What is irregular astigmatism -
It is characterized by an irregular change of refractive power in different meridia. There are multiple meridia which admit no geometrical analysis.the principal meridians are not perpendicular to each other Image : Corneal topographies in regular and irregular astigmatisms. A: Regular astigmatism of 4.0 diopters with two perpendicular main meridians. B: Irregular astigmatism of 6.5 diopters with non-perpendicular main meridians. Reference : A K KHURANA OPHTALMOLOGY,Edition 4,Page-38
Perpendicular principal meridians
Non perpendicular principal meridians
Any of the above
None of the above
Optics and refraction