retinal surface
· Facilitate controlled maneuvers in the posterior segment
In small pupil surgery, shallow anterior chambers, and cases with compromised zonular support, OVDs serve as essential space-creating devices. The "viscoelastic dissection" technique uses controlled injection pressure to expand spaces and separate tissues that have become adherent or contracted.
For surgeons facing combined cataract-vitrectomy procedures, the "viscoelastic temporally" approach maintains the anterior chamber during pars plana access, protecting the crystalline lens capsule and corneal endothelium from instrument trauma at the pars plana site.
A recent innovation, the "double-deck viscoelastic technique" (DDVT), demonstrates the continued evolution of OVD protection strategies. In this technique, surgeons layer a dispersive OVD directly over the corneal endothelium, then add a cohesive OVD on top. The combined barrier provides:
· Immediate proximity of dispersive protection to vulnerable cells
· Added volume and cushioning from the cohesive layer
· Enhanced stability under surgical manipulation
· Optimized protection during graft insertion in corneal transplant surgery
Research published in the BMC Ophthalmology journal documented successful use of DDVT in silicone oil-dependent eyes, where the viscoelastic layers effectively prevented oil-corneal contact that would otherwise cause keratopathy.
Beyond physical protection, certain OVD formulations provide chemical protection against oxidative damage. ClearVisc (Bausch + Lomb) incorporates sorbitol, which chemically bonds to free radicals and provides active scavenging activity. Laboratory studies demonstrate superior free radical protection compared to OVDs without antioxidant additives.
Clinical evidence supports these findings. Studies show that patients receiving OVDs with free radical scavenging capability demonstrate clearer corneas on postoperative day one compared to standard formulations, with 91% achieving corneal clarity immediately after surgery.
The protective efficacy of OVDs depends not only on their formulation but also on manufacturing quality standards that ensure consistency and safety.
Endotoxin Control: Residual endotoxins from manufacturing can cause sterile inflammation, toxic anterior segment syndrome (TASS), and postoperative complications. Regulatory standards mandate endotoxin levels below specific thresholds for ophthalmic use.
Sterility Assurance: Complete sterility is non-negotiable for intraocular products. Advanced aseptic manufacturing processes ensure the absence of bacterial, fungal, and viral contamination.
Molecular Weight Consistency: Consistent molecular weight distribution ensures predictable viscosity and pseudoplastic behavior across production batches.
Osmolality Control: The osmolality of OVD formulations must match or approximate physiological values to prevent corneal edema or cellular damage.
OVDs are classified as medical devices in most jurisdictions and must meet stringent regulatory requirements:
· FDA: Class III device requiring premarket approval (PMA)
· EU MDR: Class III device with rigorous clinical evaluation requirements
· China NMPA: Registration requirements for domestic and imported OVDs
Manufacturers must provide extensive safety and efficacy data, including:
· Biocompatibility testing per ISO 10993 standards
· Endotoxin testing per United States Pharmacopeia (USP) or equivalent
· Clinical data demonstrating device performance in intended use conditions
No single OVD formulation provides optimal protection for every surgical scenario. Surgeons must match protection strategies to specific clinical challenges:
Surgical Challenge | Recommended OVD Approach |
Dense cataracts with high phaco energy | Dispersive OVD or combination system |
Compromised endothelium (Fuchs dystrophy) | Dispersive OVD with extended protection |
Weak zonules | Cohesive OVD for space maintenance |
Small pupil | Dispersive for coating, cohesive for dilation |
Combined anterior-posterior surgery | Dual-layer soft-shell technique |
Silicon oil-filled eyes | Double-deck technique with high-viscosity cohesive |
As a biotechnology company with 28+ years of expertise in hyaluronic acid research and production, Shandong Runxin Biotechnology has established itself as a trusted supplier of pharmaceutical-grade sodium hyaluronate for ophthalmic viscoelastic applications.
Our vertically integrated manufacturing platform ensures complete control over the production chain—from raw material sourcing through fermentation, purification, and quality testing. With over 300 proprietary technologies and patents, we deliver:
· Consistent Molecular Weight Distribution: Precise rheological properties for predictable surgical performance
· Ultra-Low Endotoxin Levels: Ensuring biocompatibility and minimizing postoperative inflammation
· Multiple Viscosity Grades: Supporting both cohesive and dispersive formulation requirements
· Regulatory Compliance: ISO 13485, CE marking, and DMF documentation for global market access
Our sodium hyaluronate serves as the foundational ingredient in viscoelastic formulations trusted by ophthalmic surgeons worldwide. We supply to leading OVD manufacturers while maintaining the quality standards that protect patients in every surgical procedure.
Viscoelastic materials represent one of the most significant advances in ophthalmic surgery, transforming procedures that once carried substantial risk into operations with predictable outcomes and minimal complications. Through their unique combination of viscosity, pseudoplasticity, elasticity, and coatability, these remarkable substances create protective barriers that preserve irreplaceable ocular tissues.
The protection they provide extends beyond simple mechanical cushioning to encompass free radical scavenging, tissue hydration, and the creation of surgical spaces that enable precision maneuvers. As formulation science advances, viscoelastic devices continue to evolve—offering enhanced protective properties through combination systems, antioxidant additives, and optimized rheological profiles.
For manufacturers of ophthalmic viscoelastic devices, access to consistent, high-quality sodium hyaluronate remains essential. Shandong Runxin Biotechnology stands ready to partner with formulation developers and device manufacturers, providing pharmaceutical-grade hyaluronic acid that meets the exacting standards required for patient safety and surgical success.
