Description of a novel “Lock-and-key” configuration for femtosecond assisted keratoplasty A Iovieno; V Chowdhury; V Maurino Moorfields Eye Hospital, NHS Foundation Trust, London, UK The authors have no financial interest in the subject matter of this poster

Femtosecond assisted keratoplasty Femtosecond lasers are currently being used to create shaped wound incisions for penetrating keratoplasty Shaped incisions allow endothelium or epithelium-sparing keratoplasty configurations There is limited data available on the intrinsic wound strength of these shaped incisions compared to straight vertical wound incisions The aim of our study was to propose a new “Lock-and- key” architecture for femtosecond laser-assisted keratoplasty and compare wound strength in shaped keratoplasty incisions Chamberlain, 2011; Shousha, 2010; Bahar, 2008

Methods The study was carried out in freshly enucleated porcine eyes (approximate CCT 800μm) A 16 mm corneal disc was manually trephined from the eyes with a Barron trephine blade ® The corneal discs were mounted on a Barron Artificial Anterior Chamber device ® filled with HPMC 2% In n=4 corneas, a straight full thickness cut of 7.0mm diameter was made with the Intralase Enabled Keratoplasty (IEK) settings of an iFS femtosecond laser®

In n=4 corneas, a shaped full thickness cut, based on a novel “Lock-and-Key” wound architecture for a penetrating keratoplasty incision was made with the femtosecond laser The shaped “lock-and-key” wound utilizes two ring lamellar cuts and three vertical side cuts This shaped incision was reliably generated with the femtolaser Methods

After the corneas were cut with the femtolaser, the wound was opened completely and the donor disc was separated from the host rim (attached to the anterior chamber device). Viscoelastic was removed from the anterior chamber system, and it was connected to a Balanced Salt Solution (BSS) fluid infusion system The donor disc was then replaced in the host rim without suturing Fluid infusion pressure was changed manually by lifting or lowering the height of the bottle Fluid pressure of the infusion system was recorded by a fluid pressure transducer, and plotted graphically on a computer system The pressure in the system was raised until leak occurred from the wound, and this intrinsic leak pressure was recorded 2% Fluorescein solution was placed over the wound to assist in the detection of wound leak Simultaneous video recordings of the wound as well as the fluid infusion pressure was obtained in order to help assess the point at which wound leak occurred

HOST DONOR Ant. Side Cut: 250μm Shelf Side Cut: 250μm Post. Side Cut: 300μm ( Dependent on Pachymetry) Shelf Width: 0.75 mm Ant. Side Cut: 7.0 mm Shelf Side Cut: 8.5 mm Post. Side Cut: 7.0 mm “Lock-and-key” shape wound parameters. “Lock-and-key” shape cut in Porcine Cornea – Donor Disc and Host Rim. Results

Average leak pressure in the shaped “Lock-and-Key” corneal incision group was 6.85 cmH 2 O (SD 3.39 cmH 2 O), compared with a leak pressure of 6.18 cmH 2 O (SD 3.65 cmH 2 O) in the straight vertical cut incision group The difference was small, with a wide range of results in each group The “lock-and-key” shape could be reliably generated in porcine corneas with the femtosecond laser

The “lock-and-key” shaped wound is a novel second-generation architecture that allows both decreased epithelial and endothelial surface area, for a defined stromal diameter These preliminary results do not demonstrate a clear increase in intrinsic wound strength with the shaped incision. The explanation for this may be due to: i)Insensitivity of the pressure-leak measurement setup: The current fluid infusion system is causing too large a change in volume in the artificial anterior chamber device which is confounding the measurement of wound leak pressure ii)Design of the shaped incision: The width of the shelf in the current design of the lock-and-key shape (0.75mm) may be too narrow to be a significant intrinsic barrier to wound leak Conclusions ACKNOWLEGMENTS: Funded by an AMO Germany GmbH unrestricted grant