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Distance PD is the separation between the visual axes of the eyes in their primary position, as the subject fixates on an infinitely distant object. [2] Near PD is the separation between the visual axes of the eyes, at the plane of the spectacle lenses, as the subject fixates on a near object at the intended working distance. [3]
There are many ways to measure PD ranging from a simple ruler (or "PD stick") traditionally used by eye care professionals (ECP) to the so-called pupillometers to state of the art digital systems that may offer better accuracy and precision while also allowing for various other measurements (e.g., vertex distance, pantoscopic tilt, wrap, etc ...
Positive displacement (PD) flow meters measure the volumetric flow rate of a moving fluid or gas by dividing the media into fixed, metered volumes (finite increments or volumes of the fluid). A basic analogy would be holding a bucket below a tap, filling it to a set level, then quickly replacing it with another bucket and timing the rate at ...
The prism cover test (PCT) is an objective measurement and the gold standard in measuring strabismus, i.e. ocular misalignment, or a deviation of the eye. [1] It is used by ophthalmologists, orthoptists, and optometrists in order to measure the vertical and horizontal deviation and includes both manifest and latent components. [1]
Measure for the ease with which an object resists conduction of heat K/W L −2 M −1 T 3 Θ: extensive Thermal resistivity R λ: Measure for the ease with which a material resists conduction of heat K⋅m/W L −1 M −1 T 3 Θ: intensive Viscosity: η: The measure of the internal friction in a fluid Pa⋅s L −1 M T −1: intensive, scalar ...
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