**Core Concept**
The question requires the application of the visual acuity chart to determine the percentage of disability. Visual acuity is a measure of the sharpness and clarity of vision, with 6/6 being considered normal vision. The World Health Organization (WHO) defines visual impairment as follows: mild visual impairment (6/18 to 6/60), moderate visual impairment (6/60 to 3/60), severe visual impairment (3/60 to 1/60), and profound visual impairment (worse than 1/60).

**Why the Correct Answer is Right**
The Snellen visual acuity chart is used to measure visual acuity. In this case, the patient has 1/60 vision in one eye and 6/60 vision in the other eye. According to the WHO classification, both eyes are considered to have moderate visual impairment. The percentage of disability is calculated based on the visual acuity of the better eye. The formula used is: (6 - logMAR) x 100, where logMAR is the logarithm of the minimum angle of resolution. Using this formula, we get (6 - log(1/60)) x 100 = 20%.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not take into account the visual acuity of the better eye.
**Option B:** This option is incorrect because it is not a valid calculation for percentage of disability.
**Option C:** This option is incorrect because it does not use the correct formula for calculating percentage of disability.

**Clinical Pearl / High-Yield Fact**
When calculating percentage of disability, it is essential to use the visual acuity of the better eye. This is because the patient's visual impairment is determined by the better eye, and the percentage of disability is calculated based on this value.

**Correct Answer: A. 20%**