Certified Ophthalmic Assistant Practice Exam

In the 20/20 notation used to describe visual acuity, the numerator represents the distance at which a person is tested from the eye chart—specifically, it indicates the distance at which the letters on the chart subtend an angle of one minute of arc to the average observer with normal vision. This measurement is based on the ability of the human eye to resolve fine detail.

In practical terms, when a person is said to have 20/20 vision, it means that they can see at 20 feet what a person with normal vision can also see at that distance. If someone can see a letter at 20 feet that subtends an angle of one minute of arc, their vision is considered normal. Therefore, the numerator of the notation effectively marks the standard distance used in visual acuity testing and assigns a reference value to the clarity of the individual's vision based on this measurement.

Other options, while related to visual acuity testing concepts, do not accurately describe the significance of the numerator in the 20/20 notation. For example, the distance from the patient's eyes to the chart is important for determining testing conditions but does not define this specific notation. Similarly, the size of the letter is not what the numerator represents;