Lasik eye surgery is currently the best method of correction of refractive errors. It is accurate, effective and safe.

In LASIK an ultra-thin (90 to 150 micron) flap of cornea is raised and then using computer guided Excimer Laser (mostly Argon Fluoride 193 nm) is delivered to reshape the corneal stroma into predetermined curvature. The flap is repositioned back. This leads to correction of myopia, hypermetropia, and astigmatism. The procedure is short and simple and being computer controlled is highly accurate.

Patient Selection for Lasik Eye Surgery

• Case selection is an extremely important determinant of the results of Lasik surgery:
• Refractive error:  -1.50  to -10.0 diopter of myopia
• Up to +6.0 diopter hypermetropia
• Astigmatism of up to 6 diopter
• Minimum age 18 to 21 years (preferably 21 years)
• Refraction should have been stable for at least a year.
• Contraindications: Keratoconus, thin corneas, corneal inflammatory diseases, herpetic keratitis and autoimmune diseases.
• Should not be performed during pregnancy - can be done 3 months after it.

Preoperative Preparation for Lasik Surgery

• Refraction under cycloplegia
• Corneal Topography
• Pachymetry for corneal thickness
• Aberrometry to measure higher order optical aberrations
• Pupillometry to measure pupil size in low light conditions
• Intra-Ocular Pressure (IOP) measurement
• Detailed Retina Examination
• Informed consent
• Antibiotic eye drops to be instilled for about 2-5 days before surgery

Contact Lenses should be discontinued for at least 2 weeks (Soft Lenses) / 4 weeks (Rigid Lenses) before the surgery

Lasik Surgery Procedure

LASIK is performed under topical anesthesia (Proparacaine Eye Drops) and the only cooperation required of the patient is to fixate at a blinking (green) light. Current LASIK machines have an advanced eye tracker device which realigns the Laser to any changes in the position of the eye thereby ensuring proper centration of ablation. The steps are:

Lasik - Flap lifting

Excimer Laser ablates the stromal bed to resurface it into desired curvature. What makes the Excimer laser so well suited for corneal ablation is its ability to remove tissue with accuracy up to 0.25 micron with each pulse. Often, only 50 microns of tissue are removed to achieve the proper amount of correction. The Excimer produces a non-thermal light beam that eliminates the possibility of thermal damage to surrounding tissues. In current Lasers employing flying spot technology a 1 mm spot ablates the tissue to correct the refractive error and to blend this area with surrounding cornea by creating smooth transition zones.

During this step a clicking / crackling sound is heard and an odor of ablating tissue (similar to charring hair) is smelt and a light flashing close to the eye is seen. All this while patient needs to concentrate on the center of the blinking (target) spot of light.

Lasik - Laser Ablation

The corneal flap is then repositioned and allowed to dry for a few minutes. The flap self-seals without the need of sutures.

Antibiotic drops are instilled and the patient is discharged from the hospital. The patient is advised to report back the next day. Eye drops are prescribed to be started on the same day. Analgesics are rarely required and that too for 1-2 days.

Precautions to be Taken After Lasik Eye Surgery

• Avoid swimming and splashing of water on the eyes for a month.
• Avoid rubbing the eyes for a month.
• Use sunglasses to avoid bright sun, dust, wind and air pollution.
• Avoid excessive viewing of TV or computers for a week.
• Use medicines regularly as advised.
• Consult your eye surgeon in case of any problem
• Avoid eye makeup for 1-2 weeks

Complications of Lasik

No surgical procedure is without any complications. However, LASIK is a relatively safe technique of correction of refractive errors. The possible complications can be:

• Dry Eye
• Under or over correction
• Glare
• Decentration of ablation
• Astigmatism
• Flap damage
• Infection
• Corneal infiltration
• Diffuse Lamellar Keratitis (DLK or Sands of Sahara)
• Corneal Ectasia (Keratoconus)

Results After Lasik Eye Surgery

Results are generally very satisfactory and it has been reported that in carefully selected cases more than 90 % achieve unaided visual acuity of 6/12 or better (i.e., 6/12 6/9 6/6 6/5).

It is important to discuss with your surgeon about the expected results or prognosis in your case. Your surgeon will be able to explain the kind of results or problems likely in your case. A detailed discussion helps a lot in preparation for Lasik.

Wavefront Guided or Custom Lasik

Standard Lasik involves assessment of only refractive errors (myopia, hypermetropia or astigmatism) and correction of the same. But human eye may have some finer degrees of optical imperfections called aberrations. Standard Lasik does not correct these aberrations.

Wavefront guided or custom Lasik measures aberrations present in the eye (aberrometry) and attempts to correct them. Moreover, the treatment maps generated are customized to the individual eye and maintain the natural prolate profile of the cornea. This prevents induction of any aberrations. All this leads to better contrast and night vision.

Epi-Lasik or Lasek

In patients with thin corneas it may help to lift just a thin epithelial flap as in Epi-Lasik or remove epithelium using alcohol as in Lasek. This leaves behind greater amount of tissue in the coneal bed to achieve higher refractive correction.

Although it possible to correct greater amount of refractive error in these procedures but the recovery is rather slow and more uncomfortable than in Lasik and there are greater chances of development of corneal haze and regression.

Femtosecond Laser

Femtosecond Laser Intralase for Creating Flap ("No Blade" or Blade Free Lasik)

Femtosecond Laser is a new method of creating corneal flap in Lasik - here instead of Microkeratome "Blade" or Disposable Microkeratome Head, a Laser is used to cut the corneal flap. Although it is touted as "No Blade" technique but that should not mean that there is no cutting of cornea to make a flap. The advantage is that the flap reproduceability is better i.e. there is less variation in flap thickness from patient to patient. This variation is slightly more in Disposable Microkeratome Head and significantly more with Reusable Heads & Blades. However, there are reports of increased risk of complications like DLK (Diffuse Lamellar Keratitis or Sands of Sahara) caused by disintegration of corneal tissue & collateral damage. The newer ultrathin 90 micron disposable microkeratome heads offer all the advantages of Femtosecond Laser without an increase risk of DLK. All these are relevant in thin corneas or high refractive errors where one is working close to the limits of safety.

Time Involved

An optimal time schedule is as follows:

• Day 1 - Detailed eye examination (2 hours)
• Day 2 or 3 - Lasik Surgery (3-4 hours in the center / hospital)
• Actual time for Lasik is just few minutes!

Discussion: Standard Lasik vs. Custom Lasik

Standard Lasik
This is the conventional type of Lasik Laser where only the refractive error (myopia, astigmatism or hypermetropia) is taken into account in the Laser protocol and corrected. It does not correct aberrations (finer optical defects in the eye).

Custom Lasik
In this Lasik treatment in addition to refractive error, finer optical aberrations are also taken into account. The Laser ablation protocol attempts to correct the aberrations as well.
The information about the aberrations in the eye is provided by an instrument called aberrometer which forms an additional link in the treatment chain.

Which is better & why?
High levels of aberrations in the eye adversely affect contrast and night / low light vision. So if aberration level is high then certainly Custom Lasik is better as it provide better quality of vision, better contrast and better night vision by correction of aberrations along with the refractive errors.
It may be noted that the vision in bright day light is the same after both forms of Lasik (standard or custom) and it's only in mesopic or low light conditions that there is a difference in the quality of vision. And the difference is very subtle & mild - not a dramatic difference

Conclusion
LASIK is major advance in the field of refractive surgery, which combines efficacy, safety, precision and accuracy. This technique is taking us on the path that, in the past, ophthalmologists feared to tread, towards the goal of unaided natural clear vision. However, it is prudent to have realistic expectations from this surgery and never hope for miracles (although results of Lasik are no less!).
Lasik involves extensive computer analysis of the eye. Patient is then asked to come on the scheduled day for the laser treatment. Local anaesthetic eye drops are instilled in the eye to achieve a pain free procedure. The patient is now made to lie under the laser machine and asked to fix his gaze at a blinking light. The data of the patient is fed into the computer memory of the laser. A special machine called the microkeratome is used to pick up a thin corneal flap of 160 microns (equivalent to an onion skin). Laser is delivered to the cornea under this flap to correct the spectacle number. It takes 20 to 60 seconds to complete the laser delivery to one eye. The corneal flap is placed back in position where it holds strongly within two minutes due to its natural bonding properties. The entire procedure takes about 10 minutes.

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