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Monday / May 23.

The MPOD

Low macular pigment has been linked to Age-Related Macular Degeneration (AMD), but until now there has never been a definitive way to measure macular pigments levels. However, new technology, developed by the Department of Optometry at the University of Manchester in the U.K., has now made available to the Australian Optometrist the Macular Pigment Optical Densitometer, or MPOD for short.

The MPOD has its basis in heterochromatic flicker photometry, a well known segment of ocular science going back 30 years. However, the approach adopted by the MPOD is far easier for patients to use than earlier versions of the technology. In conventional methods, observers have to set the point where flicker disappears or is minimised. In the MPOD, the measurement consists of a series of button presses by the user in response to the appearance of flicker, which makes it far easier for the subject and optometrist to accurately determine the flicker thresholds.

The MPOD Test

The test consists of two stages. The observer’s sensitivity to flicker is quickly determined in the first part of the test and the luminance contrast of two lights are normalised for that particular observer. In the main part of the test, the frequency of the blue (460nm) and green (570nm) lights is ramped down from a non visible fast flicker rate for a series of luminance ratios of the two lights resulting in a distinct curve from which the minimum flicker point is detected. The observer views the target and simply presses a button when flicker appears. The difference between the minima obtained from central and peripheral viewing determines the macular pigment optical absorption level. The complete test takes only a couple of minutes.

It is also possible for the instrument to estimate a reading from known ageing processes within the eye if a peripheral test is unable to be performed. This predicts the expected peripheral curve minimum value based on a database of many thousands of eyes over six decades.

With some elementary training, it is also easy for non-technical staff to operate the screener, and allows clinicians to advise patients on whether their macular pigment is too low. Not only does the system display the Macular Pigment Optical Density, but it also shows data which provides confidence in its accuracy. The screener can be easily linked to a Windows based PC for complete display of subject responses, which also means archiving and future reference to patient results over time is simple.

Once the results are recorded, practitioners can advise patients on the benefits of modifying diet, lifestyle and taking lutein/zeaxanthin supplements to reduce the risk of future eyesight deterioration.

In addition, if an optometrist wishes, along with the MPOD test, Viteyes Advanced Beta Carotene Free Supplements can now also be offered to patients direct from the practice. The advantage with Viteyes Supplements is that along with the AREDS formulae (minus beta carotene), lutein and zeaxanthin are also included in a single, easy to swallow daily capsule. The capsule also contains selenium, bilberry and grape seed extract, and alpha-lipoic acid, which provide extra nutrients for macular health. The optometrist can now offer this comprehensive formula, without having to suggest different capsules from different bottles, avoiding the possibility of shelf confusion in some patients. Viteyes are not available from pharmacies or supermarkets.

The MPOD weight is just over four kilograms, so it is conveniently portable, making it a viable option for small clinics or home visits.

MPOD in Practice

Dr. Steven Harris, a community optometrist from Kent, in the U.K. has been using the MPOD for some time and describes its incorporation into his practice as “very successful”, despite some initial difficulties training his staff, who were not confident about using the device.1

He says he now incorporates the MPOD test into his routine eye exam, and it takes about 10 to 15 minutes.

Dr. Harris says he initially bought the machine because he sees a lot of elderly patients, but he now finds himself using the machine on much younger patients.

“The idea is to check people who are younger than you expect; younger than I expected … you should be checking people over 40. The idea is to pick it up before there’s any loss of vision.”

He doesn’t use the MPOD on all his patients, but targets those who have a familial history of macular degeneration or other risk factors.

Dr. Harris says it does take some time to explain the test and educate his patients about its benefits. And he’s found that, as he’s become more experienced, the repeatability of the results has improved.

“It’s not difficult, but when you take the time to explain it to people it seems to work out.”

He says he’s advised many of his patients to take supplements or improve their diets as a result of the test.

“(But) I don’t want to sell supplements to people who don’t need them.

“That’s the benefit. I saw a lady here, an 80-year-old. In the past, we might have suggested she take the supplements. She didn’t have any loss of vision but she had the appearance of it. I put her on the MPOD and, lo and behold, her results were really good… and I was able to say to her ‘don’t waste your money any supplements, there’s no point’,” Dr. Harris says.

References

1. Dr. Harris was interviewed on the Optometric Quarterly podcast series: http://www.docet.info/index.aspx/pcms/site.distance_learning.oq.oq73.the_mpod/

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