emmetropia
optical state of the eye in which parallel light enters the eye and focuses on the retina without the need for any corrective lenses or accommodation; this is the absence of refractive error and the "normal" or ideal state of the eye
ametropia
refractive error, "abnormal" optica...
emmetropia - ANSWER- optical state of the eye in which parallel light enters the
eye and focuses on the retina without the need for any corrective lenses or
accommodation; this is the absence of refractive error and the "normal" or ideal
state of the eye
ametropia - ANSWER- refractive error, "abnormal" optical state of the eye in
which parallel light rays enter the eye and focus on an area other than the retina;
this condition requires corrective lenses to produce clear retinal images
astigmatism - ANSWER- optical error in which refractive power is not uniform in
all meridians; light entering the eye is focused at two distinct focal points where
at least one focal point does not fall onto the retina
How can corneal astigmatism be measured? - ANSWER- keratometry
What are components of sphere-cylinder lens RX? - ANSWER- 1. Power
(magnitude in D) of sphere component
2. Power (magnitude of D) of cylinder component
3. Axis (orientation) of the cylinder
i.e. +2.00 -3.00 X 145
i.e. -5.00 -2.00 X 060
If one meridian is at 60 degrees, where is the other - ANSWER- 150 degrees
because 60+90=150
What are the possible values for magnitude of axis? - ANSWER- 1 degree-180
degrees
How can one determine the powers of the 2 principal meridians? - ANSWER-
Principal meridian 1=power of more (+) meridian
Principal meridian 2=sum of sphere and cylinder componenets
,Find primary and secondary meridians for this Rx.
+1.00 -2.00 X 110 - ANSWER- Principal meridian 1=+1.00D
Principal meridian 2=+1.00D + -2.00D= -1.00D
Find the primary and secondary meridians for the Rx.
-3.00 -4.50 X 010 - ANSWER- Principal meridian 1= -3.00D
Principal meridian 2= -3.00D + -4.50D= -7.50D
Find the primary and secondary meridians for this Rx.
+4.00 -6.50 X 175 - ANSWER- Principal meridian 1= +4.00D
Principal meridian 2= +4.00D - 6.50D= -2.50D
What are the 8 different types of refractive error? - ANSWER- 7 distance refractive
errors which assume that accommodation is at rest and that the eye is looking at
a distant target (optical infinity)
1 near refractive error that involves a target closer than optical infinity and may
involve accommodation
Define diopter - ANSWER- unit of measurement of the refractive power of the
lens, and is equal to the reciprocal of the focal length as measured in meters
What is the focal point of a +2.00D lens? - ANSWER- 0.5 m or 50 cm
What is the dioptric power of a lens that has a focal point of 20 cm? - ANSWER-
+5.00 D
Define spherical refractive error - ANSWER- Refractive error is uniform in all
meridians. No matter where cross-section is taken, the refractive error is the
same magnitude throughout
Define hyperopia - ANSWER- parallel light entering the eye is focused behind the
retina and requires a plus lens to converge the light to properly focus it on the
retina; eye has too much minus power
Define myopia - ANSWER- parallel light entering the eye is focused in front of the
retina and requires a minus lens to diverg the light to properly focus it on the
retina; eye has too much plus power
What kind of lens is necessary to correct for astigmatism? - ANSWER- the two
focal lengths need a lens with 2 different powers to bring the light to one single
, focal point on the retina; a sphere-o-cylinder lens (compound lens or sphere-
cylinder lens) has one power in one meridian and a different power in the other
meridian located 90 degrees away
Define principal meridians - ANSWER- two primary refractive cross sections of
astigmatic refractive error; each principal meridian has a power and orientation
from 1-180 degrees and are located 90 degrees away from each other
How can one describe amount of astigmatism? - ANSWER- magnitude in diopters
and orientations as measured by axis
What does with-the-rule astigmatism refer to? - ANSWER- prescription with an
axis closer to 180 degrees
What does against-the-rule astigmatism refer to? - ANSWER- prescription with an
axis closer to 90 degrees
What does oblique astigmatism refer to? - ANSWER- prescription that has an axis
closer to 45 degrees or 135 degrees
Describe simple hyperopia - ANSWER- one single focal point behind the retina
Describe simple myopia - ANSWER- one single focal point in front of the retina
Describe simple astigmatism - ANSWER- 2 focal points with one on the retina and
the other either behind or in front of the retina
Describe simple hyperopic astigmatism - ANSWER- 2 focal points with one on the
retina and the other behind the retina
Describe simple hyperopic astigmatism - ANSWER- 2 focal points with one on the
retina and the other behind the retina
What refractive error may this Rx be correcting for?
+1.50Ds - ANSWER- simple hyperopia
What refractive error may this Rx be correcting for?
-1.50Ds - ANSWER- simple myopia
What refractive error may this Rx be correcting for?
+1.50 -1.50 X 180 - ANSWER- simply hyperopic astigmatism
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