Astigmatism and Presbyopia Flashcards
When parallel rays of light enter the eye with accommodation relaxed and do not come to a single point focus on or near the retina.
Astigmatism
When the cornea has unequal curvature on the anterior surface
Corneal astigmatism
When the crystaline lens has unequal curvature on the surface or in its layers
Lenticular astigmatism
Sum of corneal astigmatism and residual astigmatism
Total astigmatism
Constitutes majority of astigmatism
Corneal astigmatism
Two principal meridians are perpendicular to each other
Regular astigmatism
Type of astigmatism in which in minus cylinder axis is found around horizontal meridian
With-the-rule astigmatism
Type of astigmatism in which in plus cylinder axis is found around horizontal meridian
Against-the-rule astigmatism
The sum of two axes of the two eyes equals approximately 180°
Symmetrical astigmatism
Infants are born with what type of astigmatism?
Against-the-rule astigmatism
The first accurate description of astigmatism was credited to?
Thomas Young
What charts are used for astigmatism?
Clock dials and fan dials
A type of symmetric astigmatism in which both eyes have with-the-rule astigmatism
Homologous astigmatism
With accommodation relaxed, both principal meridians focus in front of the retina
Compound myopic astigmatism
With accommodatoon relaxed, one meridian tends to focus behind the retina, while the other focuses in front of fhe retina
Mixed astigmatism