Brian C.K. Au, M.D.University of Arizona – Department of Ophthalmology &

University of Texas Medical Branch – Department of Ophthalmology

ASCRS 2008 Annual Symposium Poster April 5-9, 2008

Financial Disclosure

Brian C.K. Au, M.D. and co-authors do not have financial interests in any ophthalmic products or proprieties mentioned henceforth in this presentation.

Co-Authors (University of Arizona): Jason W. Friday, M.S. IV Stefano Lehman, M.D. Robert W. Snyder, M.D., Ph.D. Roxanna Ursea, M.D.

Introduction

Dislocation of the corneal donor button is a common post-operative complication and cause of decreased visual acuity in Descemet’s Stripping with Endothelial Keratoplasty (DSEK).

Clinical Question: Is there a tool or substance that can:

1) Reduce the rate of donor button dislocation after DSEK?

2) Effectively accomplish # 1 without intraocular toxicity?

Purpose and SettingPurpose:

Part 1: To quantify the adhesive strength of Tisseel fibrin glue (Baxter, U.S.A.) when allowed to react in an in-vitro aqueous environment.

Part 2: To determine whether Tisseel is toxic when injected into the anterior chamber using a rabbit model.

Setting:

Experimentation and Analysis: University Laboratory, University of Arizona Department of Ophthalmology; Tucson, Arizona, USA.

Creation of Virtual Poster: University of Texas Medical Branch, Department of Ophthalmology and Visual Sciences; Galveston, Texas, USA.

Methods – Part 1: Adhesive Strength

The adhesive strength of Tisseel fibrin glue was tested by using a Penscale tension device (My Weigh, U.S.A.), which measures the amount of force required to displace a donor button from a native cornea. Five measurements were taken with no adhesive for control, then 10 measurements were taken following injection of Tisseel between the opposing corneal surfaces submerged in balanced salt solution (BSS).

Methods – Part 2: Intracameral Toxicity

The toxicity of Tisseel was tested using five New Zealand white rabbits, where 0.05 mL of both the fibrin and thrombin components were injected into the anterior chamber. Rabbits were monitored and graded, on a scale of 0-10, for signs of toxicity post-operatively for seven days using a Panoptic ophthalmoscope and a Tono-pen.

Methods – Tension Device 10 donor + 10 recipient New

Zealand white rabbit clear corneas

Donor corneas (epithelium & Descemet’s stripped) adhered to concave glass lens by superglue

Recipients corneas (epithelium & Descemet’s stripped) adhered to convex epoxy lens by superglue

System submerged in BSS

Tisseel applied between donor and recipient corneal surfaces; then surfaces apposed in-vitro

After 5 minutes, tension applied and weight required to separate corneal surfaces was recorded

Results

Part 1 – Adhesive Strength: The average force required to dislocate the donor button with no adhesive was found to be negligible at zero Newtons (N). The average force required to displace a donor button adhered with Tisseel was 0.15N (p<0.003).

Part 2 – Intracameral Toxicity: The toxicity study showed only mild inflammation on post-operative day one (average grade of 1.8) which decreased to an average grade of 0.8 by day seven.

Results – Part 1: Adhesive Strength

Table 1: Tension Device Readings. The initial weight of the glass lens with fixed recipient button, the weight at the moment of release, and the calculated difference yields the force of dislocation (F = ma) against gravity (a = 9.8m/s2). Experimental groups were separated into those corneas previously submerged in BSS (Group 1) and those that were used directly after preparation (Group 2).

Groups Control Experimental 1 Experimental 2

Initial Wt. (grams) 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6

Wt. at release (grams)

6 6 6 6 6 22 19 18 24 20 20 27 21 19 25

Wt. Difference (grams)

0 0 0 0 0 16 13 12 18 14 14 21 15 13 19

Force (Newtons) 0 0 0 0 0 0.16

0.13

0.12

0.18

0.14

0.14

0.21

0.19

0.15

0.13

Results – Part 2: Intracameral Toxicity

Table 2. Rabbits were graded on 10 signs of inflammation using a Panoptic ophthalmoscope and a Tono-pen. Of note, rabbit #5 suffered a small puncture of the anterior capsule intraoperatively. While it was not removed from the experiment, this unintended trauma was taken into account when analyzing experimental results.

Post-Operative Day Day 1 Day 3 Day 5 Day 7

Rabbit # 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5

Lids Mild Erythema + + - - + - - - - + - - - - + - - - - +

Marked Erythema

- - - - - - - - - - - - - - - - - - - -

Edema - - - - - - - - - - - - - - - - - - - -

Conj. Erythema + + + - + - + + + + - + - + + - + - - +

Chemosis - - - - - - - - - + - - - - + - - - - -

Discharge - - - - - - - - - - - - - - - - - - - -

Corneal Edema - - - - - - - - - - - - - - - - - - - -

Hypopyon - - - - - - - - - - - - - - - - - - - -

Cell + Flare - - - - - - - - - - - - - - - - - - - -

Pressure > 21 mmHg - - + - + - - - - - - - - - - - - - - +

Total Grade 2 2 2 0 3 0 1 1 1 3 0 1 0 1 3 0 1 0 0 3

Results (4)

Rabbit # 1 on post-operative day 7 – graded as 0/10.

Conclusion

Part 1 – Adhesive Strength: Tisseel fibrin adhesive reacts in an aqueous environment and provides ample force to prevent donor corneal button dislocation following DSEK in an in-vitro model.

Part 2 – Intracameral Toxicity: Tisseel appears to be non-toxic when injected into anterior chambers of rabbits. Intracameral use of Tisseel may reduce the rate of donor button dislocation following DSEK.