A Non-ablative Technique for Femtosecond Laser-Based Refractive Correction: Development, Efficacy, and Tissue Effect

Laser-induced refractive index change is a technique that uses ultrashort pulses of laser light to change material properties---namely, refractive index---without causing overt damage. This technique is synonymous with both femtosecond laser micromachining and intra-tissue refractive index shaping (IRIS). The term "femtosecond laser micromachining" typically refers to laser-induced refractive index change in glass or hydrogel materials while the term "IRIS" refers to laser-induced refractive index change in ocular tissues. Early work by the Knox research group suggested that the technique could have potential as a novel method of non-ablative refractive vision correction. The work presented in this thesis further develops the capabilities of the laser-induced refractive index change technique, demonstrates the efficacy of laser-induced refractive index change to produce refractive changes without ablation, and investigates the effects of laser-induced refractive index change on mammalian corneal ultrastructure.;The ability of laser-induced refractive index change to create refractive phase structures in both ophthalmic hydrogels and corneal tissue is demonstrated in this thesis. This capability was achieved by developing novel laser delivery apparatuses and custom metrology tools. The development of more sophisticated laser delivery systems ultimately allowed an approximately 1.3 D cylinder phase lens to be inscribed in the corneas of live cats. The refractive changes in these cats were stable for at least 24 months post laser treatment. These cats were sacrificed at successive timepoints after laser treatment and their corneas were examined using histochemical techniques. A similar histochemical study was performed on a cohort of rabbits to further investigate the effects of laser-induced refractive index change on mammalian corneal ultrastructure. Also, the corneal ultrastructure of another cohort of laser-treated cat eyes was investigated using electron microscopy.;The results of these studies showed that laser-induced refractive index change can be used to impart refractive change to the mammalian cornea by introducing local, transient changes to the extracellular matrix (ECM) of the corneal stroma. This thesis work also suggests that laser treatment precipitates a corneal form change that imparts long-lasting refractive change. Laser-induced refractive index change continues to appear promising as a potential novel method to achieve refractive correction.