Which of the following symptoms requires prompt attention?

Sudden vision loss is a symptom that requires prompt attention because it can indicate a serious underlying condition, such as a retinal detachment, stroke, or other acute ocular emergencies. These conditions can lead to permanent vision loss if not addressed quickly. The urgency stems from the fact that timely intervention is crucial in preserving vision, making it essential for patients experiencing this symptom to seek immediate medical evaluation.

Eye redness may be caused by various factors, including allergies, irritation, or minor infections, which typically do not require urgent treatment unless accompanied by other severe symptoms. Itching eyes often indicate allergy or irritation and might need management but are not life-threatening. Blurred vision can have numerous causes, and while it may warrant attention, it does not carry the same immediacy as sudden vision loss. Therefore, among the choices provided, sudden vision loss stands out as the most urgent symptom, needing immediate professional evaluation.