Conjugacy of pupils. A, In indirect ophthalmoscopy, the observer’s pupil (O) and patient’s pupil (P) are conjugate to avoid “wasting” light. B, If the condensing lens is too close to the patient’s eye, the peripheral retina will not be illuminated. C, If the condensing lens is too far from the patient’s eye, light from the patient’s peripheral retina will not reach the observer’s eye.