Refractive Errors Flashcards
What is the primary purpose of the eye?
To focus light on the retina.
What eye part does light first enter?
Cornea.
After the light travels through the cornea, where does light travel next?
It travels through the clear, aqueous fluid, and passes through the pupil.
Why and how does the pupil change size?
The muscles in the iris relax or constricts, controlling the amount of light entering the eye
After the light travels through the pupil, where does the light travel next?
Light is then focused on the crystalline lens
What happens after light goes through the crystalline lens?
Proceeds to the viterous.
When light proceeds to the viterous, where does it go next?
It proceeds to the viterous to reach the retina.
What happens to the light rays when it reaches the retina?
In the retina, the light rays convert into electrical impulses that travels along the optic nerve to the brain, interpreted as an image.
What are one of the ways to measure visual acuity?
The Snellen Chart.
What does it mean when someone has a 20/20 vision?
When a person can see an object at twenty feet that normal person can see at twenty feet.
The patient can see at this feet/What a normal person would see at this feet
What does it mean when someone has a 20/40 vision?
The larger the bottom number is being measured the poorer the vision is being measured.
In the eye’s optical system, how much does the eye have total eye power?
Approx. 60 diopters.
Where is the eye power generated?
In the cornea and crystalline lens.
What happens if light isn’t bent properly?
If light isn’t bent properly, then the image doesn’t focus on the retina and there is a REFRACTIVE ERROR.
Define emmetropia.
Emmetropia is an eye that focuses light precisely onto the retina with NO additonal assistance from eyeglasses or contact lens.
What happens to the light rays when the eyes are myopic or nearsighted?
When it focuses an equal amount in FRONT of the retina, the light rays are no longer in focus by the time they reach the retina; happens when the cornea and/or crystalline lens generates too much plus power.
What’s an example of a simple myopic Rx?
Rx. -2.00D
What type of lens would help myopia?
A concave lens.
What happens to the light rays when the eyes are hyperopic or farsighted?
When light rays focus behind the retina. Light doesn’t actually focus behind the retina. Rather at a points where light rays reach the retina, it has not yet reached a point focus. This may be because the globe of the eye is somewhat short or not enough plus power. Far objects are clear but not near.
What’s an example of a simple hyperopic Rx?
Rx. +2.00D
What type of lens would help hyperopia?
convex lens.
What is astigmatism?
The refractive error that occurs when the light rays don’t come to a single focus, but instead focusing MORE than one point on the retina.
Whats an example of astigmatic Rx?
Rx. -2.00 -0.75 x180.
The amount of astigmatism DOES NOT indicate the power of the other meridian, but indicates the amount astigmatism.
How do you determine the power of the second meridian?
To add them together.
What’s an example of a compound myopic astigmatism?
Rx. -2.25 -0.25 x180 -2.25(+)-0.25=-2.50 Vertical Meridian: -2.50 Horizontal Meridian:-2.25 Since are ALL minus.
What’s an example of a compound hyperopic astigmatism?
Rx. +2.50 -0.50 x180 \+2.50 (+) -0.50 =+2.00 Vertical Meridian:+2.00 Horizontal Meridian:+2.50 Since are ALL plus.
What’s an example of a mixed astigmatism?
Rx. +1.00 -1.25 x180 \+1.00 (+) -1.25= -0.25 Vertical Meridian:-0.25 Horizontal Meridian:+1.00 One of the eyes focal point is in front of the retina while the other is behind the retina.
What is presbyopia?
When the crystalline becomes denser and loses its ability to change shape and focus objects at different distances.
How do you correct presbyopia eyes?
Bifocal or multifocal lenses are designated in a written Rx with an add power along with sphere, cylinder, axis.
The add power has to be the same for both eyes.
What range of add power in quarter diopters?
Between +1.00D and +2.50D.
On presbyopia lenses, how is the power written in a the Rx?
The add power is not written on Rx but rather the add power is added to the distance sphere power only.
The cylinder and the axis remains unchanged.
What is an example of a presbyopic Rx?
-3.00 -1.00 x180; +2.00D Add
Distance -3.00 -1.00 x180
Near -1.00 -1.00 x180
