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Science
Medicine
Optometry
refractive correction (midterm 2)
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Terms in this set (22)
causes of myopia
1) eye power too strong
2) axial length too long - longer than focal length (retina)
causes of hyperopia
1) eye power too weak
20 axial length too short - shorter than the focal length (retina)
an eye that has spheocylindical optics
spehrocylinder lenses are used to correct
astigmatism
astigmatism classified by what three things
1) location of conoid
2) axis orientation
3) type
position of near and far lines relative to the retina determines the name of refractive error
conoid location
compound means
more than one meridian out of focus
compound hyperopic astigmatism (CHA)
+/+
both meridians need plus lens power correction
retina in FRONT of near and far line
simple hyperopic astigmatism (SHA)
one meridian emmetropic and the other is hyperopic
mixed astigmatism (MA)
eye is neither hyperopic now myopic - just mixed astigmatism
retina between near and far line
Simple myopic astigmatism (SMA)
The refractive condition where one point of focus falls on the retina and the other point of focus falls in front of the retina.
compound myopic astigmatism
The refractive error which results in two points of focus falling in front of the retina.
with-the-rule astigmatism
F1 @ 180
- horizontal eye meridian LESS plus power
- also +/- 30 degree of 180
- most common
corrected with: MINUS cylinder x 180
- +/- 30 degrees
- between 0 degree and 30 degrees
- between 180 degree and 150 degree
against-the-rule astigmatism
F1 @ 90
VERTICAL eye meridian less plus power
also +/- 3o of 090 Degrees (060 - 120)
corrected with: MINUS cylinder x 090
-060 - 120
oblique axis astigmatism
F1 (less plus) meridian is NOT in range of either with the rule astigmatism (WTR) or against the rule astigmatism (ATR)
there are two astigmatism types
T/F
true
regular astigmatism
major meridians are 90 degrees apart
symmetry on each side of major meridians
irregular astigmatism
- major meridians AREN'T 90 degrees apart, and/or
- asymmetry on each side of major meridians
ocular refraction definition
the incoming vergence change needed to produce a point image on the retina
retinoscopy procedure (plano mode)
- fog patient (against all meridians)
- change sphere until axis meridian neutral
- add minus cylinder until opposite meridian neutral
SEQ (spherical equivalent)
- average of the two meridians
- SEQ lens will put COLC on retina ( near line front of retina, COLC on retina, far line behind retina)
* note: astigmatism isn't corrected
* commonly used for low-cyl patients (0.5 D or 0.75 D)
minus cylinder only moves
near line
lines get _______ as sturm's interval decreases
shorter
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