Grades of Vitreous Clarity

The vitreous humor is a transparent gel-like structure occupying the space between the retina, ciliary body, and the lens. The vitreous body forms very early during pregnancy and undergoes rapid transformation in three phases. The most important function of the vitreous from the sensory standpoint is to allow transmission of visible light to the retina. Vitreous clarity and light transmission capabilities also are functions of the index of refraction of the vitreous body, the specific structural composition and high level of organization of the collagen fibers. Vitreous haze from uveitis is produced by penetration of inflammatory cells and protein exudation into the vitreous from adjacent structures and is caused by inflammation itself. The clearing of the vitreous haze is dependent on factors external to the vitreous. The amount of the vitreous haze is judged currently by photographic scales. The older “NEI” scale has six ordinal grades of vitreous opacification ranging from (0) to (4 +). A newer logarithmic scale - “Miami” scale offers more levels of vitreous haze discrimination at the lower end of opacification; it has nine levels. Vitreous haze is accepted as surrogate marker for the disease activity in intermediate, posterior and panuveitis. Both scales are suitable for use for clinical grading, research trials, while the Miami scale is suitable also for reading center grading.