OL 4 Flashcards
describe myopia
image is focussed in front of the retina
blur circle is imaged on the retina
corrected with a negative lens of the same power in all meridians i.e a spherical lens
describe hyperopia
The image is focussed in behind the retina
A blur circle is imaged on the retina
Corrected with a positive lens of the same power in all meridians, i.e. a spherical lens
how can a hyperope form a clear image
by accommodating, a hyperope can bring the focus back onto the retina resulting I a clear image
describe the foci in astigmatism and blur circle
In astigmatism two foci are produced.
An elliptical blur circle is imaged on the retina
describe the image seen by an astigmatic patient
the image appears distorted
whats the term given to the midway point between the two foci that produce a blur circle in astigmatism
circle of least confusion
how can u correct astigmatism
a cylindrical lens
describe a cylindrical lens (include surfaces and any powers they may have)
Meridian AA’ is a plane surface and therefore, has no dioptric power (afocal)
- Meridian BB’ has a plano convex surface and therefore, has positive dioptric power
- Any intermediate meridian has an elliptical surface and therefore, dioptric power
- The meridian of no power is called the cylinder axis (AA’)
- The meridian of maximum dioptric power is called the power meridian (BB’)
draw stick diagram for the following:
a) +5.25DS/-3.25DC x80
b) +2.25DS/ -8.25DC x30
c) +2.00DS/ +3.25DC x 170
d) -6.00DS/ +8.25DC x120
a) +5.25D and 80, +2.00D and 170
b) +2.25D and 30, -6.00D and 120
c) +2.00D and 170, 5.25D and 80
d) +2.25D and 30, -6.00D and 120
Transpose the following:
a) +3.00 DS / -2.00 DC x 25
b) -2.00 DS / +2.00 DC x 160
c) -4.00 DS / -4.00 DC x 85
a) +1.00 DS / +2.00 DC x 115
b) plano / -2.00 DC x 70
c) -8.00 DS / +4.00 DC x 175
