Term
| What are the 5 types of monochromatic aberrations? |
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Definition
1. Spherical
2. Coma
3. Distortion
4. Oblique Astigmatism
5. Curvature of Field |
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Term
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Definition
- can be longitudinal or trasnverse
- cause color differences. Blue are blurrier and reds are clearer
- Sx: colored fringes around objects
- Gets worse with: higher powers, looking through the periphery of the lens
As Abbe Value increases, the chromatic aberration decreases |
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Term
| Which type of aberration is caused by peripheral rays being focused at different points on the optic axis, which affects the sharpness of the image points? |
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Definition
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Term
| Which two types of abberations is usually not a concern for ophthalmic lenses? And why? |
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Definition
Spherical and Coma
They are both controlled by the pupil size, and since our "aperature size" is small, it blocks out the marginal rays |
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Term
Which type of aberration resembles a tear drop or a comet?
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Definition
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Term
Pt is wearing a high minus lens. What type of distortion abberation are you worried about?
What about for a pt with high plus lens? |
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Definition
High minus: Barrel
- magn decreases in the periphery of the lens
- think, if you push your (-) specs closer to you, you get less minification
High Plus: Pincushion
- mag increases in the periphery
- think, if you look through a (+) lens, the further back you hold it, the more mag you get |
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Term
| What is oblique astigmatism and how do you get rid of it? |
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Definition
d/t rays striking the lens obliquely (similar effect as the lens being tilted), which induces cyl power
MUST be corrected when designing a spectacle lens
ELIMINATED by using the optimum base curve using the Tsherning ellipse/ Corrected Curve Model (which the lab does, not us) or Aspheric Lens (only works for spheres) |
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Term
| What is Curvature of Field? Is it considered in lens design? And when/how can you control it? |
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Definition
Curvature of Field = Power Errror
- d/t the fact that the effective power of the lens is different in the center vs the edge
- considered in lens design
- controlled ONLY if oblique astigmatism is permitted to exist. To minimize, use the manufacturer's recommendation of base curve |
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Term
| Which abberations are most bothersome for an opthalmic lens wearer? |
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Definition
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Term
| T or F: PAL wearers benefit from panto tilt |
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Definition
| because it moves the reading portion of the lens closer to the eye. The result is an increase in teh reading width of the lens |
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Term
| Which type of lens does not scratch, heavy, and has a n = 1.523? |
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Definition
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Term
| Which lens is light, scratches easily, n = 1.498? |
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Definition
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Term
| Which lens n=1.498, safer for kids, but has high chromatic aberrations and scratches easily? |
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Definition
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Term
| Slab off prism is used to compensate for _________, should be put on the most (+/-) lens, and base direction (up/down) placed on existing lens, causing an induced base direction (up/down) |
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Definition
| vertical imbalance, (-), down, up |
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Term
OD: +3.00
OS: -3.00
Pt is experiencing dipl and distortion. You want to reduce the amt of aniseikonia by changing BC, CT, and vertex distance. How do you accomplish this? |
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Definition
Ways to increase spectacle magnifcation (for both (+) and (-) lens
- steepen BC
- increase CT
- Vertex Dist: increase VD for a plus lens, dec VD for a minus lens
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Term
Lens Clock measures _______
Lensometer measures ______
Radioscope meaures _______ |
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Definition
nominal power
BVP
Base curve |
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