Localized RPE removal with a loop instrument in rabbits.

Abstract

 

Purpose

 

To surgically create a localized RPE wound with minimal trauma to adjacent structures.

 

Methods

 

Following a 23G core vitrectomy, 2 bleb retinal detachments (bRD) were raised with balanced salt solution (BSS) in 23 eyes of 21 pigmented and 2 albino rabbits. The RPE underneath the bRD was scraped with 3 prototypes of a novel custom-made instrument (Geuder) in a total of 17 eyes, 6 eyes with bRDs alone served as controls. The instrument consisted of an extensible loop folded within a 20G oval nozzle, which could widen and move forward upon release to debride a targeted RPE surface underneath a bRD. The respective loop designs differed in material and thickness (Prolene 0.1 and 0.06mm vs. metal wire 0.1mm). bRD were stabilized with various concentrations of hyaluronic acid (HA, Gelbag®, C. Zeiss Meditec), or BSS alone. All surgical procedures were analyzed by video. The eyes were enucleated following perfusion fixation immediately after the procedure and processed for standard histology. Serial sections were evaluated by lightmicroscopy by two blinded observers seeking for lacerations in BM/ CC and hemorrhages, as well as integrity of the outer retina.

 

Results

 

Prolene loops yielded smooth and continuous sliding over the targeted RPE by 3 surgeons, while the metal wire got trapped after some extension. Using 0.1 prolene with a single forward/backward stroke, an area of ca. 2.5x1.5mm was 70% devoid of RPE, yet showed few minuscule BM lacerations and random choriocapillaris blood clots. A single scrape with 0.06 prolene resulted in unsatisfactory RPE denudement, whilst repeated scraping maneuvers caused more BM defects and hemorraghes compared with the 0.1 prolene loop. The metal loop resulted in incomplete RPE removal and intraoperative subretinal hemorraghes. Controls showed normal histology. Injection of ≥ 0.25% HA into bRDs did not result in (collapsing) movements of the overlying retina during RPE scraping, reflected in pilot histologic data with normal outer retinal architecture. Blebs filled with 0.1% HA or BSS alone collapsed upon manipulation, suggesting photoreceptor trauma.

 

Conclusions

 

A novel instrument with an extensible 0.1mm prolene loop enabled satisfactory RPE removal, albeit with occasional minuscule BM breaks and CC hemorrhages. This technique may serve as surgical model for geographic atrophy and/ or RPE replacement strategies.

 

Keywords: 701 retinal pigment epithelium • 741 transplantation • 412 age-related macular degeneration