2. Macular pigment

Question 1

What is macular pigment?

Answer 1

Is a yellow oily substance composed of hydroxycarotenoids lutein and zeaxanthin.

Question 1

What are Lutein and Zeaxanthin?

Answer 1

Hydroxycarotenoids. Naturally occurring pigments found in some vegetables, plants and animals. Our body itself can’t synthesise it.

Question 2

Where is macular pigment located?

Answer 2

Located mainly in fibres of Henle. In the central 8 degs.

Question 3

What is the function of macular pigment?

Answer 3

1. To absorb harmful short wavelengths of light
2. Antioxidant
3. Anti Inflammatory

Question 4

Draw spatial profile of MP

Answer 4

Peak at 0 degs and zero at 8 degs.

Question 5

How to measure MPOD?

Answer 5

1. Heterochromatic flicker photometry
2. The MPS (Macular pigment screener)

Question 6

Describe Heterochromatic flicker photometry method

Answer 6

1. Two superimposed lights of different wavelengths (470 and 540nm) flicker at 25 Hz
2. Relative intensity is adjusted to identify minimum flicker point
3. When lights defined as equal luminance this is the point of minimum flicker
4. Equal luminance point will be different for central and peripheral viewing due to MP being in the center.

Question 7

Describe method of the MPS

Answer 7

Macular pigment optical densitometer. Instead of indentifying minimum flicker, observer detects flicker.
2 measurements taken one for central and another for peripheral.

Uses the HFP principle=
Luminance ratio (LR) = luminance of blue/ luminance of green

MPOD = LR center - LR periphery

Question 8

How does crystalline lens affect absorption of wavelength and how does this impact measuring MP?

Answer 8

With age lens becomes more yellow so blue light absorbed more. The optical density increases linearly with age.

However, this doesn’t affect the results of measuring MP because both central and peripheral results is affected. So the blue green ratio shifts but the 2 peak difference remain the same.