Course 1 Flashcards
What do Rods and Cones do?
The rods and cones send the light as nerve impulses to the brain for interpretation.
emmetropia
Is an eye with perfect vision. The rays of light entering the eye focus on the retina right where they need to be. No need for corrective lenses.
What is Refraction?
Refraction is the bending of light that occurs in a lens.
What is a refractive error?
When an individual suffers from wandering rays of light. Aka the light doesn’t come to focus on the Fovea.
What is simple myopia?
Is it nearsightedness or farsightedness?
How is this corrected?
What is the shape of the eye or cornea?
- the point of focus falls in front of the retina.
- nearsightedness
- with a minus rx. (think my-opia, mi-nus lens)
- the eye is long or the cornea is too steeply curved.
What is simple hyperopia?
Is it nearsightedness or farsightedness?
How is this corrected?
What is the shape of the eye or cornea?
- the point of focus falls behind the retina.
- farsightedness
- with a plus rx.
- the eye is short or the cornea is too shallowly curved.
What is simple myopic astigmatism?
What is the shape of the eye or cornea?
How is this corrected and what is an example?
- SOME of the rays of light fall short of the retina.
- The cornea is not perfectly round, but instead has two different curves.
- ONE focus point of the RX will provide no correction, another focus point of the RX will have minus power.
- Example: 0.00 -0.50 X 45
- 0.50 + 0.50 X 135 (transposed=zero cyl)
0. 00 -2.00 X 130
- 2.00 +2.00 X 40 (transposed=zero cyl)
Eyes with simple myopic/hyperopic astigmatism is corrected with what kind of lens?
It is corrected using lenses with variable powers. Also known as sphero-cylinder lenses, toric lenses, or sometimes compound lenses.
What is simple hyperopic astigmatism?
What is the shape of the eye or Cornea?
How is this corrected and what is an example?
-SOME of the rays of light focus behind the retina.
-The cornea is not perfectly round, but instead has two different curves.
-ONE focus point of the RX will provide no correction, another focus point of the RX will have plus power.
-Example: +1.50 -1.50 X 45 (transposed=zero cyl)
0.00 +1.50 X135
+2.50 -2.50 X 130 (transposed=zero cyl)
0.00 +2.50 X 40
What is compound myopic astigmastism?
What is the shape of the eye or cornea?
How is this corrected and what is an example?
- ALL the rays of light fall short of the retina.
- The cornea is not perfectly round, but instead has two different curves.
- All lens have minus power in all areas of the lens/RX.
- Example: -1.00 -0.50 X 45
- 1.50 +0.50 X 135
- 2.50 -2.00 X 130
- 4.50 + 2.00 X 40
What is a compound hyperopic astigmatism?
What is the shape of the the eye or cornea?
How is this corrected and what is an example?
-ALL the rays of light focus behind the retina.
-The cornea is not perfectly round, but instead has two different curves.
-All these examples have plus power in all areas of the lens/RX.
-Examples: +1.00 -0.50 X 45
+0.50 +0.50 X 135
+2.50 -2.00 X 130
+0.50 +2.00 X 40
What is mixed astigmatism?
Is it nearsightedness or farsightedness?
What is the shape of the the eye or cornea?
How is this corrected and what is an example?
- some rays of light focus ahead of the retina, some focus behind the retina.
-the cornea is misshapen. - one area of the RX has minus power while another part of the RX has plus power.
-Examples: +1.00 -2.00 X 45
-1.00 +2.00 X 135
+2.00 -2.25 X 67
-0.25 + 2.25 X 157
What is Presbyopia?
How is this corrected and what is an example?
-it is a refractive condition in which you are unable to accommodate (read fine print, thread a needle, or do fine work) without magnification.
-with an add power.
-Examples: Add +1.25
Add +2.50
What is Accommodation?
-The increase in plus power by changing the shape of the crystalline lens by relaxing the ciliary muscle.
What are the two equations to find the value of a diopter?
What do the components stand for?
- D=1/f and F=1/D
- D=diopters
f=focal length
A prism of 1.00 diopter produces the appearance of what?
-it produces a 1 centimeter shift in position of an object being viewed at a distance of 1 meter.
What produces a 1 centimeter shift in position of an object being viewed at a distance of 1 meter.
-a prism of 1.00 diopter.
What is The Nominal Lens Formula? What do the components stand for? What is it called when a cylinder is added to the equation? What is it used for? What is the flaw and why?
- DL=D1+D2
- DL=total power of the lens
- D1=the front surface power
- D2=the back surface power
- Toric Transpostion
- To calculate the total power of a lens.
- It does not calculate the total power of the lens accurately because the formula does not take into the account of lens thickness and the index of refraction.
What is the back vertex depth formula?
What do the components stand for?
What is it used for?
- power=back+ front/1-(tm/n)front
(power=back+front over 1-(tm over n) front. - back=back curve
- front=front curve
-tm=thickness of lens (calculate to meters)
-n=index of refraction. - to calculate the total power of the lens.
What is a phoropter?
-The instrument used by doctors to determine the patient prescription.
What does “n” stand for?
Index of refraction
Index of refraction is a numerical representation of what?
-how much a material will slow the speed of light when it is traveling through it.
A material with a higher index of refraction will do what to light?
slow it down.
What is the Index of refraction for a High Index lens?
1.67
What is the Index of refraction for a CR-39 lens?
1.498
