Keratometry & Togography: Corneal Measurements Flashcards
An early investigator that studied the curvature of the cornea was
A. Placido
B. Helmholtz
C. Javal
D. All of the Above
All of the Above
The doubling device of the keratometer is necessary due to
A. Poor fixation of the eye
B. Fine tremor of the eye
C. Vertex Distance
D. The transitional zone of the cornea
Fine tremor of the eye
The index of refraction used to calibrate the keratometer is
A. 1.3375
B. 4.215
C. 1.49
D. 1.51
1.3375
The size of the mire (target) on the front of the keratometer is
A. 40.0 mm
B. 32.6 mm
C. 337.0 mm
D. 64.0 mm
64.0 mm
The distance from the front of the keratometer to the front of the cornea when the instrument is in focus is
A. 40.0 mm
B. 64.0 mm
C. 75.0 mm
D. 32.0 mm
75.0 mm
The eyepiece of the keratometer should be focused
A. Daily
B. Every Other Day
C. Weekly
D. Monthly
Daily
The keratometer derives its measurements of a meridian from how many points on the cornea?
A. 2
B. 4
C. 6
D. 8
2
The range of curvatures the keratometer can measure without auxiliary lens is
A. 26.00 D - 50.00 D
B. 36.00 D - 52.00 D
C. 40.00 D - 42.00 D
D. 45.00 D - 60.00 D
36.00 D - 52.00 D
The chord length of the more measured by the keratometer without auxiliary lens is
(Hint: convert mm to diopters)
A. 3.8mm - 1.4mm
B. 2.8mm - 1.8mm
C. 3.8mm - 2.6mm
D. 4.8mm - 3.2mm
3.8mm - 2.6mm
The keratometer eyepiece if not properly focused can cause
A. Distortion of the mire
B. Cylinder to be introduced
C. The image of the mire to disappear
D. Errors in correctly reading curvature
Errors in correctly reading curvature
In addition to measuring the cornea, the keratometer can be used to
A. Check the power of a contact lens
B. Check the curvature of a contact lens
C. Check the thickness of a contact lens
D. Check the diameter of a contact lens
Check the curvature of a contact lens
Steeper curvatures than normally readable with the keratometer can be taken by adding to the front of the instrument a
A. +10.00 trial lens
B. -10.00 trial lens
C. +1.25 trial lens
D. -1.00 trial lens
+1.25 trial lens
When classic keratometry is performed by having the patient sight on the mirrored image of their eye, alignment of what is accomplished?
A. The apex with the visual axis
B. The optical axis with the apex
C. The optical axis with the visual axis
D. The posterior axis with the primary axis
The optical axis with the visual axis
If the whole mire is reflected from the apex
A. The reading is accurate
B. The reading in undependable
C. No reading is possible
D. The reading will be too flat
The reading is accurate
When a part of the mire is reflected from the transitional zone
A. An accurate reading is taken
B. An inaccurate reading is taken
C. No reading is possible
D. The mire image will be too small
An inaccurate reading is taken
Errors in keratometry occur
A. Very seldom
B. in 75% of images
C. In keratoconus and irregular astigmatism
D. In reading ball bearings
In keratoconus and irregular astigmatism
When the keratometer is properly aligned in front of an eye, the patient will see
A. The operator’s eye
B. A green light
C. The eye occluder
D. The horizontal measuring drum
A green light
The axis of corneal astigmatism when taking a “K” reading
A. Is unimportant
B. Is the las thing to align
C. Is the first thing to align
D. Cannon be found on high degrees of astigmatism
Is the first thing to align
The amount of corneal astigmatism
A. Cannot be measured with the keratometer
B. Is the difference between the reading on the horizontal and vertical drums
C. Is calculated by multiplying the axis times the horizontal drum reading
D. Is calculated by multiplying the axis times the vertical drum
Is the difference between the reading on the horizontal and vertical drums
When measuring the horizontal meridian with the keratometer
A. The minus mires are superimposed
B. The black central focusing cross hair should be in the left hand circle
C. The plus mires will be in the vertical meridian
D. The plus mires are superimposed
The Plus mires are superimposed
