Introduction

Cataract is one of the leading causes of visual impairment worldwide and represents a major public health issue, particularly in aging populations. The condition is characterized by a progressive opacification of the crystalline lens, which reduces the transmission of light to the retina and gradually impairs visual acuity. Cataract formation is associated with several biochemical and structural changes in lens proteins, including oxidative stress, non-enzymatic glycation reactions, and aggregation of crystallin proteins, all of which contribute to the loss of lens transparency. [1,2]

The only currently effective treatment for cataract is surgical removal of the opacified lens followed by the implantation of an artificial intraocular lens. Modern cataract surgery relies heavily on the use of ophthalmic viscosurgical devices (OVDs), which are viscoelastic biomaterials used during intraocular procedures to maintain ocular structures and protect delicate tissues. Among the polymers used in these devices, hyaluronic acid plays a central role because of its unique viscoelastic, lubricating, and biocompatible properties. Understanding the role of OVDs, their composition, and their production is therefore essential for appreciating their contribution to the success and safety of cataract surgery. [2,3]

Cataract Pathophysiology and Surgical Treatment

The crystalline lens is a transparent structure located behind the iris that focuses light onto the retina. Its transparency depends on the highly ordered arrangement of crystallin proteins and the maintenance of a stable intracellular environment. During aging or under pathological conditions, biochemical processes alter this organization. Oxidative stress damages proteins and lipids within the lens fibers, while glycation reactions lead to structural modifications of crystallins. These processes promote protein aggregation and the formation of light-scattering complexes, ultimately resulting in lens opacification. [1,2]

The standard treatment for cataract is surgical extraction of the opaque lens. The most widely used technique today is phacoemulsification, a minimally invasive procedure performed through a small corneal incision. During this surgery, the anterior chamber of the eye is first filled with a viscoelastic solution to stabilize intraocular structures. A circular opening of the anterior capsule of the lens, known as capsulorhexis, is then performed to access the lens nucleus. Ultrasound energy is subsequently applied through a specialized probe to fragment the opacified lens into small pieces, a process known as phacoemulsification. These fragments are aspirated from the eye, and an artificial intraocular lens is implanted into the capsular bag to restore optical function. At the end of the procedure, the viscoelastic material used during surgery is generally removed by irrigation and aspiration or gradually eliminated through the natural circulation of aqueous humor. Following this procedure, on average 95% of patients regain the expected visual acuity. [2,3]

Ophthalmic Viscosurgical Devices

Ophthalmic viscosurgical devices are sterile viscoelastic solutions composed of highly biocompatible polymers designed for intraocular use. Their primary function during surgery is to maintain the anterior chamber, protect sensitive ocular tissues such as the corneal endothelium, and facilitate surgical manipulations. Because of their viscoelastic properties, OVDs behave as temporary mechanical barriers capable of absorbing mechanical stress generated by surgical instruments or ultrasound energy. They also act as lubricating agents, reducing friction between instruments and ocular tissues and improving the precision of surgical movements. [3,4]

The rheological behavior of OVDs is particularly important during cataract surgery. These materials must be viscous enough to maintain intraocular space and stabilize tissues, while remaining sufficiently elastic to absorb mechanical forces. Their viscoelasticity allows them to adapt to different phases of surgery, providing structural support while also protecting cellular structures from damage. [3,4]

Types of Ophthalmic Viscosurgical Devices

OVDs are classified into three main categories based on their rheological properties and molecular composition: [3,4,6]

• Cohesive OVDs
  o High viscosity and strong intermolecular cohesion (typically high molecular weight sodium hyaluronate)
  o Maintain space effectively in the anterior chamber
  o Facilitate intraocular lens implantation
  o Easy to remove due to their cohesive nature
• Dispersive OVDs
  o Lower viscosity with high surface adherence
  o Spread easily across intraocular tissues
  o Provide effective protection of the corneal endothelium
  o More difficult to remove at the end of surgery
• Viscoadaptive OVDs
  o Exhibit non-Newtonian behavior
  o Adapt to surgical conditions depending on shear forces
  o Act as cohesive agents at low shear (space maintenance)
  o Behave as dispersive agents at high shear (tissue protection)

Hyaluronic Acid in Cataract Surgery

Hyaluronic acid is one of the most important polymers used in ophthalmic viscosurgical devices. The remarkable physicochemical properties of hyaluronic acid make it particularly suitable for ophthalmic applications. Its high molecular weight and hydrophilic nature allow it to retain large amounts of water, forming highly viscous solutions even at relatively low concentrations. This property contributes to the viscoelastic behavior required for OVDs. In addition, hyaluronic acid exhibits excellent biocompatibility and very low immunogenicity, minimizing the risk of inflammatory reactions when introduced into the eye. [4,5,7]

Conclusion

OVDs have become essential tools in modern cataract surgery, contributing to the maintenance of the anterior chamber, protection of ocular tissues, and overall surgical efficiency. Hyaluronic acid plays a central role in these devices due to its viscoelastic properties, high water retention capacity, and excellent biocompatibility. The development of OVDs with diverse rheological profiles now allows surgeons to better adapt materials to each step of the procedure, improving both safety and outcomes. [3–7]

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References

[1] LeMedecin.fr. Syndrome de l’Œil Sec : Symptômes, Traitements et Innovations 2025.

[2] Acuité. Sécheresse oculaire : le mal silencieux qui touche un adulte sur deux.

[3] Periman LM, Perez VL, Saban DR, Lin MC, Neri P. The Immunological Basis of Dry Eye Disease and Current Topical Treatment Options. J Ocul Pharmacol Ther. 2020.

[4] Sheppard J, Lee BS, Periman LM. Dry eye disease: identification and therapeutic strategies for primary care clinicians and clinical specialists. Ann Med. 2023.

[5] Utheim TP et al. Hyaluronic acid in the treatment of dry eye disease. Acta Ophthalmol. 2022;100:844–860.

[6] Kim DJ et al. Development of a novel hyaluronic acid membrane for the treatment of ocular surface diseases. Sci Rep. 2021.

[7] Zhang Y et al. Different concentrations of hyaluronic acid eye drops for dry eye syndrome: a systematic review and meta-analysis. J Ophthalmol. 2023.