Application of ablation cooling to cataract surgery technique using all-fibre burst-mode laser

Abstract

Cataract is the most common cause of preventable blindness in the world. Each year more than 19 million operations are performed to treat cataract. While history of cataract surgery goes as far as 2000 BC, beginning with the last quarter of the 20th century, cataract surgery procedures has benefited from advancements in ophthalmology such as phaco-emulsification, intra-ocular lens (IOL) and precision tools. There was another transformation of special interest to this thesis: In 2009, the cataract surgery was performed on a human being using a femtosecond laser for the first. Use of lasers has since gathered much attention for their high precision and repeatability in cataract surgery, but there are still challenges that their prevent wide-spread adaptation. The leading challenges can roughly be group into technical and fundamental. The technical challenges include the high cost, complexity and bulk of the associated laser technology. The more fundamental challenges relates to the interaction of ultrafast pulses with tissue. Namely, there is always interest in further reducing collateral damage and post-operation complications, which can potentially be done by reducing required pulse energies or average powers. Such an advance would also simplify the required laser technology indirectly. The principle aim of thesis has been to help overcome these challenges. In this thesis, a Yb-doped fibre laser system generating femtosecond pulses was designed to exploit recently discovered ablation-cooled laser-material removal technique. The laser system was then integrated with optical coherence tomography (OCT) for in-situ imaging during cataract surgery. In order to keep required average powers low, ablation-cooled regime is accessed through burst-mode operation of the laser. This custom-built system aims to enhance further the procedure with lower collateral tissue damage, cleaner, efficient cuts with a compact and robust structure. Preliminary experiments have been conducted on blood agar, plexiglas and extracted bovine eyes comparing the new ablation-cooled regime with the traditional regime. All experiments indicate that this regime achieves ablation with smaller pulse energies and reduced thermal effects to nearby tissue. Specically, the pulse uency required for corneal incision is decreased by a factor of 15 compared to previous publications. The system has been developed into a transportable laboratory prototype, ready to be used by medical doctors through custom-developed computer control software.