Why is astigmatism divided into positive and negative?

Astigmatism can be divided into positive and negative. Negative refers to myopic astigmatism, and positive refers to hyperopic astigmatism.

Astigmatism is mainly due to the different refractive powers of the eyeball at different meridians. The eyeball is composed of different refractive systems such as the cornea and lens. Therefore, after the light enters the eye, it is refracted on the retina through the refractive system. A clear image is formed;

If the refractive power of each meridian is different, it will cause astigmatism, and the image will be in front of the retina or behind the retina, so that the optometry result will be positive or negative.

Extended information:

Regular astigmatism can be corrected with different cylindrical lenses according to the type of astigmatism and the degree of astigmatism. Convex cylindrical lenses are used for farsighted astigmatism and concave cylindrical lenses are used for myopic astigmatism.

Mild astigmatism does not require correction if there are no clinical symptoms. If there is vision loss or symptoms of visual fatigue and visual interference, corrective glasses should also be worn.

Children, especially preschoolers, must fully correct astigmatism to prevent amblyopia. Retinoscopy and retinoscopy should be done before wearing, and for adolescents and children, a dilated retinoscopy should be performed. Measurements with a keratometer can also be combined to understand the true nature and degree of astigmatism. Only then combined with subjective audition can the prescription of glasses be determined.