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Impressum
Intraoperative assessment of stromal ablation in LASIK
Fiedler G., Schründer S.
Pilgersheimerstr. 62, 81543 München
Objective: During refractive procedures with the excimer laser
(LASIK) the actual amount of ablated tissue was calculated for the first
time by intraoperative measurement. This topologic information was compared
with the planned ablation profile.
Methods: An uv-fringe pattern (193nm)is projected onto the stromal
tissue; this excites an autofluorescence pattern of the outer stromal
layer. Topologic information before and after ablation is contained according
to the principle of triangulation. The actual amount of ablated tissue
is visualized and compared with the desired ablation profile.
Results: According to previous in vitro measurements, on Oct 4th
2000 we first succeded in performing intraoperative topographies with
this method during 12 LASIKS. Scattering was found regarding refractive
results and realization of planned ablation profiles .These results were
compared to postoperative refraction and visual accuity. Fluctuation of
intaoperative topographies and calculated ablation explains variation
of refractive and visual results found worldwide.
Conclusion: Up to now refractive procedures with the excimer laser
were performed without control of the ablation pocess.Given nomogramms
- sometimes completed by preoperative measurement of aberration or topographies
- could not be modified according to the individual operation process.Variation
of laser fluence, disturbance of the excimer beam by ablation products,
different ablation rates of the individual cornea etc. produces scattering
of quality and amount of stromal ablation. Since including those factors
in nomogramms is not possible, we recommend a procedure of online control
of refractive corneal laser surgeries. "Customized ablation"
will become feasible using this online control method.