Shared Flashcard Set

Details

11/15 Optical Disorders
Neuro
34
Medical
Graduate
11/17/2011

Additional Medical Flashcards

 


 

Cards

Term
diopter
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
Term
lens power and focal length
Definition
power of lens (in diopters) = 1 / focal length

3 diopter lens focus at a distance of 1/3 meters
Term
ocular lens system power
Definition
power of entire eye = 61D

intraocular lens = +16 diopters

cornea = +45 diopters
Term
visual optics
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
Term
accommodation
Definition
the ability of the lens to change its shape

change in lens shape to increase lens power
Term
why is accommodation necessary?
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
Term
mechanism of accommodation
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
Term
refraction
Definition
the deviation of light rays in passing through media of differing densities and surface curvature

cornea and lens contribute the most to this
Term
refractive disorders
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
Term
types of refractive disorders
Definition
emmetropia

myopia

hyperopia

astigmatism

presbyopia
Term
emmetropia
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
Term
myopia
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)
Term
etiology of myopia
Definition
congenital, developmental, meds, trauma, age (cataracts)

DM can increase risk - lens can absorb glucose when level are high and cause transient myopia
Term
accommodation and myopia
Definition
accommodation will NOT help myopia because it will further increase the power and focus the image even further in front of the retina
Term
management of myopia
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
Term
hyperopia
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
Term
etiology of hyperopia
Definition
congenital, developmental, trauma, orbital tumor, meds (anticholinergics)
Term
accommodation and myopia
Definition
the hyperope accommodates to focus rays on the retina

YES, it helps because accommodating will increase the overall dioptic power
Term
management of hyperopia
Definition
positive lenses (convex()
Term
astigmatism
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
Term
lenticular astigmatism
Definition
(much less common)

lens converges parallel rays of light to more than one focal area inside the eye
Term
accommodation and astigmatism
Definition
accommodation will NOT help because there will still be multiple points of focus
Term
management of astigmatism
Definition
correction of astigmatism requires lenses that have multiple powers in different planes

can have plus or minus lens
Term
presbyopia
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
Term
reading
Definition
normal reading distance is about 14 inches (1/3 meter)

accommodation needed for read is about 3 diopters
Term
presbyopia and hyperopia
Definition
need more diopters of power to read

can be accomplished with bifocal lenses
Term
presbyopia and myopia
Definition
don't need accommodation to see better

can just remove glasses (or wear bifocals)

not affected as must as hyperopes
Term
goals of refractive surgery
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
Term
goals of surgery for specific refractive disorders
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
Term
refractive surgery complications
Definition
(uncommon)

under/overcorrection

glare/halo

dry eyes

lamellar keratitis (inflamed cornea)

scarring

loss of best corrected vision
Term
refractive surgery outcomes
Definition
may need enhancement surgery

reading glasses may still be necessary

may still need glasses or contact lenses to achieve best vision after surgery
Term
contact lens wearer limitations
Definition
not everyone who wears glasses can wear contact lenses

astigmatism
tear film abnormalities
increased corneal sensitivity
age
Term
contact lens complications
Definition
can result on loss of vision due to infection, edema, scarring, and warpage
Term
danger signs with contact lens wear
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
Supporting users have an ad free experience!