An esthesiometer is a device for measuring the tactile sensitivity of the skin. The measure of the degree of tactilesensitivity is called aesthesiometry. The device was invented by Edward Henry Sieveking. There are different types of aesthesiometers depending on their particular function. The simplest is a manual tool with adjustable points similar to a caliper. It can determine how short a distance between two impressions on the skin can be distinguished. To differentiate between two points and one point of equal area, Dr. Sidney Weinstein created the three-point esthesiometer. A scale on the instrument gives readings in millimeter gradients. Another type of manual aesthesiometer is used to test lower thresholds of touch or pain. The tool uses nylon monofilaments with varying calibrated diameters. The force needed to cause the monofilament to buckle determines the tactile reading. The filaments are calibrated by force applied, rather than by gram/mm2 pressure ratings, because sensation follows force. The Semmes-Weinstein Aesthesiometer, and its variant the Weinstein Enhanced Sensory Test, present nylon monofilaments of approximately the same length and of varying diameters. The diameter and length are used to control the force applied. Whereas Dr. Weinstein used 3-digit numbers to reflect the force of the Semmes-Weinsein Aesthesiometer, the WEST esthesiometers use grams to describe the force. For small-area stimulating instruments like WEST, force, rather than area, is the appropriate measure. This is because an approximately equal area of skin is indented for the heavy and light forces. The area of stimulation of the Semmes-Weinstein Aestheiometer is not correctly described by the area of the stimulating nylon. Therefore, the unit gram/mm2 is descriptive of the geometry but not the function. The WEST esthesiometer has a bulb for a contacting tip, so when the tip bends it presents the same contacting face. A non-intrusive device called a corneal aesthesiometer is used to test corneanerve sensitivity by using a controlled pulse of air as stimulation. The device gives readouts in millibars. Also, a thermal aesthesiometer is used to determine sensitivity of thermal stimuli. Weinstein and group created an air-based corneal esthesiometer using gram-force. They also created an air-based oral esthesiometer. For example, smokers' upper throats are much less sensitive than nonsmokers.
