Which refractive error is most commonly observed with a "with" reflex when starting with plano in retinoscopy?

The correct answer is hyperopia. In retinoscopy, a "with" reflex indicates that the light is moving in the same direction as the movement of the retinoscope. This is commonly observed with hyperopia, where the eye focuses light behind the retina due to an underpowered optical system. When starting with plano (no refractive error), any movement of the light toward the patient results in a "with" reflex, suggesting that extra plus power is needed to focus light on the retina.

In contrast, myopia would show a "against" reflex because light rays need to be brought forward to focus on the retina, leading to the opposite movement when the retinoscope is moved. Astigmatism can present variations in reflex that don't distinctly align with a "with" or "against" reflex and can complicate interpretations. Emmetropia, indicating no refractive error, would demonstrate neutrality with no clear reflex at all, as light focuses perfectly on the retina. Thus, hyperopia is the only condition that aligns specifically with a "with" reflex when starting with plano in retinoscopy.