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Understanding the Eye Chart

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Eye charts of different variations have become a standard in vision screenings and eye exams. One of the most familiar charts associated with vision is the Snellen eye chart, designed by Dutch ophthalmologist Hermann Snellen in 1862 to measure visual acuity- how well you can see at various distances.

Although there are variations of the Snellen chart used today, a traditional Snellen chart has eleven lines of block letters. The first line has one very large letter, which is one of several letters, for example E, H, or N. The following rows have increasing numbers of letters that become smaller in size as you read from the top to the bottom of the chart. The letters used on the chart are C, D, E, F, L, N, O, P, T, and Z.

When taking a vision exam, one eye is covered and you are asked to read the letters of each row aloud beginning at the top of the chart. The smallest row that you can read correctly indicates the visual acuity in the eye being tested.

The chart is positioned at a distance of 20 feet in the United States or 6 meters in the rest of the world. The term 20/20 vision is used to indicate the clarity and sharpness of your vision measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet objects that can normally be seen at that distance. If you have 20/40 vision, it means that you need to be as close as 20 feet to see what a person with normal vision can see at 40 feet. The largest letter on an eye chart often represents an acuity of 20/200 which is associated with the term "legally blind."

You will be asked to read the letters one eye at a time. Some people can see well at a distance, but are unable to bring nearer objects into focus, while others can see items that are close, but cannot see them far away. By having you read the chart, your eye doctor is able to ascertain whether you have difficulty with distance vision and can determine which corrective lenses can be used to improve it. Near vision problems or other vision and eye health issues may not be detected with the Snellen eye chart alone, so a comprehensive eye exam is always recommended.

The next time you hop into the chair at your optometrists' office, you'll be able to understand why you have to read the letters on the chart in front of you and what the results mean for your vision.

Important notice

The Erie Street Eye Clinic team are excited to announce the upcoming office renovation. There will be a complete update in atmosphere and functionality within our clinic to provide you with best vision care possible.

As of November 2nd, 2021,

253 Erie Street will be closed during the construction phase. We will be operating temporarily from another office that is 1.5 km away,

Stratford Family Eye Care 189 Huron St. Stratford, ON N5A 5S9.

We expect to re-open at the beginning of January 2022.

If you have an appointment already scheduled at Erie Street Eye Clinic between November 2nd and December 31st, 2021, your date and time of appointment will be maintained. The same great team of professionals will be there to help you. However, physical location of your appointment has been moved to Stratford Family Eyecare (189 Huron Street).

We can still be reached at our usual phone number (519-271-1240) or email (info@eriestreeteyeclinic.com).

We apologize if this is of any inconvenience to you. We will do our best to ensure the transition is as seamlessly as possible.

Please let us know if you have any questions or concerns about any of the above information.

We appreciate your understanding and cooperation during this time, and we can’t wait to welcome you into our new atmosphere in 2022!

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Our office is currently undergoing renovations! Click here to keep-up-to-date with our progress.