Oval-tipped Cryo Probe Affords Larger, More Homogenous Burn

Increased tissue penetration and stronger adhesion are benefits of Finger-Tip cryo probe.

ROCHELLE NATALONI, CONTRIBUTING EDITOR

A new cryotherapy probe originally developed for ocular oncology applications is attracting attention across multiple specialties, including retinology. The Finger-Tip cryotherapy applicator freezes a significantly larger surface area than is possible with standard retinal cryoprobes, and this facilitates increased tissue penetration resulting in stronger adhesion, according to Paul T. Finger, MD, clinical professor of ophthalmology at the New York University School of Medicine and director of ocular oncology at the New York Eye and Ear Infirmary (NYEEI). The hand-held device was developed by Dr. Finger and is being distributed by ophthalmic equipment manufacturer MIRA Inc (Uxbridge, MA).

The MIRA Finger-Tip cryotherapy applicators were designed for treatment of malignant conjunctival tumors, but the oval-tipped probe has shown itself to be a versatile surgical tool. In Dr. Finger's practice, which is dedicated to cancers of the eye, the Finger-Tip probe is mainly used to treat orbital tumors, but, Dr. Finger says, retinal specialists will find the device's capabilities beneficial in applications including, but not limited to, retinal ischemia, neovascularization, Coats disease, and retinoblastoma.

The primary benefit of the Finger-Tip "spatulated" cryoprobe is that it can uniformly freeze a large, flat surface area of up to 70 mm². "It has the ability to provide an even, homogenous burn that is 4 to 5 times larger than a conventional retinal cryoprobe," says Dr. Finger. The Finger-Tip cryoprobe, which attaches to MIRA's Surgical Cryo System, is available in 3 sizes (Figure 1). The active surface of the small, medium (Figure 2), and large (Figure 3) spatulated probes are 8.5 mm², 25.2 mm², and 70 mm², respectively. All the metallic parts are made of stainless steel; the outer tubing is silicone and the 2 inner tubes are manufactured from polytetrafluorethylene and have a minimum burst test of 1000 psi.

Figure 1. The 3 Finger-Tip cryotherapy probes available through MIRA, Inc.

"This design allows for preferential cooling of the active surface of the applicators. Therefore, the shaft of the probe will not freeze adjacent tissues," Dr. Finger explains. MIRA tested the probes to cool to 25°C, 235°C, or 265°C on carbon dioxide, and 225°C, 255°C, or 285°C on nitrous oxide. The temperature is governed by the Joule-Thomson principle. Dr. Finger uses nitrous oxide at NYEEI and the New York Eye Cancer Center.

DESIGN DISTINCTIONS

Unlike standard cryotherapy probes, the Finger-Tip cryoprobe is similar in design to a spatula. This enables it to treat a larger and more uniform targeted zone, which Dr. Finger says decreases the chance of missing a small area of tumor. These large probes can also be used to more efficiently grasp tumors of the orbit and provide traction to help in their removal. Similarly, Dr. Finger uses it to facilitate enucleation surgery without an extra set of hands in the operating room.

"Conjunctival tumors extend onto the cornea and creep along the surface of the eyeball, as well as inside the eyelids and onto the eyelid skin," Dr. Finger explains, "so large areas are affected. Using a round-tipped applicator in this situation to make multiple little spots on the surface of the eye is dysfunctional at best because it's impossible to make the spots overlap. So almost by design, traditional cryoprobe applicators miss spots of tumor, which is the worst possible thing that can happen. When we use the Finger-Tip probe, even though we're not treating the entire eyeball or the entire area, the tip is large enough that I can treat areas as big as 16-mm long all at one time very evenly. So I achieve an even, large, complete homogenous burn," he explains.

Dr. Finger designed the applicator for maximum flexibility. "I made this a hand-held probe because in the OR we want to have the dexterity of being able to not only freeze the wall of the eye, but to freeze up underneath the conjunctiva," he says (Figure 4). "For instance, when you cut out a piece of tumor, you're left with a space where there is no conjunctiva. If you lift the conjunctiva and place the probe underneath it away from the eyeball, you can freeze additional millimeters of conjunctiva at the margins to extend the treatment margins without extending the surgical margins," he explains. The goal of destroying all malignant tissue is particularly challenging in the treatment of multifocal malignant conjunctival neoplasia, Dr. Finger points out, because these malignancies are characterized by poorly defined margins. Whereas, with resectable tumors, "surgeons usually compensate by using relatively large surgical margins instead of or as well as performing cryotherapy on the surrounding tissues," he adds.

ENUCLEATION EFFICIENCY

Enulcleation is one of several scenarios in which this spatulated cryotherapy probe is particularly effective.¹ Of the 3 tip sizes, the one employed during enucleation has an active surface of 70 mm². The design allows for preferential cooling of the active surface of the applicator, according to Dr. Finger. MIRA tested this probe to cool to up to 85° C on nitrous oxide, as governed by the Joule-Thomson principle. "The probe's shaft is relatively spared from freezing, so only the cornea touching the active surface freezes and becomes adherent," he explains.

A major benefit of this hand-held device is that procedures, such as enucleation, that normally require the availability of a nurse or assistant can be accomplished by the surgeon alone, according to Dr. Finger. "Tumor traction can be induced with one hand, while the other hand wields instruments used to sever residual tumor attachments. The surgeon can take the Finger-Tip cryoprobe and freeze it at the limbus creating an adhesion to the eyeball, and in this way it can be used (instead of grabbing the muscle stumps) to raise the eye up to allow for transaction of the optic nerve," he explains.

Figure 2. A medium-sized hand-held Finger-Tip cryotherapy applicator being used to treat the wound margin in a case of squamous carcinoma of the conjunctiva and cornea.

Having performed approximately 40 procedures using this maneuver, Dr. Finger says it works quite well. "What's really interesting is that if you are alone, you can't possibly pick up the muscle stumps and cut the nerve at the same time, whereas you can easily grab the eye with the Finger-Tip probe, lift it up, and put the scissor behind the globe and cut the nerve," he says. "Typically the surgeon grabs the superior and inferior rectus muscle stumps with forceps to raise the eye up to allow the optic nerve to be transected with scissors. Performing the procedure this way often results in slip-page of the forceps and the surgeon being left hanging onto a diaphanous piece of muscle," Dr. Finger points out. The MIRA Finger-Tip cryoprobe offers another option for the surgeon who is not satisfied with the conventional technique, according to its designer. "Ultimately," he adds, "you need one less hand. So if you are by yourself during an enucleation, which happens, you can lift the eye up with one hand and get behind the eyeball with the other hand to cut the nerve."

Figure 3. A large-sized hand-held Finger-Tip cryotherapy probe being used to induce traction on an eye prior to transection of the optic nerve (for enucleation).

Finger-Tip cryoprobes also offer an alternative to current devices used for cryoextraction of orbital tumors and cavernous hemangioma. "Treatment of orbital hemangioma is indicated when there is evidence of growth, optic nerve compression, and corneal exposure with secondary keratitis sicca or evidence of vision loss," Dr. Finger says. "The new MIRA probes enable a wonderful purchase of the tumor and allow you to pull on it and create traction and dissect out the adhesions. If you grab a hemangioma with a forceps you're more likely to pop it. So the Finger-Tip probe is very helpful for the removal of these orbital tumors," he adds.

DOCUMENTED OUTCOMES

The inventor of numerous surgical techniques and instruments specifically for patients with eye cancer, Dr. Finger pioneered the use of microwave hyperthermia, palladium 103 plaque-radiation therapy, the Finger Iridectomy Technique, and Finger's Slotted Plaques. He spent 4 years developing the Finger-Tip Cryoprobe and has chronicled its use as an alternative to traditional methods of enucleation and cryoextraction of orbital and conjunctival tumors.

For instance, in a study of a series of 12 patients being treated for squamous conjunctival neoplasia, primary acquired melanosis with atypia, and conjunctival melanoma, Dr. Finger found that the large spatulated cryotherapy applicators allowed for more uniform treatment of tissue compared to standard cryotherapy applicators and that this allowed for more uniform treatment temperatures and more homogeneous cooling rates.² "Clearly," he says, "a relatively large, flattened treatment zone decreases the chance of a geographic miss, facilitates repetition, and reduces the number of applications required to cover the targeted zone."

In a salient report of his use of the Finger-Tip cryoprobe for an anterior orbitotomy, Dr. Finger described the case of a 77-year-old patient who had a superonasal orbital tumor that was 18 mm in its largest diameter and contiguous with both the orbital portion of the frontal bone and optic nerve.³ Ultrasound imaging revealed intrinsic tumor vascularity and a cavernous hemangioma was suspected and postoperatively confirmed by histopathology. Dr. Finger used a combination of sharp and blunt dissection to expose the tumor, and then a medium sized Finger-Tip cryoprobe was used to create an adhesion to the tumor's surface. "The relatively large cryoadhesion allowed for easier handling of the tumor and improved traction. The tumor adhered to the cryoprobe for 60 seconds after the nitrous oxide was discontinued," he says. "Cryoextraction works best with tumors and cysts that contain fluids, such as blood or tears, as opposed to solid tumors and those containing lipid or keratin, such as demoids, according to Dr. Finger. "Cavernous hemangiomas are particularly good candidates because freezing occurs on both the tumor's surface and within the tumor stroma. With a well-formed fibrous capsule, the outer and inner ice balls provide a strong attachment to the probe," he explains.

Figure 4. Treating the wound margin from "underneath" the conjunctiva eliminates the risk of treating the eye ball.

The MIRA Finger-Tip cryo probe was introduced at last year's annual American Academy of Ophthalmology meeting, and will be available for further scrutiny at the upcoming Retinal Physician Symposium in Naples, FL. RP

REFERENCES

1. Finger PT. Finger-tip cryoprobe assisted enucleation. Am J Ophthalmol. 2005;139:559-561.
2. Finger PT, Finger-tip cryotherapy probes: treatment of squamous and melanocytic conjunctival neoplasia. Br J Ophthalmol. 2005;89:942-945.
3. Finger PT, Finger-tip cryoprobe assisted orbital tumour extraction. Br J Ophthalmol. 2005;89:777-778.

Dr. Paul T. Finger reports minimal financial interest in the following products/techniques mentioned in the article: Fonmicrowave hyperthermia, palladium 103 plaque-radiation therapy, the Finger Iridectomy Technique, and Finger's Slotted Plaques. He has a patent pending for the Finger's Slotted Plaques. He has no financial interest in MIRA's Finger Tip Cryoprobes.