Scale for photographic grading of vitreous haze in uveitis

Abstract

Purpose: To validate a scale for grading vitreous haze in uveitis using digitized photographs and standardized scoring.

Design: Evaluation of clinical research methodology.

Methods: Calibrated Bangerter diffusion filters inducing incremental decrements of spatial contrast were placed in front of the camera lens while photographing a normal eye to simulate vitreous haze. The photographs were digitized and an ordinal scale was created from 0 (none) to 8 (highest level of opacification at which fundus details could be seen). The scale steps correspond approximately to decimal Snellen visual acuities of 1.0, 0.8, 0.4, 0.2, 0.1, 0.04, 0.02, 0.01, and 0.002, with approximately 0.3 log step between each step. For validation, digitized fundus photographs of uveitis patients were displayed on a computer monitor for comparison with the standard photos. Three observers graded the test set twice under standard conditions. Interobserver and intraobserver variability and κ values for agreement greater than chance were calculated.

Results: Variance component analysis determined that 87.7% of the variance in grades was attributable to the test item rather than to grader or session. The intraclass correlation between graders and grading sessions varied from 0.84 to 0.91. Simple agreement within 1 grade between graders and sessions occurred in 90 ± 5.5% of gradings. κ values averaged 0.91, which is considered near perfect.

Conclusions: A 9-step photographic scale was designed to standardize the grading of vitreous haze in uveitis patients using fundus photographs. The scale is potentially adaptable to clinical trials in uveitis.

FIGURE 1

Vitreous haze scale grades 0 through 8. (Top row, from left to right) Grades 0, 1, and 2. (Second row, from left to right) Grades 3, 4, and 5. (Third row, from left to right) Grades 6, 7, and 8. The 9 images are displayed in increasing order of opacity each equivalent to approximately 0.3 log units of degradation in visual acuity based on the Bangerter calibration. Grade 8 is equivalent to or slightly more opaque than grade 3+ in the Nussenblatt vitreous haze scale. Diffraction rings from combining the Bangerter filters prevented creating increasing levels of haze beyond grade 8. A tenth grade equivalent to haze more than standard 8, and an eleventh grade in which no fundus details are visible are possible, but would not be linear.

FIGURE 2

Vitreous haze scale grading of the test set of fundus images. The bar histogram displays the 97 test objects distributed according to the scale grading 0 through 8. The y-axis corresponds to the number of photographs in each of the 9 scale grades. The x-axis gives the mean category scores with their standard deviation. The most common grades of haze in the test set were in the 4 steps from 0 to 3, but all grades were represented.