Retinoscopy -Astigmatism Flashcards
1
Q
What is astigmatism?
A
visual defect in which the unequal curvature of one or more refractive surfaces to he eye (usually cornea) prevents light rays from focusing clearly at one point on the retina
- Instead there are 2 focal points, each formed nay one of the 2 different curvatures of the cornea or lens of the eye
- These 2 different curvatures are almost always perpendicular to each other.
2
Q
What are the surfaces ?
A
the flattest meridian is the less curved surface
steepest meridian more curved surface
3
Q
What is spherical ametropia?
A
one power in all meridia
power 1=power 2
Need only spherical lenses
4
Q
What is astigmatic ametropia?
A
- Different powers in the 2 principal meridian
- Power 1 not equal to power 2
- Use spherical and cylinderical lenses
- Has 2 different curvatures
5
Q
Where does the power occur in cylindrical lenses?
A
-occurs in only one of the 2 main meridian of the lens
6
Q
How do we correct astigmatism?
A
- spherical and cylindrical lens together
- Power of sphere only in one meridian
- And the power of the sphere plus cyl in the perpendicular meridian.
