Welcome to Lasik Surgery

The Beauty of Lasik procedure lies in its simplicity

Lasik involves 2 steps- making a thin corneal flap and after that the shaping laser reshapes the corneal bed.

1. FLAP making can be done through 2 techniques. A Microkeratome and a Femtosecond laser :

A microkeratome makes a flap 90-110 micron thick. With a suction instrument the eye pressure is raised to around 60 mm Hg.You will not be able to see anything.In expert hands it takes about 10 seconds to complete a flap cut. The sudden sense of a moving vibrating object and the sound sometimes can be uncomfortable and a reflex squeezing often occurs. A foot switch controlled oscillating disposable blade cuts the flap ( A femtosecond laser also needs a suction application of around 40 mm Hg.After the docking procedure the eye pressure is very significantly raised for a much prolonged period (approx 16-20 seconds or more depending on the speed of setting time) throughout the laser cut. The femtosecond laser cuts by making bubbles of gas.To accommodate these bubbles so as to prevent a breakthrough from the cornea an extra pocket of deep cut about 250 microns is often made under the hinge of the flap.Flap thickness setting is usually kept about 90-120 microns.It is a fully automatic machine and the surgeon has only to do a proper setting up before the actual laser starts). The huge success of lasik and its worldwide acceptance for over last 20 years is possibly because of microkeratomes .
The microkeratome technology has significantly progressed over the years. Properly used with new suction tubes and blades significant complications are rare. Half and free flaps can occur sometimes if there is a suction loss with or without an obstruction during the keratome pass , however properly managed these seldom cause significant problem . Significant Flap thickness variations have been noted in very few cases.However nowadays during the procedure on- table measurements can be done in all cases (online pachymetry and ultrasound pachymetry) routinely to avoid surprises. Epithelial defects are usually of no consequence. Epithelial ingrowths may occur rarely that can be scraped out and the flap reposed .In case of a regression (small power coming back) it is very easy to lift up the same flap any time and do the necessary correction.Significant sight threatening complication is rare.

Femtosecond laser has the advantage of less risk of free cap and buttonhole.with more reliable flap thickness.. But much longer suction time with a very significant eye pressure rise occur. In case of incomplete laser ablation it is possible to retreat immediately .Chance of opaque bubble layer occurs which may delay the procedure.Overall treatment time and flap manipulation is increased.Specific to femtosecond laser, increased risk of Diffuse lamellar keratitis (DLK) is there.and delayed photosensitivity is there which may require prolonged use of steroids. An extra deep corneal cut(about 250 microns) to make a pocket under the hinge is done to accommodate the bubbles and th prevent a breakthrough of bubbles.In case of a regression ( small power coming back) it is difficult to lift up the flap after 6 months.
Overall the safety concerns with femtosecond laser flap making is the high pressure part that stops the blood flow to the optic nerve for a significantly long time. Chance of the nerve being prone to ischaemic damage in a relatively older age group is a possibility

2. CORNEAL RESHAPING :

The ultimate outcome of the procedure depends on it. Excimer laser has been a huge success to shape the corneal bed. It is possible to remove /reduce the power of the eye from -0.5 to -10 and beyond in selective cases depending on the corneal thickness , tomography readings etc. + power and cylindrical power upto the range of 5 can be removed . However a small chance of regression is always there. More the power ,more is the chance of a small power coming back.

Present generation laser machines can correct POWER and ABERRATIONS.
POWER When corrected one see better , can see upto the last lines of the vission chart depending on the capacity of the nerve behind.
ABERRATION when reduced helps you to have a better quality of vision at night/dim light condition by reducing halos and glare.it is because of various aberrations inside the eye that the light spreads out in different directions when you see a bright light source in dark/dim light.it sometimes appear to be a halo around the light source or spreading out from a point which one describes as glare or starburst.Particularly people who drive may complain more. Aberration happens because the shutter inside the eye- the pupil dilates in dark.that allows light to enter through a larger area . ABERROMETER is an instrument to measure the aberrations.There are several types of aberrations.coma,trefoil,spherical,tetrafoil etc.

Preoperative aberration measurement can give a fair idea of the disturbing aberrations
A standard lasik procedure corrects the power only but may induce new aberrations beyond the preexisting ones which can give rise to glares and halos which were not there before.
A Q-Lasik technique / Wavefront optimized technique tries to keep the q value(asphericity index) in normal/ desired range so that the spherical aberration does not change significantly.However coma, trefoil and other aberrations may not be improved/reduced
A C-Lasik (Customized )/ Topo guided techniques requires a preoperative aberration measurement .The data is analyzed and required custom treatments done to correct / reduces all aberrations significantly.However it Is not possible to eliminate all aberrations completely. But a significantly improved quality of night vision can be achieved.

Presently with tracking systems and various nomograms available the corneal reshaping is extremely precise and predictable.
VIS X – A time tested machine with a very high efficiency to do customized treatment high definition lasik
WAVELIGHT 500 - An extremely fast and accurate machine to do standard and wavefront optimized treatments.

Procedure

Types Of Lasik

Depending on the power,available corneal thickness , preoperative aberration and pupil size the type of surgery is planned. Either a standard procedure/ wavefront optimized procedure that can maintain the postoperative asphericity of the cornea and thereby controls the spherical aberration can be chosen or a wavefront guided procedure can be chosen ( customized ) which tries to reduce all the higher order aberrations like trefoil and coma etc for a better visual performance in dim /dark conditions.

• Standard Procedure : Corrects power with transition and blend zones.
• Wavefront Optimized Procedure : Treats the periphery of the ablation zone to maintain the overall asphericity of the cornea.
• Customized : wavefront guided procedure to detect and treat the individual Aberrations. Ablates more tissue than standard procedures.best possible visual outcomes in dim/dark light condition may be achieved through this technique.

Corneal Thickness Factor

It is important to save corneal tissue as much as possible. The residual corneal thickness must be over 300 microns for safety reasons. Standard lasik surgery removes about 11-12 microns for every 1 dioptre of power it corrects. A customized treatment removes little more tissue approx 15-16 microns per dioptre.

Flap Lifting

Can be done using a femtosecond laser or using a microkeratome.Both procedures are painless but a sense of intense pressure can be felt in both. The microkeratome flap is comparable to the femtosecond flap and the overall cost of the procedure can be reduced.During the process of flap making the eye pressure is raised and one may not be able to see anything for 10-15 seconds.

Surgical Safety Concerns

Intraoperative measurement of the flap and residual corneal bed is strongly recommended. Either an online pachymetry( as with wavelight ex-500) or a manual ultrasonic pachymetry is used . This procedure may not be very accurate but may help in avoiding surprises/shocks. Present generation antibiotics with better penetration also makes the procedure very safe against infections. Sight threatening complications are rare with lasik provided the safety parameters are followed.

Laser Procedure

A target light is usually given to look at.Once the laser is locked at the centre of the pupil the laser is ready to be used.laser is absolutely painless.Small eye movements are detected by the tracker and the laser adjusts itself accordingly so that the laser falls on its intended target. Accuracy of a laser machine depends on combination dynamics of the faster tracking speed and laser speed and not the laser speed alone.

Areas of concern in a FEMTOSECOND LASIK Procedure

Higher intraocular pressure through a longer time period compared to a Microkeratome flap making procedure chance of subclinical injury to the optic nerve.
Difficulty to retreat a patient in case of some power returning. PRK may be the only procedure possible to do. Accuracy of PRK may not be very high and a chance of slight corneal haze is there. IN A MICROKERATOME FLAP IT IS EASY TO RETREAT LIFTING UP THE SAME FLAP.
Difficulty to treat an epithelial in growth if it happens. Femtosecond laser flaps are very tightly adherent and lifting up the old flap may be complicated.

Areas of concern in a MICROKERATOME LASIK Procedure

Needs more expertise to handle a Microkeratome properly . Has a definite learning curve Flap thickness may vary slightly +/- 10-15 microns with present generation Microkeratomes. But it may be safer to keep more than 300 microns as residual bed depth. On line measurements and intraop measurements should be done to avoid surprises.

Ultimately what you see depends on the CORNEAL SHAPING LASER

A customized laser procedure may give a better visual outcome . Apart from the power , better correction of aberrations improves the quality of vision particularly at dim illuminations ( measuring preoperative aberrations gives an idea of the existing aberrations inside the eye and its implications ).

Our Diagnostic Workup

An accurate refraction matched with pentacam/oculyzer data and aberrometry data.

Gallery