In evaluating a patient with a red eye, which assessment best helps to rule out the most worrisome diagnoses?

• A. Usual visual acuity
• B. Pupil size and reaction to light
• C. External eyelid edema assessment
• D. Intraocular pressure measurement

Answer: (A)

In red-eye evaluation, quickly checking how well the patient can see is the key step. Visual acuity directly gauges whether vision is preserved, and preserving vision generally points toward more benign, superficial causes like conjunctival irritation. If visual acuity is reduced, it signals potentially sight-threatening conditions such as retinal issues, optic nerve problems, corneal ulcers, endophthalmitis, or acute glaucoma, all of which require urgent assessment or referral. While other assessments—like pupil size and reaction, eyelid edema, or intraocular pressure—provide useful clues about specific problems, none alone matches the breadth of information that a simple visual acuity test offers about the patient’s risk to vision. So, measuring usual visual acuity best helps determine the urgency and need for further evaluation.