This article is more than 5 years old. Information may no longer be current.
Managing cornea defects simplified by limited cornea responses
Click Here to Manage Email Alerts
LANSING, Mich.—Treating cornea diseases and inflammations can be as simple as seeing what's in front of you, Cristina M. Schnider, OD, said here at the Contact Lens and Primary Care Seminar of the Michigan Optometric Association.
"The cornea has a limited set of responses and there are not that many areas where a response can occur," said Schnider, an associate professor at Pacific University College of Optometry, Forest Grove, Ore. "The biggest difficulty in treatment is seeing cornea disease and inflammation. The cornea itself is a simple piece of tissue because it does not have a primary blood vessel supply and, therefore, no handy immune system."
As defined in a 1987 paper by Waring and Rodrigues (Patterns of Pathologic Response in the Cornea. Surv of Ophthalmol. 1987;31(4):262-266.) the zones, or layers, of pathologic response in the cornea are:
- the epithelium
- the subepithelial (the basement membrane, Bowman's membrane and anterior stroma)
- the stroma, and
- the endothelial (the endothelium and Descement's membrane)
The types of pathologic responses that occur in the cornea, Schnider said, include defects (such as erosions), fibrosis and vascularization, edema and cysts, deposits, inflammatory and immune responses and proliferation (such as pterygium).
"Your job in therapeutic management of the cornea is to identify where the process is occurring and which response is happening," Schnider said. "A million things could happen in each one of these layers but they are all the same process, and if you can see them you can treat them."
Prophylactic treatment preferred
Addressing cornea defects in particular, Schnider said foreign bodies are classic evidence of such defects and lead to epithelium loss. Cornea defects occur both in contact lens practice and in general practice and include abrasions or erosions.
"Erosions may be due to either contact lenses or, if it is a recurrent erosion problem, it could be secondary to trauma or a dystrophy," Schnider said. She advises prophylactic antibiotics to treat defects because they are not primarily infective or inflammatory conditions. Patching may be necessary for patient comfort, but it does not facilitate the healing process because it inhibits the normal exchange of oxygen to the eye.
The choice of antibiotic, Schnider said, will depend on the severity of the defect. "Smaller defects are expected to heal within 24 hours, so often you can use a milder antibiotic like sulfacetamide, gentamicin or the bacitracin-polysporin in combination and a milder cycloplegic," she said. "For more severe abrasions you need to increase the spectrum of your antibiotic as well as switch to homatropine, a relatively long-lasting cycloplegic."
Stronger antibiotics, such as tobramycin or the fluoroquinolones, are appropriate for lacerations or with penetration. Otherwise, Schnider said, "I still believe we should reserve the big guns. Use the least aggressive thing you can get away with and you can always add more later. It is more unfortunate if we waste some of these really high-powered antibiotics with relatively minor provocation."
Lubricants help heal
Lubricants are important in the healing process, too, since they protect the epithelium as it heals and allow the deeper fibers to take hold even after the cornea has apparently healed. Optometrists should be alert to any swelling response to a cornea defect, Schnider said. "When you go through the epithelium, as in a defect, you have broken that barrier function and water is allowed to seep into the cornea uninhibited, so you get local swelling."
This is not infiltration, she said, but edema, and although it might appear hazy it is a natural response to the cornea when its barrier function is compromised. "It can cause blurring, but that does not mean you have an infiltrative process."
Steroids or NSAIDs?
When tackling inflammation in the cornea, Schnider said optometrists often have to weigh the pros and cons of using steroids or nonsteroidal anti-inflammatory agents (NSAIDs). "Inflammation and problems with the auto immune and hypersensitivity reactions in the cornea are not native to the cornea. There is nothing that lives in the cornea that can cause inflammation by itself, and that means you are treating the reaction and not the cause."
Steroids, she said, work at the top of the response cycle, stopping activity immediately. NSAIDs, which are becoming more popular, may not provide as quick a response, but may be effective for longer term therapy.
"If you have a severe, non-infectious corneal reaction, you may want to start with steroids and get the response into the cornea and surrounding tissues," she said. If the patient needs long term therapy the clinician could consider NSAIDs, even overlapping the two so that as the steroids are tapered, a maintenance dose of NSAIDs can be introduced. This regimen would provide a less invasive therapy with fewer side effects.
As a final word of caution, Schnider advises ODs to be aware of viruses when treating the cornea. "Viruses are the agents that actually can do everything to all layers of the cornea. Viruses are tricky -- always keep in the back of your mind that if things are not going as you planned, a virus is probably behind the reaction you are looking at, and they do not follow the rules that well."