Keratometer or
Ophthalmometer
LECTURE NO (#)

Definition:
 Measures radius of curvature of central cornea app
(3mm)
 One of the classic method for refraction, astigmatic
 Assesses curvature, Power and toricity of the cornea
 It may be used to asses the integrity of corneal/tear
surface

Optical principle:
 The anterior corneal surface acts as a convex mirror
 Doubling system to obtain accurate measurement of
image size
 Keratometric formula
 Types:
1. Bausch & Lomb(adjust image size), one position
2. Javal Schoitz(adjust object size)two position

Basic components:
 Adjustable eyepiece
 Adjustable chin and forehead rest
 Knob to raise and lower the instrument
 Two power wheel to measure corneal power in each
meridian
 An axis scale
 Targets known as mires
 Joystick

Procedure:
 Focusing the eyepiece
 Adjust the instrument to the patient
 Aligning the instrument
 Instruct the patient
 Finding the primary meridians
 Taking the reading
 Recording the findings

Interpreting:
 R:42.00 at 180 ; 43.00 at 90
 L:42.25 at 170 ; 43.00 at 80
Interpretation:
 R: -1.00 x180
 L: -1.25 x170
 With the rule astigmatism 180
 Against the rule astigmatism 90
 Oblique astigmatism

Refractive astigmatism:
 Total astigmatism
 Increase with against the rule:
1. In the absence of corneal astigmatism -0.50 ag
2. In corneal -0.50 c rule no astig expected
3. If corneal -2.00 c refractive also -2.00 D c
4. If corneal -2.00D x the refractive -3.00 against

Indications:
Contact lens fitting
Keratoconus detection
48.00 or 50.00

Any question