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Instrument Review: GDxVCC (Glaucoma Diagnostic Device) by Carl Zeiss

Glaucoma is one of the most commonly recognised eye diseases by the general public and will affect at least 2% of a general optometric database.  Approximately 10% of your database will be glaucoma suspects.

About 8 months ago we trialed and bought the Zeiss StratusOCT, to manage our glaucoma suspects, and our macula pathology patients.  Last month we trialed the Zeiss GDxVCC Nerve Fibre Layer Analyser and compared it head to head with our:

Zeiss Stratus OCT (see our previous review).

The GDxVCC measures the phase shift (retardation) of polarized light passing through the eye. Retardation is affected by the arrangement and density of microtubules or other directional elements and tissue thickness.  An excellent explanation of this amazing technology can be found at the Zeiss Website.

A lot of the latest discussions on glaucoma have centred around "structure vs function".  The GDxVCC and the StratusOCT are objective measures of "structure", whereas threshold visual fields is a subjective measure of "function".  There is no doubt in my mind that to manage glaucoma properly we require both modalities. 

We have found that the objective measurement of "structure" has allowed us to differentiate the suspicious looking nerves.  This in turn has made us more efficient in categorising who we need to see at the appropriate time and thus refer for treatment in a more timely manner.  Glaucoma is not a black or white diagnosis, there are significant grey areas.  Introducing optic nerve head imaging has raised our level of care.

This comparison is not a discussion about the clinical validity of these instruments.  There are umpteen references in the literature supporting their relevance.  This discussion will revolve around the decision making process in purchasing this instrument.  Is it right for your practice or not?

Normal RNFL                  Early RNFL changes        Moderate RNFL changes  Advanced RNFL changes

 

Technological advance in our industry is growing exponentially.  Every year we look at new instruments and follow a simple decision making process:

  1. Can we provide better patient care?
  2. Can we fund the leasing cost by charging the patient?
  3. Can we fund the staff time and optometrist interpretation time by charging the patient?
  4. Can the instrument be used outside of the consultation room?
  5. Do we have space for it?
  6. Can our staff be easily trained to use the instrument?

If the answer to all questions is YES, then guess what?  We will normally purchase the technology.

When comparing the GDVCC to the StratusOCT I found the following:

  • GDxVCC was half the price.
  • GDxVCC was more compact and could be fitted onto our preliminary testing rotor table.  This was more efficient in testing the patient, as IOP, field screening, automatic refraction and optic nerve head analysis could all be performed without moving them.
  • The staff preferred to use the StratusOCT.  I suspect this was only because they had significantly more experience with it.
  • Dilatation of pupils is required occasionally with both instruments.
  • Patients were equally impressed with both instruments.

So what is the bottom line?  If both instruments were available in Australia late last year, when we were deciding on purchase, I still would have chosen the StratusOCT.  This is even though the cost was double.  Our practice sees many patients with reduced visual acuity.  It is imperative that we rule out retinal and macula pathology, as well as diagnose and monitor glaucoma.  The multi functionality of the StratusOCT serves us brilliantly.  The price was not an issue as we are a two optometrist practice so our patient volume is more than capable of supporting the lease.

For those that space and or patient volume is an issue, I would recommend the GDxVCC in a flash.  Purchasing this type of technology will not only impress your patients and be profitable for you, but will help you keep excited about our great profession.  Your patients will notice your enthusiasm and look forward to visiting you and your new gadgets.

 

 

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