Noninvasive in vivo optical detection of biofilm in the human middle ear

Abstract

Otitis media (OM), a middle-ear infection, is the most common childhood illness treated by pediatricians. If inadequately treated, OM can result in long-term chronic problems persisting into adulthood. Children with chronic OM or recurrent OM often have conductive hearing loss and communication difficulties and require surgical treatment. Tympanostomy tube insertion, the placement of a small drainage tube in the tympanic membrane (TM), is the most common surgical procedure performed in children under general anesthesia. Recent clinical studies have shown evidence of a direct correspondence between chronic OM and the presence of a bacterial biofilm within the middle ear. Biofilms are typically very thin and cannot be recognized using a regular otoscope. Here we report the use of optical coherent ranging techniques to noninvasively assess the middle ear to detect and quantify biofilm microstructure. This study involves adults with chronic OM, which is generally accepted as a biofilm-related disease. Based on more than 18,537 optical ranging scans and 742 images from 13 clinically infected patients and 7 normal controls using clinical findings as the gold standard, all middle ears with chronic OM showed evidence of biofilms, and all normal ears did not. Information on the presence of a biofilm, along with its structure and response to antibiotic treatment, will not only provide a better fundamental understanding of biofilm formation, growth, and eradication in the middle ear, but also may provide much-needed quantifiable data to enable early detection and quantitative longitudinal treatment monitoring of middle-ear biofilms responsible for chronic OM.

Fig. 1.

Normal ear. (A) Video otoscope image of the TM from a normal human ear. (B and C) Typical LCI depth scan (B) and cross-sectional OCT image (C) of the TM. Based on the scattering properties of the TM, a thickness of ∼95 μm was measured, which was consistent with the average thickness (100 μm) of the adult human TM. (D) Classification of the LCI scans from this normal ear, resulting in 98% normal scans and 2% abnormal scans. The circles represent LCI scans from a normal ear in terms of thickness and intensity. Blue and red circles represent the scans classified as normal and abnormal, respectively. (Scale bar in C: 100 μm.)

Fig. 2.

Chronic middle-ear infection with a thick, highly scattering biofilm. (A) Video otoscopy image showing a less-translucent TM. (B) Typical LCI depth scan showing evidence of a thick (∼200 μm average thickness) biofilm behind the TM. (C) Cross-sectional OCT image showing the lateral spatial extent of biofilm. (D) Classification results of the LCI scans demonstrating that 87% of acquired LCI scans were classified as abnormal. The crosses represent LCI scans from an abnormal ear in terms of thickness and intensity. Blue and red crosses represent the scans classified as normal and abnormal, respectively. (Scale bar in C: 100 μm.)

Fig. 3.

Chronic middle-ear infection with thinner, lower-scattering biofilm. (A) Video otoscopy image showing a cloudy TM. (B) Typical LCI depth-scan showing evidence of a thin, low-scattering biofilm behind the TM. (C) Cross-sectional OCT image showing a thinner and more spatially localized biofilm. (D) Classification results of the LCI scans from this TM demonstrating 57% abnormal scans. Blue and red crosses represent the scans classified as normal and abnormal, respectively. The relatively low number of classified abnormal scans in this infected ear is related to the geographic pattern of developing biofilm across the TM. (Scale bar in C: 100 μm.)

Fig. 4.

Portable LCI/OCT otoscopy systems. (A) Schematic of the LCI/OCT optical systems. (B) Photograph of the portable LCI-otoscopy system. (C) Schematic and photograph of the integration of the LCI fiber-based micro-optic probe into the otoscope head. (D) Schematic and beam profile of the long-working-distance LCI probe, which uses a gradient-index (GRIN) lens. (E) Photograph of the portable OCT-otoscopy system. (F) Schematic and photograph of the OCT-otoscopy hand-held scanner. The OCT-otoscopy system enables 2D and 3D cross-sectional OCT images, in contrast to the individual LCI depth scans provided by the LCI-otoscopy system. However, the OCT-otoscopy system has added complexity because of the use of galvanometer-mounted mirrors for scanning the beam across tissue.