What condition is commonly referred to as "lazy eye"?

The condition commonly referred to as "lazy eye" is amblyopia. This is a developmental disorder in which the vision in one of the eyes does not develop properly, leading to reduced vision that is not correctable by glasses or contact lenses. Amblyopia often occurs when the brain favors one eye over the other, which can stem from issues like strabismus, where the eyes are misaligned, or significant differences in refractive errors between the two eyes.

In the context of the other options, while strabismus is a condition where the eyes do not align properly and can lead to amblyopia if not treated, it is not synonymous with "lazy eye." Anisocoria refers to unequal pupil sizes and has no direct connection to eye vision in terms of amblyopia. Arcus senilis is characterized by a grey or white arc around the cornea and is a normal aging change in the eye, rather than a disorder affecting visual acuity like amblyopia does. Thus, amblyopia is the correct choice as it directly describes the condition commonly known as "lazy eye."