Final answer:
Gentle pressure is applied to the inner corner of the eyelid to prevent systemic absorption of the medication, increasing local efficacy of the eyedrops and reducing potential systemic side effects option (C).
Step-by-step explanation:
The rationale for the nurse applying gentle pressure to the inner corner of the eyelid after instilling eyedrops is to prevent systemic effects option (C). This action is referred to as ocular compression or punctal occlusion and it helps to block the drainage of the eye drops through the nasolacrimal duct, which can lead to absorption into the nasal mucosa and then into the systemic circulation. By applying this pressure, the medication is kept within the eye, thereby increasing its local efficacy and reducing the likelihood of systemic side effects.