Determining DLK After LASIK
BY WILLIAM L. MILLER, OD, PHD, FAAO
Although uncommon, adverse events do occur with LASIK. One such adverse event is an inflammatory corneal reaction known as diffuse lamellar keratitis (DLK), sometimes referred to as "Sands of Sahara" due to its sand dune-like appearance. This observed appearance results from inflammatory cells (eosinophils, neutrophils and lymphocytes) that have migrated to the area beneath the LASIK flap. This leads to a specific collagenolytic activity that weakens the corneal structure and ultimately leads to stromal melting and keratoectasia.
Although infrequent, its incidence has been reported to range between 0.2 percent and 5.3 percent and it occurs in both mechanical microkeratome and IntraLase (IntraLase, Corp.) procedures. Multiple etiologies have been implicated including surgical gloves, metal debris from the microkeratome and meibomian gland secretions. However, the most frequent isolated cause is bacterial endotoxins released from sterilizer reservoirs. DLK can occur as soon as 24 hours after surgery or as a late-onset problem, occurring many months after surgery.
Epithelial defects after surgery are known to increase the risk of DLK. And at least one report (Boorstein et al 2003) showed a higher incidence of DLK in patients who have atopic disease.
Signs and Symptoms
In early stages, your patient's symptoms may mimic dry eye dysfunction complaints. Signs and symptoms of severe cases may be similar to infectious keratitis. Any added discomfort, redness or decrease in vision necessitates a return visit to the surgery or co-management center.
Look carefully at the cornea for a grainy appearance between the flap and underlying stromal bed. The graininess will be confined to this corneal space and won't extend into the underlying stroma or the overlying flap.
The conjunctiva is typically only mildly hyperemic. This will help you in differentially diagnosing it from an infectious keratitis. Also, DLK won't exhibit a ciliary flush like that found in infectious keratitis cases. You may observe some mild superficial punctate staining which will be more coalesced as the severity increases.
Your most reliable diagnostic aid will be the biomicroscope observation of the grainy, sand-like appearance of the interface between the flap and stroma. Various grading scales range from one devised by Linebarger et al (2000) to another that defines the DLK by whether it's pupil-involved or pupil-sparing.
As the severity increases, you may also note a decrease in visual acuity, irregular astigmatism, keratoectasia and hyperopia. You may see edematous changes at the interface with resultant bullae as the condition advances.
Treatment for DLK stage 1 and 2 begins with a topical steroid (Pred Forte, Allergan). The most frequent dosing is every one to two hours with subsequent follow-up exams every day until the situation improves. You can add other topical medications when indicated, such as a topical fluoroquinolone three times a day for prophylaxis or cyclopentolate for pain management.
Severe DLK cases warrant a referral back to the corneal surgeon. In these cases the surgeon will lift the flap and irrigate the area with sterile balanced salt solution (BSS) to remove the inflammatory cells. In some severe cases your patient will be started on oral prednisolone 40mg to 80 mg per day for at least one week.
More recent novel approaches to therapy include doxycycline and sodium citrate, both of which are anti-collagenolytic.
It's important that practitioners identify and treat DLK early because its continued presence can lead to stromal melting and permanent scarring. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #145.
Dr. Miller is the Director, Cornea and Contact Lens Service at the University of Houston College of Optometry. He is a member of the American Optometric Association and serves on its Journal Review Board. You can reach him at firstname.lastname@example.org.