10+ クロスシリンダー使い方 Article

【道具紹介】クロスシリンダー眼鏡道場オリバーミーチルズ from meganenomichi.hateblo.jp

Introduction

If you work in a field that involves precision mechanics, you might have come across the term "cross cylinder" before. This device is commonly used in optics and optometry to determine the strength and axis of astigmatism, among other things. However, if you're new to the world of cross cylinders, you might be intimidated by the jargon and technicalities involved. In this article, we'll explain what a cross cylinder is, how to use it, and what to watch out for.

What is a Cross Cylinder?

Simply put, a cross cylinder is a lens that has two cylindrical surfaces of opposite power, oriented at 90 degrees to each other. The lens is mounted on a frame that allows it to rotate around its axis. By rotating the lens and observing the changes in the image, you can determine the strength and orientation of astigmatism in a patient's eye. Cross cylinders are also used to refine the prescription for toric contact lenses and to test the effectiveness of various lens designs.

Using the Cross Cylinder

Before using the cross cylinder, you need to make sure that the patient's eye is properly refracted and that any other vision problems have been corrected. The patient should be seated comfortably and the room should be dimly lit to reduce glare. The cross cylinder should be held at a distance of about 10-15 cm from the eye, with the axis of rotation aligned with the patient's line of sight. To start, you should place a spherical lens in front of the eye that corrects for any myopia or hyperopia. Then, you should rotate the cross cylinder until one of the cylindrical surfaces is aligned with the axis of astigmatism, as determined by previous tests. The patient should be asked to read letters or look at a chart while you rotate the lens and observe the changes in the image. You should note the orientation of the cross cylinder and the strength of the astigmatism in diopters.

Interpreting the Results

The results of the cross cylinder test will give you a pair of numbers, such as +1.50/-2.00. The first number indicates the spherical power of the lens that should be prescribed, while the second number indicates the cylindrical power and orientation. The axis of astigmatism is always expressed as a number between 0 and 180 degrees, with 90 degrees corresponding to the vertical meridian and 180 degrees corresponding to the horizontal meridian. It's important to note that the strength and orientation of astigmatism can vary depending on the size of the pupil, the lighting conditions, and other factors. Therefore, it's recommended to perform the test multiple times and to use various cylinder powers to confirm the results.

Tips for Using the Cross Cylinder

Here are some tips to keep in mind when using the cross cylinder: - Make sure the patient is relaxed and comfortable. - Use a dimly lit room to reduce glare. - Always start with a spherical lens to correct for any refractive errors. - Rotate the cross cylinder slowly and observe the changes in the image. - Repeat the test multiple times and use different cylinder powers to confirm the results. - Take note of any unusual responses or discrepancies between tests.

Conclusion

Using a cross cylinder can be a valuable tool for diagnosing and correcting astigmatism, as well as for refining the prescription for toric lenses. By following the steps outlined in this article and paying attention to the tips provided, you can ensure that you get accurate and reliable results. Remember, practice makes perfect, so don't be afraid to experiment with different techniques and cylinder powers until you feel confident in your skills.