What is regular astigmatism?
Astigmatism in which the principal meridians are parallel
Astigmatism in which the principal meridians are perpendicular
Asymptomatic astigmatism
Astigmatism as a result of cataract surgery
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).
Types of Errors of Refraction