**Core Concept**
Non-contact tonometry measures intraocular pressure (IOP) without physical contact with the cornea. This method is useful for patients with corneal disease or trauma.

**Why the Correct Answer is Right**
Applanation tonometry, specifically the Goldmann applanation tonometer, is considered the gold standard for measuring IOP. It works by applying a known force to a fixed area of the cornea, which results in a precise measurement of IOP. This method is accurate and reliable but requires physical contact with the cornea.

**Why Each Wrong Option is Incorrect**
**Option A:** Tonopen is a type of rebound tonometer that uses a small probe to measure IOP. While it is non-invasive, it is not as accurate as the Goldmann applanation tonometer.
**Option B:** Air puff tonometry is a type of non-contact tonometer that uses an air puff to flatten the cornea and measure IOP. However, it is less accurate than the Goldmann applanation tonometer, especially in patients with irregular corneas.
**Option C:** Schiotz tonometer is a type of indentation tonometer that measures IOP by indenting the cornea with a known weight. While it is useful in certain situations, it is not as accurate as the Goldmann applanation tonometer.

**Clinical Pearl / High-Yield Fact**
When measuring IOP, it's essential to use a tonometer that is calibrated regularly to ensure accurate readings. Incorrect calibration can lead to significant errors in IOP measurement.

**Correct Answer: C. Schiotz tonometer is not the best option, however, the correct answer is not provided in the options; the correct answer should be Goldmann applanation tonometer, so I will provide the correct answer in the correct format.**