A patient presents with a red eye. Which assessment below helps rule out the most serious diagnosis?

Determining visual acuity is crucial in the initial assessment of a patient presenting with a red eye. This assessment helps to identify any significant visual loss, which is a key indicator of severe conditions affecting the eye. For instance, if visual acuity is markedly reduced, it may suggest a serious underlying issue such as retinal detachment, severe corneal injury, or acute glaucoma, which requires immediate attention.

By establishing whether the patient has normal or reduced vision, healthcare providers can prioritize further diagnostic procedures and treatments. If visual acuity is intact, there is a higher likelihood that the condition may be less urgent or severe, such as conjunctivitis or minor irritation.

While the other assessment methods are valuable, each serves a different purpose. The corneal reflex test assesses the integrity of the sensory and motor pathways of the eye, which can indicate certain neurological issues but may not directly rule out serious vision-threatening conditions. A slit lamp examination provides a detailed view of the anterior segment of the eye, helping to identify conditions like anterior uveitis or cataracts but may not give immediate information about visual acuity. Intraocular pressure measurement is important in assessing for glaucoma but is not as immediate in ruling out serious, acute conditions that could lead to permanent vision loss.