We explain your vision,
prescription and options
for great vision.

Understanding Your Vision – Nearsightedness / Farsightedness / Astigmatism

Eye chart test measures visionThe key to understanding refractive surgery is to understand how the eye works. Once you’ve read about your vision below, check out what your prescription 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 correction improves the way the eye focuses light by modifying the curvature of the cornea and re-focusing the light directly on the retina.

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 with LASIK 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, 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 with LASIK or PRK.

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 with LASIK 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.

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 of farsightedness, 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 with LASIK 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.

Monovision refractive surgeryMonovision 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
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 are nearsighted with a cornea that is too steep. A positive number means that you are farsighted with 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 of astigmatism you 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.

Vision correction procedure for the range of prescriptions

Range of Prescription

Lauren S.
Downtown, Campbell, CA


Dr. Furlong and his entire staff have changed my life! After 11 years of dealing with contacts and glasses, I finally took the Lasik plunge and am SO thankful I did! Dr. Furlong and his staff were so informative, friendly, and reassuring. They made everything so easy and made me feel 100% comfortable...

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Nlramesh R.
Mount Hope KS


Amazing doctors and staff.  Dr. Mona Sane did my cataract surgery and she was absolutely awesome!! The staff at Dr. Furlong's and at the surgery center were super professional and you just knew you were going to be alright at the end of the procedure.  The post op care was just excellent !! If...

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McKinley S.
Marina, CA


I had Lasik 1 year ago and I am still amazed by how well I can see. I have worn glasses and contacts for many years.  I could see well with my contacts so I was expecting to see like that after Lasik. What I didn't expect, was how much better I see now after Lasik. The quality is SO MUCH BETTER. I...

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Kim M.
Santa Clara, CA


This review is long overdue. I actually had my surgery done about a year ago. I had been told for several years from various optometrists I would never be able to even have the surgery because of an eye condition. But when I started to see Dr. Ratra at Dr. Gold & Associates, she referred me to...

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Jennifer B.
Prescott, AZ


In October I underwent LASIK surgery with Dr. Furlong and his staff and I couldn't be happier. It has been life changing after 23 years of wearing contacts and glasses. I had a high astigmatism prescription and at my first last post op checkup about a two months post op I was at -20/20 in the left...

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Rosa M.
Monterey, CA


I got referred to Dr.Furlong by my optometrist. She couldn't have referred me to a better doctor. I had LASIK done less than a week ago & I am beyond amazed with the results. I've worn glasses for 15 years & contacts for 13 years. I was a bit nervous the day of surgery but Dr.Furlong...

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Leah F.
San Francisco, CA


Gotta pay my overdue Yelp gratitude here. Furlong has an all-star staff. Carol specifically is a wonderful human being and professional. They're prepared for every possible scenario. My story varies slightly from others in that I did experience bad halos/glares for roughly 2 weeks following surgery (which is...

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Matt C.
Fullerton, CA


Dr. Furlong was a recommendation from my optometrist. My first visit was fast and easy. My optometrist had already done my dilation so they just needed to take measurements and double check that I was a candidate. Everyone was very professional and friendly. I was nervous about everything but my patient counselor...

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Shilpi R.
Sunnyvale, CA


I recently had LASIK done with Dr. Furlong and it was an amazing experience. I wanted to have LASIK so that I could wake up first thing in the morning and not worry about contacts or glasses! As an optometrist myself I knew the ins and outs a little bit more but everything was on point! Their waiting room is always...

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Gabriel N.
Union City, CA


This has easily been one of the best decisions I have made in my life. After having glasses for most of my life, it's crazy to think I can now wake up and see clearly. I was referred here by my optometrist, Dr. Toy, in early 2016. I came for the free consultation where Dr. Furlong and his staff determined that I...

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Randy M.
San Jose, CA


Five stars.  Why?  I was suffering from rapidly progressing cataracts at the relatively young age of 37.  I was forced to take time off of work until the first surgery was complete.  My left eye had deteriorated from 20/300 in January to "hand motion (I could see light differences and movement only)" the day...

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Himi A.
Fremont, CA


My lasik surgery experience at the center was fabulous! The staff is very friendly, customer service is great! Interaction with Dr. Furlong was directly in the surgery room. Everything was very smooth and the location is super hygienic and has the top technology.

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Betty M.
San Francisco, CA


Just got my lasik surgery done last week by Dr. Furlong, and so far so good! I got referred to Dr. Furlong from my optometrist. A little pricier than competitors, but it's YOUR EYES, not the situation to be looking for a discount. They take a lot of time to make sure that you're comfortable and informed, and the...

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Jennifer H.
Fremont, CA


One of the best decisions I've made in my life! It took me about 2 years before I actually made a decision and not to sound super corny or anything... I should've done it sooner! It's definitely easier saying that knowing my LASIK surgery went well so I completely understand anyone's fear or hesitation with...

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A S.
Sunnyvale, CA


My mom had cataract surgery with with Furlong Vision this past month. It was a smooth experience.  She had one eye done first, followed by the second eye a few weeks later.  She saw Dr. Furlong for consultation in June.  He gave her a detailed exam and performed various scans.  She decided to go with femto laser...

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Leigh B.
Half Moon Bay, CA


Dr.Furlong did PRK for my insanely farsighted eyes in September 2016. I am now seeing 20/20!!! I couldn't be happier with the results. I also appreciated that he was honest when he didn't recommend PRK for my thin corneas... better safe than sorry! Thanks again, best money I could have spent on myself.

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Mike B.
Santa Cruz, CA


I rarely write reviews on Yelp, but for something as important as LASIK, I did a lot of research & visited several places in Silicon Valley. I recommend you do too! You get what you pay for...don't budget on your eyes! You want the best technology & an experienced & personable  Doctor. Dr. Furlong is...

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Yee L.
Palo Alto, CA


Super thorough and professional.  The staff accurately explained exactly what to expect and answered all my questions in an even-handed way with lots of detail about risks and benefits.

Theres no guarantee of results, but turns out my vision was corrected to better than 20/20 and I'm very happy with the results.

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Voted Best LASIK Doctor by Santa Cruz Good TimesTwice named a Premiere Cataract Surgeon by Ocular Surgery NewsSponsor of Santa Clara County Optometric SocietyJefferson Award - the "Nobel Prize" for community and public service for the Furlong Vision Correction Gift of Sight programOfficial laser vision correction and eye surgeon and Legacy Partner of the San Jose Earthquakes