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30 Cards in this Set
- Front
- Back
- 3rd side (hint)
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invaluable uses of
Keratometry .regular Astigmatism . Asymmetric Astigmatism . Oblique Astigmatism ETC...... |
invaluable uses of
Keratometry .regular Astigmatism . Asymmetric Astigmatism . Oblique Astigmatism . Conical astigmatism Nystagmus |
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Styles of Kerotometers
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Bausch&Lomb
-manual Alcon Systems hand-held automated Humphrey auto-refractor/Keratometer automated keratometry using infra-red rays or xenon light to measure the corneal cap zone |
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Principals of
Keratometry |
If an object of a specific size is
illuminated at a fixed distance from a mirror, we can calculate the radius of curvature of the mirror from the size of the reflected image from the illuminated object |
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K
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Uses the cornea as a mirror~
The visual axis is aligned along the optical axis of the instrument so the central front surface of the cornea reflects the mires in the Keratometer. |
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MIRES=:
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illuminated target projected
on cornea ( one circle split with prism to three) |
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Against the Rule
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steepest meridian
horizontal |
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With the Rule
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Steepest meridian vertical
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Clear: added to the end of the K reading to indicate a good K -reading
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Clear: added to the end of the K reading to indicate a good K -reading
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Distorted/ difficult: added to K- reading if corneal surface is irregular
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Distorted/ difficult: added to K- reading if corneal surface is irregular
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CLEAR added to K- reading if corneal surface is GOOD
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CLEAR added to K- reading if corneal surface is GOOD
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back radius of contact lens is same radius as K-reading
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Fitting on K:
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Fitting steeper or flatter than K:
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look up
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Each mark on the
vertical and horizontal dial represent |
.125
or 1/8 of a dioptor |
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Reading K - reading Dials:
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number is usually
rounded out to Read: .25, .50, .75 etc but usually recorded using.12 for first reading following whole number .25, .50, .75 example: 44.12, 44.37, 44.62 and 44.87 |
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Recording Flat-K First
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Record flattest (smallest) K readirg first with the steeper to follow, axis on the steepest
42.37 / 43.50 X 90 41.00/ 41.50X 135 44.87/ 45.00X 180 (Ms.Margie prefers) 42.12/ 44.37 X65 |
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Recording Horizontal
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Recording the horizontal reading first, regardless of which is the "flattest"
44.00/ 4 3.00X 180 42.37/ 40.12X137 46.50/ 42.00X90 41.00| 42.50X165 |
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Recording both Axis
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You can also record both the
horizontal and the vertical with the axis of each one: 44.00X 90 / 45.00X 18 42.50X135| 44.37X 45 |
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Average K -Reading
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44.00 diopters is the average corneal
curvature Steep curvatures > 4 8.00 D associated with myopia Flat curvatures < 4 0.00 D associated with hyperopia |
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Keratometer Maintanance
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Change the bulb by removing the two
screws from the lower part of the lamp housing |
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CALIBRATION (if out of alignment it MUST be trained prof. personnel that fix it)
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Attachment consists of three test
ball bearings with specific radii (40.50D, 42.50D and 44.75D), When the correct radius of curvature of the test ball is obtained the accuracy of the kerotameter can be confirmed. |
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Uses for K-Readings
1) |
Corneal curvature following
cataract surgery when the IOL reflection make retinoscopy difficult. Gives the base line refraction. |
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Uses for K-Reodings
2) |
For contact lens fitting
Dioptor to Millimeter conversion 43.75D = 7.72mm 42.00 D = 8.04 mm 10.00D : 8.44mm 47:15 D = 7.07 mm 46.00 D : 7.34 mm |
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Uses for K-Readings
3) 4) 5) |
3)Difficult refractions
4) diagnosis of Keratoconus 5) For acccurate corneal curvature i n the determination of an IOL implant power Limitations |
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Limitations
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Only able to measure the 3mm optic
zone |
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Limitations
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Kerotometricr ranges> 36.00D & <52.00 D
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LIMITATIONS
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Must use conversion table & use
additionl lenses: > 52.00 D (+1.25) < 36.00 D (-100) assumes symmetry of the flat and steep axis of cornea (topography can check more accurately) |
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Some helpful hints....
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Always adjust your eye Piece
With significant astigmatism, mires appear oval rather than circular. Encourage blinking a, wet cornea measures more easily Artificial tears helpful. Ask patient to blink, open wide, don't move! |
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Some MORE helpful hints....
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Discourage head movement. Talking
patients are impossible! . One hand on the focus knob at all times! . Occlude opposite eye, excep when Pt.... - When other eye is Poor sighted - When an ocular muscle deviation is present |
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1. Eyepiece Focusing
2. Instruct/Inform and Positioning of Patient :Silent/Still/Wet,Wet/Blink open wide 3. Leveling/position the Keratometer 4. Fixation Alignment 5.Mires Focusing 6.Drum Adjustment 7. Cylinder Axis Location 8. Horizontal (principal)Meridian Measurement Plus Signs superimposed 9. Vertical meridian Measurement Superimposing the minus signs Toggle/Toggle 10. Record Results +/- knob(diopter)/drum(meridian) 11. Repeat 4-9 for OS 12. Demonstrate bulb replacement |
~Focus eyepiece
~Instruct/ position Pt. ~Position Keratometer ~Adjust mires a.Focus mires b.Rotate drum c.Superimpose plus + d.Superimpose minus- ~Recording results a. horizontal knob (diopter) record b. horizontal drum (meridian) record c. vertical knob (diopter) record d. vertical drum (meridian) record |
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Pt.'s eyeglasses RX and current spect
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1.Are you satisfied with these glasses?(DV and NV)
2.Do you see well with the glasses; do you see better without the glasses? 3.Do your eyes feel comfortable with this pair or do you experience eye strain, blurry vision, fatigue, double vision, a sensation of pulling, or headaches? 4.Are you able to see/read what you need to at a particular required distance; for instance the computer distance (20 inches), the blackboard, driving, small print? 5. Can you read for extended periods of time? 6. After K-reading and Refraction...remark this is your old RX; and this is your new RX Ask: Is this pending change worth $200 bucks? |
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