Term
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Definition
the unit of measurement of divergence or convergence of light rays
1 diopter of power of a lens system converges parallel light rays to a focus at 1 meter from the from the lens system |
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Term
| lens power and focal length |
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Definition
power of lens (in diopters) = 1 / focal length
3 diopter lens focus at a distance of 1/3 meters |
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Term
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Definition
power of entire eye = 61D
intraocular lens = +16 diopters
cornea = +45 diopters |
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Term
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Definition
the intraocular lens has a variable power because it can change shape
changes in lens shape can increase power with convergence as the lens becomes more spherical |
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Term
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Definition
the ability of the lens to change its shape
change in lens shape to increase lens power |
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Term
| why is accommodation necessary? |
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Definition
when objects are brought in closer, change in focus is necessary to see the image clearly - thus, need to increase power to change the focal length
helps see items from far and close with only a short time in between
needed for reading/up close work |
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Term
| mechanism of accommodation |
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Definition
input: burred image --> CNII/optic nerve --> brain
output: CNIII --> accommodation
accommodation
^
lens becomes more spherical
^
loosening of zonules that insert into the lens
^
contraction of ciliary body muscle
^
CNIII/oculomotor nerve |
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Term
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Definition
the deviation of light rays in passing through media of differing densities and surface curvature
cornea and lens contribute the most to this |
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Term
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Definition
focusing problems that can be corrected with glasses, contact lenses, or refractive surgery
occurs when the image is not focused on the retina
most common (and treatable!) causes of visual impairment |
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Term
| types of refractive disorders |
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Definition
emmetropia
myopia
hyperopia
astigmatism
presbyopia |
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Term
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Definition
the eye with the lens at "rest" converges parallel rays of light to focus on the retina
clear distance vision without ant refractive error |
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Term
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Definition
nearsightedness
too much focusing power causes image to be focused in FRONT of the retina, not on it
blurry distance vision
combo of a powerful lens system and long eyeball (increased axial length) |
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Term
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Definition
congenital, developmental, meds, trauma, age (cataracts)
DM can increase risk - lens can absorb glucose when level are high and cause transient myopia |
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Term
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Definition
| accommodation will NOT help myopia because it will further increase the power and focus the image even further in front of the retina |
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Term
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Definition
nee to bring the object closer to the eye
minus lenses (concave) will focus the image further away so it lands on the retina |
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Term
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Definition
farsightedness
eye is short and/or the cornea is flat
not enough focusing power, light focused BEHIND the retina
blurry near vision
increasing difficulty with age |
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Term
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Definition
| congenital, developmental, trauma, orbital tumor, meds (anticholinergics) |
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Term
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Definition
the hyperope accommodates to focus rays on the retina
YES, it helps because accommodating will increase the overall dioptic power |
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Term
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Definition
| positive lenses (convex() |
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Term
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Definition
uneven corneal curvature (more football, less basketball shaped) blurry distance and near vision because light is converged to more than one focal area inside the eye
one meridian of cornea is steeper than the other
can be present with either hyperopia or myopia |
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Term
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Definition
(much less common)
lens converges parallel rays of light to more than one focal area inside the eye |
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Term
| accommodation and astigmatism |
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Definition
| accommodation will NOT help because there will still be multiple points of focus |
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Term
| management of astigmatism |
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Definition
correction of astigmatism requires lenses that have multiple powers in different planes
can have plus or minus lens |
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Term
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Definition
loss of accommodation with time/age
reading (near) vision affected around age 40
decrease in ability to converge due to increased lens thickness and loss of lens elasticity with age |
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Term
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Definition
normal reading distance is about 14 inches (1/3 meter)
accommodation needed for read is about 3 diopters |
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Term
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Definition
need more diopters of power to read
can be accomplished with bifocal lenses |
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Term
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Definition
don't need accommodation to see better
can just remove glasses (or wear bifocals)
not affected as must as hyperopes |
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Term
| goals of refractive surgery |
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Definition
reduce dependency on glasses or contact lenses
improve eye's natural focus by altering shape of the cornea or placement of an intraocular lens |
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Term
| goals of surgery for specific refractive disorders |
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Definition
myopia: flatten cornea to reduce power
hyperopia: steepen cornea to increase power
astigmatism: reshape uneven curves of cornea to make it even, improve overall lens system power |
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Term
| refractive surgery complications |
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Definition
(uncommon)
under/overcorrection
glare/halo
dry eyes
lamellar keratitis (inflamed cornea)
scarring
loss of best corrected vision |
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Term
| refractive surgery outcomes |
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Definition
may need enhancement surgery
reading glasses may still be necessary
may still need glasses or contact lenses to achieve best vision after surgery |
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Term
| contact lens wearer limitations |
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Definition
not everyone who wears glasses can wear contact lenses
astigmatism
tear film abnormalities
increased corneal sensitivity
age |
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Term
| contact lens complications |
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Definition
| can result on loss of vision due to infection, edema, scarring, and warpage |
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Term
| danger signs with contact lens wear |
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Definition
spectacle blur-edema - ischemia to cornea
cornel scarring/warping
-fs glasses look blurry: you've fundamentally altered the cornea (temporarily)
corneal vascularization, papillary conunctivitis
corneal infections |
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