Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Keratometry
Dr. Karan Bhatia
Senior Resident
AEH, Pondicherry
Keratometry (Ophthalmometry)
• Kerato = Cornea
• Metry = Measurement
Zones of the Cornea
• Central Zone (apical zone/corneal
cap/central spherical zone) – 4 mm,
radius of curvature does not v...
What is Keratometry ???
Measurement of the anterior surface of the cornea,
across a fixed chord length, usually 2-3 mm,
wh...
Uses of Keratometry
• Measurement of corneal astigmatism.
• Estimate radius of curvature of cornea  helps in contact lens...
Uses of Keratometry
• IOL Power calculation (Pre-op Cataract Surgery workup).
• Pre & post surgical astigmatism.
• D/D of ...
Principle
• Anterior surface of cornea –
CONVEX MIRROR
• ↑ Curvature – ↓ Image Size.
• From Image Size formed by
anterior ...
Principle
Therefore ,
B’P/A’B’ = BP/AB
F/i = u/o
r/2 i = u/o ( since F = r/2)
r = 2 ui/o
A
B
Q
S
A’
B’P
u (BP)  constant ...
Relationship b/w Radius of curvature and
Diopteric Power of cornea
D = n-1/r
r=1.3375-1/D mm
D – Dioptric power of cornea
...
Doubling Principle
Miniature involuntary
eye movements during
fixation of eye
Image formed by
anterior surface of
cornea a...
Doubling Principle
Biprism
2 images
Move equally as eye moves
Depending on the position of prism – if distance↓, doubling ↑
Keratometers
Fixed Doubling
• Bausch and Lomb, Topcon &
Mognon
• Variable – Image size & mire
separation.
• Fixed – Object...
Keratometers
One position Keratometer
• Double images are produced side
by side as well as at 90º from each
other.
• The p...
Keratometers
Ziess Oberkochen Keratometer
Keratometers
Humphrey Keratometer Javal Schiotz Keratometer
Keratometers
Bausch & Lomb Keratometer
OCCLUDER
FOREHEAD REST
ASSEMBLY
CHIN REST
LAMP ASSEMBLY
SIGHTING POST
AXIS ASSEMBLY
EYEPIECE
ROTATING GRIP
ELEVATION ASSEM...
FOREHEAD
REST
KNOB
FOCUSING
KNOB
LOCKING
KNOB
VERTICAL
MEASURING
DRUM
HORIZONTAL
MEASURING
DRUM
CHINREST
KNOB
ELEVATION
KN...
Caliberation
• Should be done regularly to ensure the accuracy of “K” readings
• Mount a 5/8 inch steel ball bearing at th...
Preparation
• Focus the eyepiece of the keratometer
for the examiner’s eye
• Set the adjustable eyepiece as far
counter-cl...
Preparation – Adjust
instrument for patient
• Adjust height of patient’s chair & instrument to a
comfortable position for ...
Procedure – Instruct patient
• Keep eyes open wide and blink
normally.
• Try not to move the head nor speak.
• Look at the...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Procedure
• Look into the keratometer and refine the
alignment of the image of the mires (three
circles) on the patient’s ...
Oblique Astigmatism
2 + signs will not be
aligned
Entire optical instrument
is rotated till the two plus
signs are aligned
• A scale associated with it indicates in
degrees, one meridian of oblique
astigmatism.
• Corneal radius of power is then
...
Astimatism
• Irregular: principal meridians are not perpendicular to each other
• Produce distorted mires
• Regular: princ...
Bausch & Lomb Keratometer
• Range – 36.00 to 52.00 D
• Normal values – 44.00 to 45.00 D
• To increase the range – Place +1...
Automated Keratometers
• Focuses the reflected corneal image on to an
electronic photosensitive device,which
intantly reco...
Surgical Keratometer
• Attached to operating microscope.
• Helpful in monitoring the astigmatism during Corneal
surgery.
•...
ProblemsSolutions
• Unable to locate keratometric mires  instrument and/or patient not aligned
properly.
• Transient Mir...
Limitations of Keratometry
• Measures refractive status of a very small central area of cornea (3 mm), ignoring
the periph...
“You can't invent Google, Facebook or the
iPod
unless
you've mastered the basics.”
-- Amy Chua
ThankyouAcknowledgements – ...
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Keratometry
Upcoming SlideShare
Loading in …5
×
Upcoming SlideShare
Keratometer Slides
Next

249

Share

Keratometry

Keratometry - definition, uses, principle, types, procedure.

Related Books

Free with a 30 day trial from Scribd

See all

Related Audiobooks

Free with a 30 day trial from Scribd

See all

Keratometry

  1. 1. Keratometry Dr. Karan Bhatia Senior Resident AEH, Pondicherry
  2. 2. Keratometry (Ophthalmometry) • Kerato = Cornea • Metry = Measurement
  3. 3. Zones of the Cornea • Central Zone (apical zone/corneal cap/central spherical zone) – 4 mm, radius of curvature does not vary by more than 1 D or 0.05 mm • Area where refraction differs by <0.25 D • Paracentral zone – 4 - 8 mm. • Peripheral zone – 8 - 11 mm. • Limbal zone – rim of cornea, 0.55 mm wide. Optical zone
  4. 4. What is Keratometry ??? Measurement of the anterior surface of the cornea, across a fixed chord length, usually 2-3 mm, which lies within the optical spherical zone of the cornea.
  5. 5. Uses of Keratometry • Measurement of corneal astigmatism. • Estimate radius of curvature of cornea  helps in contact lens fitting. • Assess integrity of cornea and/or tear film. • Detection of irregular astigmatism – keratoconus/pterygium/corneal scarring. • Assess refractive error in cases with hazy media (Rough estimate, comparison of two eyes). • Establish baseline data – should be done in all patients. • Patient may later want Contact lens or develop an injured/diseased cornea.
  6. 6. Uses of Keratometry • IOL Power calculation (Pre-op Cataract Surgery workup). • Pre & post surgical astigmatism. • D/D of axial versus curvatural anisometropia. • Detect Rigid Gas Permeable lens flexure. • Progressive myopia.
  7. 7. Principle • Anterior surface of cornea – CONVEX MIRROR • ↑ Curvature – ↓ Image Size. • From Image Size formed by anterior surface of cornea (1st Purkinje image) – radius of curvature of cornea can be calculated
  8. 8. Principle Therefore , B’P/A’B’ = BP/AB F/i = u/o r/2 i = u/o ( since F = r/2) r = 2 ui/o A B Q S A’ B’P u (BP)  constant for any instrument
  9. 9. Relationship b/w Radius of curvature and Diopteric Power of cornea D = n-1/r r=1.3375-1/D mm D – Dioptric power of cornea n – Index of refraction of cornea (1.3375) r – Radius of cornea in metres
  10. 10. Doubling Principle Miniature involuntary eye movements during fixation of eye Image formed by anterior surface of cornea also moves (impossible to measure) DOUBLING PRINCIPLE
  11. 11. Doubling Principle Biprism 2 images Move equally as eye moves Depending on the position of prism – if distance↓, doubling ↑
  12. 12. Keratometers Fixed Doubling • Bausch and Lomb, Topcon & Mognon • Variable – Image size & mire separation. • Fixed – Object height & doubling device distance. Variable Doubling • Haag Streit, Javal Schiotz • Variable – Object height & doubling device distance. • Fixed – Image size & mire separation.
  13. 13. Keratometers One position Keratometer • Double images are produced side by side as well as at 90º from each other. • The principle meridians are assumed to be at right angle to each other. Two position Keratometer • Require rotation about the axis to measure each of the principle meridians.
  14. 14. Keratometers Ziess Oberkochen Keratometer
  15. 15. Keratometers Humphrey Keratometer Javal Schiotz Keratometer
  16. 16. Keratometers Bausch & Lomb Keratometer
  17. 17. OCCLUDER FOREHEAD REST ASSEMBLY CHIN REST LAMP ASSEMBLY SIGHTING POST AXIS ASSEMBLY EYEPIECE ROTATING GRIP ELEVATION ASSEMBLY BASE ASSEMBLY
  18. 18. FOREHEAD REST KNOB FOCUSING KNOB LOCKING KNOB VERTICAL MEASURING DRUM HORIZONTAL MEASURING DRUM CHINREST KNOB ELEVATION KNOB
  19. 19. Caliberation • Should be done regularly to ensure the accuracy of “K” readings • Mount a 5/8 inch steel ball bearing at the position close to that normally of the patient’s eye. • The steel ball has a known radius of curvature, which upon proper calibration of the keratometer, can be correctly read.
  20. 20. Preparation • Focus the eyepiece of the keratometer for the examiner’s eye • Set the adjustable eyepiece as far counter-clockwise as possible • Place a white sheet of paper in front of the instrument’s objective lens to retroilluminate the reticle (i.e., cross hairs) • Turn the eyepiece clockwise until the reticle is first seen in sharp focus
  21. 21. Preparation – Adjust instrument for patient • Adjust height of patient’s chair & instrument to a comfortable position for both patient & examiner. • Instruct patient to place chin on chin rest & forehead against forehead rest & adjust for the patient. • Raise or lower chin rest until patient’s outer canthus is aligned with hash mark on upright support of instrument. • From outside instrument, roughly align barrel with patient’s eye by raising or lowering instrument and by moving it to left or right until a reflection of mire is seen on patient’s cornea.
  22. 22. Procedure – Instruct patient • Keep eyes open wide and blink normally. • Try not to move the head nor speak. • Look at the reflection of own eye in the keratometer barrel.
  23. 23. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea.
  24. 24. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea.
  25. 25. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea. • Focus the mires and adjust the instrument so that the reticle is centered in the lower right hand circle.
  26. 26. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea. • Focus the mires and adjust the instrument so that the reticle is centered in the lower right hand circle. • Adjust the horizontal and the vertical power wheels until the mires are in close apposition.
  27. 27. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea. • Focus the mires and adjust the instrument so that the reticle is centered in the lower right hand circle. • Adjust the horizontal and the vertical power wheels until the mires are in close apposition.
  28. 28. Procedure • Look into the keratometer and refine the alignment of the image of the mires (three circles) on the patient’s cornea. • Focus the mires and adjust the instrument so that the reticle is centered in the lower right hand circle. • Adjust the horizontal and the vertical power wheels until the mires are in close apposition. • To locate the two principal meridians of the patient’s cornea, rotate the telescope until the two horizontal plus signs of the mires are perfectly continuous with one another.
  29. 29. Oblique Astigmatism 2 + signs will not be aligned Entire optical instrument is rotated till the two plus signs are aligned
  30. 30. • A scale associated with it indicates in degrees, one meridian of oblique astigmatism. • Corneal radius of power is then measured in this meridian and in the meridian 90 degrees.
  31. 31. Astimatism • Irregular: principal meridians are not perpendicular to each other • Produce distorted mires • Regular: principal meridians are perpendicular • With-the-rule: more power in the vertical meridian (greatest curvature) and horizontal meridian is flatter • Example: 45.00 D @ 90º/43.25D @180º • Against-the-rule: more power in the horizontal meridian and vertical meridian is flatter • Example: 42.50 D @115º/44.87 D @025º • Oblique: principal meridians lie between 20° & 70° and 110° & 160°
  32. 32. Bausch & Lomb Keratometer • Range – 36.00 to 52.00 D • Normal values – 44.00 to 45.00 D • To increase the range – Place +1.25 D lens in front of aperture to extend range to 61 D • ADD 9 D • Place -1.00 D lens in front of aperture to extend range to 30D • SUBTRACT 6 D
  33. 33. Automated Keratometers • Focuses the reflected corneal image on to an electronic photosensitive device,which intantly records the size and computes the radius of curvature. • No doubling device is needed. • Measures angle size in many meridians so it computes angle as well as power in many meridians. • Absence of annoying glare of brightly illuminated mires. • Do not calculate clarity of cornea.
  34. 34. Surgical Keratometer • Attached to operating microscope. • Helpful in monitoring the astigmatism during Corneal surgery. • Accuracy limited – • Difficulty in alligning patients visual axis & Keratometers’s optical axis. • Caliberated for a fixed distance from anterior cornea. • Different microscope objective lenses result in different focal lengths and therefore different working distance. • Air in the anterior chamber results in the second target reflection. • External pressure on the globe results in a change in a corneal curvature.
  35. 35. ProblemsSolutions • Unable to locate keratometric mires  instrument and/or patient not aligned properly. • Transient Mire clarity  Ask patient to blink & measure quickly/put artificial tears. • Transient Mire focus  Ensure that patient’s forehead is secured against the headrest. • Unsteady Patient gaze  Close other eye. • H & V mires cannot be measured concurrently  Irregular Astigmatism. • Only 1 minus sign is visible  Patient’s eyelid drooping . • Only 1 plus sign is visible  Occluder is in the way.
  36. 36. Limitations of Keratometry • Measures refractive status of a very small central area of cornea (3 mm), ignoring the peripheral corneal zones. • Accuracy lost when measuring very flat or very steep cornea. • Small corneal irregularities would preclude the use of keratometer due to irregular astigmatism. • One position instruments assume regular astigmatism. • Distance to focal point is approximated by distance to the image. • Autokeratometers do not evaluate the quality of cornea
  37. 37. “You can't invent Google, Facebook or the iPod unless you've mastered the basics.” -- Amy Chua ThankyouAcknowledgements – Dr. Swapnil Chinche You Tube
  • EsatayRasulHridoy

    Sep. 27, 2021
  • ADARSHRATANSINGH

    Sep. 15, 2021
  • VivekIghare

    Sep. 15, 2021
  • ArukSahu

    Sep. 9, 2021
  • MuskanChauhan34

    Sep. 6, 2021
  • alshabnashajahan1

    Aug. 31, 2021
  • aishwaryaash96

    Aug. 5, 2021
  • ssuserf401591

    Jul. 22, 2021
  • AhmedRaafat151

    Jul. 21, 2021
  • deveshrao10

    Jul. 8, 2021
  • AsifFarazNasir

    Jul. 6, 2021
  • ShivaniBansal42

    Jul. 4, 2021
  • AnannaRifat

    Jun. 22, 2021
  • JananiGanesan5

    Jun. 19, 2021
  • PRECIOUSOKEZIE

    Jun. 2, 2021
  • NikitaArakeri

    May. 29, 2021
  • ManasiPatil32

    May. 28, 2021
  • BrijeshParikh3

    May. 25, 2021
  • ChetnaSharma146

    May. 15, 2021
  • PronitaDas1

    May. 8, 2021

Keratometry - definition, uses, principle, types, procedure.

Views

Total views

61,412

On Slideshare

0

From embeds

0

Number of embeds

102

Actions

Downloads

327

Shares

0

Comments

0

Likes

249

×