**Core Concept**
Visual acuity is a fundamental measure of the sharpness of vision, which is a critical aspect of visual function. It is defined as the ability to distinguish between two closely spaced objects, typically measured on a Snellen chart. Form sense, also known as visual acuity, is a complex process that involves the transmission of visual information from the retina to the brain.

**Why the Correct Answer is Right**
The correct answer, **B. Form sense**, is the most accurate description of visual acuity. Visual acuity is specifically concerned with the ability to perceive and distinguish between different shapes, forms, and patterns. This is achieved through the coordinated effort of the cornea, lens, retina, and optic nerve. The retina's photoreceptors (rods and cones) convert light into electrical signals, which are transmitted to the optic nerve and ultimately processed in the visual cortex. The visual cortex then interprets these signals as visual information, allowing us to perceive and recognize shapes, colors, and patterns.

**Why Each Wrong Option is Incorrect**
**Option A:** Light sense refers to the ability to perceive light, which is an essential aspect of vision but not directly related to visual acuity. While light sense is necessary for vision to occur, it does not measure the sharpness of vision.

**Option C:** Contrast sense refers to the ability to distinguish between different levels of brightness or darkness. While contrast sense is important for visual function, it is not the primary aspect of visual acuity.

**Option D:** All of the above is incorrect because visual acuity specifically refers to the ability to perceive and distinguish between different shapes and forms, not light sense or contrast sense.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that visual acuity is usually measured using a Snellen chart, with a normal visual acuity of 20/20. This means that a person with normal vision can read the 20/20 line at a distance of 20 feet, which is the standard for normal visual acuity.

**✓ Correct Answer: B. Form sense**