The Retina

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Retinal diseases are mainly inflammatory, vascular or degenerative in aetiology

Primary retinal diseases are degenerative or, uncommonly, infective.

In the elderly, prolonged exposure to light is eventually revealed as damage to the retinal pigment epithelium, leading to secondary loss of photoreceptors. This mainly occurs at the macula, the site of cones and of high-resolution colour vision, and is termed senile macular degeneration. This is one of the most common causes of severe loss of vision in the elderly. 

In macular degeneration lipid material accumulates under the retina. Later vascular and proliferative changes occur. In this case the macula shows advanced degeneration. This is a very common cause of visual handicap.

Pathology of common fundoscopic abnormalities

Vascular diseases of the retina are a common cause of blindness

Vascular disorders are a major cause of eye disease, having their main impact on the retina. The main predisposing factors for vascular disease are hypertension and diabetes mellitus. Retinal complications of diabetes mellitus are now one of the most common causes of blindness in Western countries. 

Among the main vascular diseases is benign hypertension, which is associated with development of hyaline thickening in retinal vessels. In accelerated-phase hypertension, flame haemorrhages, exudates, and areas of retinal ischaemia develop, causing microinfarcts termed cotton-wool spots.

Diabetic retinal disease causes thickening of the basement membrane of capillaries and hyaline arteriolosclerosis. Microaneurysms occur as dilatations of arterioles and capillaries with abnormally fragile and permeable walls. Exudates develop, with blot haemorrhages from leaking capillary vessels. Areas of ischaemia cause cotton-wool spots. Retinal ischaemia causes secretion of angiogenesis factors, inducing formation of new vessels (proliferative retinopathy). Neovascularization is the term used to describe the formation of new vessels on the inner surface of the retina (leading to haemorrhages) and on the anterior surface of the iris (leading to secondary closed-angle glaucoma).

Retinoblastoma is an uncommon tumour of childhood

In retinal detachment the retina is separated from the pigment epithelium, thereby losing metabolic support

Retinal detachment occurs when the neural retinal layer becomes separated from the retinal pigment epithelium. Provided that the photoreceptor layer is brought back into contact, the retina may regain function; however, prolonged detachment leads to loss of metabolic support from the retinal pigment epithelium, with degeneration of photoreceptor cells and permanent loss of function.

There are three main reasons for retinal detachment:

1 Traction on the retina from abnormalities in the vitreous. This occurs with organization of previous inflammation or haemorrhage into the vitreous. In diabetics, traction from newly formed blood vessels can also cause detachment.

2 Shearing of the retina may cause formation of small retinal tears and development of detachment. These tears develop when the vitreous focally loses contact with the retina at the vitreoretinal junction. Instead of transmitting rotational forces uniformly, loss of contact with vitreous causes forces to be focally concentrated, leading to tearing of the retina. This loss of contact is 
predisposed in patients with severe myopia.

3 Pressure on the retina from accumulation of fluid in the sub-retinal space, commonly from inflammatory exudate, haemorrhage, or neoplasm.
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