Final answer:
An asymmetrical nose often occurs when a nose has been altered. For accurate placement of the lenses, the asymmetry of the nose needs to be considered.
Step-by-step explanation:
When a nose has been altered, an asymmetrical nose may occur, where the nose positions itself somewhat to the left or right. This factor must be taken into account when measuring Monocular PDs (Pupillary Distances) using a frame for eyeglasses. For accurate placement of the lenses, the asymmetry of the nose needs to be considered.