What is Vitreous Haze Index (VHI)

The vitreous humor is a gelatinous body occupying the posterior segment, diffusely adherent to the retina. It acts as a metabolic repository for surrounding structures, with studies demonstrating close relationships between retinal changes and alterations in the vitreous’ biochemistry. Structurally, with a viscosity of two to four times that of water, the vitreous is composed of abundant cross-linked collagen fibers, hyaluronic acid, and glycosaminoglycans, helping to preserve the eye’s shape. But more importantly, the vitreous is a transparent media that enables light passage, playing an irreplaceable role in maintaining optimum visual acuity. The clarity of vitreous is related to disease activity, and corresponds to one’s vision.

Therefore, intraocular diseases that compromise the vitreous’ integrity can lead to media opacity, resulting in significant visual deficits. Uveitis is a group of diseases characterized by intraocular inflammation, with a myriad of bizarre causes ranging from infective to autoimmune. With the exception of anterior uveitis, inflammatory infiltrates and proteinaceous exudates build- up within the vitreous regardless of the etiology. On examination, the diseased vitreous assumes a ‘hazy’ appearance, which can be qualitatively classified as various grades of ‘vitreous haze’.

Our group has developed a new biomarker named ‘Vitreous haze index‘ (VHI), which quantifies vitreous haze by measuring signal strength with respect to retinal pigment epithelium. VHI is currently computed by vitreous analysis software (VITAN), allowing both manual and automated computation. VHI has become a widely accepted research tool amongst uveitis specialist in UK and USA and also been reviewed with pharma and FDA as possible end point measurement for intraocular inflammatory diseases. VHI has the potential as a practical tool for monitoring, diagnosing and prognosticating intraocular inflammatory disease, with significant implications on clinicians’ therapeutic decision making.