In against movement, the far point is between the examiner and the patient. Therefore, to bring the far point to the peephole of the retinoscope, a minus lens is placed in front of the patient’s eye. Similarly, in the case of with movement, a plus lens is placed in front of the patient’s eye. This procedure gives rise to the simple clinical rule: If with movement is observed, add plus power (or subtract minus power); if against movement is observed, add minus power (or subtract plus power) (Fig 4-9).
Because it is easier to work with the brighter, sharper with movement image, one should “overminus” the eye and obtain a with reflex; then reduce the minus power (or add plus power) until neutrality is reached. Be aware that the slow, dull reflexes of high-refractive errors may be confused with the neutrality reflex. Media opacities may also produce dull reflexes.
Once neutrality is found, the lens to correct for the working distance must be removed, whether it is the built-in retinoscopy lens in the phoropter or by subtracting the appropriate correcting lens based on the working distance used.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.