The impact of conjunctival flap method and drainage cannula diameter on bleb survival in the rabbit model

Abstract

PurposeTo examine the effect of cannula diameter and conjunctival flap method on bleb survival in rabbits undergoing cannula-based glaucoma filtration surgery (GFS).MethodsTwelve New Zealand White rabbits underwent GFS in both eyes. The twenty-four eyes were divided into four groups. Two of the four groups (N = 12) received limbus-based conjunctival flaps (LBCF), and the other two (N = 12) received fornix-based conjunctival flaps (FBCF). Six FBCF rabbit eyes were implanted with 22-gauge drainage tubes, and the other six were implanted with 26-gauge tubes. Likewise, six LBCF rabbits received 22-gauge drainage tubes and six received 26-gauge tubes. Filtration blebs were evaluated every three days by a masked observer. Bleb failure was defined as the primary endpoint in this study and was recorded after two consecutive flat bleb evaluations.ResultsGroup 1 (LBCF, 22- gauge cannula) had a mean bleb survival time (Mean ± SD) of 18.7 ± 2.9 days. Group 2 (LBCF, 26-gauge cannula) also had a mean bleb survival time of 18.7 ± 2.9 days. Group 3 (FBCF, 22-gauge cannula) had a mean bleb survival time of 19.2 ± 3.8 days. Group 4 (FBCF, 26-gauge cannula) had a mean bleb survival time of 19.7 ± 4.1 days. A 2-way analysis of variance showed that neither surgical approach nor cannula gauge made a statistically significant difference in bleb survival time (P = 0.634 and P = 0.874). Additionally, there was no significant interaction between cannula gauge and conjunctival flap approach (P = 0.874), suggesting that there was not a combination of drainage gauge and conjunctival flap method that produced superior bleb survival.ConclusionLimbus and fornix-based conjunctival flaps are equally effective in promoting bleb survival using both 22 and 26-gauge cannulas in the rabbit model. The 26-gauge drainage tube may be preferred because its smaller size facilitates the implantation process, reducing the risk of corneal contact.

Modulating Ocular Scarring in Glaucoma Filtration Surgery Using the Epigenetic Adjunct Suberoylanilide Hydroxamic Acid

“…The GFS procedures were performed by a single surgeon exactly as described in our previous publications. 5,23–25 Before the procedure, a blend of xylazine (Xyla-ject, 10 mg/kg; Phoenix Pharmaceuticals, Inc.) and ketamine (Ketaject, 50 mg/kg; Phoenix Pharmaceuticals, Inc., Burlingame, CA) was injected intramuscularly for anesthesia. Proparacaine (0.1%) eye drops (Bausch and Lomb, Tampa, FL) were used as a topical anesthetic.…”

Experimental models of glaucoma filtration surgery

“…Since IOP does not demonstrate any appreciable reduction following glaucoma surgery in experimental models despite establishing patent connections between the anterior chamber and subconjunctival space, it may be that maintaining functional distal drainage pathways away from the subconjunctival space is critical in ensuring surgical success. This is particularly relevant with the advent of minimally invasive glaucoma surgery, where animal models may enable more thorough evaluations of different surgical approaches ( ab interno versus ab externo ) and the impact of different types of devices on distal outflow pathways (Rodgers et al 2018). The effect of chronic glaucoma medication on the human ocular surface has been studied in great detail, although these findings have yet to be translated to preclinical platforms for further testing.…”