Term
| What are the two types of lens systems? |
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Definition
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Term
| What are the two optical systems called? |
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Definition
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Term
| What is the difference between the Lens system and the Pinhole System? |
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Definition
Pinhole: Only lets a few light rays through to form a focuses image.
Lens: Aperture (pupil) lets many rays through and the lens bends (refracts) the rays so they converge to form a focused image |
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Term
| What happens to light when it travels into a new medium? |
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Definition
| It slows down and changes direction. Exception: When the light hits perpendicularly to the medium, it will not change direction. |
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Term
| The amount of refraction depends on what? |
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Definition
1. Angle of incidence
2. The index of refraction |
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Term
| What type of lens do you see more biologically? |
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Definition
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Term
| What does a convex lens do to light rays? |
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Definition
| Converges to form a focused image |
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Term
| Where the image comes into focus depends on what? |
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Definition
1.Distance of the object from the lens
2. Curvature of the lens (fatter lens refract more) |
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Term
| What does a concave lens do to light rays> |
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Definition
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Term
For a fixed lens system:
Near object causes image formation where and what does this cause? Mid-distance? Far object? |
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Definition
Near object:Image formation behind retina and causes a blurry picture
Mid distance: On retina, focused
Far object: In front of retina, blurry |
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Term
| What two parts of the eye have the ability to change in order to focus an image? |
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Definition
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Term
Variable Lens System:
For a near object the lens would be what thickness? Mid-object? Far object? |
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Definition
Near object: Thick
Mid-Object: Middle thickness
Far object: Thin |
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Term
| What allows us to change the thickness of our lens? |
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Definition
| By accommodating action of the ciliary muscle which changes the ability of the lens to refract light. |
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Term
| What happens if the retina is fixed and the distance between the retina and the lens is fixed? |
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Definition
| There is only one distance that an object can be at and form a focused image on the retina |
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Term
| What is the visual angle? |
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Definition
| How we measure the size of an image on the retina |
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Term
| What do animals do in terms of focusing an image? |
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Definition
| Animals will move lens forward and back to accommodate for distances (moving fixed lens) |
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Term
| The visual angle is ____ when it is closer to the eye? |
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Definition
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Term
| 1 degree visual angle = ____ mm on the retina |
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Definition
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Term
| What are the four types of vision problems? |
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Definition
1. Natural Imperfections / Optical defects in the eye that we don't usually worry about
2. Focusing Problems that we worry about
3. Retina Problems
4. Optic Nerve Problems |
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Term
| What are the 5 Natural Imperfections / Optical Defects? |
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Definition
1. Chromatic Aberration
2. Spherical Aberration
3. Random Variations in cornea or lens
4. Diffraction
5. Other light scatter |
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Term
| What is chromatic aberration? |
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Definition
When different wavelengths come into focus at different distances from the lens. The lens is refracting different wavelengths differently which creates a blur.
Note: Short wavelengths come into focus in front of retina. Med on retina. Long behind retina. |
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Term
| What is Spherical Aberration |
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Definition
| Refractive power of lens is different at edges that in the middle. Causes blurriness. You would be seeing red on top and blue on the bottom (colors go with example from class) |
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Term
| What is random variations in cornea or lens? |
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Definition
| Cornea or lens are not perfect and this can be anywhere from normal to severe. |
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Term
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Definition
| Photons hit edge of iris/pupil and scatter into eye (a little image degradation) |
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Term
| What does other light scatter refer to? |
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Definition
| Photons reflect off of other things in the eye |
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Term
| What are the steps for Cataract surgery? |
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Definition
1. Remove lens leaving capsule intact
2. Small slit in eyeball and use ultra sound to break up lens and suck it out of capsule.
3. Insert a plastic lens in the capsule |
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Term
| What are the 5 focusing problems that we worry about? |
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Definition
1. Astigmatism
2. Cataract
3. Myopia
4. Hyperopia
5. Presbyopia |
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Term
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Definition
| Cornea is not spherical. Looks like a rugby ball |
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Term
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Definition
| Clouding of the lens. The lens is opaque. |
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Term
| What delays the onset of Cataracts? |
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Definition
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Term
| What is actually happening within the eye that causes Cataracts? |
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Definition
| Proteins in the lens oxidate and become damage. This occurs over the course of your life. Smoking and UV increase risks. |
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Term
| What does it mean in terms of the lens to be nearsighted (myopia)? |
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Definition
| Lens cannot get thin enough to focus on far objects so the image comes into focus in fron of retina. |
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Term
| What type of corrective lens are used for nearsighted vision? |
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Definition
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Term
| What are the two ways to be nearsighted? And what does each one mean? |
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Definition
1. Axial: Eye too long
2. Refractive: Cornea and lens bend light too much
Note: You have different curvature on the horizontal plane then the vertical plane |
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Term
| What does it mean in terms of the lens when you are farsighted (hyperopia)? |
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Definition
| Lens cannot get far enough to focus on near objects, so image comes into focus behind retina. Lens cannot get fat enough to focus on near object. |
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Term
| What type of corrective lens is used for farsighted people? |
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Definition
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Term
| What are the two ways to be farsighted? And what does each one mean? |
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Definition
1. Axial: eye too short
2. Refractive: cornea and lens bend light too little (too flat) |
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Term
| What does it mean to have presbyopia? |
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Definition
| It is the hardening of the lens. So you cannot focus on near objects |
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Term
| Why does presbyopia occur? |
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Definition
| It happens because of the accumulation of lens fibers |
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Term
| When does lens fiber accumulation occur? What does this mean for the flexibility of the eye? |
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Definition
| It starts when you are born. The lens continually gets less and less flexible. |
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Term
| Define nearpoint? What happens to nearpoint as you age? |
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Definition
| Nearpoint: closet an object can be to you and still be in focus. The older you get the farther from you the object must be. |
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