This prospective cohort study involved 39 pseudophakic eyes of 31 patients who underwent DSAEK surgery due to Fuchs’ corneal endothelial dystrophy at the Eye clinic, Careggi University Hospital of Florence, Italy, between March 2011 and September 2012. The study followed the tenets of the Declaration of Helsinki and was approved by the local ethic committee (Careggi University Hospital of Florence). All patients signed a surgical informed consent form before DSAEK and an informed consent for the study.
Exclusion criteria for this study were concurrent eye pathology as glaucoma, macular/retinal diseases significantly affecting visual acuity, amblyopia, optic neuritis, uveitis, scleritis, ocular infection, pre-existing severe corneal scarring.
At the preoperative visit all patients underwent a complete ophthalmological evaluation including best corrected visual acuity (BCVA, LogMAR), slit lamp biomicroscopy, intraocular pressure measurement, fundus ophthalmoscopy, white light IVCM (Confoscan 4, Nidek Technologies, Birmingham, UK) and time domain AS-OCT (Visante OCT, Carl Zeiss Meditec Inc, Dublin, California, USA).
IVCM was performed with a 40 X magnification and the z-ring adapter . Lamp brightness was set at 80 in all examinations. Images obtained by Confoscan 4 were approximately 460x345 microns wide.
Before the exam, a drop of topical anesthetic (Benoxinate) was instilled. The patient was then asked to steadily fixate a target and IVCM was performed on the central cornea. The exam lasted approximately 3 min. At the end of the examination, an antibiotic eye drop (gentamicin 0.3 %) was administered.
The preoperative subepithelial haze was measured as the mean between the peak value of LRU (light reflectance units) in the subepithelial area and the values at 25 microns in the endothelial direction and 25 microns in the epithelial direction. Since at each examination Confoscan 4 performed three different scans of the cornea, three mean values, one for each scan, were obtained and averaged.
Two trained investigators performed the examination and one masked investigator selected and analyzed IVCM and AS-OCT scans.
All patients underwent DSAEK surgery alone.
All procedures were performed under monitored anesthesia with peribulbar block.
The posterior lamellar grafts were supplied from the Cornea Bank of Lucca (Italy), after having been cut by a microkeratome with a a 350-micron head (Moria SA, Antony, France).
They were trephinated by the surgeon with a Hessburg-Barron donor corneal punch (Barron Precision Instruments, LLC, Grand Blanc, Michigan USA) to a diameter of 8.25–8.75 mm. All grafts had an endothelial cell count of at least 2500 cells/mm2. Graft thickness provided by the Bank was recorded.
The anterior chamber of the eye was then entered through a 4 mm clear corneal incision, and in order to prevent the anterior chamber collapse a maintainer was used. Descemet membrane was stripped from the central 8-8.5 mm diameter. The rolled endothelial graft was inserted using a Busin glide (Moria Inc, Antony, France) and a small air bubble that was injected to lift the graft. After centering the graft, the anterior chamber was completely filled with an air bubble that after 10 min was reduced to about the 80 % of the size of the endothelial graft.
All surgical procedures were performed by the same skilled surgeon, RM.
Patients were evaluated 1 day, 1 week, 1 month, 3, 6 and 12 months after surgery. Whereas each visit consisted of complete ophthalmic examinations, including BCVA and slit-lamp examination, at 3, 6 and 12 month visits AS-OCT (graft thickness measurement) and IVCM (graft thickness, interface haze and subepithelial haze evaluation) were also performed.
Graft thickness was measured by IVCM by assessing the distance from the endothelium to the change of reflectance that suggests the beginning of donor-recipient interface, then calculating the mean between the values obtained in each of the three scans performed by IVCM at each examination. The donor-recipient interface was identified as the area where a change in cell morphology and/or extracellular matrix was detected.
The donor-recipient interface haze, the characteristic gain in reflectance that may be observed at the border between the donor graft and the recipient cornea, was also evaluated by IVCM. It was measured as the mean between the peak value of LRU at the interface and the values at 25 microns in the endothelial direction and 25 microns in the epithelial direction; then we averaged the three mean values obtained, one for each scan.
Postoperative subepithelial haze was measured as already described in the preoperative evaluation section.
Graft thickness was measured by AS-OCT on a horizontal cross sectional image obtained at the anterior corneal vertex, using the software-imbedded flap-tool (high-resolution corneal scan mode).
Linear mixed models were used to compare the change of the covariates of interest (logMAR BCVA, haze and thickness-related variables) at various follow-up times, accounting for correlated data using time as a random slope at the subject level. In order to simultaneously assess the correlation between covariates at different follow-up times, while accounting for individual correlation, structural equation modeling (SEM) of standardized variables was performed. Intraclass correlation coefficient (ICC) was used to compare graft thickness measured by means of AS-OCT and IVCM.
All analyses were carried out using Stata software (StataCorp 13.1, College Station, TX).
Results were expressed as mean and standard deviation (SD). A value of P < 0.05 was considered statistically significant.