Laser & Cryotherapy

LASER THERAPY

A laser beam is made of light of the same color (wavelength) and the light is synchronized so the beam is very focussed (coherent). The word laser is an acronym standing for Light Amplification by Stimulated Emission of Radiation. Lasers are useful in treating retinal diseases. Anything than can be seen in the eye can be treated with laser. Because of that, some of the earliest lasers were developed for ophthalmology (the Krypton laser). Laser treatments fall into three major categories:

  • Lasers to seal up leaky blood vessels
    • Focal laser for diabetic macular edema
    • Laser for macroaneurysm
    • Laser for wet macular degeneration (rarely done today)
  • Lasers to destroy damaged retina to protect healthy retina
    • Pan retinal photocoagulation for proliferative diabetic retinopathy or sickle retinopathy
  • Laser to create an adhesion when the retina is torn or detached
    • Laser for retinal tear
    • Laser for retinal detachment

We use green, yellow, and red lasers to treat the retina. These color lasers are all useful for treating leaking blood vessels or tacking down the retina. Green is useful for tacking down the retina. Yellow is useful for sealing leaky blood vessels. Red is useful for treating through blood. Other lasers used in ophthalmology (the eye) but not by retina specialists inlcude YAG laser to open membranes in the eye, excimer laser to shape the cornea, and argon laser for glaucoma. Retina specialists also use photodynamic laser which is a combination laser drug treatment. A drug (visudyne) is injected into an arm vein. Once it reaches the eye, it can be activated with a low energy red laser to seal up abnormal and leaking retinal vessels. It is useful in macular degeneration and also to treat some choroidal tumors and in central serous retinopathy.

CRYOTHERAPY

“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.