Prescription For Contact Lenses – Can you convert an eyeglass prescription to a contact lens prescription? The answer is not straightforward, but it can be approximated by the point conversion formula.
Read on to learn about the main differences between the two types of glasses and learn how to get the right contact lens prescription for a variety of refractive errors.
Prescription For Contact Lenses
Although prescriptions for glasses and contact lenses are similar, there are many differences between the two, which can cause differences in visual acuity depending on which refractive error you have.
How To Read Contact Lens Power
The glasses are placed about 1 cm from your eyes, while the lenses are placed directly on your eyes. This difference is very important because the power your lens feels depends on how close or far the lens is from your eye.
When performing an eye test for glasses, the lenses are placed about 12-13mm from the eye to mimic the distance between the glasses and your eye. Increase knot distance
Will add more positive power to the lens while reducing the vertex distance will add more negative power to the lens. Because contact lenses are directly above the eye, they do not have a vertex spacing which adds more negative power to the lens.
Therefore, contact lens prescriptions need to be adjusted, otherwise people who are nearsighted may get contact lenses that are too strong, while people who are farsighted may get lenses that are not strong enough. This can cause discomfort, blurred vision, and eye fatigue, which we want to avoid at all costs.
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When you look at eyeglass prescriptions and contact lens prescriptions side by side, you’ll notice significant differences in cylinder and axis values in eyeglass prescriptions, which you usually won’t find in contact lens prescriptions (unless you get toric or multifocal lenses). ).
Likewise, because contact lenses must fit in your eyes, they require a certain size that prescription eyeglasses don’t have. One of these specifications is the base curve or the curvature of the lens which is based on the shape of your eye. Another example is the diameter or size of the lens, which must also be adjusted to your eye.
A handy tool that optometrists use to save time in calculations and eye tests is the point conversion table, which contains different numbers for different lens powers. If you are nearsighted, you will see a negative or minus sign (-) on your prescription, but if you are nearsighted, you will see a positive or plus (+) sign on your prescription.
The vertex conversion table is quite easy to use. You just need to know where to look and understand what the columns mean. The ‘lens power’ column refers to the strength of your current prescription. If this number is negative, you will be converted to the number on the left in this column. If the number is positive, the number you’re converting will be on the right.
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One important thing to know about vertex conversion charts is that most start at +/- 4.00D prescription glasses. The reason why they often exclude lower power lenses is because the converted power is not too far from the original. If the point distance conversion formula produces a difference of less than 0.25, then there is no significant difference in visual acuity. In other words, if your prescription falls within this range, you can get away with the same strength as yours. The only exception to this rule is if you have astigmatism, as additional measurements will need to be taken to account for differences in the shape of your cornea.
Now that you’ve learned how to get a contact lens prescription through the vertex conversion chart, you can easily purchase a wide selection of contact lenses here. We have clear lenses for those who want to let their natural eye color shine through, as well as a range of colored prescription contact lenses for those who want to change their appearance. Check out our gorgeous range and find your new favorite pair today. In the previous lesson, “How to Convert Prescription Eyeglasses to Contact Lenses,” I only covered situations where astigmatism correction is not required. In this lesson, I’ll only cover how to convert prescription eyeglasses to contact lenses if you have astigmatism.
Before I get into it, I just want to say that some of it may seem difficult. Sure, it takes a little longer, but it’s literally nothing more than a little addition, subtraction, and looking up numbers in our node distance conversion table.
Let’s get straight into it. Everything is done one eye at a time, so complete steps 1-5 for the right eye and again for the left eye.
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Power cross is the primary tool used in visualizing and organizing the calculations involved in this conversion process.
Look at the prescription glasses you are using and find the ‘Axis’ number. This number represents the degree value and will be between 1 and 180. Now draw a line in the direction of the axis.
In our example rule, it is 45. That means the line at 45° must be drawn on the power cross. This is the Sphere Power Line. This represents the power of the ball, so write it next to that line.
Then add 90 to the axis number and draw another line in that direction. For the recipe example above, that would be 90 + 45 = 135.
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This is the step where we actually turn prescription eyeglasses into contact lenses. Now that we have classified the spherical and sphere+cylindrical forces, you can use the vertex distance conversion table above to convert them and write them down as well.
At this point, the eyeglass prescription is converted to contact lenses, but not in the correct Sphere/Cylinder/Axis format. Follow these 3 rules to get back to the correct format:
This time the axis is 020, so the high tension line of the ball must be drawn at 20°. The bulb’s power is -7.00 so it’s next to the bulb’s power line.
Then add 90 to the ashes to the recipe. In this case it is 90 + 20 = 110, so the line of force for the sphere + cylinder must be drawn at 110°.
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The ball+cylinder power for this recipe is -7.00 + (-1.50) = -8.50, so it’s next to the ball+cylinder line.
The vertex distance conversion table is now used to convert sphere power and sphere+cylinder power. Converted privileges are written to help with the next step.
Despite the simplicity of converting prescription glasses with astigmatism to contact lenses using the 5-step process described above, it’s not always necessary. There are several keyboard shortcuts that can save you a lot of time in a real-world environment.
If the cylinder in prescription glasses converted to contact lenses is -0.25, there is no need to go through the 5-step power cross procedure. In fact, there’s usually no need to do anything.
How To Rapidly Determine A Contact Lens Prescription
With a -0.25 cylinder, the cylinder will remain -0.25 or even decrease after the conversion process. Since absolutely no contact lens company offers astigmatism contact lenses with a -0.25 cylinder correction, conversion is a wasted exercise.
Instead, the most common solution is to ignore it altogether. Simply put, the cylinder and shaft are removed from the contact lens prescription and only the glass bulb is changed according to these guidelines.
This is probably the most difficult situation. Contact lenses are not available in the -0.50 cylinder style, but the -0.50 cylinder style is significant enough not to be overlooked. So what’s the solution?
However, the -0.50 cylinder and axis are still omitted from contact lens prescriptions to compensate, and an additional -0.25 is added to the glass bulb. That means you don’t need to use the power cross method. Normal:
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And there you have it. You now have all the tools and knowledge needed to convert prescription eyeglasses into contact lenses. But are you ready to prescribe contact lenses now? Not enough! In fact, we are currently still in the early stages of fitting contact lenses.
You know how to convert prescription eyeglasses to contact lenses, even if you have astigmatism, but what if contact lenses aren’t available in the quantities you count?
Have you noticed that many conversions in the vertex distance conversion table end up with odd numbers like 0.12, 0.37, 0.62 & 0.87? Have you noticed that only certain cylindrical powers and axes are available for contact lenses?
If the conversions you calculated do not match those available in contact lenses, additional adjustments are required to order samples for patients/customers. And that’s what we’re going to study next!
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If you have any questions about the process described in this article, let me know in the comments and I’ll help you out
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