Is Astigmatism caused by abnormal contraction of the cillary muscle?!
Question: Is Astigmatism caused by abnormal contraction of the cillary muscle?
Answers:
No.
Astigmatism is caused by the refracting surfaces of the eye (cornea & lens) not being 3D symetrically curved (like a surface of a sphere, eg soccer ball). Instead it is irregularly curved like a surface of a football (eg grid-iron ball). In rare cases, the surface of the retina can be curved irregularly to cause astigmatism too.
But most commonly, it's the Cornea - the clear front surface of the eye that has the irregular curve. The cornea is made of layers of collagen fibres. Each adjacent layers, the fibres run perpendicular to each other... now, genetics dictate the strengths of these fibres, and if there is consistently more tension in the layers in one direction, it will cause the cornea to bow from its original sphere shape.
Lastly, abnormal contractions of the cilliary muscle would give you a condition known as Pseudo Myopia (if there is cramping), or less severe... active accommodation.
It's caused by an irregular surface of the eye.