Ocular micrometer

Size is important in the differentiation of parasites and is most accurately determined with a calibrated ocular micrometer, thus, each laboratory performing diagnostic parasitology must have such a micrometer. 

An ocular micrometer is a disk on which is etched a scale in units from 0 to 50 or 100. To determine the micrometer value of each unit in a particular eyepiece and at a specific magnification, the unit must be calibrated with a stage micrometer. A stage micrometer has a scale 2 mm long ruled in fine intervals of 0.01 mm (10 finl). 

Insert the micrometer in the eyepiece so that the micrometer rests on the diaphragm, with the etched scale facing the eye. In many new microscopes, the micrometer can be dropped in and secured with a ring retainer. (It is helpful to have an extra ocular in which the micrometer may be left.)... 

Find a point far down the scales at which a line of the stage micrometer coincides with a line of the ocular micrometer. Count the number of ocular units and the number of stage units from zero to these coinciding lines. 

Use of the micrometer. Insert the eyepiece containing the calibrated ocular micrometer in the microscope. Count the number of ocular units which equal the structure to be measured. Multiply the number by the micrometer value of the ocular unit for the objective being used. If an ocular micrometer is properly used, parasites which are similar in appearance but different in size can be readily differentiated. 

The most commonly employed method for measuring bacteria is by means of an ocular micrometer. Measurements may also be made by using a camera-lucida attachment and drawing oculars, or by projecting the real image on a screen and measuring the bacteria. 

Before carrying out particle sizing on a sample, the microscope s ocular scale must be calibrated. This is normally done with a stage micrometer, which has a linear graduated scale. The micrometer is aligned with the eyepiece ocular to determine the length per ocular scale division. The ocular can then be used to read the diameters of particles on a slide. When sufficient particles are sized, the length-number mean can be calculated ... 

T reatment is indicated for ocular hypertension if the patient has a significant risk factor such as IOP greater than 25 mm Hg, vertical cup-disk ratio greater than 0.5, or central corneal thickness less than 555 micrometers. Additional risk factors to be considered include family history of glaucoma, black race, severe myopia, and presence of only one eye. 

If the reduction ratio is independently known in terms of the distance between the object and the camera, then the bubble size can be known by measuring the size of image by means of an ocular micrometer. 

The radius of the drop is calculated from m and td, and rc is measured with a microscope and ocular micrometer. 

In field use, the camera system was suspended from a large float and allowed to drift freely. An initial 30-min delay in the timing circuit provided time for deployment of the apparatus before the first exposure, and permitted the movement of the ship downwind at least 0.5 km. Following the delay, photographs were made at 30-sec intervals until the entire roll of film was exposed. Following development, bubble images on the film were measured directly by microscope with the aid of an ocular micrometer (ref. 33). 

This method of obtaining the measure of uniformity is generally useful when particles are measured with an ocular micrometer. While there are many different methods of expressing uniformity, we shall confine ourselves to the three most widely used. 

In measuring microscopic objects it is necessary to make use of a micrometer of some kind. That pretty generally used is the ocular micrometer. It is a circle of glass suitable for insertion within the ocular with a scale etched on its surface. The scale is divided to tenths of a millimeter (o.i mm.) or the entire surface of the glass may be etched with squares (o.i mm.), the net micrometer. 

The value of each division of the ocular micrometer scale must be ascertained for each optical combination (ocular, objective, and tube length) by the aid of a stage micrometer. 

Insert the ocular micrometer within the tube of the ocular by placing it on the diaphragm of the ocular, and adjust the stage micrometer by placing it on the stage of the microscope. 

Focus the scale of the stage micrometer accurately so that the lines of the two micrometers will appear in the same plane. Make the lines on the two micrometers parallel each other. This can often be done by turning the ocular to the right or left while looking into the microscope. 

Make two of the lines on the ocular micrometer coincide with two on the stage micrometer. Note the number of included divisions. 

Multiply the number of included divisions of the stage micrometer scale by the value in microns given for each division and divide the result by the number of included divisions of the ocular micrometer scale. The quotient represents the value of each division of the ocular micrometer scale. 

Note the optical combination (number of ocular, objective and tube length) used and keep a record of it with the calculated micrometer value. Repeat for each of the combinations. 

To measure an object by this method read oS the number of divisions it occupies of the ocular micrometer scale, and express the result in microns by looking up the recorded value for the optical combination used. 

Indentation measurement a measuring mechanism of the ocular micrometer allows measurements in the field of the indentation image. 

It was found advantageous to use as ozone measure the sum of the depth of all cracks as measured imder the microscope (lOOx) using an ocular micrometer. The measurement of crack depth was made on freshly cut surfaces exposed by making longitudinal cuts through the test strip 1 mm. from the edges. 

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