About four years ago I invested a new visual field technology called Frequency Doubling. To find out more about this novel technology, an internet search will reveal umpteen peer review articles, which will describe the visual pathways that it measures and that it is a legitimate field measuring device.
I had many reliable years from my Humphrey Visual Field analyzer (with Fastpac), so why in my right mind would I spend another $12,000 for another field analyzer? There were a number of very important reasons:
At the time I had delegated preliminary testing such as, non-contact tonometry, automatic refractor and automatic vertometry to my reception and dispensing staff. To include visual field testing was impractical due to having to move the patient and setting them up on the field tester, which was in another room.
- A visual field screening using the FD technology was as quick as 40 seconds per eye. When including set up time and patient explanation a reliable field could be obtained in less than 5 minutes. A normal field screening could take as long as 15 - 20 minutes.
- The unit was so small it could be included on a four instrument rotor table, which meant the no moving of the patient.
- An added bonus was that early glaucomatous defects could be found up to five years earlier than with conventional white-on-white field testing (Ref: 1, Ref: 2).
- After 20 years of acquiring many Humphreys products, I was certain that I was buying a reliable instrument, even though at the time the literature was a little thin.
Once we had the instrument in the practice for a month or two we discovered that it was perfect for detecting early glaucoma but not great for moderate and severe glaucoma when defects were more accurately monitored using the older white-on-white technology. It also was poor at plotting out narrow arcuate defects that were related to neural retinal rim notches. Nevertheless we were delighted with its inclusion in our preliminary testing procedures and we could detect focal rim notches by optic nerve examination.
Over the next four years, many instances come to mind where this screening protocol picked up cases that would have been totally missed. Lesions of the visual cortex and of the chiasm are examples that not only amazed myself and the patient, but also the surgical neurologists, as they were totally asymptomatic.
We are now in the year 2004 and we finally have a visual field item number. Legislation for therapeutics has been passed in a number of states and independent Optometrical management of glaucoma will be a reality in the short-term. At very least co-management with an ophthalmologist is a reality right now. We have been co-managing glaucoma for well over ten years using our very reliable white-on-white Humphreys Field Analyser and late last year I was seriously considering upgrading to the latest generation Humphreys Field Analyser II - i, with SITA software. Whilst carefully researching this option I discovered that Humphreys was releasing a new Frequency Doubling Unit called the Humphrey Matrix. The advantages over the bigger unit seemed to be immense:
- Quick screening results under 1 minute.
- Ease of use - could be delegated to staff with 15 minutes of training.
- No eye patch necessary.
- No trial lenses required between +3.00D and -3.00D and habitual spectacles could be worn outside this range.
- Networking soon to be available.
- 20GB hard Drive can store up to 1 million tests.
- Video eye monitoring.
- Clinical validation and normative database
- Small and compact.
- Testing in ambient light and therefore a separate room is not required.
- The printout looks similar to the HFA printout, so referral to an ophthalmologist is simple.
- And here is the kicker, the HFA was about $30,000 and the Matrix was about $17,000.
Decision was made. We trialed the unit for a couple of weeks and bought the first one sold in NSW. To date this is probably the most significant purchase our practice has made. We are now looking at an Optical Coherence Tomographer but I have to save my pennies.
We are still using our older FDT for screening but have retired our older HFA, which did not have a hard drive, so results had to be printed, scanned and filed. The Humphrey Matrix will increase our efficiency immensely, as glaucoma management represents a significant part of our practice.
Landers JA, Goldberg I, Graham SL. Detection of early visual field loss in glaucoma using frequency-doubling perimetry and short-wavelength automated perimetry. Arch Ophthalmol. 2003 Dec;121(12):1705-10
Sampaolesi R, Brusini P, Sampaolesi JR. Correlation between confocal tomography of the optic nerve (HRT) and the perimetric frequency doubling technology. Klin Monatsbl Augenheilkd. 2003 Nov;220(11):754-66