That famous vision test with the large E and various letters in descending sizes is called a Snellen chart. It measures visual acuity, which is how clear your vision is at 20 feet, with the ideal measurement of 20/20 allowing someone to see objects clearly at 20 feet away.
While this measurement is consistently used to determine your refractive error (nearsightedness, farsightedness or astigmatism), it’s not the only measurement of good vision. It simply indicates the sharpness of your vision at certain distances, which is important for basic tasks like driving or reading.
In an exam, an optometrist or ophthalmologist will measure more than just the clarity of your sight. They use the Snellen chart, but also other tools to determine if you need your pupils dilated or retinas examined, which can help find underlying causes for poor visual acuity. Eye doctors also examine your color vision, focusing ability, eye coordination, depth perception and peripheral awareness.
You can print a Snellen chart and test your vision acuity at home, but it is no substitute for thorough, regular eye exams by an eye doctor.
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