Which of the following is NOT one of the main types of amblyopia?

• A. Form deprivation
• B. Functional
• C. Refractive
• D. Strabismic

Answer: (B)

Amblyopia types are defined by how the input to the developing visual system is degraded. The three classic categories reflect distinct mechanisms: deprivation occurs when something blocks or blurs the image during early development (for example, a dense cataract or ptosis), strabismic amblyopia arises from misalignment of the eyes that leads the brain to suppress input from one eye, and refractive (anisometropic) amblyopia results when the eyes have markedly different refractive errors, causing the brain to favor the clearer eye and neglect the blur in the other.

Functional amblyopia is not considered one of these main categories. It’s a term sometimes used historically to describe reduced vision without an obvious anatomical or alignment problem, but it does not denote a distinct pathophysiology like the other three. So the term that describes functional amblyopia isn’t part of the standard three main types.