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Many means are available by which one can arrive at an estimation of the amount of astigmatism present in a given case. Among these are subjective testing with trial lenses, retinoscopy and use of the keratometer, the cross cylinder and the astigmatic chart. In all cases of astigmatism it may be shown that if the eye looks at a number of lines drawn in different directions some lines will be seen more clearly than others. Contrarily, freedom from astigmatism exists when all lines are equal. The possible variations of astigmatism are of course many, owing to the number of degrees of the circle and the possibility of variation in one axis or in many. Even with the most careful examination there may remain some doubt about the correctness of the findings.
Use of the astigmatic chart has, in my estimation, often been unsatisfactory and the results difficult to interpret. Many
WILSON A. COMBINATION OF CROSS CYLINDER AND ASTIGMATIC CHART IN CORRECTION OF ASTIGMATISM. Arch Ophthalmol. 1942;28(3):490–492. doi:10.1001/archopht.1942.00880090124008
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