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Surgeon: microassay beneficial for dry eye diagnosis
Dry eye can stem from many different problems, and the microassay can help determine which one.
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NEW ORLEANS — Knowledge of the root of dry eye problems is an important tool for a surgeon wishing to determine the best way to treat the syndrome. A tear microassay can help surgeons learn preoperatively which patients might experience dry eye after LASIK.
“It’s important to keep the different problems apart because they don’t all respond to the same therapy. This led us to consider using a tear microassay system,” said Marguerite B. McDonald, MD.
Dr. McDonald said a key component of determining the root of dry eye is examining the tear lactoferrin.
“There are some new data coming out to microassay the tear lake,” she said. “If you find low lactoferrin in the tears, this might be a candidate for punctal occlusion and also indicates this person might be at risk for regression. If they were nearsighted, they might become myopic again and have an increased chance of needing a re-treatment.”
Microassay
According to Dr. McDonald, a clinical professor of ophthalmology here at Tulane University Medical School, punctal plugs should be used if patients test low in lactoferrin. She urged surgeons to use the microassay system before many refractive surgical procedures to avoid future problems.
“If you have low lactoferrin on your microassay, that means you are a candidate for punctal occlusion. This is a tear-deficient dry eye and these people are great candidates. You can spot these people in advance, explain to them that they have a high chance of regression and put the plugs in,” she said.
“We should care about microassay and the tears before we fit contacts, when treating dry eye complaints, before treating conjunctivitis and before LASIK and PRK,” she said. “It’s simple to use but right now the biggest drawback is that they take about 15 minutes of a technician’s time. The companies are trying to make them cheaper and faster. I think if you do a lot of anterior segment it’s worth having.”
Tear composition
In 1995, the National Eye Institute classified dry eye into two groups: tear-deficient and evaporative. Each of these has many subcategories as well.
“The microassays are rapidly being improved. They already show corneal protection levels, separate tear-deficiency from evaporative dry eye, show who is at risk for LASIK regression or contact lens failure, and show who needs punctal occlusion,” Dr. McDonald said.
“Only about 60% to 70% of the time can we actually distinguish accurately among bacterial, viral, allergic, toxic or drug-related conjunctivitis early in its course. Our current diagnostic techniques are not very objective or very specific, and often we’ll give patients a therapy that doesn’t work and they have to come back.
“We are looking at incorporating new technology into our practices to really do a highly specific and highly sensitive analysis of the tears to help make a proper diagnosis, and to reduce the number of visits and the number of prescriptions written for drugs that are not needed.”
According to Dr. McDonald, a key component in the tear makeup that needs to be examined is the lactoferrin.
“The secretory cells produce 93% of tear protein,” she said. “Lactoferrin is one of these. It’s an iron-binding protein. It’s actually bacteriostatic, anti-inflammatory and it modulates cell growth. Also, there is lysozyme, which is a natural protease antibiotic. There’s secretory IgA, which is a primary protector of mucosal surfaces.
“Lacrimal deficiency results in decreased protection, nutrition and increased inflammation, and its symptom is dry eyes. There are trends and patterns. Lactoferrin and lysozyme tend to go up and down together while secretory IgA increases in inflammation,” she said.
An eye with low lactoferrin is actually at greater risk for dry eye syndrome.
“When you have low lactoferrin, you have a low iron-binding state,” Dr. McDonald said. “When you have a low iron-binding state, you then end up with more hydroxyl-free radicals, which gives oxidated stress to cornea and inflammation. In addition, when you have low lactoferrin and low lysozyme, this is a situation that sets up for increased chance of infection.”
For Your Information:
- Marguerite B. McDonald, MD, can be reached at the Southern Vision Institute, 2820 Napoleon Ave., Suite 750, New Orleans, LA 70115; (504) 896-1240; fax: (504) 896-1251; e-mail: mbm2626@aol.com.