Objective 5

Question 1

What is the normal range of the keratometer?

Answer 1

36.00 D to 52.00 D (or 9.39mm to 6.49mm)

Question 2

How much can the range of the keratometer be extended by placing a +1.25 D trial case lens over the aperture?

Answer 2

9 Diopters

Question 3

The value of the measurements taken with the keratometer or ophthalmometer can be expresses in what two units?

Answer 3

Diopters & mm of radius

Question 4

The illuminated targets of known size reflected back from the corneal surface in a keratometer or ophthalmometer are referred to as what?

Answer 4

Mires

Question 5

What does adjusting the eyepiece compensate for?

Answer 5

Operator’s refractive error

Question 6

Why should one avoid moving the eyepiece back and forth when focusing it?

Answer 6

Accommodation is stimulated, causing an erroneous focus point

Question 7

If the horizontal drum reading is flatter than the vertical drum reading, the patient is said to have what type of astigmatism?

Answer 7

With the rule astigmatism

Question 8

A -1.00 D sphere trial case lens will extend the range of the keratometer by how much?

Answer 8

6 diopters

Question 9

If a patient has a horizontal drum reading of 46.25 D and a vertical drum reading 44.75 this patient has what type of astigmatism?

Answer 9

Against the rule astigmatism

Question 10

Where should the cross hairs of most keratometers be centered?

Answer 10

Lower right circle (focusing circle)

Question 11

What is the measurement of central corneal curvature?

Answer 11

Keratometry

Question 12

When focusing the eye piece what should you be viewing?

Answer 12

White occluder or white piece of paper

Question 13

While measuring with either drum, the other hand should be constantly on the ___________ to keep the meridian being measured in sharp focus.

Answer 13

focusing knob

Question 14

If the cornea is _______, it will be impossible to get the plus and minus signs, (both principal meridians) in focus at one time. For greater accuracy, focus the plus or horizontal mires sharply then refocus for the minus or vertical readings.

Answer 14

astigmatic

Question 15

For greater accuracy on an astigmatic cornea, with the keratometer focus the _______mires sharply then refocus for the _______ readings.

Answer 15

Plus (horizontal) first then refocus for the minus (vertical)

Question 16

Rotate the drum (B) of the instrument to locate the axis. This is accomplished by positioning the _______ signs tip to tip

Answer 16

Plus

Question 17

Rotate the horizontal drum (L) on the left so that the plus signs are

Answer 17

superimposed

Question 18

If the upper minus sign is not visible, the _________ is obstructing the view.

Answer 18

patient’s upper lid, Instruct the patient to open the eye as widely as possible.

Question 19

If the image goes out of focus, ask the patient to _____.

Answer 19

blink: As the tear layer breaks up, the reflected image will become indistinct. The blink will spread a new layer of tear across the ocular surfaces and give a new crisp reflecting surface to allow for accurate measurement. Further indication of dry eye.

Question 20

The difference between the horizontal and vertical drum readings is the amount of _____________ of the eye. It is know as _________

Answer 20

Corneal astigmatism,

Delta K

Question 21

The meridian indicators of the keratometer are white lines on the instrument body facing the ______.

Answer 21

operator

Question 22

The horizontal marks on each side indicate the meridian measured on the __________.

Answer 22

horizontal Drum

Question 23

The vertical mark on top indicates the meridian measured on the __________.

Answer 23

Vertical drum

Question 24

The ________ measurement generally is recorded first

Answer 24

horizontal

Question 25

If the vertical drum reading is flatter than the horizontal drum the patient is said to have _______ astigmatism.

Answer 25

against the Rule,

Vertical is considered from 060 - 120 degrees for the purpose of this course (within 30 degrees of vertical).

Question 26

The keratometer or ophthalmometer measures only the ________, which is the central 4 or 5 millimetres of the cornea

Answer 26

corneal cap

Question 27

Corneal topographers give a very accurate image of the corneal surface in the form of a topographical map. These maps are colour coded to indicate areas of steepening and flattening. Generally, the ____ colours are the flatter areas and the _____ colours are the steeper areas.

Answer 27

Cool (flatter)

Warmer (steeper)