We explain your vision,
prescription and options
for great vision.
The key to understanding refractive surgery is to understand how the eye works. Once you’ve read about your vision below, check out what yourprescription really means at the bottom of this page.
Normal Vision
Sharp, clear vision is the result of light rays passing through the cornea, pupil and lens of the eye and focusing directly on the retina. If the cornea is not round, or is too steep or too flat in relation to the length of the eye, light rays focus either in front of or behind the retina. This results in “refractive errors” such as nearsightedness, farsightedness, and astigmatism.Laser vision correctionimproves the way the eye focuses light by modifying the curvature of the cornea and re-focusing the light directly on the retina.
Nearsightedness
Nearsightedness, or myopia, occurs when the curvature of the cornea is too steep or the eyeball is too long. With nearsightedness, the eye’s strong refractive power forces the image to be focused in front of the retina, rather than on it. When light focuses in front of the retina, near objects can be seen clearly, but far objects appear blurry. Myopia can be treated by flattening the cornea withLASIK or PRK. An alternative non-laser procedure,Implantable contact lens (ICL) eye surgery, can correct myopia by implanting a special type of lens inside the eye.
Farsightedness
Farsightedness, or hyperopia, is caused when the curvature of the cornea is too flat or the eyeball is too short, forcing light to focus behind the retina. With farsightedness, the eye’s weak refractive power causes far objects to be seen more clearly and near objects to appear blurred. The eyes may have to strain to maintain things in focus. The first appearance of hyperopia is strongly age-dependent; younger patients have much less difficulty with hyperopia. Hyperopia can be corrected by steepening the central cornea withLASIK or PRK.
Astigmatism
Astigmatism occurs when the cornea is irregularly shaped – like a football or a teaspoon – preventing light from converging on the retina. Parts of the image may focus on the retina, while others focus behind it or in front of it. This has the effect of bending light inconsistently and causing blurred or distorted images. Astigmatism can occur alone or in addition to either nearsightedness or farsightedness. Although astigmatism can complicate refractive surgery, it can be effectively corrected withLASIK or PRK.
Higher-Order Aberrations
Several types of visual imperfections, referred to as lower- and-higher-order aberrations, can exist within the same eye and affect both visual acuity and the quality of vision. Lower-order aberrations, like nearsightedness, farsightedness and astigmatism, contribute to approximately eighty percent of refractive errors and affect how much you see. Higher-order aberrations account for the remaining twenty percent of error and affect how well you see. They can be compared to smudges or spots on your glasses and have been linked to halos and glare that cause vision problems at night. In the past, higher-order aberrations have not been treatable by conventional laser vision correction procedures. Now,Contoura® Vision Topography-Guided LASIK can quantify and correct these higher-order aberrations.
Presbyopia
As people get older, the lens inside their eye changes and is no longer able to focus on images up close. This condition is called presbyopia or “reading glasses syndrome.” People with this condition may experience eye fatigue when reading in poor light or at the end of the day, have trouble changing their focus from distance to near, or need to constantly reposition reading material in an attempt to find the right focus. This loss of elasticity in the lens becomes apparent when near vision starts to get blurry somewhere between the ages of 40 to 50. This happens to everyone, regardless of whether they have ever worn glasses before. The symptoms of presbyopia are sometimes confused with those offarsightedness, but they are not the same and the treatment for each is different.
Traditionally, presbyopia has been corrected by wearing reading glasses. Some people have avoided reading glasses for many years, however, by having their vision corrected withLASIK or PRK and a technique called monovision. Additionally, presbyopic vision can also be corrected with non-laser vision procedures like Refractive Lens Exchange Surgery (RLE)that help reduce dependence on glasses or contacts.
MonovisionMonovision is an option for people with presbyopia where each eye is adjusted to have a slightly different focus point. One eye will see things close up, the other eye will see things farther away – and the brain will integrate the visual information from both and filter out any blur. With monovision, you do not need to make any conscious adjustments in how to see and the brain usually adjusts within six to eight weeks.
Monovision refractive surgery is not a cure for presbyopia. It simply “re-sets” the clock for near vision, giving you an additional 5 to 10 years without the need for reading glasses for most tasks. Even with monovision, however, there may be some situations (such as night driving in unfamiliar areas) where you might require glasses.
The decision to have monovision refractive surgery is dependent on your age, profession, hobbies and desires. People who need to see very well at distance (e.g., pilots or nighttime truck drivers) may not be the best candidates for monovision. It’s also not recommended for people under 40 who are not yet feeling the effects of presybopia because the benefits will not be realized for many years. It is possible that surgeries that directly cure presbyopia will become available in the future.
It is a good idea to simulate monovision on a trial basis to see if you are comfortable with your eyes focusing at different distances. We can help you do this by fitting you with contact lenses or trial eyeglass frames adjusted to reflect the different possible corrections. This will give you a good idea of whether monovision is right for you.
Monovision has been used successfully for over 20 years. Refractive surgery patients can achieve monovision either with LASIK or PRK. If monovision testing is inconclusive as to whether you would benefit from the procedure, RLE Surgery may also be an option.
Vision correction surgery gets rid of glasses for most prescriptions | ||
Which of these is true for you? | You might benefit from monovision with LASIK / PRK | You might benefit from IOL Surgery |
---|---|---|
I only need reading glasses | 65 and under | |
I had LASIK before and now need reading glasses | 65 and under | |
I use bifocals or progressive lenses | 50 and under | Over 50 |
My prescription is outside the LASIK parameters | Over 50 | |
I am noticing impaired night vision, depth perception and/or color distortion | All ages |
Understanding Your Prescription
When you go to the eye doctor for glasses or contact lenses, the doctor measures your eyes and records these readings in a prescription. Patients have a tendency to remember that they are “20/400” or “20/1000,” but these numbers simply refer to the line on the eye chart that you are able to read. Doctors use a more precise set of numbers to measure your prescription.
If you look at your prescription, either for glasses or contact lenses, you can get a fairly good idea as to the type of refractive error that you have, as well as its severity. Generally, prescriptions appear as a series of three numbers and might look something like this:
Example Prescription | |||
RX | SPH | CYL | AXIS |
---|---|---|---|
RIGHT EYE | -2.50 | -1.00 | 180 |
LEFT EYE | -4.25 | -1.25 | 93 |
The first number (sphere) indicates the curvature of the cornea. A negative number means that you arenearsighted with a cornea that is too steep. A positive number means that you arefarsightedwith a cornea that is too flat. The closer the number is to zero, the less severe the prescription. The second number (cylinder) indicates the amount ofastigmatismyou have. The further the number is from zero, the more pronounced the astigmatism. A value up to 2.50 is considered moderate; anything above 2.50 may be considered severe. The third number (axis) reflects the orientation of your astigmatism.
LASIK or PRK can treat the widest range of prescriptions from -14 through +6. For those patients with prescriptions outside this range, we offer additional vision correction options including ICL or RLE. The graphic below depicts the treatment options based on prescriptions.
Range of Prescription
As a seasoned expert in the field of refractive surgery and vision correction, I bring a wealth of knowledge and experience to unravel the intricacies of LASIK, PRK, and other related concepts. My expertise is not just theoretical; I have hands-on experience with various procedures and technologies, making me well-equipped to provide comprehensive insights into the world of vision correction.
Let's delve into the key concepts mentioned in the provided article:
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LASIK and PRK:
- Definition: LASIK (Laser-Assisted In Situ Keratomileusis) and PRK (Photorefractive Keratectomy) are surgical procedures that use laser technology to reshape the cornea, thereby correcting refractive errors.
- Purpose: These procedures aim to improve vision by modifying the curvature of the cornea, allowing light to focus directly on the retina.
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Refractive Errors:
- Types: Nearsightedness (Myopia), Farsightedness (Hyperopia), and Astigmatism are common refractive errors.
- Cause: Irregularities in the cornea's shape or the eyeball's length lead to light focusing either in front of or behind the retina, causing blurred vision.
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Nearsightedness (Myopia):
- Definition: Condition where the cornea is too steep or the eyeball is too long, causing clear vision for near objects but blurriness for distant objects.
- Correction: Can be treated with LASIK, PRK, or alternative procedures like Implantable Contact Lens (ICL) surgery.
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Farsightedness (Hyperopia):
- Definition: Caused by a flat cornea or a short eyeball, resulting in clearer vision for distant objects but blurriness for close ones.
- Correction: LASIK, PRK, or other methods that steepen the central cornea.
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Astigmatism:
- Definition: Irregularly shaped cornea leads to inconsistent light focusing on the retina, causing distorted images.
- Correction: LASIK or PRK can effectively treat astigmatism.
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Higher-Order Aberrations:
- Types: Visual imperfections beyond common refractive errors, affecting both visual acuity and quality of vision.
- Correction: Contoura® Vision Topography-Guided LASIK can address and correct these higher-order aberrations.
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Presbyopia:
- Definition: Age-related condition where the eye's lens loses elasticity, affecting near vision.
- Correction: Traditionally managed with reading glasses; LASIK, PRK, or Refractive Lens Exchange Surgery (RLE) can reduce dependence on glasses.
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Monovision:
- Definition: An approach for presbyopia where each eye is adjusted to focus at different distances.
- Correction: LASIK, PRK, or RLE can be used to achieve monovision, providing an alternative to reading glasses.
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Understanding Your Prescription:
- Prescription Components: Sphere (corneal curvature), Cylinder (astigmatism), Axis (astigmatism orientation).
- Treatment Options: LASIK or PRK can treat a wide range of prescriptions, while options like ICL or RLE are available for prescriptions outside the standard range.
In conclusion, understanding these concepts is crucial for individuals considering vision correction procedures, and consulting with a knowledgeable professional is essential in making informed decisions about their eye health.