Lecture 6 & 7- Ret through a Manual Phoropter Flashcards
The ret. result needed with a minus cylinder phoropter before cylinder can be introduced in: ____ in one meridian and ____ in the second meridian
neutral; against
____ measures the curvature of the central ____ cornea in about the center 3 mm of the cornea and determines its contribution to the total refractive power. Curvature of the cornea accounts for ___ ___ of the eyes refracting power
Keratometry; anterior; two thirds
what is keratometry useful for
- used in the fitting of contacts to determine the base curve needed on the back of the contact lens
- useful for identifying patients with keratoconus
- useful for determining the quality of the tear film and the integrity of the anterior central corneal surface.
data on the keratometer is usually expressed in ____ even though the instrument does not actually measure refractive power. It really measures the _____ of curvature for a small portion of the central cornea
diopters; radius of curvature
On the keratometer. The first line after the big line would be .12, then .25, then ____, then. .50, ___, .75 and lastly _____You want to get down to the nearest eighth.
.37; .62; .87
The steeper the radius of curvature, the diopter value ______, the flatter the radius of curvature, the D value ____
increases; decreases
the corneal refractive index is 1.376 but we use _____
1.3375
the keratometer provides both quantitative and ____ data
qualitiative
what shape is the cornea?
prolate (flattening)ellipsoid; the true apical radius is slightly steeper than the measured value; about 0.25 D steeper.
the normal range of measurement for a keratometer is from ____ to ____. In keratoconus, the cornea is often steeper than 52.00
36.00; 52.00
If cornea is too steep, extend the range of the keratometer by taping a _____ trial lends over the keratometer and afterwards multiply the diopteric reading by ____
+1.25; 1.1659
If the cornea is too flat, tape a ____trial lens over the keratometer and measure the corneal curvature and multiply the reading by _____
0.8576
for a contact lens fitting, normal K’s are _____. Patients with K’s of 48.00 more likely have ____. Patients with K’s of 40.00 most likely have _____.
44.00; myopia; hyperopia
what is the use of keratometer data
- determining the amount of corneal astigmatism
- determining the refractive astigmatism.
- javal’s rule
In WTR astigmatism, the ____ principal meridian is horizontal. In ATR astigmatism, the flatter principal meridian is ___
flatter; vertical
in oblique astigmatism, the flatter principal meridian is +/- ____ degrees of the 045 or 135 meridians
15
Javal’s rule is useful when a patient has high astigmatism and is difficult to refract. It allows an estimate of both the ___ axis and ____ based upon the keratometry data. The avg patient has ____ D of against the rule astigmatism inside the lens of eye.
cylinder; power; 0.50
For Javals rule when we have WTR astigmatism, we would ____0.50 for the internal ATR astigmatism. For ATR astigmatism, we would ____ 0.50
subtract; add
If vertical meridian is steeper, it has a _____ radius of curvature
shorter
If the corneas have similar K’s, the aniso is secondary to ____ length
axial
If the corneas have different K’s, the aniso is secondary to a _____ etiology
refractive
