Development of a scale for grading pre-plus and plus disease using retinal images: A pilot study

Abstract

When screening infants for retinopathy of prematurity, evaluating posterior pole vascular characteristics (ie, the presence or absence of pre-plus or plus disease) is subjective and prone to error. ROPtool, a semiautomated computer program, measures retinal vessel tortuosity and dilation. In this pilot study, we created an abbreviated pictorial scale of varying vascular tortuosity and dilation based on expert perception of vascular characteristics. We used ROPtool to evaluate the experts' ability to arrange these images in order of increasing vascular tortuosity and dilation. ROPtool values confirmed successful arrangement of images in order of increasing vascular tortuosity and dilation. This pictorial scale could serve as a reference to decrease subjectivity when diagnosing pre-plus or plus disease.

FIG. 1

Abbreviated pictorial scale of increasing vascular dilation and tortuosity created by consensus of 3 fellowship-trained pediatric ophthalmologists. Judgment of vascular dilation increases from left to right. Judgment of vascular tortuosity increases from bottom to top. The ROPtool measurements of both tortuosity index and dilation index are listed for each image. ROPtool measures tortuosity as the length of the traced vessel divided by a smooth curve generated from points spaced about 40 pixels apart on that vessel and dilation as the average vessel width over its length divided by the area of the optic nerve. The tortuosity and dilation indices are calculated by multiplying the raw tortuosity or dilation values by an adjustment factor so that indices of 10 represent the minimum abnormality necessary for plus disease, as defined by the standard photograph.