Instead of scraping the cornea, sending it off to a lab and waiting days for the results, imagine analyzing samples in-office in two hours. A promising technique, now available only in laboratories, would allow practitioners to do just that, according to a report in the May Archives of Ophthalmology.
This technique uses real-time polymerase chain reaction (PCR), which copies and multiplies DNA segments to detect pathogens in the sample. The authors note the value of this technique in identifying the causes of corneal ulcers, such as bacterial keratitis, fungal keratitis and Acanthamoeba keratitis.
“Bacterial culture and smear examination using corneal scrapings is the conventional method to detect causative pathogens of corneal ulcer,” the authors write. “However, bacterial culture is time-consuming, and results of smear examination depend on the laboratory technician’s skill.”
Using corneal scrapings, the researchers compared real-time PCR with bacterial culture; the PCR assay delivered results in two hours vs. 48 hours for the culture. Of the 40 eyes examined, the same pathogen was detected in 20 eyes by both methods. Six eyes showed negative results by both methods. But, in 14 eyes, results differed—11 eyes demonstrated a false positive on PCR, two had false positives on culture only, and one eye had positive results for two pathogens.
“Although PCR has a high risk of false positivity, we actually treated the patients with positive PCR results only according to their PCR results,” the authors write. “The treatment outcomes were all satisfactory.”
With its increased sensitivity and speed, real-time PCR could be developed as a pathogen-specific, in-office diagnostic kit for busy eye care practices, the authors conclude.
Itahaski M, Higaki S, Fukuda M, Shimomura Y. Detection and quantification of pathogenic bacteria and fungi using real-time polymerase chain reaction by cycling probe in patients with corneal ulcer. Arch Ophthalmol. 2010;128(5):535-40.