LASIK (Laser Assisted In Situ Keratomileusis) :
LASIK is a type of eye surgery
done to correct refractive errors of the eye.
Refracrive error is based on two factors:
1.
Anterior-Posterior length of the eyeball (normally 23 mm)
·
Increased A-P length of the eyeball = myopia
·
Decreased A-P length of the eyeball = hypermetropia
a.
Steep corneal curvature > More bending / refraction >
Image will form in front of retina > Myopia (refractory power is more)
b. Flat
cornea > Decreased bending > Image will form behind retina >
Hypermetropia (refractory power is less)
c.
If corneal curvature is unequal > 2 images will be
formed > Astigmatism
Principles of LASIK:
Reshaping of cornea (alter shape of cornea):
·
In myopia > make cornea flat
·
In hyper metropia > make cornea more steep
How much correction is possible?
·
Hypermetropia > up to 7 D
·
Astigmatism > up to 7 D
Procedure of LASIK:
2.
Treat bed with Excimer laser. Ablate Bowmen’s layer and
stroma with laser > precisely cur tissue without disturbing surrounding
structure.
3.
Reposition of flap
For 10µm ablation = correction of 1D myopia.
eg if you need 5 D correction = 50 µm tissue has to be
ablated.
Note: Before LASIK, asses corneal thickness by pachymetry.
·
Normally centre = 0.56 mm
·
Periphery = 1.00 mm
Complication of LASIK:
1.
Wrinkling
2.
Decentration
3.
Cellular proliferation in between interface = becomes hazy
4.
Overcorrection or under-correction
5.
Ectesia (procedure not done in center, but to one side)
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