This article was reviewed by Russell Van Gelder, MD, PhD
Endophthalmitis is one of the most feared consequences of surgery in the United States—the pathology is a purulent inflammation of the aqueous and vitreous that is usually the result of infection.
In addition to its appearance postoperatively, it also may be endogenous or sterile, according to Russell Van Gelder, MD, PhD.
The incidence rates of endophthalmitis following cataract extraction vary from 0.03% to 0.1% in large studies, and the incidence rates following injections vary from 0.05% to 0.1% in large studies.
“Because of the increasing number of injections administered to treat macular degeneration, the incidence of endophthalmitis has re-emerged as a significant public health issue,” said Dr. Van Gelder, holder of the Boyd K. Bucey Memorial Chair and professor of ophthalmology, University of Washington School of Medicine, Seattle.
Though most cases prove to be coagulase-negative Staphylococcus, Dr. Van Gelder noted that a wide variety of pathogens have been associated with the infection, including gram-negative, fungi, and other organisms. Interestingly, the Endophthalmitis Vitrectomy Study reported a 30% rate of culture negativity, and other studies have suggested up to a 50% culture-negative rate.
Identifying the pathogens
Microbial disease diagnosis was revolutionized with the introduction of polymerase chain reaction technology (PCR).
“This is a technology that can amplify minute amounts of DNA to facilitate analysis. When applied to microbes, the presence of microbial DNA is considered to be evidence of potential infections,” Dr. Van Gelder explained.
Primers can amplify all bacteria and demonstrate the bacterial DNA in a sample via 16S metagenomics, a method that relies on the fact that all bacteria have a conserved structure to their 16S ribosomal DNA that is amplifiable.
“The conserved sequences form the basis of the primers, and the intervening sequences are unique to the bacteria. By sequencing, the bacteria can be identified definitively by the intervening sequences,” he said.
Biome representational in silico karyotyping (BRiSK)is a technology developed by Dr. Van Gelder and Aaron Lee, MD, to identify pathogens.
“Using this method, about 1% of the DNA in a sample is sequenced exhaustively to identify any existing bacteria,” he explained.
Whole genomic shotgun sequencing has become a more feasible method of identifying pathogens because of reductions in the costs of sequencing.
“In this procedure, all the DNA in a sample is fractionated for human bacteria, all is sequenced, and sequence is parsed piece by piece to determine the bacterial, fungal, viral, or human components,” Dr. Van Gelder explained.