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cornea is evaluated, close attention should be paid to any anterior membrane
dystrophy, stromal scarring or vascularization that may influence the type of surgery or

whether it should be done at all. Any variation in stromal thickness, as in pellucid or
Terrien’s degeneration, keratoconus or stromal dystrophies should alert the surgeon to
reconsider performing a refractive procedure. The crystalline lens should be examined
in detail after full dilatation, especially in patients above the age of 40 years. A
progressive myopia, during middle age should alert the clinician about the early stage
of immature cataract. In case of doubt, an axial length measurement can be estimated
and if there is any discrepancy, further testing can then be ordered. A baseline
intraocular pressure measurement, like the preoperative keratometry reading, serves
as an useful adjuvant, since post lasik intraocular pressure measurement using
Goldman’s applanation tonometry is less than accurate.

A detailed indirect ophthalmoscopic evaluation with and without indentation should be
an integral component of the whole screening processes. Lattices with multiple holes
and horse shoe tears can be subjected to barrage laser and laser surgery can be
performed after a period of 1 month. Round atrophic holes and simple lattice
degenerations need not be treated as a routine. Even as there is no proof of increased
occurrence of retinal detachment following refractive surgery, it will be prudent to
treat any predisposing condition first.
5. Evaluation of tear film: The level of tear meniscus and the quality of the tear film
should be assessed before any instrument touches the eye. Although mild dryness due

to intolerance of contact lens wear may be an indication for refractive surgery, more
significant dryness may pose a threat to successful epithelial healing.
6. Evaluation of ocular motility and alignment
7. Topography: for evidence of irregular astigmatism, corneal warpage, or abnormalities
suggestive of keratoconus or other corneal ectasias, because all may be associated with
unpredictable refractive outcomes and latter with progressive ectasia following
surgery. The detection of the posterior corneal elevation adds an extra safety
dimension before Lasik procedure.
8. Pachymetry: To identify unusually thin corneas and estimate residual stromal bed
thickness. Corneas with central corneal thickness values less than 500 μm should be

considered potentially abnormal.

Excimer Laser Systems
Laser assisted in situ keratomileusis (LASIK) is the most commonly performed refractive
surgery worldwide. Good visual results, quick rehabilitation and negligible complication
rates have been the main reasons for the widespread acceptance rate of this procedure.
Technological advancements have brought in many evolutions from the initial era of broad
beam lasers to the more recent ones using flying spot technology. These refinements have
helped the new generation lasers to have more accurate predictability than the earlier

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