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Some have been alarmed at the papers read at recent international congresses on biastigmatism and a suggested triastigmatism, and at the complicated way of discovering and treating such conditions. It is known by all that astigmatism is usually due to an unequal curvature of the anterior surface of the cornea, and that this astigmatism may be masked or increased by an unusual curvature of the posterior corneal surface or of either or both surfaces of the lens, or by a partial dislocation or tilting of the lens.
These difficulties arise only when one trusts to the readings of the ophthalmometer for finding the power and the axis of the correcting cylinder. When ordering glasses, one wishes to find the total astigmatism of the eye and the cylinder that will correct it when placed at the assigned distance (say, 13.6 mm.) from the cornea. Retinoscopy when carefully done will determine