Draw A Large Cross With A Thin Pen On A White Paper To Test The Eyeglasses Optical Center
Test the optical center displacement of the cheap eyeglasses near me by drawing a large cross with a thin pen on white paper, with clear and straight strokes.
Place the handheld lens between the eye and the cross, and observe the shape of the cross stroke through the mirror with one eye. If the strokes inside and outside the mirror are not on the same line. Move the lens so that the cross strokes inside the lens are aligned with the cross strokes outside the lens. Use a brush or fountain pen to make a small dot at the center of the lens cross, which is the optical center.
After both the cheapest eyeglasses lenses point out the optical center, observe and compare whether the optical centers on both sides are symmetrical. Use a small ruler to measure whether the distance between the two center points is consistent with the prescribed pupil distance. If the cross stroke in the lens is bent, it indicates that there is an internal stress or uneven optical density problem in the lens.
Measure the axial direction of the astigmatic lens, rotate the lens 30 centimeters above the cross shape, and the cross in the lens can be seen to cross. When the strokes of the cross shape inside and outside the lens are connected, the shape becomes a regular cross. At this time, the axis of the prism is aligned with the straight line, and then the lens is repeatedly moved along the straight line; Observe which line deviates more from the line outside the lens during movement, and this line is the direction of the astigmatism axis.
Move the discountglasses lens to align the inner and outer straight lines, which is the astigmatism axis. Mark the lens and measure the angle between the axial and horizontal lines at the center of the lens using a measuring tool, which is called an axial degree.
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