Zeiss: AMD Screening Improvement

Carl Zeiss has just released the Visucam, the first commercially available fundus camera in the world, to offer the ability to measure Macular Pigment Density (MPD) for identifying patients at risk of Age-related Macular Degeneration (AMD).

The Visucam 200 is used for the capture of colour, red-free, blue, red, anterior and stereo images and the Visucam 500 has the additional functionality of fluorecein angiography, fundus autofluorescence and ICG.

A low level of macular pigment is an important risk factor for AMD, the largest cause of blindness in the Western world

The Visucam is able to measure MPD for identifying patients at risk of AMD by capturing images with a specific blue filter and using the single wavelength reflectometry method as described by Delori et al in 2001¹ and Schweitzer et al in 2010.²

In practise, it means that a clinician selects MPD mode and takes a 30-degree image in the same way as any other image. They then click on the MPD icon and the analysis appears.

The benefits of using the reflectometry method are that it takes only seconds to complete and it is totally objective. Additionally, because it uses existing fundus camera technology, it adds functionality to an already highly useful tool.

The analysis has a number of elements. Firstly, it displays quantitative information using four parameters: the surface area within which macular pigment is detectable (area), the sum of all optical densities (volume), the maximum optical density (max OD) and the mean optical density (mean OD).

In addition, a colour coded graphic laid over the fundus image and a 3D map gives the clinician additional qualitative information that is not available through the numbers alone.

Finally, to track the level of macular pigment density over time, the MPD module can display an MPD progression chart.

Why Measure MPD?

Macular pigment is made up of two hydroxycarotenoids: lutein and zeaxanthin, the concentrations of which peak at the centre of the fovea. They cannot be produced by the body and therefore their origins are purely dietary.

The function of macular pigment is thought to be both passive and active. Firstly, its 460nm peak absorption spectrum helps to protect the macula from the toxic effects of blue light. Secondly, it is likely that it protects the macula from photochemical damage by acting as a free radical scavenger, thus having an antioxidant effect.³

It has been shown in studies that a low level of macular pigment is a risk factor for AMD, the largest cause of blindness in the Western world.⁴ Additionally, there is evidence to support the hypothesis that macular pigment may actually protect against AMD.³

As mentioned above, diet can influence our level of macular pigment. It has been shown that increasing consumption of foods containing lutein and zeaxanthin can increase the level of macular pigment and that these levels stay elevated for months, even after returning to a normal diet.⁵ Other studies have suggested that higher dietary intake of lutein and zeaxanthin reduces the risk of long-term incidence of AMD.⁶

As a result of the abovementioned research, it has been hypothesised by investigators that increasing macular pigment density might actually retard age-related changes leading to AMD,⁴ however this is not yet proven and currently under investigation.

Identifying Patients at Risk

Thus the intended use of the MPD module on the Visucam series is to help clinicians to identify patients at risk of AMD by identifying those with low macular pigment levels.

This will give clinicians the option to monitor at-risk patients so that any AMD-related changes are detected early. It gives clinicians the opportunity to educate these patients on related lifestyle and dietary matters. And finally, the serial analysis display will help to identify if any change in diet or supplementation actually increases macular pigment density over time.

Tracking Patients with Dry AMD

A related function of the Visucam 500 is fundus autofluorescence (FAF). FAF is an imaging technique that uses a specific exciter and barrier filter to image the natural fluorescence produced by lipofusin in the retinal pigment epithelium (RPE). Lipofuscin is thought to be a by-product of photoreceptor function and accumulates in the RPE with advancing age. There is evidence to show that excessive lipofuscin accumulation has adverse effects to the RPE and it is implicated in a number of retinal diseases, including dry AMD.⁷

In FAF images, an area of increased autofluorescence denotes high density of lipofuscin and areas where autofluorescence is absent denotes areas where lipofusin is absent.

One disease where this may be useful is geographic atrophy (GA) associated with AMD. An FAF image of such an eye shows an absence of autofluorescence in areas of geographic atrophy surrounded by a thin band of increased autofluorescence. Interestingly, it has been shown that there is a strong correlation with these areas of increased autofluorescence and the future progression of atrophy over time⁷.

Considering the fact that there are a number of treatments for dry AMD currently being developed, this application of FAF imaging has the potential to be an important tool for quantifying disease progression.

These two tools can be used either separately or in a complementary way. The MPD module can assist in identifying patients at risk of AMD and fundus autofluorescence can track progression of dry AMD if it develops. Together they increase the usefulness and functionality of the already well-used traditional fundus camera.

Matthew Wensor is the Ophthalmic Systems Product Manager for Carl Zeiss. He has worked with the company since 1997, initially in sales and then as Education and Clinical Support Manager.

References:

1. Delori FC, Goger DG, et al. Macular pigment density measured by autofluorescence spectrometry: comparison with reflectometry and heterochromatic flicker photometry. J Op Soc Am (A) 2001; 18: 1212-1230.

2. Schweitzer D, et al. Simple and objective method for routine detection of the macular pigment xanthophyll. J Biomed Optics 2010, 15(6), 061714.

3. Beatty S, et al. Macular Pigment and Age-Related Macular Degeneration. Br J Ophthalmol. 1999;83:867-877.

4. Beatty S, et al. Macular Pigment and Risk for Age-Related Macular Degeneration in Subjects from a Northern European Population. Invest Ophthalmol Vis Sci. 2001;42:439-446.

5. Hammond BR, et al. Dietary Modification of Human Macular Pigment Density. Invest Ophthalmol Vis Sci. 1997;38:1795-1801.

6. Tan JS, et al. Dietary antioxidants and the long-term incidence of age-related macular degeneration: the Blue Mountains Eye Study. Ophthalmology. 2008;115(2):334-41.

7. Schmitz-Valckenberg S, et al. Fundus Autofluorescence and Progression of Age-related Macular Degeneration. Surv Ophthalmol. 2009;54:96-117.

Macular Degeneration: The Facts

What is Macular Degeneration (MD)? The macula is the central part of the retina, the light sensitive tissue at the back of the eye. MD causes progressive damage to the macula resulting in central vision loss. Central vision loss can affect your ability to read, recognise faces, drive and see colours clearly. Early detection of MD and immediate treatment is vital in saving sight. How many Australians have MD? MD is the leading cause of blindness and severe vision loss in Australia. 50 per cent of all blindness for Australians over the age of 40 is due to MD. MD is responsible for 48 per cent of all severe vision loss in Australia. One in seven Australians over the age of 50 is affected by MD and the incidence increases with age. It is often called Age- related Macular Degeneration (AMD). What’s the difference between Wet and Dry MD? Wet MD is characterised by a sudden loss of vision and is caused by abnormal blood vessels growing into the retina. Dry MD results in a gradual loss of central vision. 67 per cent of cases of severe vision loss from MD are due to the wet form of the disease, with the remaining 33 per cent of severe vision loss from MD attributed to the dry form. What are the symptoms of MD? Difficulty in reading or doing any other activity that requires fine vision. Distortion – straight lines appear wavy or bent. Distinguishing faces becomes a problem. Dark patches or empty spaces in the centre of one’s vision. What are the risk factors for MD? People over the age of 50, smokers and those with a family history of MD are most at risk of developing the disease. What can you do to reduce your risk? Have your eyes tested and make sure the macula is checked. Don’t smoke. Keep a healthy lifestyle. Control your weight and exercise regularly. Eat a healthy, well-balanced diet – eat fish two to three times a week, dark green leafy vegetables and fresh fruit daily and a handful of nuts weekly. Limit your intake of fats. In consultation with your doctor, consider taking an appropriate supplement for macula health which could include a zinc and antioxidant supplement; a lutein supplement; or a high strength lutein, zeaxanthin and concentrated omega-3 supplement. Provide adequate protection for your eyes from sunlight exposure, particularly when young. What treatments are available for MD? There is presently no treatment for Dry MD. Treatment for Wet MD relies upon early detection. The changed treatment landscape in ophthalmology with the development and use of lucentis (ranibizumab) for AMD, has meant that sight can now be saved. However, early detection is critical. What is the Macular Degeneration Foundation? The MD Foundation is a not-for-profit organisation that aims to reduce the incidence and impact of Macular Degeneration in Australia. The MD Foundation’s objective is to provide education, awareness, research, and support services; as well as being the voice of the MD Community. Ita Buttrose AO OBE, is the Foundation’s Patron. The MD Foundation offers healthcare professionals a range of resources on Macular Degeneration and recently introduced a simple, easy ‘referral bookmark’ to assist optometrists to direct patients to the Foundation for information, guidance, understanding and support. A One Decade Gala Fundraising Dinner will be held at the Hilton Hotel Sydney, on 20 May to celebrate the Foundation’s 10 years of service to the Macular Degeneration Community. MD Awareness Week 2011 will run from Sunday 22 May to Saturday 28 May 2011. For information on MD Awareness Week, contact the MD Foundation on (AUS) 1800 111 709, or visit www.mdfoundation.com.au