Ocular Pathology

Anatomy and pathology of the human eye. Use it to review eye pathology for Ophthalmology Board Review or OKAP.

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Sunday, February 04, 2007

LASIK Complications

The pathologic complications of LASIK are legion. The most common seen in the ocular pathology laboratory include: keratectasia requiring corneal transplant, corneal perforation requiring cornea transplant, stromal scarring, epithelial implantation and ingrowth, and infectious keratitis. For a more complete list click on this link.

Scar formation after Lasik
Any incision in the corneal stroma results in the disruption of the stromal lamellae. LASIK entails an initial tangential incision to a hopefully predetermined depth. Then the flap is extended with a broad horizontal cut. If all goes well the disruption may be minimal. A thin faint line is visible at the interface between the lamellar flap and the residual stroma that is accentuated in PAS stains (arrows 3). Focal scarring may be present (arrow 4).
However, occasionally, there may an exuberant scar formation. If revisions or "enhancements" are attempted, the risk of scarring becomes greater. In the figure, the LASIK wound (arrows 1) is seen as a linear configuration that merges with its associated scarring (number 2). The scar is evident as a focal absence of keratocytes and an obliteration of corneal lamellae. In this case, the scar is particularly exuberant. The stroma is actually bulging centrally because of the scar. Several enhancements were performed in this case.

Keratectasia after LASIK

Definition: thinning of the corneal stroma with bulging of the cornea

Etiology: There is a debate whether keratectasia is a forme fruste of keratoconus. In some cases this is clearly not the case as the flap was either made too deeply or the remaining stromal bed was too thin after the usual obliteration with laser. In the image provided the lighted arrow points to the LASIK wound which is very deep in the stroma. In this case the cornea was removed for scar formation. One can see that Bowman's layer is quite irregularly thinned as well. In about 1/2 of the cases of keratectasia the residual stromal bed, that can be calculated from published data, is greater than 250 microns. This suggests that the arbitrary target of 250 microns for calculated residual stromal bed at the time of surgery may be too low or perhaps irrelevant in some cases. At the minimum this complication should be carefully explained to the patient as it is one of the most common sources of litigation.

Incidence/Prevalence: The reported incidence of keratectasia after LASIK is about 0.7%. Clinical Findings: Keratectasia usually occurs within about 30 months (mean 11.8 months) after LASIK. The patients often notice a change in their refraction and frequently some LASIK "enhancement" is made, which makes matters worse. The patients may be fit with contact lenses to at least partially restore vision. But if the keratectasia is progressive, the patient may no longer be able to be fit and then will require a penetrating keratoplasty.
Gross: The keratectatic cornea is thinned and usually shows scar formation. The bulge associated with the clinical appearance may not be obvious because of fixation of a thin cornea often produces folding and distortion.
Microscopic: The central cornea is markedly thinned (number 5). The interface between stromal bed and flap is evident as a thin line even at low magnification (arrows 3). Often there is an area of iron staining in the epithelium just as one sees in keratoconus. The absence of any abnormalities of Bowman's layer other than the LASIK incision would be evidence against a previous diagnosis of keratoconus.

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