The Snellen Chart (Part 3 of 3 )

Snellen, inventor of said chart, defined “standard vision” as the ability to recognize one of his optotypes when it subtended 5 minutes of arc. Thus the optotype can only be recognized if the person viewing it can discriminate a spatial pattern separated by a visual angle of 1 minute of arc.

In the most familiar acuity test, a Snellen chart is placed at a standard distance, twenty feet in countries where that is the customary unit of measure. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 20/20, is the smallest line that a person with normal acuity can read at a distance of twenty feet.
Three lines above, the letters have twice the dimensions of those on the 20/20 line. The chart is at a distance of twenty feet, but a person with normal acuity could be expected to read these letters at a distance of forty feet. This line is designated by the ratio 20/40. If this is the smallest line a person can read, the person's acuity is "20/40," meaning, in a very rough kind of way, that this person needs to approach to a distance of twenty feet to read letters that a person with normal acuity could read at forty feet. In an even rougher way, this person could be said to have "half" the normal acuity.
In countries using the metric system, the standard chart distance is six meters, normal acuity is designated 6/6, and other acuities are expressed as ratios with a numerator of 6.

Acuity charts are used during many kinds of vision examinations, such as "refracting" the eye to determine the best eyeglass prescription. During such examinations, acuity ratios are never mentioned.
The biggest letter on an eye chart often represents an acuity of 20/200, the value that is considered "legally blind." Many people with refractive errors have the misconception that they have "bad vision" because they "can't even read the E at the top of the chart without my glasses." But in most situations where acuity ratios are mentioned, they refer to best corrected acuity. Many people with moderate myopia "cannot read the E" without glasses, but have no problem reading the 20/20 line or 20/15 line with glasses. A legally blind person is one who cannot read the E even with the best possible glasses.

An Easter of Equality

An Easter of Equality

The Resource Centre for the blind is making preparations to carry out this theme as they plan their Kite making and kite fly Easter Event.

Said event is scheduled for the 17th of March 2010 where the blind and visually impaired students of Grenada will assemble together with the necessary material at the Mt. Erie playing field, St. David between the hours of 9am-3pm.

Under the supervision of their teachers they will put together their very own kites

After which students will provided with lunch and a short presentation. Reminding them, of the reason behind Grenada’s Easter celebrations.

To end the day the students as well as their teachers will proceed to the adjoining pasture where teachers and students, blind and sighted will fly their self made kites together displaying by example that disability truly is NOT inability.