Value is the dimension of lightness/darkness. In terms of a spectral definition of color, value describes the overall intensity or strength of the light. If hue can be thought of as a dimension going around a wheel, then value is a linear axis running through the middle of the wheel, as seen below:
Drusen are tiny yellow or white deposits in a layer of the retina called Bruchs membrane. They are the most common early sign of dry age-related macular degeneration. Drusen are made up of lipids, a type of fatty protein. They may be the result of a failure of the eye to dispose of waste products that are produced when the photoreceptors of the eye drop off older parts of the cell. There are several types of drusen with different levels of risk.
The amount of central vision loss is directly related to the location and amount of retinal thinning caused by the drusen. The early stage of dry age-related macular degeneration is associated with minimal visual impairment and is characterized by large drusen and pigmentary abnormalities in the macula (5). Drusen are accumulations of acellular, amorphous debris subjacent to the basement membrane of the retinal pigment epithelium (6).