Objective 5 Flashcards
What is the normal range of the keratometer?
36.00 D to 52.00 D (or 9.39mm to 6.49mm)
How much can the range of the keratometer be extended by placing a +1.25 D trial case lens over the aperture?
9 Diopters
The value of the measurements taken with the keratometer or ophthalmometer can be expresses in what two units?
Diopters & mm of radius
The illuminated targets of known size reflected back from the corneal surface in a keratometer or ophthalmometer are referred to as what?
Mires
What does adjusting the eyepiece compensate for?
Operator’s refractive error
Why should one avoid moving the eyepiece back and forth when focusing it?
Accommodation is stimulated, causing an erroneous focus point
If the horizontal drum reading is flatter than the vertical drum reading, the patient is said to have what type of astigmatism?
With the rule astigmatism
A -1.00 D sphere trial case lens will extend the range of the keratometer by how much?
6 diopters
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?
Against the rule astigmatism
Where should the cross hairs of most keratometers be centered?
Lower right circle (focusing circle)
What is the measurement of central corneal curvature?
Keratometry
When focusing the eye piece what should you be viewing?
White occluder or white piece of paper
While measuring with either drum, the other hand should be constantly on the ___________ to keep the meridian being measured in sharp focus.
focusing knob
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.
astigmatic
For greater accuracy on an astigmatic cornea, with the keratometer focus the _______mires sharply then refocus for the _______ readings.
Plus (horizontal) first then refocus for the minus (vertical)
Rotate the drum (B) of the instrument to locate the axis. This is accomplished by positioning the _______ signs tip to tip
Plus
Rotate the horizontal drum (L) on the left so that the plus signs are
superimposed
If the upper minus sign is not visible, the _________ is obstructing the view.
patient’s upper lid, Instruct the patient to open the eye as widely as possible.
If the image goes out of focus, ask the patient to _____.
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.
The difference between the horizontal and vertical drum readings is the amount of _____________ of the eye. It is know as _________
Corneal astigmatism,
Delta K
The meridian indicators of the keratometer are white lines on the instrument body facing the ______.
operator
The horizontal marks on each side indicate the meridian measured on the __________.
horizontal Drum
The vertical mark on top indicates the meridian measured on the __________.
Vertical drum
The ________ measurement generally is recorded first
horizontal
