Zeiss AT 030, Product Documentation Set

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5 Daily startup Instruction for use
AT 030 5.2 Measuring spherical corneal surfaces
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5.2 Measuring spherical corneal surfaces
With a spherical cornea, the applanation surface is a circle. The
optical system generates two fluorescein semicircles to be coinci-
denced.
The measuring prism has a graduated scale. The measuring prism
holder has a white and a red index line.
With spherical cornea, rotate the measuring prism until the 0° line
of the angle scale coincides with the white index line of the
measuring prism holder. In this case, the line of coincidence of the
measuring prism is horizontal.
5.3 Measuring toric cornea surfaces
With a toric cornea, the applanation surface is an ellipse. The
coincidence of the half ellipses provides correct pressure values only
if the surface of the ellipse is equal to the surface of the appla-
nation circle. This condition is to be met for a definite angular
position of the major semiaxis of the ellipse with regard to a
principal direction of curvature of the cornea. The calculation
shows that an astigmatism of below 3 D is negligible for tonometer
measurement. With higher astigmatism, correct measurements are
taken at an angle of about 43° between the major diameter of the
ellipse and the direction of the minor principal section.
The measuring prism has a graduated scale. The measuring prism
holder has a white and a red index line.
Astigmatism is taken into account as follows:
Action
u
With an astigmatism up to 3 D, rotate the measuring prism
until the 0° line of the angle scale coincides with the white
index line of the measuring prism holder. In this case, the
separating line of the measuring prism is horizontal.
u
With astigmatism above 3 D, the axial position of the lower
refracting principal section (larger radius of curvature) must be
known from a previous measurement with an ophthalmometer.
Set the corresponding axis angle at the angle scale of the
measuring prism to the red index line of the measuring prism
holder. In this setting, the separating line of the measuring
prism forms an angle of 43° to the horizontal.
5.4 Preparing for measurement
CAUTION!
Risk due to improper locking of the slit lamp
The patient may be injured if the slit lamp moves during the
measurement.
u
Ensure that the instrument table is horizontal to avoid
movement of the slit lamp with attached measuring prism
towards the patient.