Repeatability of Spectralis OCT measurements of macular thickness and volume in diabetic macular edema.

PURPOSE: We estimated coefficients of repeatability for Spectralis optical coherence tomography (OCT)-derived automated retinal thickness and volume measurements in subjects with center-involving diabetic macular edema (DME). METHODS: A total of 50 eyes of 50 consecutive patients with center-involving DME underwent four consecutive "fast" volume scans at a single session using one OCT device operated by one of two experienced operators. Bland-Altman coefficients of repeatability (CR) were calculated for automated retinal thickness measurements in the nine Early Treatment of Diabetic Retinopathy Study (ETDRS) subfields, center point thickness, and total macular volume. Scans were evaluated for significant automated retinal boundary detection error and revised estimates for CR calculated with these scans excluded. RESULTS: CR in the central subfield was 8.03 µm (95% confidence interval [CI] 7.70-8.35 µm). In other subfields, CR ranged from 6.54 to 18.25 µm. Scan sets from 13 subjects had significant boundary detection error; reanalysis with these excluded yielded a CR for the central subfield of 7.44 µm with CR for all other subfields <8 µm. CONCLUSIONS: Retinal thickness measurements in subjects with DME obtained using Spectralis OCT are considerably less variable than has been reported with other devices. Changes in central subfield thickness >8 µm can be considered more indicative of true clinical change rather than measurement variability. This finding informs clinical practice and clinical trial design.

Diagnostic accuracy of microbial keratitis with in vivo scanning laser confocal microscopy.

AIMS: To determine the accuracy of diagnosing microbial keratitis by masked medical and non-medical observers using the Heidelberg Retina Tomograph II/Rostock Cornea Module in vivo confocal microscope. METHODS: Confocal images were selected for 62 eyes with culture- or biopsy-proven infections. The cases comprised 26 Acanthamoeba, 12 fungus, three Microsporidia, two Nocardia and 19 bacterial infections (controls). The reference standard for comparison was a positive tissue diagnosis. These images were assessed on two separate occasions by four observers who were masked to the tissue diagnosis. Diagnostic accuracy indices, kappa statistic and percentage agreement values were calculated. The Spearman correlation coefficient (r(s)) was calculated for the number of correct diagnoses versus duration of disease. RESULTS: The highest sensitivity and specificity values were 55.8% and 84.2%, respectively, and the lowest sensitivity and specificity values were 27.9% and 42.1%, respectively. The highest positive and lowest negative likelihood ratios were 2.94 and 0.59, respectively. Agreement values were: fair to moderate (kappa 0.22-0.44) for reference standard versus observer diagnosis, moderate to good in intraobserver variability (repeatability, kappa 0.56-0.88) and poor to moderate in interobserver variability (reproducibility, kappa 0.15-0.47). The correct diagnosis was associated with duration of disease for Acanthamoeba keratitis (r(s)=0.60, p=0.001). CONCLUSIONS: The diagnostic accuracy of microbial keratitis by confocal microscopy is dependent on observer experience. Intraobserver repeatability was better than interobserver reproducibility. Difficulty in distinguishing host cells from pathogenic organisms limits the value of confocal microscopy as a stand-alone tool in diagnosing microbial keratitis.