Choice of OVDs in Cataract Surgery

Ophthalmic viscosurgical devices (OVDs), first introduced in the 1970s,^1-3 are solutions of varying viscosity with pseudoplastic properties. They are used to maintain space in the eye during IOL implantation, stabilize and deepen the anterior chamber, and protect ocular structures during anterior segment surgery.

Pseudoplasticity is a property that alters with viscosity, and substances with higher molecular weights have a higher pseudoplasticity index. Their viscoelastic property enables these substances to move down a fine cannula but to retain their viscosity once they are in the anterior chamber.⁴

OVDs can be classified as cohesive, dispersive, or viscoadaptive according to their rheologic properties.^5,6 There is a spectrum of commercially available viscosurgical products ranging from more cohesive to more dispersive.

Cohesive OVDs, such as Healon (sodium hyaluronate; Advanced Medical Optics, Inc., Santa Ana, California), have a high molecular weight and high surface tension and tend to be made up of large molecules. Dispersive OVDs, such as Viscoat (sodium chondroitin sulfate, sodium hyaluronate; Alcon Laboratories, Inc., Fort Worth, Texas), have a lower molecular weight and lower surface tension.

Cohesive OVDs are better than dispersive OVDs for maintaining the anterior chamber, helping to perform the capsulorrhexis, and creating and maintaining space. They are easy to remove from the eye because of their high surface tension. However, a large amount can be lost through an open wound during capsulorrhexis creation, and they may not protect the endothelium well because they tend to be removed with bulk fluid flow.

Dispersive OVDs tend to be smooth and better than cohesive OVDs for coating tissues. They are better at protecting the corneal endothelium, but they do not maintain space as well and are less easy to remove.

Some newer products that exhibit properties of both cohesive and dispersive OVDs, such as Healon5 (sodium hyaluronate 2.3%; Advanced Medical Optics, Inc.) are termed viscoadaptive OVDs. Viscoadaptive OVDs typically have high molecular weights and exhibit dispersive or cohesive properties depending on the conditions at the time.⁷

Cohesive, dispersive and viscoadaptive OVDs can be used individually or in combination during cataract surgery.^3,8,9 With the development of different types of OVDs, additional indications have been reported.¹⁰

In recent years, there has been a trend toward using different OVDs for specific tasks in cataract surgery. Dispersive OVDs are widely used to coat the cornea for better view during cataract surgery. In the soft shell technique,^11,12 a dispersive OVD is initially injected to coat the endothelium, and then a cohesive OVD is injected to fill the anterior chamber, improving corneal endothelial protection. This maneuver is especially useful in eyes with low endothelial cell counts. Viscoadaptive OVDs have been suggested as appropriate tools for pediatric cataracts and for mature cataracts.

The study described in this paper was performed to assess what factors influence an ophthalmologist's choice of OVD(s) for use in cataract surgery.

SURVEY DESIGN AND DATA ANALYSIS
A survey was conducted among a randomly selected sample of consultant ophthalmologists who had experience in performing cataract surgery, to elicit their perceptions surrounding the use of OVDs in cataract surgery.

A questionnaire was developed to elicit the features and benefits of using OVDs in cataract surgery as perceived by consultant ophthalmologists. The questionnaire was mailed to 400 consultant ophthalmologists throughout the United Kingdom. An honorarium was offered for completion of the questionnaire. Questionnaires with all answers completed were received from 147 consultant ophthalmologists; all were used in the analysis.

Completed questionnaires were entered into a spreadsheet for analysis. Multivariate regression analysis was performed to assess whether there was any correlation between any variables in the data set and whether any parameter would be predictor for an ophthalmologist choosing to use a particular OVD.

RESULTS
Respondents said they had been performing cataract procedures for a mean 20.7 (95% confidence interval [CI]: 19.6; 21.8) years. At the time of the survey, respondents reported performing a mean 417 (95% CI: 368; 447) procedures per year. Of these, 86% (95% CI: 84%; 89%) were undertaken within the UK's National Health Service.

Regarding instrumentation, 39% of respondents said they used the Millennium phaco machine (Bausch & Lomb, Rochester, New York); 28% the Legacy (Alcon Laboratories, Inc.); 14% the Sovereign (Advanced Medical Optics, Inc.); and 14% the Infiniti (Alcon Laboratories, Inc.). Five percent of respondents reported using other machines.

Almost all respondents (99%) said they use OVDs in all types of cataract surgery. Healon was reported as the preferred OVD by 57% of respondents, and Provisc (sodium hyaluronate; Alcon Laboratories, Inc.) by 6% of respondents. Thirteen percent of respondents said they do not have a preferred brand, and other brands were preferred by 2% or less of the respondents.

FEATURES AND BENEFITS of OVDs
More than half of respondents (53%) said their choice of OVD was influenced by patient type, and almost two-thirds (63%) said they adjusted their choice of OVD according to the type of cataract surgery to be performed. More than two-thirds of respondents (68%) said they did not vary their choice of OVD in routine cataract surgery, but almost all (97%) said they varied their choice in complicated cases.

Sixty-four percent of respondents said they use only one type of OVD during the whole phaco procedure, whereas 36% said they use a combination. The primary reasons for using either only one type of OVD or a combination during different phases of cataract surgery included endothelial protection (32% of respondents), soft-shell technique (29%), corneal protection (10%), cost (9%), and ease of IOL insertion (5%).

The key factors that respondents said influenced their choice of OVD are summarized in Table 1. The properties that respondents said they sought when choosing a particular OVD are summarized in Table 2. The primary reasons given for choosing a higher molecular weight OVD (cohesive or viscoadaptive) were better anterior chamber stability (84% of respondents), better retention in the eye (78%), and better endothelial protection (77%).

Other reasons for choosing a higher molecular weight OVD included pupil widening, complications, shallow anterior chambers, anterior capsule tamponade in white liquefied cataracts, bulgy eye syndrome, tamponade for rupture in cases of posterior capsule rupture, intraocular manipulations using heavy visco, manipulation of tissue, pediatric capsulorrhexis, prolonged phaco time anticipated, very shallow anterior chamber, to perform continuous curvillinear capsulorrhexis, to control expected cases of intraoperative floppy iris syndrome, and vitreous loss.

DISCUSSION
The use of hyaluronic acid during IOL implantation was first suggested in 1977,¹ and the patent for purified hyaluronic acid and for using it in IOL implantation was first presented at a symposium in 1979.¹³ In 1980, the first commercially available OVD was launched under the name Healon, and US Food and Drug Administration (FDA) approval followed in 1983. Healon is still the gold standard to which all other OVDs are compared, and this is reflected in our survey, in which the majority of surgeons (57%) named Healon as their preferred OVD.

OVDs have been in routine use since the late 1980s and have changed the face of ophthalmic intraocular procedures, making them safer and technically easier. These materials are now an integral component of routine intraocular surgery. This is borne out by our survey, which found that 99% of respondents use OVDs routinely.

Our survey found that most respondents (68%) do not vary their OVD in routine cataract surgery, but 53% of respondents adjust the OVD for the type of surgery. Moreover, the great majority (97%) vary their OVD choice in complicated cataract surgery. This indicates that most ophthalmic surgeons adopt a tailored use of different OVDs, which are now seen as a supportive tool to handle specific tasks in cataract surgery.

From a demographic perspective, it is interesting to note that the cohort of ophthalmic surgeons who participated in this survey tended to be those who were senior trainees or just finished their training at the time OVDs were introduced. This was a time when much was made of their properties and the theory behind such properties. OVDs were relatively expensive when originally introduced (because only one product was available), but since competing products have come onto the market the purchase price has fallen, and their use has become routine in cataract surgery. Therefore, it is perhaps not surprising that the cohort of ophthalmic surgeons who participated in the survey were, in the main, those exposed to the initial educational marketing and have thus been using them since their introduction. It would be interesting to match the marketing information provided for each OVD with the reasons given by their users justifying the choice of a particular product.

Cost was mentioned only a small number of times as the reason for using a particular product, but this may change in times of economic difficulty. Some units may prefer to use the cheaper hydroxypropylmethylcellulose (HPMC) for routine cases. HPMC is not a true viscoelastic and exhibits virtually no pseudoplasticity with a very low pseudoplasticity index (28 vs 10,000 for Healon GV).

The volume of OVDs contained in each syringe is now considered to be adequate for surgery, whereas when the products were introduced the volumes were smaller. In the days when OVDs were expensive, the training of junior ophthalmic surgeons was often given as the reason for their use. Trainers used to cite greater patient safety as an important factor in their use of OVDs. Interestingly, this was not mentioned in the survey as the products are now in routine use.

In summary, this survey showed that OVDs are used routinely during cataract surgery and that although a majority of ophthalmic surgeons use just one type of OVD for routine cases, they adjust their choice of product in accordance with the type of surgery to be performed. Nearly all the respondents (97%) adjust their choice of OVD for difficult cases.

Susanne Althauser, FRCS, MD, is a Consultant Ophthalmic Surgeon at the Royal Free Hospital, London.

Larry Benjamin, DO, FRCS, FRCOphth, is a Consul-tant Ophthalmic Surgeon at Stoke Mandeville Hospital, Buckinghamshire, England. Dr. Benjamin is a member of the CRST Europe Editorial Board. He may be reached at e-mail: larry.benjamin@btopenworld.com.

Julian F. Guest, PhD, is Director of Catalyst Health Economics Consultants in Northwood, Middlesex, England, and Visiting Professor of Health Economics at the Postgraduate Medical School, University of Surrey, Guildford, England. Professor Guest may be reached at tel: +44-1923-450045; fax: +44-1923-450046; e-mail: julian.guest@catalyst-health.co.uk.

Marianne T. Helter, MSc, is a Research Assistant at Catalyst Health Economics Consultants in Northwood, Middlesex, England.

Andrew F. Smith, PhD, is a Health Economist with Alcon Laboratories, Inc., Hemel Hempstead, Hertfordshire, England, and at the Nuffield Laboratory of Ophthalmology, University of Oxford, Oxfordshire, England.

The authors state that this study was sponsored financially by Alcon Laboratories, Inc. However, the authors have no conflicts of interest that are directly relevant to the content of this article.

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