As we get older, the macula (the central part of the retina responsible for detailed vision) can begin to break down, causing blurred vision. The macula allows us to see fine detail for activities such as reading, recognising faces, watching television and driving. It also helps us to see colour.
The earliest sign of macular degeneration is often the appearance of small yellow deposits called drusen, which form under the retina. These are accumulated waste products which, as they get larger, stop the flow of nutrients to the retina and cause the layer of supporting cells beneath it to become very thin. When cells in this layer die, the overlying macula degenerates and loses its visual function.
There are two main types of AMD: dry and wet. The extent of the degeneration may be different in each eye and may not progress at the same rate. It is very important to seek early examination and treatment if there is sudden distortion or reduction in vision. There are now some very effective drugs available which can be injected into the eye to stabilise and in some cases improve vision.
Diabetic Eye Disease
Patients with diabetes are more likely to develop eye problems such as cataracts or glaucoma, but the principal threat to vision is through diabetic retinopathy which is damage to the retina. Diabetes is a chronic metabolic disorder characterised by insufficient insulin production or insensitivity to insulin, which leads to too much sugar (glucose) in the blood.
Regulating blood glucose levels is extremely important. Untreated diabetes can result in damage to blood vessels, nerves and organs such as the kidney and the eye. The retina is situated at the back of the eye and responsible for detecting light and transmitting this signal to the brain, resulting in a visual image. Nutrients and oxygen are transported to the retina via numerous blood vessels. These vessels can be damaged by the high blood sugar levels often seen in non-treated diabetes or diabetes that is not completely controlled. This is known as diabetic retinopathy, which has several forms.
Most patients with diabetes will have developed some signs of diabetic change in the retina after 20 years. Treatments range from observation, laser, injections and vitrectomy surgery.
Epiretinal Membrane (ERM) is a condition characterised by the growth of abnormal tissue across the surface of the macula, the central part of the retina. It behaves as a form of scar tissue which, as it contracts, “puckers” the underlying macula causing distortion and visual loss.
The cause of the majority of epiretinal membranes is unknown (idiopathic) but the condition is frequently associated with previous posterior vitreous detachment. It is more common when vitreous detachment has resulted in retinal tearing (requiring laser or freezing therapy) or retinal detachment. Less commonly ERM is associated with previous occlusion of retinal blood vessels or inflammation in the eye.
Common symptoms of epiretinal membrane or macular pucker include distortion of straight lines, blurred central vision and disparity in image size between the two eyes. The procedure to treat this condition involves removal of the scar tissue from the retina. This is known as epiretinal membrane peeling and requires a vitrectomy operation.
Vitreomacular traction is an uncommon condition in which shrinkage of the vitreous jelly within the eye pulls on the central macular area of retina. This causes central visual impairment, either in the form of a generalised blurring or distortion.
Rarely, the shrinkage of the vitreous jelly within the eye results in a partial separation, with some jelly remaining attached to the very central macular area of retina. The cause of this is unknown and it is only in the last few years with the advent of OCT retinal scanning that we have been able to recognise this appearance.
The normal ageing process of the vitreous results in shrinkage of the gel and ultimately a separation from the retina. There are points on the retina where the vitreous jelly can be unusually adherent; one of these is in the very central macular area.
The retina is multi-layered and ongoing traction (“pull”) from the jelly can result in a swelling of the macular area as the retinal layers separate. The inner layers are pulled inwards towards the vitreous cavity whilst the outer layers remain adherent to the eye wall. The situation worsens as normal eye movements cause the jelly within the eye to rotate, this movement producing a relentless pull on the macula.
Common symptoms of vitreomacular traction include:
- the appearance of a blurred patch in the central vision;
- distortion of straight lines, which appear broken or bent;
- a loss of contrast sensitivity – “greying” of central vision;
- loss of colour vision
The procedure to treat this condition involves removal of the vitreous jelly, and requires a vitrectomy operation. The purpose of surgery is to separate the vitreous gel from the underlying macula, such that the retinal layers can return to a more normal position. As this happens, there is every chance that further visual loss will be avoided and in most cases a degree of visual improvement is possible.