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23 Cards in this Set
- Front
- Back
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What is Keratometry?
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Measures the curvature of the
cornea at four points located at approximately the 3mm optic zone along two perpendicular meridians. One pair of points is aligned along the steepest axis of the corneal surface, with the second pair 90 degrees away. |
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What is Keratometry?
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^Measures the curvature of the
cornea at four points located at approximately the 3mm optic zone along two perpendicular meridians. One pair of points i s aligned along the steepest axis of the corneal surface, with the second palr 90 degrees away. |
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What is Topography?
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^Measures 6000 to
8000 points on the cornea surface from Inside the 1mm . optic zone to the 9mm optic Zone. ^Provides a complete Color coded representation of the comea's shape |
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Topography
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^Provides ability to monitor corneal
curvature changes from the apex to the periphery |
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REFRACTIVE POWER OF EYE
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^The anterior tear film surface of the cornea provides most of the
refractive power of the eye. ^Approximately 75 % of the overall focusing of the normal adult eye is provided by this air / tear film interface on the cornea |
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BENEFITS OF TOPOGRAPHY
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^Allows us to measure refractive
power across the corneal surface ^Allows us to follow corneal shape changes induced by coneal pathology and surgery. ^Give us a greater understanding of the refractive complaints of the patient. |
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Topography Basic Design Features
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Based on the concept developed in 1880 by A. Placdo. Using a planar concentric ring target with alternating black and white rings In front of a patients eye and observing the shape of the rings In the virtual image of that target created from the reflection off the patients cornea.
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^ Uses a video camera to
visualize the virtual image ^Analyzes the data ^Displays the data in a variety of useful formats |
Modern Topography Instruments
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Spherical Vs Astigmatic
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If the cornea is spherical, the rings appear circular and concentric.
^Deviations of the cornea will give distortions in Graphc or concentrlcity of the rings. |
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PATIENT POSITIONING
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^The working distance for
topography can be 2cm to 8cm from the eye. Instructions need to be given to the patient regarding the proximity of the instrument to the eye, the need for the patient to blink hold very still and open eye wide. |
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tell Pt. no air will be blown into their face
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tell Pt. no air will be blown into their face
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TOPOGRAPHY CONSIDERATIONS
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^The tear film generates the reflected
lmage captured by the video camera. This film smooths surface irregularities. Poor tear film produces poor topography readings. ^Corneal coverage depends on the Individual topographic system. Larger is usually better |
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TOPOGRAPHY CONSIDERATIONS
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^The tear film generates the reflected
lmage captured by the video camera. This film smooths surface irregularities. Poor tear film produces poor topography readings. ^Corneal coverage depends on the Individual topographic system. Larger is usually better ls usually better. |
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CALIBRATION
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Should b e performed carefully if
accurate in formation is to be obtained in topography. . Follow the manual instructions for your individual unit |
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MORE CONSIDERATIONS
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Edged etecflonr, eferst o the abilityt o
center a spedfic polnt on or within a ring that can be retsrened b or calibrated om. The instrument lll ask )or.r to center the cross it is not sure where the center is located. |
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MORE CONSIDERATIONS
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Edge d etecflon r efers t o the ability t o
center a specific point on or within a ring that can be refrenced to or calanhted fr om. The Instrument will ask yor to center the cross if it ls not sure where the center is located. |
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SCALING
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Refers to how the topographic
information is displayed.For most systems the data is on a isodioptric color coded display. |
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CLINICAL USES
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Primary importance in
Keratoconus. . Irregular cornea surfaces. . Elevated lesions of the cornea. . Refractive surgery. Margie V. Wilson |
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COLORS AND WHAT THEY MEAN
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Red, orange and yellow:
Steep Green, blue and purple: Flatter |
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6000 to 8000
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keratometry measures four polnts
located at the 3mm optic zone. How many p olnts does topography measure? |
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Keratometry is useful for measuring
healthy corneas. For which conditions of the cornea ls Topography useful? |
Keratoconus, irregular corneal surfaces,
and elevated lesions of cornea. |
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Scaling
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Scaling refers to how the info. is displayed. For most
systems the data is on a isodioptric color coded display. . |
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1) focus eyepiece (EP)
2) Position Pt. 3) Find the Mires (3 circles) 4) Focus 5) : "Target" in lower R Circle 6) Lock (finger tight) 7) Align Axis 8 ) Horizontal 9) Vertical 10) |
1. Turn dial counterclockwise first
2. have Pt. lean into chin and headrest 3. Look down "tube" or "tunnel". "Stay very still. Keep teeth together". 4. Focus, Focus, Focus (if blinking) 5.If Pt. blinks: re-focus 6. Just finger tight 7. (Diagram B rotating grip) 8.( + ) 9.( - ) "Good job, good job, blink" (MNUS becomes one & toggle 10. As per MD's and clinic's style |
