From an evolutionary point of view the vitreous humor has only an essential function until birth. Afterwards the corpus vitreum may be removed without optic harms. Reasons for removing can be the loss of transparency (vitreous haemorrhage due to diabetic retinopathy, opacity in consequence of inflammations). Another frequent reason may be retinal detachment due to inflammatory or age-related shrinkage of the vitreous and traction of the retina.
By removing the vitreous humor, the optic function may even be improved, the retina can be reattached, or a blood inflammation can be removed. After removing the vitreous, the “empty” room will be filled by intraocular fluid (produced by the eye) or temporary filled by injection (gas, air, silicon oil).