“Cryo” refers to “freezing”. Cryotherapy involves placing a very cold metal probe against the wall of the eye so that all of the eye’s layers are frozen, including the retina that lines the inside of the eye. Cryotherapy creates an adhesive scar that seals the retina against the wall of the eye. The effect of cryotherapy (the adhesive scar) is similar to laser treatment, but the treatment effect is accomplished using cold rather than heat. Unlike laser, cryotherapy can be used to form an adhesion that will hold detached retina to the eye wall once the retina attaches. In this way, cryotherapy is like glue where laser is more like a stapler. For laser to work, the retina has to be already attached. It takes cryotherapy about a week to form a strong adhesion. So during the first week after cryotherapy for a retinal tear, it is best to avoid jarring activity. During a week following cryotherapy combined with a gas bubble for a retinal detachment (a pneumatic retinopexy), positioning is important because the bubble holds the retina in place while the cryotherapy adhesion matures. If the cryotherapy held the retina immediately, positioning for more than a few hours would not be needed. Since cryotherapy takes a while to work, positioning for a few days or a week is usually needed.
First, the eye is anesthetized, often with an injection of numbing medicine just beneath the skin-like covering of the eye called the conjunctiva. The patient usually feels nothing during this injection. Topical anesthesia before the injection keeps the injection of anesthesia from hurting. Sometimes the eye will get red from the injection and or from the cryotherapy. After the eye is appropriately numbed, the doctor uses a head light and a lens to look into the eye so the freezing probe can be placed in the correct position, immediately adjacent to the retinal tear. The retina surrounding the tear is frozen, usually with several separate cryotherapy spots. Its common to feel pressure on the eye during cryotherapy.
Rarely, cryotherapy is used to treat tumors or to destroy peripheral retina. Small tumors can be frozen and destroyed. This is done for small retinoblastomas, hemangiomas, and angiomas. Sometimes patients with proliferative retinopathy are treated with cryotherapy in the very far periphery of the retina where it is difficult to reach with the laser. Since cryotherapy is applied from the outside of the eye, it is also useful in treating the retina when the view into the retina is poor. The laser has to travel through the eye to reach the retina and can be hindered by a vitreous hemorrhage (blood inside the eye) or a dense cataract. Cryotherapy can be used in those situations because it does not need to traverse the cornea, lens, or vitreous like the laser does.