Astigmatism And Correction Of Astigmatism Flashcards
Astigmatic systems do not form
Points, they form lines
How many people have some form of astigmatism
80%
One line is on the retina, one is in front of the eye. the vertical part of E would look clear
Simple myopic astigmat
One line focused on retina, one focused behind retina
Simply hyperopic astigmat
Both lines are in front of the retina
Compound myopic astigmat
What state are you in when you are fogging the patient in refraction
Compound myopic astigmat
Both lines behind retina
Compound hyperopic astigmat
One line in front, one behind retina. CTC not on retina
Mixed astigmat
One line in front retina, one behind the retina. CLC on retina
Equal mixed astigmat
What does plus cylinder do?
Moves on line forward, moving CLC in front of retina
What does minus cylinder do
Moves one line behind retina
What does cylinder do
Moves just one line
In what direction does minus cyl move the lone
Behind retina
What direction does the plus cyl move a lone
In front of the retina
What moves both lines in astigmatism?
Sphere
A common vision condition that causes blurred vision. It occurs when the cornea is irregularly shaped or sometimes because of the curvature of the lens inside the eye
Astigmatism according to the AOA
Methods for correcting astigmatism
- glassses (spherocylindrical lenses)
- contact lenses (toric)
- squinting (narrows aperture, lids can push on cornea)
- refractive surgery
How many dimensions to a cylinder
3
How do you generate a cylinder
Taking 2 parallel lines and roatating one around the other
What is the center of rotation for a cylinder
Axis
All points on the cylinder are ________ from the axis
Equidistant
How can you create a cylinder
By taking a flat plane and rolling it so that the ends are circles
Make sure you study the different shapes of optical lenses
Study it
Power of a cylindrical lens
P1=(n2-n1)/r1
If you shine a light through the ends of the cylinder what happens
Parallel light coming in, creates parallel light coming out
What happens if you shine light on the side of the cylinder
Focuses into vertical line if standing up on end
What direction does the light go through a cylinder
Same direction as cylinder is positioned, becomes line as it goes up and down cylinder
A point object is located 25cm in front of a thin +10.00 D cylindrical lens with a vertical axis. The lens as a 50mm round aperture in front of it. What is the location of the image? Is it real or virtual?
+6D=1/6cm in back
Real because converging to a point
Cylinders cannot exceed ______ degrees or be less than _____
180
0
Angle increases from patients _____ to ______
Left to right
Study cylinder crosses
Study it
