Session Title: Cornea
Session Date/Time: Sunday 17/02/2013 | 08:30-11:00
Paper Time: 08:54
Venue: Hall 2
First Author: : V.Dhillon UK
Co Author(s): : H. Dua
Purpose:
We aimed to investigate the state of corneal nerves in eye bank preserved corneas using the acetylcholinesterase (AChE) technique. This is the first and largest study to provide histological evidence that corneal nerves can in fact be preserved in donor corneas when kept in the conventional organ culture (OC) storage for several weeks prior to corneal transplant surgery.
Setting:
Division of Ophthalmology & Visual Sciences, Queens Medical Centre, University of Nottingham.
Methods:
22 eye bank preserved corneas were divided in Group A and B according to the length of time preserved via OC storage from the time after death; at 4 weeks and more than 5 weeks respectively. Group A consisted of 17 corneas which were suitable for corneal transplantation; its endothelium was used for Descemet’s Stripping Endothelial Keratoplasty (DSEK), so the anterior 2/3 was available for this study, while Group B consisted of 5 corneas found unsuitable for transplantation after processing at the eye bank. Full thickness corneas from Group B were used in this study. All corneas were stained as whole mounts using the Karnovsky & Roots direct coloring thiocholine modification of acetylcholinesterase (AChE) technique. Each specimen was then scanned enface using the Hamamatsu Nanazoomer digital pathology microscope to view corneal nerves in multiple layers. High resolution, magnified, color images were produced to allow detail analysis of nerve architecture and distribution of stromal and sub-basal nerves and its ‘perforation sites’.
Results:
The average age of the donors from Group A and B were 77.6 and 88 years respectively. A total of 15 of the 22 corneas (68.2%) had AChE positive stromal nerves; 12 of 17 in Group A, and 3 of 5 in Group B. No nerves were detected in 7 samples. The average number of stromal nerves entering peripherally were 6 (range 0-20 nerves) in Group A, and 8 (range 0-16) in Group B. Central stromal nerves were seen in 6 samples in Group A and 2 in Group B. Many stromal nerves were seen to terminate abruptly. No sub-basal nerves or its corresponding ‘perforation sites’ were detected in any of the samples from either group. The diameter of larger stromal nerves averaged ~12 µm, while that of thinner nerves was ~5 µm. Most nerves present in these samples were thinner that the normal average diameter of 20 µm seen in fresh, unpreserved corneas.
Conclusions:
Re-innervation in corneal grafts has been shown to be a slow process, occurring from months to years after surgery, with virtually absent corneal sensation during the early post-operative period. Corneal nerves are therefore thought to be non-existent in the donor cornea in the early post-postoperative period.
Using AChE staining, this study therefore proves that stromal nerves can be seen several weeks post-mortem when preserved via OC storage. A previous study using in-vivo confocal microscopy showed stromal nerve preservation in Optisol-GS storage; however their sample size was small and there was no histological correlation.
Several studies have noted the presence of stromal nerves within the first few days to months after PKP, while sub-basal nerves only seemed to appear some years after. Also it has been reported that stromal nerves do not contribute to epithelial re-innervation and most sub-basal nerves are seen to regenerate peripherally from the host. Therefore, it has been assumed that the stromal nerves seen in grafts also regenerate from the host. However, since stromal nerves are seen to be present in 68.2% of eye bank corneas prior to transplantation, it is possible that Schwann cell elements from host nerves may guide them to regenerate with donor nerves.
Financial Disclosure:
None
