Equipment
Equipment used in cryotherapy includes the following:
-
Cryoconsole
-
Appropriately sized cryoprobe for the procedure – The cryoprobe connects to the cryoconsole with insulated tubing that is part of the probe itself; probes with varying tip sizes and angulations have been developed for different applications; generally, the larger the probe tip is, the colder it will become
-
Source of electricity to run the cryoconsole
-
Tank of gas, usually carbon dioxide, that is attached through valves and tubing to the cryoconsole
-
In all retinal cases, an indirect ophthalmoscope and condensing lens
In addition to a substance that is extremely cold (ie, a cryogen), cryotherapy requires a delivery system by which the cold can be brought into contact with the target tissue. Cryogens can be applied to tissue either with an aerosol spray or with a cryoprobe (connected to a cryoconsole, which in turn is connected to a gas tank and an electricity source).
A cryoprobe is a closed system where the cryogen is circulated within a metal probe and the cold probe is applied to the tissue. Specifically, the probe is supplied with a cryogen (eg, liquid nitrogen) from a pressurized source. Liquid nitrogen converts to gaseous nitrogen within the probe, cooling the probe to extremely low temperatures.
The cryoprobe connects to a cryoconsole with insulated tubing that is part of the probe itself. Probes with varying tip sizes and angulations have been developed for different applications; generally, the larger the probe tip is, the colder it will become.
Patient Preparation
Anesthesia
Topical anesthesia using proparacaine drops is adequate for most cases of retinal cryopexy. Local infiltration of lidocaine is used in cryotherapy for conjunctival neoplasms, lid neoplasms and trichiasis.
Retrobulbar or peribulbar anesthesia is used in cryoablation of choroidal tumors (melanomas or metastatic tumors), peripheral cryoablation of the retina or choroid, cryotherapy for ocular toxoplasmosis or Coats disease, and cyclocryotherapy for neovascular glaucoma.
General anesthesia is used in cryotherapy for retinopathy of prematurity and retinoblastoma.
Positioning
Most ocular cryotherapy procedures are performed with the patient in a recumbent position on a narrow table so that the surgeon can approach the patient from the head of the table or from either side.
