What is the relationship between effective power and vertex distance?

The correct assertion regarding the relationship between effective power and vertex distance is that decreased vertex distance increases effective power. This means that as the distance between the lens and the eye decreases, the effective power of the lens increases.

To understand why this occurs, it's important to consider how lenses work optically. The effective power of a lens is the power that is "felt" by the eye and can be influenced by the distance at which the lens is positioned from the eye. When the vertex distance is shorter, the lens will provide a higher effective power because the light rays converge more quickly as they approach the eye; thus, the visual system receives a stronger stimulus.

When the vertex distance is shorter, the way in which light refracts as it passes through the lens is altered, effectively enhancing its power for the wearer. Conversely, a longer vertex distance would result in a decrease of the effective power because the lens would be positioned farther away from the eye, leading to a reduced optical effect.

This relationship is particularly important in the dispensing of corrective lenses, as understanding how vertex distance impacts effective power can assist in ensuring proper vision correction for individuals with varying prescriptions. Adjusting the fit of frames or the style of lenses may affect the vertex distance and thus require consideration of