Keratometer Slides

  • 42,980 views
Uploaded on

How to use a manual keratometer

How to use a manual keratometer

  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
No Downloads

Views

Total Views
42,980
On Slideshare
0
From Embeds
0
Number of Embeds
6

Actions

Shares
Downloads
0
Comments
6
Likes
32

Embeds 0

No embeds

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
    No notes for slide

Transcript

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