Vitreous haemorrhage is the term used to describe bleeding into the vitreous cavity of the eye, which is the space at the back of the eye occupied by the vitreous gel. Symptoms of vitreous haemorrhage may range from a few floaters in mild cases, to complete loss of vision if the haemorrhage is more severe.
In order to understand the effect vitreous haemorrhage has on vision it is helpful to understand how the eye works. The eye can be compared to a camera. The pupil of the eye is like the aperture of a camera, regulating the amount of light entering the eye. Light passes through the cornea, pupil, lens and vitreous and is focussed on the retina.
The retina is the light-sensitive nerve tissue that lines the inner wall of the eye, like the film in a camera. Rays of light enter the eye, passing through the cornea, pupil and lens before focusing on to the retina. The retina contains photoreceptors which convert light into electrical impulses. In the healthy eye these impulses are sent via the optic nerve to the brain, where sight is interpreted as clear, bright, colourful images.
The vitreous is the clear jelly-like substance which fills the hollow space behind the lens. As we age this vitreous gel changes in structure. At some point in time, the back of the vitreous gel pulls away from the retina, a process known as posterior vitreous detachment or “PVD”. This event is very common, and occurs in up to three quarters of all people by the age of 65. It does not cause permanent loss of vision, but some patients are troubled by slight blurring of vision in the affected eye, or by an increase in floaters. Very occasionally PVD results in tearing of the retina (link: retinal tear), with the risk of retinal detachment.
The normal vitreous contains no blood vessels. Bleeding into the vitreous usually occurs due to bleeding from abnormal blood vessels on or below the retinal surface, or from trauma to the retina. Many different eye conditions can cause a vitreous haemorrhage. The commonest causes include:
Retinal tear: as the vitreous contracts during posterior vitreous detachment (“PVD”) it may pull a hole or tear in the retina. Sometimes as this occurs one of the retinal blood vessels may be torn, causing bleeding into the vitreous cavity.
Diabetic retinopathy: in severe cases of diabetic retinopathy abnormal new blood vessels grow on the surface of the retina and may bleed into the vitreous.
Retinal vein occlusion: Blockage of one of the retinal veins can result in abnormal new blood vessels growing on the surface of the retina, much as in severe diabetic retinopathy. These vessels may bleed into the vitreous. Retinal laser treatment may be recommended to reduce this risk after a retinal vein occlusion.
Macular degeneration. Rarely, bleeding may occur as a complication of wet macular degeneration.
Eye tumours: Very rarely the first sign of an eye tumour may be bleeding into the vitreous.
The effect of vitreous haemorrhage on vision depends upon the amount of bleeding into the vitreous cavity. If the haemorrhage is only mild a shower of tiny red or brown spots may be seen. If more severe then larger clumps or clouds may be seen and interfere with the vision. If there is a dense vitreous haemorrhage all vision may be lost from the affected eye.
The condition is easily diagnosed by an ophthalmologist, who will perform a dilated fundus examination after dilating eye drops have been instilled into the eyes.
If there is no view to the back of the eye then an ultrasound B-scan will be performed to inspect the retina and rule out a retinal detachment or eye tumour.
In mild cases no treatment may be necessary. Blood within the vitreous cavity will break down and become reabsorbed, and the haemorrhage will clear spontaneously. Often it is reasonable to wait a period of some weeks to allow this to occur. However, in more severe cases, surgery may be necessary, if the haemorrhage is so dense that it is unlikely to clear spontaneously, or if a retinal tear or retinal detachment is suspected.
Vitrectomy surgery (link) is performed under local or general anaesthetic. The vitreous and the blood lying within the vitreous cavity are removed with microsurgical instruments, and any underlying retinal condition such as a retinal tear or detachment or severe diabetic retinopathy can then be treated as necessary.