Which visual symptom might suggest a need for immediate referral to a specialist?

Sudden visual loss is a visual symptom that often indicates a serious underlying issue that requires immediate medical attention. This condition can result from various critical causes, such as retinal detachment, vitreous hemorrhage, or other acute ocular emergencies. These conditions can lead to permanent vision loss if not addressed promptly.

In contrast, the other symptoms—such as blurred vision after reading, persistent eye redness, and decreased night vision—while potentially concerning, do not typically represent an immediate threat to vision in the same way. Blurred vision after reading may signal issues like presbyopia or uncorrected refractive errors, which are generally manageable but do not necessitate urgent care. Persistent eye redness could indicate conditions such as allergies or mild infections, which usually can be treated on an outpatient basis. Decreased night vision might suggest conditions like cataracts or retinitis pigmentosa, which also require attention but not necessarily within a time-sensitive context.

Hence, the presence of sudden visual loss is the most critical symptom that signifies an urgent need for specialist intervention.