In retinoscopy, when starting with plano at 66 cm, a "with" reflex is most commonly observed in which refractive error?

In retinoscopy, when starting with plano at 66 cm, the observation of a "with" reflex is most commonly associated with hyperopia. This is because in hyperopia, the light rays entering the eye are focused behind the retina. When performing retinoscopy, if the examiner moves the light in the same direction as the reflex, it appears to move along with the light, indicating that the eye is not able to bring the light rays to a point of focus on the retina. This results in the observation of a "with" reflex.

In contrast, myopia would typically show a "against" reflex because the focal point is in front of the retina, which means the light appears to move in the opposite direction to that of the retinoscope's movement. Astigmatism can result in varying reflexes depending on the axis and the type of astigmatism involved. Presbyopia primarily affects near vision and generally results in the need for plus lenses for reading, which reflects a different refractive condition and may not be relevant to the context of retinoscopy at distance. Therefore, hyperopia is the situation where a "with" reflex is most commonly observed when starting with plano.