Vision Correction Procedures FAQs

What are refractive errors?
The eye functions similar to a camera with two lenses: the crystalline lens inside the eye and the cornea. The cornea, which is the clear tissue or window covering the front of the eye, is the stronger of the two lenses of the eye and contributes about 2/3 of the focusing power of the eye. For images to be seen clearly, they must be focused on the retina, the light-sensing tissue inside the eye that functions like the film in the camera. An eye that does not require corrective lenses to achieve this is called “emmetropic”. A refractive error—which includes myopia (nearsightedness), hyperopia (farsightedness), and astigmatism—exists if glasses or contact lenses are needed to properly focus images on the retina.

Myopia exists when the focusing power of the eye is too strong and images are focused in front of the retina. This is due to an eye that is too long or a cornea that is too steep. Hyperopia occurs when the focusing power of the eye is too weak and images are focused behind the retina. This condition is caused by an eye that is too short or a cornea that is too flat. Astigmatism is present when the focusing power of the eye is different in different directions so that images are brought to focus at more than one point. This results from uneven corneal curvatures so that the shape of the cornea is more elliptical than spherical (more like a football than a baseball).

Glasses, contact lenses, and refractive surgery are methods of correcting refractive errors.

What is laser vision correction?
Refractive surgery includes many procedures that change the way the eye focuses light on the retina. Laser vision correction is a remarkable advance in refractive surgery for myopia, hyperopia, and astigmatism. The two most common forms of laser vision correction— LASIK (laser in-situ keratomileusis) and PRK (photorefractive keratectomy)—use an FDA approved excimer laser to reshape the cornea to help improve the natural focus of the eye. Excimer laser technology is extremely precise with each pulse of the laser removing microscopic amounts of tissue (0.25 micron) under computerized control. The unpredictability in laser vision correction occurs because every person and every eye heals differently.

The goal of refractive surgery is to reduce one’s need for corrective lenses.

Will I need reading glasses?
If you are over the age of 40, you will probably notice poorer near vision. This is due to the natural aging process of the lens inside the eye and is called presbyopia. Presbyopia cannot be corrected with laser vision correction and therefore you will eventually require reading glasses for near vision. Monovision is an alternative in which one eye is corrected for distance and one eye for near. If you are interested in this option, a monovision trial with contact lenses can be performed prior to surgery to see if you are a good candidate.

What other types of refractive surgery exist?
There are many different procedures that can be used to correct refractive errors. Laser vision correction is currently the most popular type of refractive surgery, but alternatives do exist.

RK (radial keratotomy), which uses deep incisions in the cornea to correct myopia, was very popular prior to laser vision correction but is less predictable and structurally weakens the cornea.

AK (astigmatic keratotomy) is a similar technique in which peripheral corneal incisions are used to reduce astigmatism. This procedure is still utilized, often in conjunction with other techniques.

Intacs are small plastic ring segments that are placed into the peripheral cornea to correct low levels of myopia. Intacs spare the visual axis and are reversible, but the long-term effects of an intracorneal foreign body are not known, and this technique cannot correct moderate or high levels of myopia. Intacs are also being investigated for the correction of hyperopia and astigmatism.

Refractive lens exchange (RLE or presbyopic lens exchange (PRELEX)) is an intraocular surgery in which the natural lens in the eye is removed and replaced with a lens implant. Essentially this is cataract surgery prior to the formation of a cataract. This technique is extremely predictable, however, there are added risks because it is an intraocular procedure rather than just surgery on the surface of the eye.

Thermal keratoplasty (laser (LTK) or conductive energy (CK)) is a technique of heating the peripheral cornea to change its shape and correct low levels of hyperopia. It is extremely safe but the effect tends to fade with time. This procedure has been advertised for correcting presbyopia, however, it does not truly reverse this condition but rather can be used to make the eye slightly nearsighted. This compensates for presbyopia by allowing near vision without glasses, but the distance vision will become blurrier.

Who is a candidate for laser vision correction?
You may be a candidate for LASIK or PRK if you are at least 21 years of age, have healthy eyes, are free of any medical or ocular disorders that may interfere with healing, and have had a stable prescription for a minimum of one year. The amount of correction that has been approved for treatment varies slightly among the different lasers but in general, the lasers are used to treat: nearsightedness between -1.0 and -10.0 D, astigmatism between 0.75 and 4.0 D, and farsightedness between +1.0 and +4.0 D.

While the majority of patients are pleased with their results, no one can promise that you will be able to “throw away your glasses” after surgery. If your goal is to reduce your dependency on glasses or contact lenses, then laser vision correction may be right for you. Understanding the limitations of refractive surgery and having realistic expectations is an important factor for a successful outcome.

Your suitability for the procedure can be determined following a comprehensive eye examination. At that time, special measurements of the eyes will be performed to detect any unseen abnormalities, and you will have the opportunity to have all of your questions answered. If you wear contact lenses, you should discontinue them for at least 1week (soft contacts) or 4 weeks (gas permeable or hard lenses) before this examination, since contact lenses can temporarily change the amount of myopia, hyperopia, and/or astigmatism in your eye and interfere with obtaining accurate measurements.

The decision regarding refractive surgery is a very individual one and you should be fully informed about your options before making a choice. Our goal is to provide the safest and most effective procedure tailored to your individual needs.

What is a wavefront or custom treatment?
All of the laser manufacturers are developing a new generation of laser software to allow for wavefront or customized treatments. The technology is based on individualizing treatments to match the unique refractive errors and aberrations in your eye. A new device is used to measure and map the eye's optics. This information produces a unique wavefront map or wavescan for each eye, and the wavescan is then used to guide the laser ablation so that a customized treatment is performed. Wavefront treatments may result in improved quality of vision.

What happens during the procedure?
Eye drops are used to anesthetize the eye, a small device called a speculum is positioned to keep your eyelids open and prevent blinking, and you will be asked to look at a fixation light in the laser. The laser portion of the treatment lasts less than 60 seconds and the entire procedure usually takes about 10 minutes.

With LASIK, a thin corneal cap is created with a specialized scalpel called a microkeratome which glides across the surface of the cornea. A suction ring is placed on the eye to stabilize it during this part of the procedure, and while the suction ring is in place, the vision in your eye will gradually dim and then go dark. This is normal and indicates that the appropriate level of suction, to safely make the corneal flap, has been achieved. The suction ring is removed, the flap is folded back, and then the laser treatment is performed on the underlying cornea to reshape the surface. The laser makes a loud clicking/popping noise. The flap is repositioned and held in place by the natural pump mechanism of the cornea.

With PRK, rather than making a flap, the surface cells of the central cornea are gently removed and the laser is applied to the underlying corneal tissue. Then a thin contact lens is placed in the eye as a bandage to help with healing and discomfort.

Two other procedures that are variations of the above, epi-LASIK and LASEK (laser-assisted subepithelial keratectomy), combine the techniques of LASIK and PRK to create a flap of only surface cells without cutting the cornea. Theoretically designed to offer the advantages of both procedures without the complications, epi-LASIK and LASEK have not proven to be any different than PRK except that they take longer to perform.

What are the risks?
All surgical procedures have potential risks. Laser vision correction is a comparatively safe procedure, but complications do occur. Therefore, you should fully understand all the potential risks before undertaking any procedure.

Fortunately, complications are rare and serious complications are very rare. Once the eye heals, you may be under- or overcorrected. In almost all cases, this can be improved by a second procedure. Glare or halos around lights at night are often noticeable (as they can be with contact lenses) but rarely disabling. This phenomenon tends to resolve after 6-12 months but may be permanent. The eyes do get drier after surgery, but this is usually a temporary and asymptomatic effect that improves over 6-12 months. In very rare cases, someone without preexisting dry eye can develop permanent dryness.

There is a very small risk of infection, scarring, or irregular astigmatism, and sometimes these complications may cause a decrease in “best-corrected visual acuity”, which means that your vision with corrective lenses may not be as clear as it was before the surgery. Other complications include healing problems, progressive corneal thinning, or other unexpected results. Any of these, if significant, may require the use of corrective lenses for good vision. In rare instances, as with any eye surgery, vision can be permanently reduced as a result of a complication. In extremely unusual circumstances, additional surgery such as a corneal transplant is needed.

With LASIK, there can also be complications with the corneal flap. If the flap is not perfect, the laser portion of the procedure is not performed. The cornea is allowed to heal and then the surgery can be attempted again. Similarly, adequate suction to create the flap sometimes cannot be achieved and the procedure will have to be rescheduled. Other flap problems include dislocation of the flap, wrinkles in the flap, inflammation under the flap, and surface cells growing underneath the flap. With PRK, steroid drops are used after the surgery for 1 to 4 months, and this carries a small risk of causing high pressure in the eye which may lead to glaucoma. Very rarely a cataract may develop.

The occurrence of a significant complication with laser vision correction is very rare, generally 1% or less. However, even though the risks are low, there is no such thing as risk-free, guaranteed surgery for any condition.

Will I have any pain?
During the surgery, your eye will be anesthetized and you will not feel any pain. With LASIK, some patients notice a pressure sensation from the suction device when the flap is being prepared. After the procedure, there is a variable amount of discomfort. This is more with PRK but is helped with the bandage contact lens and diminishes after several days. If necessary, pain medication may be prescribed.

Which procedure is better?
This is a decision that is best made by you and your doctor. In general, both procedures give similar results for low to moderate levels of correction, while for very high levels of correction, LASIK appears to be more predictable and stable because there is less likelihood of scarring and regression. LASIK also offers the advantages of rapid recovery, less discomfort, and fewer postoperative visits as compared to PRK. However, LASIK requires an additional step (the creation of a flap) and rarely the flap is not perfect and the laser treatment must be delayed.

Whichever procedure you choose, the most important aspect is that you are confident and comfortable with your decision.

What can I expect after surgery?
Patients notice an improvement in vision immediately after laser vision correction. Your vision is initially blurry but clears rapidly over the ensuing days. Some fluctuation in vision may occur for weeks after the treatment. Depending on the type and degree of your refractive error, the chances of seeing 20/40 or better after surgery may exceed 95%.

After LASIK, most people are able to drive and resume work the next day. The healing process is longer with PRK, so patients may not feel comfortable driving or returning to work for several days. The majority of patients undergoing laser vision correction will experience some degree of glare or halos, particularly at night. This improves with time and commonly is not noticed after six months. Some people notice more dryness of the eyes for weeks to months after the surgery. After LASIK, there may be small red patches on the whites of the eye from the suction ring.

Undercorrections or overcorrections may occur, and therefore glasses or contact lenses may be necessary to provide sharper vision. Once the eye has stabilized, usually three months after the initial surgery, a second treatment or enhancement procedure is sometimes performed to fine tune the results.

What restrictions will there be after surgery?
Almost all routine activities may be resumed within 1 to 3 days. You cannot rub your eye for 1 month and should not get water in the eye for 2 weeks. No eye make-up should be worn for 1 week.

Mid-Peninsula Ophthalmology Medical Group

Ophthalmologists located in Menlo Park, CA

Mid-Peninsula Ophthalmology Medical Group, located in Menlo Park, CA, was founded in Palo Alto in 1960 and has established a legacy of superior comprehensive and specialty eye care in the peninsula over the past 55 years.

The true difference in our practice is our commitment to you, the patient. We make it our mission to take our time with you to discuss your concerns, and we use state of the art diagnostic and therapeutic technologies to take care of all of your eye issues.  We pride ourselves on being easily accessible, having very limited wait times, personally contacting you with your medical information, and being personally involved in all aspects of your exam and care. We value your time and the way our practice runs demonstrates that. 

We are committed to excellence, and our doctors provide the highest quality of care with a personalized approach that will best serve the individual needs of each patient. Our goal is to create a partnership with you, to ensure that you make informed decisions regarding your vision. Our physicians are board-certified ophthalmologists, members of the American Academy of Ophthalmology, and faculty members at Stanford University.

We want our office to be your one-stop destination for all of your eye care needs. Our physicians are trained in the most advanced techniques in eye exams, glaucoma evaluation, diabetic eye care, cataract surgery, vision correction surgery, eyelid surgery, and cosmetic facial rejuvenation. We also offer an array of glasses and contact lenses and operate a complete optical dispensary for your convenience.  Finally, we have a brand new in-office procedure room for your convenience. 

From treating vision disorders in all age groups to diagnosing ocular diseases or performing sophisticated eye surgery, MPOMG has a team of trusted specialists who make sure that you and your family receive the best eye care on the Peninsula.

Please contact our friendly staff to make an appointment or obtain information regarding our services.

Read more
Mid-Peninsula Ophthalmology Medical Group

Mid-Peninsula Ophthalmology Medical Group, located in Menlo Park, CA, was founded in Palo Alto in 1960 and has established a legacy of superior comprehensive and specialty eye care in the peninsula over the past 55 years.

The true difference in our practice is our commitment to you, the patient. We make it our mission to take our time with you to discuss your concerns, and we use state of the art diagnostic and therapeutic technologies to take care of all of your eye issues.  We pride ourselves on being easily accessible, having very limited wait times, personally contacting you with your medical information, and being personally involved in all aspects of your exam and care. We value your time and the way our practice runs demonstrates that. 

We are committed to excellence, and our doctors provide the highest quality of care with a personalized approach that will best serve the individual needs of each patient. Our goal is to create a partnership with you, to ensure that you make informed decisions regarding your vision. Our physicians are board-certified ophthalmologists, members of the American Academy of Ophthalmology, and faculty members at Stanford University.

We want our office to be your one-stop destination for all of your eye care needs. Our physicians are trained in the most advanced techniques in eye exams, glaucoma evaluation, diabetic eye care, cataract surgery, vision correction surgery, eyelid surgery, and cosmetic facial rejuvenation. We also offer an array of glasses and contact lenses and operate a complete optical dispensary for your convenience.  Finally, we have a brand new in-office procedure room for your convenience. 

From treating vision disorders in all age groups to diagnosing ocular diseases or performing sophisticated eye surgery, MPOMG has a team of trusted specialists who make sure that you and your family receive the best eye care on the Peninsula.

Please contact our friendly staff to make an appointment or obtain information regarding our services.


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Mid-Peninsula Ophthalmology Medical Group
1225 Crane Street
Suite 200
Menlo Park, CA 94025