Experimental Ocular Surgery with the Free Electron Laser at Vanderbilt

(TH-Wrk-1-01) (Invited)

K.M. Joos, J.H. Shen, L. Mawn, D. Shetlar, F.Y. Shieh, K. Topadze, M.K. Powers, V.A. Casagrande Blindness, Inc.  

Vanderbilt University, Nashville, TN

Purpose. Amide band II wavelength (6.45 $\mu$m), which can ablate tissue with minimal surrounding thermal damage, and Amide band III wavelength (7.7 $\mu$m), reported to produce more effective cutaneous contraction than the CO₂ laser independent of collagen denaturation, generated by the free electron laser may be useful for ocular surgery.

Methods. 1) Optic nerve sheath fenestration was performed with either the FEL (6.45 $\mu$m, 30Hz, 2-3mJ) through a hollow waveguide surgical probe or with a knife or scissors in monkey eyes. The monkeys survived one month with the fellow optic nerve operated acutely just prior to perfusion. Optic nerves were evaluated histologically. 2) Trabeculectomies with mitomycin C were performed on 14 rabbits. A leaking hole was punctured in the bleb and closed randomly with one of 7 techniques: suture, glue, Tisseel, Tisseel + glue, FEL @ 7.7 $\mu$m, Tisseel + FEL @ 7.7 $\mu$m, or Tisseel + FEL @ 7.5 $\mu$m (control flanking wavelength). The FEL was delivered through a hollow waveguide at 2 mJ. The healing characteristics were followed for 1 month. Acute trabeculectomies, bleb holes, and closures were performed on the contralateral eyes immediately prior to euthanasia. All trabeculectomies were examined histologically with serial sections.

Results. 1) Dural incisions were technically more efficient using the FEL. ERGs were normal following both types of incisions. The tissue responses using either method were similar following either chronic or acute incisions. 2) At 1 week following trabeculectomy, all suture treatments, and Tisseel combined with FEL @ 7.7 $\mu$m treatments, as well as one glue alone treatment showed complete healing of the trabeculectomy bleb holes.

Conclusions. 1) The FEL energy at 6.45 $\mu$m delivered through a hollow waveguide appears capable of efficiently and safely producing an optic nerve fenestration without direct damage to the nerve and with minimal glial reaction indicating that it could be a beneficial alternative for use in human surgery. 2) In a rabbit model of trabeculectomy bleb holes, faster healing occurred with suture, or application of Tisseel combined with FEL treatment @ 7.7 $\mu$m FEL wavelengths may be useful for ocular surgery.