Keratometer Slides


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How to use a manual keratometer

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Keratometer Slides

  1. 1. Keratometer (Ophthalmometer) Review ‘ Keratometer is a trade name of Bausch & Lomb, Inc’
  2. 2. Function <ul><li>Measures the central anterior curvature of the cornea (i.e., 3 to 3.2mm zone), detecting and measuring corneal astigmatism </li></ul><ul><li>The measurement provides dioptric power of the steepest and flattest meridians, and defines its location </li></ul><ul><li>A skilled operator can detect astigmatism, irregular astigmatism, oblique astigmatism, and keratoconus </li></ul>
  3. 3. Types of Astigmatism <ul><li>Simple Astigmatism – One focal line falls on the retina (one meridian is emmetropic); the other meridian may fall in front or behind the retina </li></ul><ul><ul><li>Simple Myopic Astigmatism: Plano / -2.00 x 180 </li></ul></ul><ul><ul><li>Simple Hyperopic Astigmatism: Plano / +2.00 x 180 </li></ul></ul><ul><li>Compound Astigmatism – Both focal points lie either in front or behind the retina </li></ul><ul><ul><li>Compound Myopic Astigmatism: -1.00 / -2.00 x 180 </li></ul></ul><ul><ul><li>Compound Hyperopic Astigmatism: +2.00 / -1.00 x 180 </li></ul></ul><ul><li>Mixed Astigmatism – One focal point lies behind the retina, the other focal point lies in front of the retina </li></ul><ul><ul><li>Mixed Astigmatism: +1.00 / -2.00 x 180 </li></ul></ul>
  4. 4. Types of Astigmatism <ul><li>Irregular astigmatism – the flat and steep axes are not at right angles </li></ul><ul><ul><li>Can be due to surgery, trauma, inflammation, scar tissue, or developmental anomalies </li></ul></ul><ul><li>Oblique astigmatism – occurs along the 45˚ or 135˚ meridians </li></ul>
  5. 5. Astigmatism <ul><li>With the Rule Astigmatism: the vertical meridian has the steepest curvature </li></ul><ul><ul><li>Minus axis at 180 (within 30 degrees) </li></ul></ul><ul><ul><li>Plus axis at 090 (within 30 degrees) </li></ul></ul><ul><li>Against the Rule Astigmatism: the horizontal meridian has the steepest curvature </li></ul><ul><ul><li>Minus axis at 090 (within 30 degrees) </li></ul></ul><ul><ul><li>Plus axis at 180 (within 30 degrees) </li></ul></ul>
  6. 6. Astigmatism <ul><li>The difference between the horizontal meridian and the vertical meridian constitutes the corneal astigmatism </li></ul><ul><ul><li>45.25 @ 180 / 44.25 @ 090 = 1.00 diopter of cylinder </li></ul></ul><ul><ul><li>Plus cylinder, the axis is the axis of the higher diopter power </li></ul></ul><ul><ul><li>Minus cylinder, the axis is the axis of the lower diopter power </li></ul></ul>45.00 @ 180 / 46.50 @ 090 Difference is 1.50D Minus cylinder: -1.50 x 180 Plus cylinder: +1.50 x 090
  7. 7. Recording Measurement Values <ul><li>A common practice is to record the horizontal reading first; however, some sites will record the flattest meridian followed by the steepest meridian and its axis </li></ul><ul><li>44.00 @ 160 / 42.75 @ 070 </li></ul><ul><li>Or </li></ul><ul><li>42.75 @ 070 / 44.00 @ 160 (42.75 / 44.00 @ 160) </li></ul><ul><li>Values can be expressed in diopters or millimeters of radius (e.g., Javal-Schiötz Ophthalmometer) </li></ul><ul><ul><li>Refer to handout for Diopter to Millimeter Conversion chart </li></ul></ul>
  8. 8. Manual vs. Automated <ul><li>Manual keratometry is preferred in patients: </li></ul><ul><ul><li>With poor fixation </li></ul></ul><ul><ul><li>Corneal abnormalities </li></ul></ul><ul><ul><li>With distorted mires </li></ul></ul><ul><ul><li>When the cornea is highly toric </li></ul></ul><ul><ul><li>When the cornea is dry </li></ul></ul><ul><li>Corneal topography is preferred in patients with readings less than 40 diopters or greater than 46 diopters </li></ul>
  9. 9. Manual vs. Automated <ul><li>Some physicians prefer corneal topography over manual keratometry in patients with keratoconus, and previous corneal surgery </li></ul><ul><ul><li>Corneal topography provides readings of nearly the entire anterior corneal surface </li></ul></ul><ul><li>For automated keratometry, the validation criteria is three measurements within 0.25D in each of the principal meridians </li></ul>
  10. 10. Toric IOLs, Manual vs. Automated <ul><li>Toric Calculator </li></ul><ul><ul><li>Manual keratometry is recommended method </li></ul></ul><ul><ul><ul><li>Determines the axis and magnitude of corneal astigmatism </li></ul></ul></ul><ul><ul><ul><li>Auto-K’s and Sim-K's can be off by 10˚ resulting in a 33% reduction in the effect of the toric IOL ( </li></ul></ul></ul><ul><ul><ul><li>Automation may result in a greater number of under corrections due to angular errors ( </li></ul></ul></ul><ul><ul><li>Topography is used to verify no corneal abnormalities and astigmatism is regular </li></ul></ul><ul><li>IOL Master </li></ul><ul><ul><li>IOL Master K-readings and axial length are used to calculate IOL power </li></ul></ul><ul><ul><li>Manual K-readings used for Toric Calculator </li></ul></ul>
  11. 11. Standard Keratometry Readings <ul><li>In the average eye, keratometry readings are in the range of 43 to 44 diopters </li></ul><ul><li>When comparing to the fellow eye, keratometry readings and corneal cylinder should be within 1 diopter </li></ul><ul><ul><li>Differences should be double checked </li></ul></ul><ul><li>Keratometry readings less than 40 and more than 47 diopters are unusual and should be double checked </li></ul>
  12. 12. Keratoconus / Rating <ul><li>Keratoconus – a degenerative corneal disease resulting in a generalized thinning and cone-shaped protrusion of the central cornea, usually in both eyes </li></ul><ul><li>Mild < 45 diopters in both meridians </li></ul><ul><li>Moderate 45 – 52 diopters in both meridians </li></ul><ul><li>Advanced > 52 diopters in both meridians </li></ul><ul><li>Severe > 62 diopters in both meridians </li></ul>
  13. 13. Common Mistakes and Pointers <ul><li>The majority of errors are related to: </li></ul><ul><ul><li>Inadequate instrument calibration </li></ul></ul><ul><ul><li>Incorrect examination technique </li></ul></ul><ul><ul><ul><li>Unfocused eyepiece (can lead to an error of up to 1 diopter in the K-reading) </li></ul></ul></ul><ul><ul><ul><li>Distorted mires </li></ul></ul></ul><ul><ul><ul><li>Off-axis measurements </li></ul></ul></ul><ul><ul><li>Corneal abnormalities </li></ul></ul><ul><ul><ul><li>Irregular contour or shape of cornea </li></ul></ul></ul><ul><ul><ul><li>Inadequate or excessive tear film </li></ul></ul></ul><ul><ul><ul><li>Ointment on the cornea </li></ul></ul></ul><ul><ul><ul><li>Eyelid interference </li></ul></ul></ul>
  14. 14. Common Mistakes and Pointers <ul><ul><li>Inadequate patient fixation and/or cooperation </li></ul></ul><ul><ul><li>Examiner has uncorrected refractive error resulting in fluctuating accommodation </li></ul></ul><ul><li>Pointer: </li></ul><ul><ul><li>Keratometry should be performed prior to tonometry, pachymetry, and biometry or any other applanation testing </li></ul></ul>
  15. 15. Calibration <ul><li>Verify or properly focus eyepiece </li></ul><ul><li>Obtain and verify readings from several steel spheres of differing radii of curvature </li></ul><ul><li>Routine measurement of a bench-mark eye to verify accuracy (e.g., one individual in office with little or no corneal refractive error) </li></ul>
  16. 16. Overview
  17. 17. Overview <ul><li>Appearance of mires when they are out of focus </li></ul><ul><li>Appearance of mires when they are in focus </li></ul><ul><li>Note: The reticle is centered in the bottom right circle or focusing circle </li></ul>
  18. 18. Astigmatism: Horizontal Meridian <ul><li>Vertical misalignment of plus signs indicates astigmatism </li></ul><ul><li>Correct axis alignment when the horizontal lines of the plus appear continuous </li></ul><ul><li>Measuring the Horizontal meridian: </li></ul><ul><ul><li>Turn the horizontal measuring drum to superimpose the plus signs </li></ul></ul><ul><ul><li>Leave horizontal measuring drum in this position </li></ul></ul>
  19. 19. Astigmatism: Vertical Meridian <ul><li>Turn the right-hand vertical measuring drum until the minus signs are superimposed </li></ul><ul><li>Note: if corneal astigmatism is present, it is impossible to get both principal meridians in focus at one time </li></ul>
  20. 20. Recording the Values <ul><li>Horizontal Measuring Drum </li></ul><ul><ul><li>The power is established for the cornea in the meridians nearest to 0 - 180 degrees </li></ul></ul><ul><li>Vertical Measuring Drum </li></ul><ul><ul><li>The power is established for the cornea in the meridian nearest to 90 degrees </li></ul></ul><ul><li>The difference between these two readings is the amount of corneal astigmatism </li></ul><ul><ul><li>If they are the same, there is no measurable astigmatism </li></ul></ul>
  21. 21. Javal-Schiötz Ophthalmometer
  22. 22. Popular Brands/Models <ul><li>Reichert MK1 </li></ul><ul><ul><li> </li></ul></ul><ul><li>Bausch & Lomb </li></ul><ul><ul><li> </li></ul></ul><ul><li>Marco Keratometer I and II </li></ul><ul><ul><li> </li></ul></ul><ul><li>Topcon OM-B1 Ophthalmometer </li></ul><ul><ul><li> </li></ul></ul><ul><li>Haag-Streit AG Javal-Schiötz Ophthalmometer </li></ul><ul><ul><li> </li></ul></ul>
  23. 23. Thank You