Astigmatism and Contact Lens Prescription Guidelines

Q: Astigmatism and Contact Lens Prescription Guidelines

Hello： When determining the prescription for contact lenses, the higher the degree of myopia, the more it can be reduced. <br>Both of your eyes have a myopia of -5.75 (with the left eye's astigmatism measured as half of the value and converted), so you can reduce it by 50 degrees

Contact Lenses and Astigmatism

1.
For a prescription of -5.75 diopters in the right eye and -5.50 diopters with +0.50 cylinder in the left eye, what should the contact lens prescription be?
2.
Is it correct that the contact lens prescription is determined by reducing the myopia degree by 0.25? If there is astigmatism, can we substitute it by dividing the astigmatism degree by 2 and adding it to the myopia degree (if not fitting astigmatism contact lenses)? For example, for the left eye with -5.50 myopia and +0.50 astigmatism, the contact lens prescription would be -5.50 - 0.25 + (0.50/2) = -5.50.
Is this information accurate?
3.
When wearing glasses or contact lenses, is there a threshold below which astigmatism can be ignored?
4.
Can the measurements for myopia and astigmatism be taken at an optical store, or do they need to be done at an ophthalmologist's office?
5.
How can one prevent the progression of astigmatism?
I apologize for the many questions, and thank you for your assistance, doctor.

Niming, 20~29 year old female. Ask Date: 2018/09/28

Dr. Gao Pilin reply Ophthalmology

Hello: When determining the prescription for contact lenses, the higher the degree of myopia, the more it can be reduced.
Both of your eyes have a myopia of -5.75 (with the left eye's astigmatism measured as half of the value and converted), so you can reduce it by 50 degrees, resulting in a prescription of -5.25.
This can be measured at a reputable optical store.
Of course, it would be even better to have an eye examination by an ophthalmologist.
Astigmatism typically does not worsen, but it is important to avoid squinting or rubbing your eyes, as these actions can put pressure on the eyeball.
In Taiwan, the Department of Ophthalmology at Puzi Hospital is open on Mondays, Tuesdays, Thursdays, and Fridays from 8:00 AM to 12:00 PM, and on Wednesdays from 1:00 PM to 4:30 PM.
Online responses should only be used as a reference; it is necessary to seek medical attention at a healthcare facility.
I hope to have the opportunity to serve you.
Gao Pi-Lin

Reply Date: 2018/09/28

More Info

Astigmatism is a common refractive error caused by an irregular shape of the cornea or lens, leading to blurred or distorted vision. Understanding how to properly prescribe contact lenses for individuals with astigmatism and myopia (nearsightedness) is crucial for achieving optimal vision correction. Let’s address your questions one by one.

1. Contact Lens Prescription for Myopia and Astigmatism: For your right eye with a myopia of -5.75 (575) and your left eye with a myopia of -5.50 (550) plus a cylinder of +0.50 (indicating astigmatism), the contact lens prescription will differ from your glasses prescription. Generally, when fitting contact lenses, the prescription is adjusted to account for the distance between the lens and the eye. A common rule of thumb is to reduce the myopic prescription by about -0.25 to -0.50 diopters. Therefore, for your right eye, you might consider a contact lens prescription of approximately -5.50 to -5.75, and for your left eye, around -5.25 to -5.50, depending on the specific fitting and comfort.

2. Calculating Contact Lens Power: Your understanding of adjusting the prescription for astigmatism is partially correct. When calculating the contact lens power, you typically reduce the spherical component by -0.25 to -0.50 diopters. For the left eye, if you are not using a toric lens (which is designed specifically for astigmatism), you can use the formula you provided:
- For the left eye: Myopia - 0.25 + (Cylinder / 2) = -5.50 - 0.25 + (0.50 / 2) = -5.50 - 0.25 + 0.25 = -5.50.
However, if you were to use a toric lens, you would need to account for the cylinder power as well.

3. Ignoring Low Degrees of Astigmatism: Generally, astigmatism of 0.75 diopters or less can often be ignored in contact lens prescriptions, especially if the individual is comfortable with their vision. However, this can vary based on personal preference and visual demands. It’s always best to consult with an eye care professional who can evaluate your specific situation.

4. Measuring Myopia and Astigmatism: While some optical shops can measure basic refractive errors, it is highly recommended to visit an eye care professional, such as an optometrist or ophthalmologist, for a comprehensive eye exam. They can provide a more accurate measurement of your refractive error and assess your overall eye health, which is crucial for proper contact lens fitting.

5. Preventing Astigmatism from Worsening: While the exact cause of astigmatism can be genetic or due to environmental factors, there are some general practices that may help prevent worsening vision:
- Regular eye exams to monitor changes in your vision.

- Proper use of corrective lenses as prescribed.

- Reducing eye strain by taking breaks during prolonged screen time and ensuring proper lighting.

- Maintaining a healthy lifestyle, including a balanced diet rich in vitamins A, C, and E, which are beneficial for eye health.

In conclusion, managing astigmatism and myopia requires careful consideration of your specific prescription needs and regular consultations with eye care professionals. They can provide tailored advice and adjustments to ensure you achieve the best possible vision correction with contact lenses. If you have any further questions or concerns, please feel free to ask.

Similar Q&A

How to Choose the Right Contact Lens Prescription for Clear Vision?

Hello Dr. Chen, I would like to inquire about the prescription for my contact lenses. My right eye prescription is -5.25 with a -0.50 astigmatism. When I visited the optical store, they provided me with -4.75 lenses without adding the astigmatism correction, but I found it diffi...

Dr. Chen Anping reply Ophthalmology
1. To read the newspaper, you need to reduce your prescription by 200 degrees, so your prescription should be 325 degrees, which means you will need two pairs of glasses. 2. If you only have 50 degrees of astigmatism, it is considered physiological astigmatism and does not requir...

Choosing the Right Toric Contact Lenses for Astigmatism: A Guide

My prescription is right eye: sph -1.5, cyl -2.25, x 175; left eye: sph -1.0, cyl -2.50, x 180. I would like to ask about disposable toric contact lenses, as most of them only correct astigmatism up to 175 degrees. Previously, an optical shop helped me increase my myopia prescrip...

Dr. Gao Pilin reply Ophthalmology
Hello, Xiao You: Using glasses for myopia to correct astigmatism may not be effective and does not cause harm to the eyes. If the vision remains blurry, the only option would be to fit long-wear contact lenses. At the e-Hospital in Puzi, Taiwan, the ophthalmology department is op...

Choosing the Right Contact Lenses for Astigmatism: A Guide for Young Adults

Hello Doctor, I am currently 20 years old and will be turning 21 soon. Recently, I measured my vision and found that my left eye has a myopia of -4.75 with no astigmatism, while my right eye has a myopia of -4.00 with astigmatism of -1.25. 1. At my age of 20, do I still need to...

Dr. Gao Pilin reply Ophthalmology
Hello: 1. Regarding your current vision condition, your left eye has a myopia of -4.75 diopters, and your right eye has a myopia of -4.00 diopters with astigmatism of -1.25 diopters, which does not require special treatment. 2. The degree of astigmatism is relatively stable, and ...

Understanding Eye Issues: Contact Lenses, Astigmatism, and Workplace Discomfort

Hello Doctor, I have myopia with a left eye prescription of -5.00 and astigmatism of -2.00, and a right eye prescription of -4.75 and astigmatism of -1.00. When I wear contact lenses, they are prescribed without astigmatism correction, so sometimes my vision is not clear. Is this...

Dr. Cai Wenyuan reply Ophthalmology
Wearing contact lenses requires a proper fitting, not just relying on the prescription. Contact lenses can be prescribed for astigmatism and myopia. Environmental factors may also play a role. Thank you.