WHAT IS LASER EYE SURGERY?
Refractive or Laser Eye Surgery (LES) is a laser reshaping of cornea thus changing its focusing power (1), (pictures 1,2). For patients with moderate refractive errors this ambulatory procedure is a quick way to get free of glasses or contact lenses.
Picture 1. Eye doctor performing laser eye surgery
(source: whmc.af.mil)
COST OF LASER EYE SURGERY
The cost of LES can vary widely but it is rarely under $1,000 per eye (2).
REFRACTIVE ERRORS TO CORRECT WITH LES
The light from an observed object penetrates through the cornea, lens and viscose liquid of the eye globe, refracts, and focuses on retina as an image. In farsightedness - hyperopia the eye globe is too short, and since the lens cannot refract the light from near objects enough, the light will fall behind retina and give a blurred image. In presbyopia (farsightedness of the aged) the lens becomes rigid and cannot refract the light from near objects efficiently, so it will again focus behind the retina. In nearsightedness (myopia), the eye globe is too long and light from distant objects will focus in front of the retina, so images of distant objects will be blurred. In astigmatism blurred vision is caused by irregularities in the corneal or lens shape (3). All mentioned refractive errors can be corrected with laser eye surgery.
HOW TO FIND A LASER EYE SURGEON?
A convenient way is to ask an eye doctor for advice. Before undergoing any investigation or procedure a thorough talk has to be made with a surgeon; contact with his previous patients is also appreciated. Results of LES are often permanent, can’t be changed sometimes so patient has to find a trustable surgeon.
EYE EXAMINATION BEFORE SURGERY
Ophtalmologist (not necessary the surgeon) will ask questions about patient’s general health and will perform some eye tests (refraction, glaucoma test, visual field test, wavefront test for eye aberrations…) then will recommend appropriate treatment (10). Surgeon who will actually operate will maybe want to add or repeat some tests before the operation.
Who are CANDIDATES for LES? Patients over 18 (or over 21 in some cases) with stable (at least one year) mild or moderate refractive error.
CONTRAINDICATIONS for LES: contact lenses or glasses prescription in the last year, Herpes zoster around the eye, glaucoma, eye inflammations/injuries, dry eyes, keratoconus, corneal scarring, cataracts, rheumatoid arthritis, diabetes, lupus, HIV, pregnancy or breastfeeding, medications that may influence vision (narcotics) or cause slow wound healing (steroids), sports like boxing.
Precautions: Large pupils can cause glare, halos after surgery. With thin corneas blinding complications can appear. Previous refractive surgery, job regulations (pilots) can be additional reasons to reject LES.
CARE BEFORE THE EYE SURGERY?
Contact lenses change the shape of the cornea so they should be replace with glasses 1-4 weeks before eye examination for LES. The day before surgery using eye cosmetics should be stopped also.
TYPES OF LASER EYE SURGERY
The most commonly used laser in LES is Exscimer laser which produces a beam of ultraviolet light to vaporize and thus remove the tissue. Many variants of this laser are in use (4).
Picture 2. Laser eye surgery (LASIK) procedure:
The cornea is cut with a knife (microkeratome), a corneal flap is folded back,
cornea reshaped with a laser beam, and corneal flap placed in its original position.
PRK
In PRK (Photo-Refractive Keratectomy, developed in 1987) the top layer of cornea -epithelium is removed with a surgical blade and the desired amount of underlying corneal tissue (stroma) is vaporized using an Excimer laser. Removed epithelium then regrows naturally in about 2 weeks (5).
LASIK
In LASIK (Laser Assisted in Situ Keratomileusis, first used in 1993) a 200-300 µm thick flap in the cornea is cut using a knife - microkeratome. A hinge is left at one end and the flap is folded back revealing the stroma of which a portion is vaporized with an Excimer laser. Afterwards, the flap is put back and the eye heals more quickly than with PRK. LASIK is the most commonly used refractive surgery procedure (picture 1).
PRESBY (MULTIFOCAL) LASIK is for presbyiopic people. Cornea’s center is altered to enhance near vision while the outer periphery provides zones for distance vision (9). This method currently does not represent a permanent solution, since presbyopia develops with time.
WAVEFRONT LASIK
WAVEFRONT LASER (used from 2002) sends a beam of light to the retina which then bounces back to a sensor, which measures the irregularities of the cornea and lens and produces a 3-D map of the eye’s visual system. Surgeon uses this map to program the computer that controls the operating laser. After WAVEFRONT LASIK (CUSTOM LASIK) 90-94% of patients reached 20/20 vision or better as opposed to 80% with traditional LASIK (8).
LASEK
LASEK - Laser Epitelium Keratomileusis - (e-LASIK, epithelial LASIK) is using a finer blade (trephine) and is thus appropriate for correcting thin or flat corneas. Flap edges heal in about a day (6).
INTRALASE
With INTRALASE technique an infrared laser is used instead of microkeratome to make a flap (ALL LASER LASIK). Thinner flap (100 µm) and its vertical edge which fits tightly with the rest of the cornea are major advantages. There is no obvious difference in vision improvement reported using microkeratome or intralase, but there is less complications like scarring etc. (7).
MONOVISION
MONOVISION is situation (intended for the presbyotic patient) when one eye is operated to be adjusted to near sight and the other one for distant sight. Trial period with special contact lenses for some days is available to find out if the patient will be able to cope with expected loss of depth perception and permanent blur in one eye. These effects of monovision are most noticeable at night and when sharp vision is needed. In these situations a patient may still need to wear glasses or contact lenses.
LASER EYE SURGERY PROCEDURE
The surgery should take less than 30 minutes as outpatient procedure. Patient lies on its back on an operating chair, a drop of anaesthetic is placed in the eye and a lid speculum is used to hold eyelids open. A ring is placed on the eye and pressures is applied to create suction to the cornea. This can cause some discomfort, but is usually not irritating. The cutting instrument is attached to the ring and a flap in the cornea is cut and folded back on its hinge.
The laser is then positioned over patient’s eye and he/she is asked to stare at a light (for about 60 seconds) to keep eye fixed. A computer controls the pulses of laser energy needed. Laser beam vaporizes the corneal tissue and after that the displaced flap of corneal tissue is put back into the original position.
A shield should be placed over the treated eye at the end of the procedure since no stitches are used to hold the flap in place. It is important not to rub eyes and protect them from pressure during sleep. Patients are usually back to work in few days.
It is recommended that the second eye is operated after the first one is completely healed and the vision stabilizes (after some months). Operation of both eyes in one procedure is possible though.
AFTER SURGERY CARE
Immediately after the procedure the patient can experience discomfort or pain, so a mild pain reliever can be prescribed. Both eyes may tear and vision may be blurred. Over-sensitivity to light and eventual bruises should improve in few days. A few days off the work and sport activity is recommended. If any unexpected pain, tension or excretion appears doctor should be attended immediately.
To prevent infection, eye cosmetics should be avoided for at least two weeks. Swimming and sports with possible eye exposure to hits should be avoid for 1-2 months. It may take up to 3-6 months for vision to stabilize after surgery. Glare, haloes, difficulty driving at night may persist during this time.
EFFECT of LES
Most patients are pleased with the results of their refractive surgery.
One study running from 2000-2003 in U.S. showed that 86% achieved 20/20 or better vision and 98% achieved 20/40 or better (11).
Results are generally not as good in patients with very large refractive errors of any type. For some farsighted patients, results may diminish with age.
COMPLICATIONS OF LASER EYE SURGERY
Up to 5% of people undergoing the procedure experienced some type of problem (15).
Some patients after surgery lose vision ability in the way which can’t be corrected with glasses, contact lenses, or another surgery. Persisting glare, halos or double vision can seriously affect night vision. Someone may still need glasses or contact lenses after surgery. Some patients may develop severe dry eye syndrome which may be permanent and intensive drop therapy may be required.
Picture 3. Bleeding beneath conjunctiva is a minor and transient, but common post-LASIK complication
CLASSICAL EYE SURGERY
Radical keratotomy (RK) is a classic surgical procedure for cornea shape correction, and is now obsolete. Conductive keratoplasty (Nearvision CK) uses low heat radio waves to steepens the cornea. Implanted lenses are used as additional artificial lenses for higher levels of nearsightedness. Natural lens remains intact. At Refractive Lens Exchange (RLE) the natural lens is removed and replaced with artificial one (12).
Laser is also used for treatment of retinal detachment (13).
References:
- http://fda.gov/cdrh/lasik/
- http://allaboutvision.com/visionsurgery/cost.htm
- http://www.allaboutvision.com/eye-exam/refraction.htm
- http://www.allaboutvision.com/visionsurgery/lasik_laser_2.htm
- http://www.allaboutvision.com/visionsurgery/prk.htm
- http://www.allaboutvision.com/visionsurgery/lasek.htm
- http://www.allaboutvision.com/visionsurgery/intralasik.htm
- http://www.locateadoc.com/articles.cfm/372/1277
- http://www.allaboutvision.com/visionsurgery/presby-lasik.htm
- http://www.allaboutvision.com/eye-exam/expect.htm
- http://www.allaboutvision.com/visionsurgery/lasik_complication_1.htm
- http://www.allaboutvision.com/visionsurgery/other.htm
- http://www.eyemdlink.com/EyeProcedure.asp?EyeProcedureID=52
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