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A. O'Brien, C. Dainty; Simple Device to Measure the Optical Density of the Macular Pigment in vivo. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1715.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate and present the performance of a new device to measure the macular pigment optical density (MPOD) in vivo. The device is easy to use and comfortable for the patient, while maintaining high consistency and accuracy in rapidly screening subjects who may be at risk of developing AMD.
A small population of subjects were measured using the MacPI device. The device is optically simple, portable and easily controlled. A combination of a mirco-controller, bespoke software and custom built electronics, ensures that the complete behaviour of the system can be managed from a single intuitive interface. An objective method of reflectance and a subjective method of heterochromatic flicker photometry are employed for the measurement of the MPOD. The objective technique is based on the behaviour of a three colour LED system. Two LEDs are utilised to measure directly the MPOD, while a third LED is utilised to estimate the influence of the crystalline lens on the acquired data. The subjective technique utilises two LEDs and novel software and hardware alternations to achieve sufficient accuracy and consistency in the measurement of MPOD. The strategy employed to achieve dynamic and independent control over the LEDs is pulse width modulation, via the micro-controller and Labview. Triggering of the system is also controlled via the micro-controller, again dictated by Labview. Alignment is achieved by use of a fixation target and mounting of the device on a fully adjustable stand. The subject is stabilised by use of a head rest.
The results demonstrate the control of the system from a single user interface. The control refers to the development of an appropriate strategy to coordinate LED, filter wheel and camera activity. The control screens are presented. The results of a small population study and inter-device comparison of the two techniques employed are also presented These results illustrate the systems ability to measure the peak density as well as the distribution of the pigment across the macula, for both eyes for two different techniques.
We have developed a simple, portable, inexpensive device to measure the macular pigment optical density in vivo. Its versatility should allow both for a clinical screening application, as well as establishing the physiological role of the MP in a laboratory based environment. This paper concentrates on the design of this new device and its utilisation to measure the MPOD of a small population of subjects using a novel objective strategy as well as a improved subjective technique.
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