What does a visual acuity of 20/40 indicate about a patient's vision?

A visual acuity of 20/40 indicates that the patient can see at 20 feet what a person with normal vision can see at 40 feet. This measurement means that the patient's vision is not as sharp as what is considered standard or "normal" vision, which is 20/20. In practical terms, if a person with normal vision can recognize an object at 40 feet, the patient with 20/40 vision would need to be much closer—standing at 20 feet—to see that same object clearly. This standard helps in assessing the level of clarity and sharpness of vision and can indicate the need for corrective lenses or further evaluation.