Astigmatism
Definition Cause
Classification
Symptoms
Signs
Correction
Astigmatism
• Definition: Is an aspherical refractive error. An eye is astigmatic when the eye's refractive parts are not rotationally symmetric about the optical axis.
• Cause: the cornea is irregularly shaped, sometimes because of the curvature of the lens inside the eye.
• Occurs frequently with MY and HY
• It often leads to blurry, distorted vision
• Types:
• Regular
• Irregular
Regular Astigmatism (regularis)
■ Most astigmatisms are regular and are of the cornea. The principal meridians are perpendicular to each other and form a 90° angle.
■ Classification due the focal line position:
■ a. simple myopic (simplex)
■ a. simple hyperopic
■ a. compound myopic (compositus)
■ a. compound hyperopic
■ a. mixed (mixtus)
■    a. typically mixed
Astigmatism - regularis
■   REGULAR ASTIGMATISM (regularis) - classification due the focal line position:
■ a. simple myopic (simplex) - one plane is located at infinity and the other is at a finite distance in front of the eye
■ a. simple hyperopic - one plane is located at infinity and the other is located behind the eye
Astigmatism - regularis
■ a. compound myopic (compositus) - two fair point planes are located at different distances in front of the eye
■ a. compound hyperopic - both planes are located at different distances behind the eye
Astigmatism - regularis
■   a. mixed (mixtus) - one fair point plane is located in front of the eye and the
other is located behind the eye
Astigmatism - regularis
■   a. mixed (mixtus)
■   a. typically mixed
			1     1 1 ■                  ■ ■ V  i i v 1
			
		>	yi i S 1 1
			
I I
Homework
Regular astigmatism can be further classified into three types that include with-the-rule, against-the-rule, and oblique astigmatism.
Astigmatism - irregular
• It has in different meridians a different refraction (symmetry is impossible to find in irregular astigmatism)
• Is difficult to correct with spectacle lenses
• Best correction: RGP, hard lenses, hibrid lenses (HOMEWORK) Aetiology:
■ congenital
■ post-traumatic
■ serious infections
■ postoperatively
■ after some medication therapy
■ keratokonus
Astigmatism — symptoms
■ n|/VA for far and near
■ blurred vision
■ headaches
■ eye - strain
■ irritated eye
■ half shutting of the eyes
■ blepharitis
■ recurrent hordeolum
■ irritability
■ asthenopia
Astigmatism - signs
■ Changeing of the optotype signs at the chart ( C, G, O, D, S,...)
■ Half shutting of the eyes
■ Compensating position of the head (ast. oblique)
■ Astigmatic corneas -„squeezed ball"
Astigmatism - signs
Tests for astigmatism
• Dial test, Astigmatic test (depends on the coutry)
• A simple test for detecting the presence of astigmatism
• One of the examination methods and screening methods
• All the lines are black. You are likely to have some degree of astigmatic error if some lines appear black while others seem gray.
Correction of astigmatism
• cylindrical lenses (toric spectacle lenses and contact lenses)
• up to 0,5 D - individual correction
• children - full cylindrical correction
• adults - individual binocular tolerability
• refractive surgery