Deep Stromal Dissection for Endothelial Keratoplasty Obtained with a Femtosecond Laser and a Microkeratome with Different Head Advancement Speeds. A Scanning Electron Microscopy Study

P. Scaroni, R. Leaci, D. Dallatana, A. Neri, L. Fontana°, C. Macaluso.

Ophthalmology, University of Parma, Parma, Italy.°Eye Bank Institute of Emilia Romagna, Bologna,

Italy.

FINANCIAL DISCLOSURE FOR ALL AUTHORS :NONE

Purpose:

To explore the surface quality of deep stromal

dissections in bank eyes obtained with either a

femtosecond laser or a microkeratome used with

three different head advancement speeds.

Methods:12 sclerocorneal donor buttons, not suitable for human transplantation,

mounted on an artificial chamber. 1000 KHz Femtosecond laser (Femto LDV, Ziemer, Switzerland) at 400µm

depth :– FEMT group: 3 Corneas

Microkeratome Carriazo Barraquer, Moria, France. Mounting a 300µm head.Different speeds to perform the dissection:

– Microkeratome FAST 2-4 sec– Microkeratome MEDIUM 8-10 sec– Microkeratome SLOW 18-20 sec

Following routine preparation, all endothelial buttons were analyzed with a scanning electron microscope (SEM 501, Philips, Germany) at 20X (allowing visualization of the whole corneal specimen) and 160X magnifications.

Qualitative evaluation: • Overall homogeneity of the cut at low (20x) magnification• Detection of surface irregularities of the central cornea at high (160x)

magnification. A masked technician examined the rest of the corneal surface for areas showing any difference in surface quality when compared to the center.

• As in the femtolaser group the technician found significant differences in areas quality, both best and worst areas were selected

3 corneas each group

20X magnifications

The stromal surface of the endothelial buttons of the FEMTOLASER group showed a generally excellent smoothness, but with some small rough areas (red arrow).

FEMTOLASER

BEST QUALITY AREAS

(160X magnifications)

Best areas obtained with the femtolaser: the surface is regular and the stromal fibers have been cut and not ripped off

FEMTOLASER

WORSE QUALITY AREAS

(160X magnifications)

In the images above it’is clear that many stromal fibers have been torn and not cut and the quality of the surfaces is poor

FEMTOLASER

FAST GROUPperforming the cut to obtain the lamellas in 2-4 sec

(160X magnifications)

Differently from the FEMTOLASER group, all microkeratome dissected endothelial buttons failed to show significant variations in smoothness

across the cut surface.

MICROKERATOME

MEDIUM GROUPperforming the cut to obtain the lamellas in 8-10 sec

(160X magnifications)

MICROKERATOME

SLOW GROUP

performing the cut to obtain the lamellas in 18-20 sec(160X magnifications)

While the surface of the MEDIUM and of the SLOW groups were regular, the FAST group showed a rougher surface.

The smoothness obtained in the best areas of the FEMTOLASER group was unmatched by the surfaces obtained in any of the microkeratome groups.

MICROKERATOME

Microkeratome

Femtolaser

Stroma after Descemet stripping

The quality of the surfaces obtained with microkeratome and femtolaser can be compared. And both can be compared with the smoothness of the receiving bed for endothelial transplantation, i.e. the stroma after Descemet stripping

Conclusions:

1. MICROKERATOME dissection of endothelial corneal

buttons resulted in consistent regular cut surfaces, but

it is advisable to complete the head movement rather

slowly, in at least 8-10 seconds.

2. FEMTOSECOND laser technology has the potential for

generating endothelial corneal buttons with extremely

smooth surfaces, even better than those that can be

obtained with a microkeratome. Nevertheless, the deep

stromal location of the cut may limit the overall

regularity of the dissected surface. It is conceivable that

the suboptimal optical properties of rejected eye bank

tissues could have heavily contributed to this problem,

limiting proper laser focusing in the deep stroma. Thank you…