<prompt> Which one is Against the Rule astigmatism- 2.00 x 90deg- 1.50 x 180deg2. 00 x 90deg1.50 x 180deg  <response>: Astigmatism:- Definition:- When the rays are focused at different points due to unequal refraction in different meridians. With the Rule Astigmatism:- Veical meridian is more curved than the horizontal meridian Eg : Normal eyes 0.25 D, pterygium 90deg axis 180deg axis lens at 90deg- lens at 180deg Against the Rule Astigmatism:- When the horizontal meridian is more curved than the veical meridian 180deg90deg axis - lens at 90deg lens at 180deg Eg: Post op astigmatism -suture related Oblique Astigmatism :- The two principal meridias are at right angles to each other ; but not the veical and horizontal meridian like 45deg and 135deg Bioblique Astigmatism:- The two principal meridias are not at right angles and also not the veical and horizontal meridia.eg : 30deg 100deg Reference :- Parsons Diseases of the eye 22nd edition; page:- 53,76 