Tutorial

Slides

Corneal Wound Healing after LASIK Surgery

Daniel G. Dawson, MD · Hans E. Grossniklaus, MD · Henry F. Edelhauser, PhD

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	Slide 1. Photomicrograph of the histology and clinical slit lamp photos (insets) of a 5-year post-LASIK cornea. Four long-term histological findings were present in this representative post-LASIK cornea: epithelial modifications (i.e. basal epithelial hypertrophy and/or hyperplasia), Bowman’s layer undulations, hypercellular fibrotic stromal scarring, and hypocellular primitive stromal scarring. Note that the only histological finding that could consistently be seen on slit-lamp examination was the area of the hypercellular fibrotic stromal scar (black outlines and arrowheads). Toluidine blue x25.
	Slide 2. Transmission electron micrographs of a 4-month post-LASIK cornea showing a representative hypercellular fibrotic stromal wound margin scar (arrow). The initial 42-µm length of the scar was 5.1 µm thick (between arrowheads). The extracellular matrix of this scar is consistent with fibrosis because it predominantly was composed of a dense network of disorganized collagen fibrils (arrows in main and top-right inset). Arrowhead in the top-right inset shows focal electron dense material that progressively disappears from this scar over 3 to 4 years after LASIK (ie, remodeling). The bottom-left inset is an immunofluorescent photomicrograph using anti-alpha-smooth muscle actin antibody (light green) and propridium iodide as a nuclear counterstain (red). Bar indicates 1 µm. Main transmission electron microscopy photo x4,750.
	Slide 3. Transmission electron micrographs of a 6-month post-LASIK cornea showing a representative hypocellular fibrotic stromal scar that resides in the central and paracentral interface wound. The thickness of the central scar varied from 5.8 µm thick (between arrowheads on the left) and 1.1 µm thick (between arrowheads on the right). High magnification views of this scar (top-right inset) showed that it is primarily composed of electron dense granular material (arrows on top-right inset) with sparsely interspersed collagen fibrils (arrowhead on top-right inset). A tangential cupromeronic blue-stained TEM (bottom-right inset) showed that most of the electron-granular material was an abnormally-large (360 nm x 20 nm), non-fibril-bound type of proteoglycan. Bar indicates 1 µm. Main transmission electron microscopy photo x4,750.
	Slide 4. Summary diagram of the immunofluorescent studies performed on human post-LASIK corneas.
	Slide 5. Diagram of normal corneal healing pathways (black) and pathologic pathways (blue). Pharmacologic adjunctive medications (red) are included.
	Slide 6. Summary diagram demonstrating the biologic reason why regression occurs after myopic LASIK surgery. The post-LASIK cornea immediately after surgery is depicted in black solid lines. The light blue solid lines represents the typical stromal scar deposition, which occurs over the first 6 months after surgery; the light blue dashed lines represent how this scarring affects the central anterior surface of the LASIK flap (i.e. partial myopic regression). Similarly, the red solid and dashed lines represent the occasional case that regresses in the hyperopic direction (usually, in these cases, the flap wound margin is poorly aligned).
	Slide 7. Chronology of the deposition and persistence of the hypocellular primitive stromal scar (between arrowheads) is depicted in transmission electron micrographs from 1-month post-LASIK to 3-years post-LASIK. (A) A 1-month post-LASIK cornea showed early deposition of the stromal scar, a few migratory keratocytes, and numerous highly activated keratocytes (not shown in main picture). Inset is from a 2-month post-LASIK cornea, which showed highly activated keratocytes more clearly. (B) A 6-month post-LASIK cornea showed even more deposition of the stromal scar than at 1 to 2 months after surgery and less activation of the keratocytes. (C) A 1-year post-LASIK cornea showed no more deposition of the stromal scar than at 6 months after surgery. Notice that the keratocytes are now quiescent with more than normal amount of cytoplasmic vacuoles (inset). (D) A 3-year post-LASIK cornea showed again no more deposition of the stromal scar than at 6 months after surgery; more importantly, it persisted and did not appear to remodel or regenerate into normal corneal stroma. The inset in (D) is from a normal cornea to show what a normal, quiescent keratocyte looks like. Bar indicates 1 µm. Main transmission electron microscopy photos x4,750.
	Slide 8. Representative cohesive tensile strength line graphs of a normal cornea (A) and a post-LASIK cornea (B) are shown. Both tracings are plotted from left to right. (A) The tracing showed the interlamellar cohesive tensile strength of a normal, control cornea mechanically separated in a lamellar fashion. All control corneas were similar to the graph shown here. The cornea from limbus to limbus was measured between the arrows and the tracing outside the arrows represents the sclera. (B) Cohesive tensile wound strength tracing of a 5-year post-LASIK cornea showed that the weakest point of separation of post-LASIK cornea was at the lamellar interface scar. All LASIK corneas had tracing similar to this one. The location of separation in the LASIK wound is labeled in the graph with accompanying arrows and the quantitative results are labelled in italic print for this case.
	Slide 9. A scatter graph of all the cohesive tensile strength measurements plotted versus the time after LASIK in the region of the hypocellular primitive stromal scar (open circles) is shown in (A) and the hypercellular fibrotic stromal scar (black solid circles) is shown in (B). Best curve fit lines (dashed lines) were made for each of the two data sets. No evidence of a gain in tensile wound strength over time was measured in the hypocellular primitive scar best fit curve (A), whereas a gradual increase was measured up to 3.5 years after LASIK in the hypercellular fibrotic scar (B) before plateauing. Square represents mean value of 5 normal controls.