Question

An optician while testing the eyes finds that the vision of a patient is 6/12. By this, he means that:
A) The person can read the letters of 6 inches from a distance of 12m.
B) The person can read the letters of 12 inches from 6m.
C) The person can read the letters from 6m which the normal eye can read from 12m.
D) The focal length of the eye lens has become half that of the normal eye.

Answer 1

Hint: Visual activity of a person is measured with respect to the distance between the person and a clear object, according to the person. This distance is compared to the visual activity of a normal eye. Ophthalmologists usually use a Snellen’s chart to record the visual activity of a person.

Complete step by step answer:
It is common to see numbers or fractions in eye reports written by our ophthalmologists. These numbers convey the visual activity of our eyes. For example, we might have seen fractions like 6/9, 12/12, 6/12 etc in report cards after getting our eyes tested. It is important to understand that the number written above is the maximum distance for clear vision using our eyes. The number below mentions the maximum distance, a normal eye can see things clearly. Both the distances are usually measured in meters.
Here, in the question, the optician tells that the patient’s vision is 6/12. This means that the patient can see things clearly up to a distance of 6 meters compared to a normal eye, which can see things clearly up to a distance of 12 meters. The test is usually carried out using Snellen’s chart and the patient is asked to read out letters, numbers or alphabets of varying sizes to check his/her vision. The ophthalmologist can easily sort out the treatment using this technique. In the case mentioned above, the treatment is done by providing the patient a double concave lens because he is suffering from near-sightedness i.e., he can only see near objects clearly and not the far objects.

So, the correct answer is “Option C”.

Additional Information: In humans, the two common vision defects with respect to distance of an object are myopia and hypermetropia.
Myopia is a condition in which a person cannot see far objects clearly whereas he can see near objects clearly. The condition is also called near-sightedness. This condition can be corrected using a double concave lens. Hypermetropia is a condition in which a person cannot see near objects clearly whereas he can see far objects clearly. The condition is also called far-sightedness. This condition can be corrected using a double convex lens.

Note: Students should not get confused with the measurement units provided in the options. For example, options having measurements in inches can be ruled out easily. It is also important to understand that the fraction (of visual activity) has nothing to do with focal lengths.