Refining Cylinder Power in Subjective Refraction: Cross-Cylinder Method

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What is the primary reason to confirm the sphere power before starting the cross-cylinder test?

To verify the circle of least confusion is on the retina (correct)

To determine the correct cylindrical axis

To avoid unnecessary repetitions of the test

To ensure the patient's comfort during the test

When performing the cross-cylinder test, what should the practitioner ask the patient to compare?

The size of the two lenses

The clarity of the two lenses (correct)

The shape of the two lenses

The brightness of the two lenses

What is the significance of the patient's response 'same' during the cross-cylinder test?

The cylindrical power is incorrect

The axis of the cylindrical power needs to be rechecked

The spherical power is incorrect

The test is complete and the final refraction can be determined (correct)

What is the purpose of rechecking the cylindrical axis during the refraction routine?

To ensure the correct axis of the cylindrical power Signup and view all the answers

What is the expected outcome of the final refraction?

A visual acuity better than the spherical refraction Signup and view all the answers

What is the result of adding -0.25DC to the cylindrical power in the example given?

A new power of -1.25DC Signup and view all the answers

What is the primary objective of refining cylindrical power using the cross-cylinder method?

To determine the axis and power of astigmatism Signup and view all the answers

What is the ideal time limit for determining the amount and axis of astigmatism using the cross-cylinder method for both eyes?

10 minutes Signup and view all the answers

What is the purpose of rechecking the sphere power after using the cross-cylinder method?

To refine the spherical power of the lens Signup and view all the answers

What is the primary goal of subjective refraction in relation to astigmatism?

To refine the cylindrical power of the lens Signup and view all the answers

What is the prerequisite for refining the cylindrical power of the lens using the cross-cylinder method?

Retinoscopy result Signup and view all the answers

What is the primary benefit of using the cross-cylinder method in subjective refraction?

It enables the determination of the axis and power of astigmatism Signup and view all the answers

What is the recommended starting cylindrical power for a patient with a vision of 6/12 or worse?

0.50DC Signup and view all the answers

How do you determine the axis of the cylindrical lens using the x-cyl method?

By illuminating the circles on the white background and holding the x-cyl with the handle pointing in the same direction as the trial lens axis Signup and view all the answers

What is the purpose of using a larger target during the x-cyl method?

To improve the patient's vision Signup and view all the answers

What is the recommended step size for rotating the trial lens during the x-cyl method?

10-15 degrees Signup and view all the answers

What is the significance of the patient's response 'Both lenses are equally blurred' during the x-cyl method?

The cyl axis of the trial frame matches the patient's cyl axis Signup and view all the answers

What is the range of uncertainty in axis estimation?

The range of axes where the patient reports both lenses are equally blurred Signup and view all the answers

What is the purpose of using alternative techniques such as Fan and block or keratometry?

To refine the cylindrical power when the results are unreliable Signup and view all the answers

What is the recommended cylindrical power for a patient with a vision of 6/24 or worse?

0.75DC Signup and view all the answers

How do you adjust the spherical power during subjective refraction?

By checking the sphere power with a duochrome test Signup and view all the answers

What is the purpose of rotating the trial lens during the x-cyl method?

To estimate the axis of the cylindrical lens Signup and view all the answers