**Core Concept**
The disability certificate for poor vision is based on the visual acuity, which is a measure of the sharpness of vision. Visual impairment is categorized based on the visual acuity, with specific thresholds indicating the level of impairment.

**Why the Correct Answer is Right**
A visual acuity of 4/60 indicates significant visual impairment, and according to guidelines, this corresponds to a specific percentage of visual impairment. The exact percentage can vary, but a commonly used threshold is around 40% impairment for a visual acuity of 4/60 or worse in the better eye.

**Why Each Wrong Option is Incorrect**
**Option A:** This option would correspond to a different level of visual acuity, not 4/60.
**Option B:** Similarly, this would represent a different threshold of visual impairment.
**Option D:** This option does not align with the standard classification of visual impairment based on visual acuity.

**Clinical Pearl / High-Yield Fact**
It's crucial to remember that visual impairment classification can vary between guidelines, but a key point is that significant visual acuity loss, such as 4/60, qualifies an individual for a disability certificate, indicating a substantial impact on daily functioning.

**Correct Answer:** D. 40%