PHOENIX OPHTHALMOLOGISTS EYE CARE AND LASER CENTER  
     
     

MAD COW DISEASE AND LASIK



Prion disease, which is a neuro-degenerative infectious disease can be transmitted by surgical instruments. Normal sterilization techniques are ineffective in killing the prion agent. The disease can occur from 2-20 years after exposure!
The re-use of Lasik blades BETWEEN patients is a potential source of spread of this dangerous disease. Re-use of blades is fairly common as a cost reduction technique in many of the high volume and discount centers.
Be sure to ask if you will be guaranteed NEW blades rather than re-used blades for you LASIK surgery!!!

SEE THE ARTICLE BELOW. THE LAST TWO PARAGRAPHS CONCERN LASIK, SPECIFICALLY!!!


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CLINICAL UPDATE: CORNEA

HOW TO PROTECT YOUR PRACTICE FROM PRION DISEASE


Until recently, only bacteria, viruses, fungi or parasites were thought to cause infectious diseases. When Stanley
B. Prusiner, MD, offered the idea that mutant proteins called prions could cause transmissible disease, some researchers were amused.
Nobody laughed, however, when prions were proved the source of "mad cow disease" and its human counterpart, new variant Creutzfeldt-Jakob disease (CJD), as well as other neuro-degenerative diseases. Dr. Prusiner won the Nobel Prize for his discovery in 1997.
Prions are relevant in ophthalmology because they have been found in the optic nerve, retina and cornea of infected individuals. This creates issues for cornea transplant screening as well as surgical instrument sterilization.
Transplant Transmission In the United States, one case of prion disease was transmitted during 1974 via a donated cornea to a transplant recipient, noted Ronald E. Smith, MD, professor and chair of ophthalmology at the University of Southern California, Los Angeles and medical director of the Doheny Eye and Tissue Transplant Bank.
"There is no question that the donor had it [and] that the recipient had it. This is the only solid case, and the only reason we know that the cornea has any infectivity at all," added Nick Hogan, MD, PhD, associate professor of ophthalmology and pathology, neurology and neurosurgery at the University of Texas-Southwestern Medical Center, Dallas.
Another case from Germany suggests probable transmission. The patient developed CJD 30 years after his transplant. "Several 'red-herring' cases have arisen in recent years," Dr. Hogan said, noting that anecdotal associations have also been reported with cataract surgery patients in Britain. "Of course, this is an older population and the fact that they had cataract or corneal transplant surgery and CJD may be a coincidence," said Dr. Hogan, perhaps the only ophthalmologist in the United States currently doing basic research on prions and the eye.
While working as a fellow with Dr. Prusiner, Dr. Hogan helped conduct animal experiments showing that the optic nerve and retina contained prions. The two researchers also found prions in the cornea, albeit at low levels.
There has never been a case showing iatrogenic transmission after retinal or optic nerve surgery. "Is it happening and not being reported? That is certainly possible," Dr. Hogan said. "The only reason anybody pays any attention to corneas is because of the case in 1974."

Screening Issues
Since 1974, about 600,000 corneal transplants have been performed in the United States using a historical screen. "We take the history from the family of the deceased to identify persons known to have this rare condition, and [look for] specific evidence of this neurological disease," Dr. Smith explained. At present, this is the only way to check for the disease.
Prion disease produces no febrile response, no leukocytosis or pleocytosis and no humoral immune response, Dr. Prusiner said. The patient dies without any sign of an immune response to a "foreign infectious agent.'"
Although many researchers are trying to develop a screening tool, no proven, clinical or laboratory test for prions currently exists. Thus, there is no way to know if someone has the disease in the early phase. "We have to be alert and vigilant. Until we have a screening test, there is no way to prevent this 100 percent, short of stopping all organ and tissue transplantation," Dr. Smith said.
What is the risk, then, of prion-infected corneas being transplanted into U.S. patients? Without historical screening, some 1.3 corneas—out of the 45,000 donated each year—might be affected, according to epidemiologic analysis. "There are problems with the epidemiologic data, however, and I think the risk is probably somewhat higher. Epidemiologists at the PDA and the CDC agree," Dr. Hogan said. "With historical screening, the risk is extremely low, but not zero. We are all human. It is possible that a case could get through and be transplanted."
To avoid this, the standard screening procedures of the Eye Bank Association of America (EBAA) have been revised. In particular, no patients with any dementia of any sort will be allowed to donate any organ, including corneas. "In the past, they accepted demented patients with a bona fide diagnosis of Alzheimer’s, which is different than CID. But that has been amended," Dr. Hogan explained.
The EBAA wants to avoid what happened in Europe, when an autopsy was performed on a demented patient. The brain was taken, the cornea donated And transplanted—and three months later, researchers looked at the brain and found CJD.
When a reliable screening test for prions becomes available, the PDA wants to review the requirement that all cornea donors be tested. "That would mean a huge amount of cost and administrative problems," Dr. Hogan said. "Corneas are only viable for about 10 days after they are removed, so it is going to be a difficult problem. But someday we may have to do that."
In the meantime, Dr. Smith thinks that eye banks are doing all they can. "We have the safest donor pool possible for corneas in the world," he said.
Sterilization and Surgery Instruments that touch the eye in a CJD patient can transmit the disease to another patient, and prions are hard to kill with the usual techniques. "Prions are extremely resistant to inactivation by ultraviolet and ionizing radiation," Dr. Prusiner reported.
The World Health Organization, PDA, EBAA, CDC and others have offered two recommendations: If a known CJD patient requires eye surgery, such as a retinal detachment repair, those instruments should be destroyed, regardless of the expense, Dr. Hogan reported.

Procedures such as LASIK should not be performed on a patient with known CJD.
The larger problem is patients with unknown CJD who might receive eye surgery. "It is scary that some LASIK surgeons reuse disposable equipment, and the minimal sterilization procedures between cases would not destroy the prion agent," Dr. Hogan said.
The best way to kill prions is either to immerse instruments in 1 percent sodium hydroxide for about 60 minutes and then autoclave for one hour at 121 degrees Centigrade, or immerse instruments in 5 percent sodium hydrochloride for one hour and then autoclave. "Unfortunately, both of those techniques eventually kill delicate instruments, such as cornea scissors," Dr. Hogan said.
The WHO suggests several measures that offer "a compromise between killing the agent and killing the instruments”
Dr. Hogan said:
Sterilization. Instruments that touch the eye are kept moist after use, so that no tissue could dry onto them. They are sterilized at 136 degrees Centigrade under vacuum in boiling water for 30 minutes. The instruments are then cleaned and re-sterilized at standard conditions (101 degrees Centigrade for 20 minutes).
Separation. Each set of instruments is numbered and kept separate, so that no instruments from group A could go to group B. The instruments used on each patient are logged in case tracking is necessary. "That has all been instituted in eye banks recently," Dr. Hogan said.
Dr. Hogan is a non-paid consultant for the Transmissible Spongiform Encephalopathy Advisory Committee to the FDA and for the Eye Bank Association of America. Dr. Smith has no financial interests.
I ProcNatlAcadSci USA 1998;95(23):13, 363,13,383