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Patient Selection for Lasik
Preoperative Preparation for Lasik
Lasik Procedure
Precautions to be taken after Lasik
Complications of Lasik
Results of Lasik
Wavefront Guided or Custom Lasik
  Lasik 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 a computer guidance 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.

Lasik - Allegretto Machine

  The steps are detailed below.
Patient Selection for Lasik

Case selection is an extremely important determinant of the results of Lasik surgery:

  • Refractive error: -1.50 to -10.0 diopter of myopia or up to +6.0 diopter hypermetropia (in patients older than 40 years Lasik is not beneficial for low myopia of up to -3.0 D)

  • Astigmatism of up to 6 diopter

  • Minimum age 18 to 21 years (preferably 21 years)

  • Refraction should have been stable for 2 years.

  • 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
  • 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 Procedure (see Video)

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:

  • After the anesthesia the face of the patient is covered with a drape just exposing the eye and an eyelid speculum is applied to retract the eyelids (patient feels a stretch on the lids). The patient fixates his gaze at a blinking (target) light.

Lasik - Patient target blinking green light

  • A suction ring is placed around the cornea and serves to stabilize the eyeball and act as a platform for the microkeratome. When suction is activated vision be comes hazy and a pressure on the eye is felt.

Lasik - Microkeratome Ring

Pressure in the eye builds up and is measure to ensure proper level.

Lasik - Tonometry - Pressure check

  • The automated microkeratome dissects through the superficial layers of the cornea and the corneal flap is folded back. During this step the patient hears the sound of a motor in front of the eye.

Lasik - Microkeratome - Flap creation

Then the flap is lifted and turned back to lye on flap rest.

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 needs to rest with eyes closed for about an hour before 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.

Lasik - Patient recovery

  • Lasik Surgery is painless and the patient only feels slight stretch on the eye lids and mild pressure on the eye.

Precautions to be taken after Lasik
  • 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. Lubricant or artificial tears eye drops may be required for about 2-6 months

  • 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

  • Reduced contrast sensitivity

  • Glare

  • Decentration of ablation

  • Astigmatism

  • Flap damage

  • Button holing of flap

  • Free Cap

  • Corneal perforation

  • Central Island

  • Infection

  • Corneal infiltration

  • Corneal Ulceration

  • Diffuse Lamellar Keratitis (DLK or Sands of Sahara)

  • Corneal Ectasia (Keratoconus)

Results of Lasik

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).

There is a subjective difference in degree of satisfaction among the patients. Some patients with a vision of 6/12 may feel very happy while others may be dissatisfied even with a vision of 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 and may actually induce some aberrations leading to decrease in contrast and problems with low light conditions and night vision. 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.

Before the surgery it is important to dilate the pupil of the eye with use of various eye drops which may take about 1-2 hours.

The surgery is quite painless, however, the patient may feel some pressure & touch on the eye. Patient needs to stare straight up into the bright light of the microscope through.

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 or 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.

SBK (Sub Bowman's Membrane Keratomileusis)

In thist ype of Lasik Surgery an ultrathin flap of 110 micron is created lifting only the epithelium & Bowman's membrane layers of Cornea. As result more tissue is left in the corneal bed providing strength to the eye after surgery and preventing complications like ectasia or keratoconus.

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)
Day 3 or 4 - First post-Lasik examination (1 hour)
Day 7-10 - Second post-Lasik examination (1 hour)

Patient may return after the second examination and follow-up with local eye care practitioner every 2-4 weeks for 3 months.

Discussion: Standard Lasik vs. Custom Lasik

What is standard Lasik & what is custom Lasik? Which is better for me & why? I am often asked this question by my patients.

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.
This type of Lasik treatment does not correct aberrations (finer optical defects in the eye) and may actually increase them.

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 (RMSh > 0.25) 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.
If the aberration level is low (RMSh < 0.25) then Custom Lasik is not really required and standard Lasik works as well.
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

  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 Surgery performed by Dr. Sanjay Dhawan
Author: Dr. Sanjay Dhawan
Last Updated on: 1 March, 2014

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