LASIK Information
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LASIK Information
Learning basic ocular anatomy and the related optics will help you understand LASIK and your refractive error. You can then decide if this surgery is appropriate for your visual needs.
Light passes through two ocular refractive elements, the cornea and the lens. LASIK changes the focusing power of the cornea. (It does not change the lens!) Images are focused on the retina and transmitted to the brain. The retina is protected by several structures; one of these layers is the sclera (the white part of the eye).Emmetropia means a distant image (in this case a “5”) is focused perfectly on the retina. This occurs when the curvature of the cornea, the shape of the lens and their distances from each other and the retina are in harmony.
This configuration of cornea, lens, and retina produce perfect focus for a distant object.
If you had this anatomy you wouldn’t be here!
Myopia (or nearsightedness) is extremely common. Distant images (like the pencil) are focused in front of the retina.
This configuration of cornea, lens, and retina produce perfect focus for a distant object.
If you had this anatomy you wouldn’t be here!
Myopia (or nearsightedness) is extremely common. Distant images (like the pencil) are focused in front of the retina.
Devices like glasses and contact lenses produce a sharp image.
LASIK is a three part surgical procedure designed to focus images by changing the corneal shape. First a corneal flap is created using a microkeratome.
A corneal flap is produced.
This allows access to the minimally reactive corneal stroma.
An excimer laser is used to sculpt the corneal shape without heat, discomfort, or scar.
The excimer laser is applied and corneal tissue is removed.
A complex computer program controls the ablation pattern and thereby produces the final corneal shape.
The surgeon must then carefully reposition the flap.
Notice the change in contour. This yields a new refractive power for the cornea.
Hyperopia (or farsightedness) is also common. Distant images (like the pencil) are focused behind the retina.
Some prefer to think the eye is too short for the cornea and lens.
Traditionally, hyperopia is corrected with spectacles or contacts. These devices converge the light rays prior to reaching the eye. This yields proper retinal focus.
Devices like glasses and contact lenses produce a sharp image.
The changes in corneal contour correct the underlying refractive error.
Astigmatism is an oval character in the cornea. By analogy a basketball has no astigmatism while a football has considerable astigmatism. Some patients with myopia and hyperopia also have astigmatism. Astigmatism distorts vision.
These reflections show astigmatism in the left cornea but none in the right cornea.
LASIK can be used to treat astigmatism, myopia, and hyperopia. It can also treat myopia with astigmatism and hyperopia with astigmatism.
The natural lens ages and becomes less flexible. This flexibility or accommodation makes it possible for us (in our youth) to focus both distant and near objects (parallel and diconverging light rays). The loss of accomodation is called Presbyopia and occurs in all patients, eventually. It mandates the use of reading glasses or bifocals.
LASIK will not prevent presbyopia. If you are nearsighted and don’t get LASIK you might avoid presbyopia. (Of course, you’ll need glasses for distance.) Once you have LASIK you get back in sync with your friends who never needed glasses or contacts and instead require reading glasses after forty.
Think of it as a variation of hyperopia for near objects only. It occurs as we age.
The natural lens can not flex enough to focus divergent light rays onto the retina.
LASIK will not prevent the need for reading glasses once you reach forty.
(Remember, you can’t take off your glasses after LASIK!)
We do not entirely understand the process of presbyopia. All we know is that like death and taxes, presbyopia will occur for all patients.
Presbyopia may result from lens thickening, changes in the supporting zonules, weakening of the surrounding musculature or increased scleral rigidity.
While some procedures for correcting presbyopia are on the drawing board, only one has gained widespread acceptance.
Clear lensectomy is a procedure in which the natural lens is removed and replaced with a bifocal (multifocal) intraocular implant. This technique is appropriate for those patients highly motivated to eliminate spectacles for both distance and near. They must be willing to experience a more involved procedure with a different risk benefit ratio. This has been call PRELEX.
Some patients benefit from monovision LASIK. This technique corrects one eye for distance and one eye for near. (We use the term monovision-R when the right eye is the near vision eye; similarly monovison-L means the left eye is set to near.) Patients who have been successful with this approach in their contact lenses adjust nicely to monovision LASIK. Only a few patients who have not experienced monovision before LASIK are happy selecting this option. They often complain of imbalance and lack of depth perception.
Sometimes a contact lens trial of monovision is advisable before monovision LASIK is performed. Fortunately, reversal of monovison LASIK is easily accomplished. (Note: you can not easily reverse standard LASIK and achieve monovision LASIK…so make this decision carefully.) These issues should be considered preoperatively.
Physiology
The cornea has five significant layers. The surface is called the epithelium. It repairs itself after injury (corneal abrasion) and is highly populated with nerve fibers . This explains the effectiveness of mace as well as the severe pain following corneal abrasion.LASIK avoids the highly sensitive epithelium and instead effects refractive changes by targeting the minimally reactive stroma.These attributes explain why patients with LASIK have considerably less discomfort and relatively rapid healing when compared to those with other refractive procedures like PRK or RK. These features in addition to an absence of scarring in almost all LASIK surgeries has lead to the procedure’s widespread acceptance, popularity and success.
During LASIK excimer energy in applied to the central stromal layer.
This structure is only a half millimeter in thickness.
PRK predates LASIK and still has some uses today. In PRK the epithelial layer is removed and excimer laser is applied to the anterior most portion of the stroma.
LASEK and Epi-LASIK are variations of PRK. Excimer energy is then applied to the anterior corneal stroma. Speed of visual rehabilitation and post-operative comfort are similar to PRK.
RK (radial keratotomy) and AK (astigmatic keratotomy) are incisional techniques developed in Japan and perfected in the former Soviet Union. They do not utilize a laser and has only a few indications today.
The innermost cellular layer is the endothelium. It allows the cornea to remain transparent by pumping fluid from the stroma and epithelium. Following any surgical intervention, including LASIK, some swelling or corneal edema occurs. The endothelium pumps out the excess fluid over time removing edema and improving vision.
Corneal transparity is maintained by the endothelial pumping mechanism.
Limitations
There are several ways to assess visual acuity. The most common technique was developed by Snellen in the 1800’s. The expression “20/20 vision” is associated with this measuring system. (Europeans and others who use the metric equivalent and refer to normal vision as 6/6.)The smallest letters a patient with 20/20 vision can distinguish at 20 feet are the same letters the idealized “normal patient” can see at 20 feet. The smallest letters a patient with 20/60 vision can distinguish at 20 feet are much larger. In fact, they are letters the normal patient can see as far away as 60 feet! (Basically, 20/60 is not good enough to drive.) Many patients who select LASIK see 20/200 or worse without glasses or contacts.
This measure of distance vision compares ones acuity to a normal patient.
It only tests black letters on a white background and may be misleading.
Most surgeons are careful to describe 20/20 as normal, not perfect.
Contrast sensitivity, glare, halos, and other measures of visual function are not assessed by Snellen acuity.
Nevertheless, we still use this method as the gold standard is determining the success of our refractive surgical procedures.
Physicians often measure the success of a refractive procedure by the amount of residual “error”.
A nearsighted patient with seven diopters of myopia may return in three months with a quarter of a diopter of residual myopia.
Patients usually see 20/20 or 20/15 in these cases and would not realize any benefit by wearing such a weak pair of new glasses.
We evaluate every patient with a topographer (computerized corneal mapping device) to make certain they do not have corneal warpage or irregular astigmatism. This condition, known as ectasia, is best treated with other modalities.
Patients with this condition should not have LASIK.
All patients are screened for this rare disease before surgery.
In some cases patients have had successful LASIK despite suggestive evidence of keatoconus.
Other contraindications include an unstable refraction, pregnancy, breast feeding, severe corneal and lid disease, and most importantly, unreasonable expectations.
Other issues such as youth (under 21), extremely large pupils with profound glare sensitivity, severe dry eye, amblyopia (lazy eye), collagen-vascular disease, immune deficiency, pre-existing viral keratitis, etc. must be addressed during your evaluation.
There may still be some vocations and avocations (commercial pilots, professional drivers, police work, deep sea divers, military service, martial arts professionals, etc.) in which refractive surgery is regulated. It is important that you check to make certain that having his procedure will not disqualify you from these activities.
Better One, Better Two
Most patients have LASIK on both eyes during the same surgical session. Despite the overwhelming trend for bilateral simultaneous surgery there are some proponents who support operating on one eye one day and the other on a different day. Their numbers are dwindling. The debate continues and we are happy to comply with your preference. There are rare occasions when we will suggest operating on only one eye during the first surgical session. Of course, some patients only want or need LASIK in one eye.
Enhancements
Enhancements are a refinement of the intended corneal sculpting through reapplication of the excimer laser. They are the result of numerous factors including biological variation and different rates of healing. Surgeons report enhancement rates anywhere from 1.8% to 20%. Enhancements can be performed after the eye has stabilized (>3 months) but can be performed years later. Enhancements are not failures. They are decisions to “tune-up” the refractive results when it is medically and clinically prudent.
Dry Eye
Many patients who seek LASIK have failed contact lens wear. A good percentage of them are predisposed to developing dry eye or actually have dry eye prior to surgery. Every patient can develop dry eye after LASIK. This is thought to be the result of an interruption in the nerve supply to the cornea, trauma to the conjunctiva while fashioning the flap, and changes in the corneal morphology and tear flow patterns. This dry eye is treated vigorously after surgery (and sometimes prior to surgery) with artifical tears, warm compresses, lipolytic agents, topical steroids, other topical medications, and temporary or permanent punctal occlusion if necessary. New methodologies have been developed including LipiFlow, Intense Pulsed Light (IPL) and Meibo. Artificial tears based on stem cells can also treat dry eye.
Dry eye is successfully treated and comfort returns in almost all cases.
Resources
The Internet has become an important resource for LASIK information. Its greatest strength is the easy of information dissemination. Unfortunately, it is also its greatest weakness. Many corporations, manufacturers and practitioners use the Internet to advertise. They disguise their promotions, opinions, and rhetoric as education or public service information. Some have a particular agenda while others are just inexperienced or inept. Nevertheless, the Internet is a great starting point for your exploration of LASIK. Consider visiting http://www.lewislasik.com for additional information and links. Friends, relatives, co-workers, and colleagues who have had the procedure are an excellent source of information. Finally, the best resource is your evaluation and a detailed discussion with your doctor.
Goals
LASIK has an outstanding record of safety and effectiveness. In fact, the FDA has approved it. Nevertheless, it is still major ophthalmic surgery with serious risks as well as highly rewarding benefits. Alternative forms of visual correction must be compared before any decision is made. LASIK has proven to be highly successful in dramatically reducing one’s dependence on glasses and/or contact lenses for most distance vision tasks. Results vary from person to person. The recovery of excellent vision can be different between two patients and even between two eyes of the same patient. It is important to anticipate and tolerate the vagaries of your eye’s visual rehabilitation.
Success depends on the surgeon, the operating room and support staff, the excimer laser, the instrumentation, the patient, and the patient’s expectations. Results can not be guaranteed.
Our goal is to achieve the best visual result in the safest manner. We want glasses and contact lenses to be a much smaller part of your life.
Night driving glasses and reading glasses may still be needed following LASIK.
LASIK
LASIK is an exciting procedure with the potential to change your life.
LASIK in 3d
- Creating the Flap
- Folding the Flap Back
- Applying the Laser
- Flap Return and Smooth
