We examined 6 males and 10 females (16 patients, 18 eyes). The mean age was 74
8.3 and ranged from 56 to 85
provides the demographics of the study population.
Interface reflectivity was 2.17
1.2 and significantly correlated with visual acuity (Spearman correlation coefficient −0.83; P
0.001), and with time after surgery (Spearman correlation coefficient −0.87; P
0.001); Figure A and B.
Figure 1 A. Negative correlation between interface reflectivity and BSCVA. The higher the interface reflectivity, the lower the visual acuity (Spearman correlation coefficient −0.83; P<0.001) B. Negative correlation between interface (more ...)
Visual acuity averaged over all the patients was 0.67
0.27. The number of particles was 205
117.8. No correlation was found between the number of particles at the interface and visual acuity (Spearman correlation coefficient −0.41; P
0.15); Figure C.
Moreover, we did not find a significant correlation between the time from surgery and the number of interface particles (Spearman coefficient 0.53, P
Interface quality assessment with slit-lamp and LCM appeared consistent (Figure ).
Figure 2 Panel A. Representative slit lamp and confocal pictures of a low reflectivity (i.e. good quality) interface. Note the clear interface observed at the slit lamp, which corresponds to a dark confocal image. The BSCVA in this patient was 20/20. Panel B. (more ...)
DSAEK surgery is considered a valuable alternative to PK in cases of dysfunctional endothelium such as in Fuchs’ dystrophy as it selectively replaces it. DSAEK is less invasive and better tolerated by patients [4
], allows prompt improvement and stability of visual acuity. However, being a lamellar surgery, it creates an interface between the donor and the recipient tissue, where the healing process is thought to be critical to optimal visual recovery [11
]. DSAEK grafts present increased haze at least up to three months, when compared to PK grafts [12
]. Loss of corneal transparency and swelling in Fuch’s dystrophy have been object of extensive studies [13
The most common cause of DSAEK failures is secondary to endothelial cell loss, followed by “dysfunctional” donor-host interface. These include lenticule dislocation, interface fibrosis or hemorrhage, epithelial downgrowth [14
LCM is a low-invasivity, repeatable method which allows to study the interface histology in vivo, and hence is suitable to study the interface healing process.
Previous studies have evaluated the interface on a smaller sample of patients, or at lower resolution with white-light confocal microscopy. Our study shows a correlation between visual acuity and interface grading. Interestingly, the deep part of the stroma, where DSAEK surgery takes place, is interested by a number of pathological changes. For example, it has been shown that fluid entering the cornea causes more swelling in the posterior than in the anterior lamellae. Also, posterior lamellae can reach higher degree of final hydration, and collagen-free regions (known as “lakes”) exist in Fuch’s dystrophy corneas which are thought to be caused by dead cells and fibril disordering. The selective distribution of fluid into the corneal stroma might reflect a different glycosaminglycan concentration in the posterior part of the cornea [13
]. All these observations contribute to explain the formation of an interface haze following DSAEK, and corroborate a correlation between haze extent and visual acuity loss. To our knowledge, this is the first report finding a correlation between a published confocal HRT2 measure and BSCVA. This finding is in contrast with what previously reported by Espana et al. [17
], using a different microscope (ConfoScan as opposed to HRT). However, caution should be used in comparing these two studies, as the axial resolution provided by HRT is more than double than the ConfoScan, and this could explain the different findings.
Similarly to others [17
], we found no correlation between particle number and visual acuity. Small particles located at the interface are a common finding following DSAEK, and are also observed after LASIK surgery [19
]. The origin of interface particles has been object of research: they are generally thought to be associated with the use of the microkeratome [20
], but they were also observed after femtosecond laser application [23
]. Although previous studies suggested a deleterious effect of particles on visual acuity [5
], it is now becoming clear that this may not be the case [17
]. Our study confirms that small debris should not represent a concern to the surgeon. Interestingly, we did not find any correlation between the particle number and time from surgery (Spearman correlation coefficient 0.53, even though the P value (0.06) was not extremely low). In contrast with this, Kobayashi et al. reported a progressive reduction of particle number with time [11
]. Our findings could also be due to a difference in the materials used and/or environment encountered during the surgery and/or the relatively small size of our sample. Similarly to other authors, we did not find activated keratocytes or dendritic cells at the interface [11
]. This could be due to either the low density of these cells in the posterior stroma, or to the time passed from surgery, which would allow keratocytes to become quiescent.
A correlation between interface grading and time form surgery- suggested by this study- was confirmed by other papers [11
] implying that a healing process occurring at the interface - an actual surgical wound in the cornea - is associated with a progressive gain in visual acuity.
We would like to point out that this study also had limitations. One of these is represented by the small sample number; hence bigger samples would be needed to confirm our findings. Secondarily, other potentially useful outcomes such as topography and pachymetry were not considered. We anticipate this may be the object of future studies.