The document discusses the keratometer, an instrument used to measure the curvature of the cornea. It describes the keratometer's parts including the focusing knob, rotating grip, and measuring drums. The optical principle is that the cornea acts as a convex refracting surface and the keratometer uses the doubling principle to measure the corneal curvature. The document outlines the procedure for taking keratometry measurements, which involves adjusting the instrument height, focusing on the patient's eye, and reading the values from the measuring scales to determine the corneal curvature and astigmatism. Keratometry is important for contact lens fitting, evaluating keratoconus, and determining intraocular lens power for cataract surgery.

1. Keratometer
Presented by
Dhaneshwar pal
2017 Batch
B.Optometry 5th sem

2. Topics which include
Introduction
Instrument parts
Optics of the keratometer
Types of keratometer
Keratometry
Recordings

3. Introduction
• The radii of curvature of the cornea.
• The directions of the principal meridians of
the eye, determining whether the astigmatism
is with-the-rule or against-the-rule -- a key
factor in contact lens fitting.
• The degree of corneal astigmatism.
• The presence of any corneal distortion.

4. • Keratometry is essential in the fitting of
contact lenses.
• Evaluating the patients with keratoconus.
• The determination of appropriate intraocular
lens implant power for patients undergoing
cataract surgery.

5. Keratometer
Parts
A. Focusing Knob
B. Rotating Grip for Locating the
Axis
C. Chin Rest
D. Locking Knob
E. Elevating Knob
EP. Eyepiece
G. Head Rest Adjusting Knob
H. Occluding Shield
HR. Head Rest
J. Chin Rest Adjusting Knob
K. Leveling Sight
M. Horizontal Measuring Drum
N. Vertical Measuring Drum
S. Axis Scale

6. Optical Principle
• Cornea is a convex refracting surface
• Doubling principle
https://books.google.co.in/books?isbn=07506
75756

7. Optics
Primary Care Optometry-Grosvenor
page 224

8. Bausch & Lomb Keratometer
• One position keratometer: it measures two
meridians at the same time.
• It contains two prisms.

9. PROCEDURE
Step:1 Eyepiece Adjustment : Turn the eyepiece
(EP) counterclockwise (anticlockwise) fully.
Place a white sheet of paper in front of the
Telescope part.
https://www.youtube.com/watch?v=gDytKVnlp98

10. Step:2 Turn the eye piece clockwise until the
specified target in the instrument becomes in
sharp focus.
https://www.youtube.com/watch?v=gDytKVnlp98

11. • Step 3: Adjust the height of the instrument
and align the outer a canthus of the patient
with the leveling sight sign
https://www.youtube.com/watch?v=gDytKVnlp98

12. • Step :4 Occlude the non-tested eye
• Step:5 Ask the patient to look at the center of the
instrument. If you are aligned, you can see the circles
in the eye. The patient can see the picture of their
eye in the instrument.
https://www.youtube.com/watch?v=gDytKVnlp98

13. • Step:6 Adjust the focusing knob, such that
you get a single image of the central circle.
https://www.youtube.com/watch?v=gDytKVnlp98

14. • Step:7 Use the horizontal alignment knob(M)
to bring the crosses on each other.
https://www.youtube.com/watch?v=gDytKVnlp98

15. • Step:8 Use the vertical alignment knob(N) to
bring the crosses on each other.
https://www.youtube.com/watch?v=gDytKVnlp98

16. • step:9 Read the values from the scales.
https://www.youtube.com/watch?v=gDytKVnlp98

17. REFERENCES
• Theodore Grosvenor, Primary Care Optometry;
Fourth edition pg:315-317, DOI:
• Optivision 2020; Retrieved from
http://www.optivision2020.com/keratometer.html;
retrieved on 28th July’15
• Retrieved from
https://www.youtube.com/watch?v=gDytKVnlp98;
retrieved on 28th july’15