When we go to optical shop or eye clinic for eye test, the optometrist or the ophthalmologist will first test your ability to see using a Snellen chart or a logMAR chart. These charts are specially design in order for optometrist or ophthalmologist to measure the abilities to distinguish small object.
Some are easy to see cause the distance of testing room is short while other might be harder because the distance is farther.
Do the distance for vision testing significant during visual testing?
Let look at how our eye use the energy while we look at an object.
The optic of the eye itself is design to see infinite far distance. When we see infinite far object, our accommodation energy or our focusing requirement is zero. Unfortunately infinite object is hard to be measured. Therefore an alternative method would be a testing distance closer. So how close we can mimic an infinite object distance.
Technically, when we bring an object to 1 meter, we required to exert 1 dioptre of accommodation energy. if 2 meter, we need 0.5 dioptre of accommodation. So the energy required is actually recripocal of distance we see. For instance at 4 m, the accommodation energy required would be 0.25 Dioptre.
It is recommend that the testing distance is at 6 meter, which accommodation asserted would be 0.167 DS which is consider minimum and realistic for an examination room design.
If your eye have been test using a room distance of shorter than 4 meter, it would be difference from your actual refractive power. Therefore you might see that, some testing room requir a mirror to double the distance of viewing.
Our recommendation is always look for 6 meter refraction or examination room or a mirror refraction if room is smaller.
