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What is What is regular astigmatism? and explain in detail?
Ans. is 'b'i.e., Astigmatism in which the principal meridians are perpendicular Types of AstigmatismA) Based on axis of the principal meridians1) Regular stigmatism : Principal meridians are perpendicularo With-the-rule astigmatism-the vertical meridian is steepest.o Against-the-rule astigmatism-the horizontal meridian is steepest.o Oblique astigmatism-the steepest curve lies in between 120 and 150 degrees and 30 and 60 degrees.2) Irregular astigmatism - principal meridians are not perpendicular.B) Based on focus of the principal meridians1) Simple astigmatismo Simple hyperopic astigmatism - first focal line is on retina while the second is located behind the retinao Simple myopic astigmatism - first focal line is in front of the retina while the second is on the retina.2) Compound astigmatismo Compound hyperopic astigmatism-both focal lines are located behind the retinao Compound myopic astigmatism-both focal lines are located in front of the retina.3) Mixed astigmatism - focal lines are on both sides of the retina (straddling the retina).