Flap relift for retreatment after femtosecond laser-assisted LASIK.

PURPOSE: To analyze the results of LASIK retreatment performed by relifting the original femtosecond laser-created flap. METHODS: A retrospective analysis was performed on 1298 eyes from 688 patients treated with LASIK using the femtosecond laser to identify 88 consecutive eyes of 71 patients that underwent attempted flap lift to treat residual refractive error. The eyes were separated in groups in which the flap lift was possible or flap lift was not possible to investigate factors that could make flap lifting more difficult. The main factors evaluated were bed and side-cut energy and time between original surgery and retreatment. In addition, all retreated eyes were studied as a group to evaluate the refractive outcomes of flap lift retreatment. RESULTS: In 10 (11.3%) retreated eyes, flap lift was not possible without risk of flap injury due to strong healing of the original femtosecond laser interface. The group of eyes in which the flap could not be relifted had the attempted retreatment performed a longer time period after original LASIK (10.3±3.3 months) compared to the group in which the flap could be re-lifted (5.24±3.14 months) (P<.001). No significant differences were found between groups in any other parameters, including bed and side-cut energies. After retreatment, 82% of eyes achieved 20/20 or better uncorrected visual acuity. CONCLUSIONS: This study provides clinical evidence that flap lift retreatment after femtosecond laser-assisted LASIK achieves excellent clinical results and is significantly easier to perform in the first 6 to 8 months after primary LASIK.

Spectroscopic studies of the interaction of ferrous bleomycin with DNA.

Bleomycin is an antibiotic used in cancer chemotherapy for its ability to achieve both single- and double-strand cleavage of DNA through abstraction of the deoxyribose C4'-H. Magnetic circular dichroism (MCD) and X-ray absorption (XAS) spectroscopies have been used to study the interaction of the biologically relevant FeIIBLM complex with DNA. Calf thymus DNA was used as the substrate as well as short oligonucleotides, including one with a preferred 5'-G-pyrimidine-3' cleavage site [d(GGAAGCTTCC)2] and one without [d(GGAAATTTCC)2]. DNA binding to FeIIBLM significantly perturbs the FeII active site, resulting in a change in intensity ratio of the d d transitions and a decrease in excited-state orbital splitting (5Eg). Although this effect is somewhat dependent on length and composition of the oligonucleotide, it is not correlated to the presence of a 5'-G-pyrimidine-3' cleavage site. No effect is observed on the charge-transfer transitions, indicating that the H-bonding recognition between the pyrimidine and guanine base does not perturb Fe-pyrimidine backbonding. Azide binding studies indicate that FeIIBLM bound to either oligomer has the same affinity for N3-. Parallel studies of BLM structural derivatives indicate that FeIIiso-PEPLM, in which the carbamoyl group is shifted on the mannose sugar, forms the same DNA-bound species as FeIIBLM. In contrast, FeIIDP-PEPLM, in which the -aminoalanine group is absent, forms a new species upon DNA binding. These data are consistent with a model in which the primary amine from the -aminoalanine is an FeII ligand and the mannose carbamoyl provides either a ligand to the FeII or significant second-sphere effects on the FeII site; intercalation of the bithiazole tail into the double helix likely brings the metal-bound complex close enough to the DNA to create steric interactions that remove the sugar groups from interaction with the FeII. The fact that the FeII active site is perturbed regardless of DNA sequence is consistent with the fact that cleavage is observed for both 5'-GC-3' and nonspecific oligomers and indicates that different reaction coordinates may be active, depending on orientation of the deoxyribose C4'-H.