Refractive Errors Flashcards
What is Myopia?
- Myopia is when the eyeball is too long, or the cornea is too curved
- Light rays are focused in front of the retina
- Near objects are clear
What is Hyperopia?
- Hyperopia is when the eyeball is too short or the cornea is too flat,
- Light rays are focused behind the retina
- Far objects are clear
What is Astigmatism?
- Light rays don’t come to a single focus but instead, focus on more than one spot
As we age what happens to the lens?
The lens becomes less flexible which can lead to hyperopia because the lends struggles to focus on nearby objects
What contributes to developing myopia in the vision?
Prolonged screen time, reading without proper lighting, and not spending enough time outdoors
What type of lens helps with myopia(minus) sight and how do they help?
Concave lens: (thinner in the center) helps diverge light rays, allowing them to focus on the retina
What type of lens helps with hyperopia(plus) sight and how do they help?
Convex lenses:(thicker in the center) converge light rays, allowing them to focus on the retina.
What type of lens helps with astigmatism?
Cylindrical lenses are used to correct the irregular curvature of the cornea
What does OD stand for and what does it refer to?
Oculus Dexter: Refers to the right eye
What does OS stand for and what does it refer to?
Oculus spinster: left eye
What does SPH stand for and what does it do?
Sphere: indicates the degree of myopia or hyperopia
What does ClY stand for and what does it do?
Cylinder: indicates degree of Astigmatism
What does the axis do?
Ensures that the cylindrical correction is oriented correctly to address the specific shape of the eye
What does the ADD do for the spectacle prescription?
Add in additional magnifying power for reading (used for presbyopia)
Explain what this prescription is trying to say.
OD: -2.00 sph, -1.00 cyl, 180 degree axis
OS: -1.50 sph, -0.50 cyl, 90 degree axis
The OD (right eye) needs a concave lends of -2.00 diopter for myopia while the -1.00 diopter cylindrical correction for astigmatism with the cylindrical axis at 180 degrees.
The OS (left eye) needs a concave lens of -1.50 diopters of myopia while the -0.50 diopter cylindrical correction for astigmatism at 90 degrees
what is myopia corrected with?
Minus lenses
What is hyperopia corrected with?
Plus lenses
What is the primary purpose of the eye?
- To focus light on the retina.
What are the steps of how vision works.
- Vision begins when light enters the eye through the cornea.
- It travels through the clear aqueous fluid and passes through the pupil
- As muscles in the iris relax or constrict, the pupil changes size to adjust the amount of light entering the eye
- Light rays are then focused through the crystalline lens.
- Proceed through the vitreous
- Then reaches the retina where the light rays are converted into an electrical impulse that travels along the optic nerve to the brain where it is interpreted as an image
What is emmetropia?
- An eye that focuses light precisely on the retina with no additional assistance from eyeglasses or contact lenses.
What is another name for Nearsightedness?
- Myopia
What is another name for Farsightedness?
- Hyperopia
What is compound myopic Astigmatism?
- Two myopic or minus power
What is compound hyperopic astigmatism?
Two hyperopic power
What is mixed astigmatism?
- One focal point is in front of the retina, while the other is behind.
What is presbyopia?
- When the crystalline lens is no longer able to change shape and focus on objects at different distances.
What corrects presbyopia?
- Bifocal or multifocal lenses
Approximately how much power can be generated by the eye’s optical system?
- 60 diopters
What is simple myopic Astigmatism?
- Some of the rays of light entering the eye fall short of their intended spot on the retina but some fall directly on the fovea.
What is simple hyperopic Astigmatism?
- Some of the rays of light entering the eye focus on the spot beyond the retina, but some fall directly on the fovea where they need to be.
Is the problem below simple myopic astigmatism or simple hyperopia astigmatism?
-2.00 +2.00 x 40
Simple myopic astigmatism
Is the problem below simple myopic astigmatism or simple hyperopia astigmatism?
-0.50 + 0.50x135
Simple Myopic Astigmatism
Is the problem below compound myopic astigmatism or Compound hyperopia astigmatism?
-1.50 +0.50x135
compound myopic astigmatism
Is the problem below compound myopic astigmatism or Compound hyperopia astigmatism?
+2.50 -2.00 X 130
Compound hyperopia astigmatism
Is the problem below compound myopic astigmatism or Compound hyperopia astigmatism?
+0.50 +0.50 X 135
Compound Hyperopia Astigmatism
Is the problem below compound myopic astigmatism or Compound hyperopia astigmatism?
-4.50 + 2.00 X 45
Compound Myopic Astigmatism
What type of Astigmatism is this?
-1.00 +2.00 X 135
Mixed Astigmatism
What ocular structure does light interact with first when light enters the eye?
Cornea
