New terminology: Ophthalmic viscosurgical devices (2000)

We live in a medical world in which we are constantly exposed to longer and longer descriptions of procedures, devices, and drugs. Who among us, when asked by a patient if the cataract procedure is to be done by laser, explains that “no, actually the procedure I do is correctly described as phaco slice and separate, a modification of a lenticular chopping procedure, itself a variation of endolenticular phacoemulsification using an ultrasonic phacoemulsifier with simultaneous irrigation and aspiration based on peristaltic fluidics”? Clearly, the complexity of what we do has surpassed the ability of the English language to supply succinct, yet accurate, descriptive terminology. I would like to address the issue of terminology, specifically a terminology problem with which I have been involved for over a decade: What should we call the devices collectively clustered under the name “viscoelastics”? The problem is that viscoelastic is an adjective, referring to a substance exhibiting both viscous and elastic behavior; viscoelasticity is the corresponding noun. Our reference to this group of devices as viscoelastics is clearly imprecise, if not incorrect, for both viscosity and elasticity exhibit extreme variability within the group and viscous products are not necessarily elastic. It is a problem that has nagged the editors of the journal for over a decade without resolution. During the past 5 years, I have been one of Canada's designated experts to the Ophthalmic Implants Working Group of an International Standards Organization (ISO) technical committee. The ISO is a worldwide federation of national standards bodies established to prepare international standards through the work of expert technical committees comprised of delegates from participating countries. The ISO meetings are open to national delegates only, but other governmental and nongovernmental agencies can participate in the work of preparing the documents for these meetings. Among the objectives of Working Group 7 has been “the development of an International Standard for the safety, performance and approval requirements for viscoelastics under a new designation of ophthalmic viscosurgical devices (OVDs).” The OVD project began as an initiative of the American Academy of Ophthalmology and the American National Standards Institute under the chairmanship of John Alpar. It has now passed to the ISO under the project leadership of my Canadian colleague, John Emes, with the guidance of John Alpar and other distinguished scientists and physicians from more than 20 countries. The ISO working group struggled over a name for these products, finally settling on OVD. All ophthalmologists must now consider the reasons for the new designation. Not all ophthalmic viscoelastics have to be viscous or elastic. But at what point do we call something viscous: 100 times more viscous than water? as viscous as honey? A similar argument can be made for use of the term elastic. Hydroxypropyl methylcellulose-based products have negligible elasticity and, except for the chemically modified ones, are not very viscous when compared with long-chain commercial hyaluronic acid preparations. At least all intraocular viscoelastics, to date, are more viscous than elastic. However, new devices, intended for extraocular use (tear preparations, corneal surgical shields) are, by design, more elastic than viscous. The manufacturers often describe them as “elastoviscous.” Are we now to have “elastoviscouses”? We are headed for a linguistic crisis, and a solution is needed. Clarity and precision are improved by use of the acronym OVD instead of older, sometimes confusing, terms. It excludes the “elastoviscouses” because of their extraocular use, although these devices would fit into OVDs if they were used during intraocular surgery. In addition, the term does not imply that all OVDs are highly viscous or elastic. It merely states their intended surgical role. Often, authors, surgeons, and companies will continue to refer to a device, or a group of proprietary devices, with different names, intending to highlight a specific characteristic of the device, such as viscoadaptives, although they are more appropriately referred to as viscoadaptive OVDs. As the classification of OVDs is as yet not well know by ophthalmologists, it is recommended that when an author refers to a specific class of OVDs, a classification table be included for reference by the reader (see Table 1). Finally, it appears that the time has come for the ophthalmic community to accept ISO's acronym of OVD in place of our previous “erronym.”Table 1: Classification of OVDs.