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

In retinoscopy, observing a "with" reflex indicates that the light is moving with the direction of the retinoscope beam as it reflects off the retina. When starting with a plano (zero diopter) position at a distance of 66 cm, the patient is being tested for their refractive error at that specific distance.

For hyperopia, the eye is unable to focus sharply on near objects without the help of accommodation. Therefore, if a retinoscope is aimed at a hyperopic eye, the light reflex will appear to move "with" the retinoscope beam, as the eye needs to accommodate to bring the image into focus.

In contrast, myopia typically produces a "against" reflex because the focused light from distant objects falls in front of the retina, and the light reflex will move opposite to the movement of the retinoscope. Emmetropia would not show a pronounced reflex, as the light focuses perfectly on the retina without additional correction. Astigmatism can lead to variable reflexes depending on the axis and nature of the refractive error.

Thus, the observation of a "with" reflex in retinoscopy at plano indicates the presence of hyperopia, making this option the correct choice for the