What is Astigmatism?

Astigma stigma=point.

Astigmatism is a refractive error where in parallel rays of light, coming from infinity, after refraction through the eye, do not come to a point focus on the retina when the accommodation is at rest.

What are the causes for Astigmatism ?

(1) Corneal  

(A)  Congenital

(B)  Acquired

                          i.      Following surgery to the eye (cataract, corneal )

                         ii.      Corneal scar

                        iii.      Pterygium

                        iv.      Large chalazion

(2) Lenticular

(A)  Congenital à Subluxation of lens, lenticonus.

(B)  Acquired à Subluxation of lens

What are the types of astigmatism?

 Regular astigmatism: - Here the 2 meridia( greatest & least curvature) with the minimum and maximum refractions are at right angles to each other and they correspond to the vertical and horizontal meridian.

(1)   Simple myopic astigmatism: Rays from one meridian come to a point focus on the retina and from the other in front of retina.

(2)   Compound myopic astigmatism: Rays from both meridia are myopic and come to a focus in front of retina but at different places.

(3)   Simple hypermetropic astigmatism: Rays from one meridian focus on the retina from the other meridian behind the retina.

(4)   In compound hyupermetropic astigmatism rays from both meridia come to focus behind the retina but at different places/parts/points.

(5)   Mixed astigmatism: - Rays from one meridian are focused in front and rays from the other meridian are focused behind the retina.

Regular astigmatism is called with vertical curvature horizontal curvature  by 0.25D. This is physiological the rule if the vertical meridian is more myopia than the horizontal. It is called as against the rule (As age advances, reversal occurs (horizontal curvature in surgical aphakia  vertical) astigmatism if the vertical meridian is more hypermetropia (flatter) than the horizontal.

What are the SYMPTOMS?

(1)   Defective near or distant vision.

(2)   Eyestrain

How to diagnose?

By Retinoscopy after cycloplegia.

   For cycloplegia:

        Use short acting:            1. Cyclopentolate eye drops 1% in adults.

OR

                                                   2. Tropicamide eye drops 1%

     Long acting                         (1) Atropine eye ointment 1% in children.

What is the TREATMENT?

(1)   For minimal astigmatism :– corresponding spectacle correction is given

                                                     i. Either simple cylindrical glass or

                                                    ii.  A combination of cylindrical and spherical  glasses.

(2)   Contact lens:-   is a better way of treating astigmatism as it eliminates much of the astigmatism.

(3)   Surgery.