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A pinhole occluder is an opaque disk with one or more small holes through it, used by ophthalmologists, orthoptists and optometrists to test visual acuity. The occluder is a simple way to focus light, as in a pinhole camera , temporarily removing the effects of refractive errors such as myopia .
Pinhole glasses, also known as stenopeic glasses, are eyeglasses with a series of pinhole-sized perforations filling an opaque sheet of plastic in place of each lens. Similar to the workings of a pinhole camera , each perforation allows only a very narrow beam of light to enter the eye which reduces the size of the circle of confusion on the ...
An example of the Landolt C eye chart (also known as the Japanese eye chart). Numerous types of eye charts exist and are used in various situations. For example, the Snellen chart is designed for use at 6 meters or 20 feet, and is thus appropriate for testing distance vision, while the ETDRS chart is designed for use at 4 meters. [16]
An occluder is placed over the eye that is not being tested (e.g.: over the left eye, to test the right eye's vision). A pinhole occluder is then placed before the patient's eye, and their vision is then tested again (each eye separately) to determine if the patient's poor visual acuity is a result of optical irregularities, or pathological issues.
The term replacement cost or replacement value refers to the amount that an entity would have to pay to replace an asset at the present time, according to its current worth. [1] In the insurance industry, "replacement cost" or "replacement cost value" is one of several methods of determining the value of an insured item. Replacement cost is the ...
Wide-field micrograph of a damaged 80 μm pinhole Natural pinholes formed by tree leaves – Solar eclipse of August 21, 2017 in Washington state. A pinhole is a small circular hole, as could be made with the point of a pin. In optics, pinholes with diameter between a few micrometers and a hundred micrometers are used as apertures in optical ...
A cost index is the ratio of the actual price in a time period compared to that in a selected base period (a defined point in time or the average price in a certain year), multiplied by 100. Raw materials, products and energy prices, labor and construction costs change at different rates, and plant construction cost indexes are actually a ...
The fiber may be geometrically asymmetric or have a refractive index profile which is asymmetric such as the design using an elliptical cladding as shown in the diagram. Alternatively, stress permanently induced in the fiber will produce stress birefringence ; this may be accomplished using rods of another material included within the cladding.