Vitreous Particles Seen Using OCT May Reveal Uveitis Classification

The size and density of hyperreflective particles seen in the vitreous of uveitis patients on spectral-domain optical coherence tomography (SD-OCT) images may be used for classifying uveitis type and assessing inflammation, according to a study published in Clinical Ophthalmology. This is the first study that tests the morphological characteristics of the particles and compares them between 3 types of uveitis, according to the researchers.

The researchers retrospectively reviewed 33 eyes of 23 patients (mean age, 54±17.1 years; 9 men, 14 women) who visited Kobe University Hospital between January 2016 and January 2017 and were diagnosed with active posterior or panuveitis. Included patients had one of the followings: Inflammatory chorioretinal or retinal vascular lesion, macular edema due to ocular inflammation, and vitreous haze grade 2+ or higher (according to the standardization of uveitis nomenclature grading system).

Based on clinical findings and additional tests such as lab tests, multiplex PCR in aqueous humor, and vitreous samples, all eyes were classified into  3 groups: infectious uveitis (IFU), noninfectious granulomatous uveitis (NIGU), and noninfectious nongranulomatous uveitis (NINGU).

Both 9 mm horizontal and vertical SD-OCT B-scans with B-scan averaging higher than 50 were used by the researchers in this analysis. The number of hyperreflective dots in the vitreous was manually counted, the area of the vitreous was manually segmented and measured, and their density (defined as the number of dots divided by the area of the vitreous) was calculated. In addition, the team measured the horizontal and vertical lengths of the smallest and largest particle.

All measurements were performed three times by 3 independent masked graders. The average of their measurement was used in the statistical analysis.

The IFU group had a significantly higher number of particles (77±81.3) than the NIGU (18.7±6.7) and NINGU groups(13.6±8.5) (P =.03 and P <.001, respectively). Significant differences were also found between the vitreous particle density of the IFU group (16.8±18.9 µm²) and that of the NIGU (4.2±1.8 µm²) and NINGU groups (3.3±2.0 µm²), (P =.03 and P =.003, respectively).

No significant difference was found between the mean length of the smallest particle among the 3 uveitis groups. In contrast, both the IFU (146.0±70.01) and the NIGU (84.0±20.3) groups had a significantly larger mean length of the largest particle when compared with that of the NINGU group (60.7±38.5) (P =.014 and P =.03, respectively). The length of the largest particle was found to correlate with the grade of vitreous haze (P =.01). 

Several infectious diseases included in the IFU group, including cytomegalovirus (CMV) retinitis, varicella zoster virus (VZV)-associated uveitis, acute retinal necrosis caused by VZV, ocular toxocariasis, and ocular tuberculosis are known causes of granulomatous inflammation, the researchers explain. This type of inflammation is associated with a larger immune complex and thus explains the increased mean length of the largest particle found in the IFU and NIGU groups. 

“The distinction between granulomatous and nongranulomatous inflammation is useful in directing treatment and targeting a systemic workup,” according to the researchers..

The limitations of the study include its retrospective nature, small sample size, manual measurements, and impurity of the sample with resident cells of the vitreous.