A cataract is a clouding of the lens of the eye. Vision can become blurred as a result of a cataract.

The lens is a clear tissue located behind the iris. It helps to focus light on the retina at the back of the eye where the image is formed. The lens must be clear in order to form a sharp image.

As well as blurred vision a cataract can also cause dazzle due to bright lights such as car headlamps and changes in colour vision resulting in “washed out” colours.

Cataracts can form at any age. The most common type of cataracts is age-related. In younger people cataracts can result from conditions such as diabetes, certain medications and other longstanding eye problems. Cataracts can also be present at birth (congenital cataracts). Cataracts come in a variety of forms including Cortical (pictured), nuclear sclerosis, posterior subcapsular and mature

The most effective treatment for cataract is an operation to remove the cloudy lens. In the past, eye specialists often waited until the cataract became mature and vision was very poor before removing the affected lens. However, now the operation is usually done as soon as a reduction in eyesight interferes with an individual’s quality of life. This includes difficulty with cooking, driving, being able to read, work etc.

Drusen are tiny yellow or white accumulations of extracellular material that build up in Bruch’s membrane (the layer that separates the retina from the choroid in the eye). The presence of a few small ("hard") drusen is normal with advancing age, and most people over 40 have some hard drusen. However, the presence of larger and more numerous drusen in the macula (pictured) is a common early sign of age-related macular degeneration (AMD).

AWhether drusen promote AMD or are symptomatic of an underlying process that causes both drusen and AMD is not known, but they are indicators of increased risk of the complications of AMD.

The source of the proteins and lipids in drusen is also not clear, with potential contributions by both the retinal pigment epithelium and the choroid.

AMD or Age-related macular degeneration is the most common form of registered blindness in this country; it is thought to affect one in ten people over 50. Key symptoms are a blurring of central vision and straight lines appearing wavy, for example doorframes and steps. Everyday activities such as driving, watching TV, and even recognising faces can become impossible over time.

There are two types of AMD – a wet form and dry form. The wet form is a more severe but less common with more rapid degeneration of vision. The dry form is more common but less severe and degeneration taking place over a longer period. At present people with macular degeneration have three possible treatment options: thermal (heat laser); Photodynamic Therapy; or anti-VEFG drugs.

Similar to a freckle on the skin, naevi (plural) can be found inside the eye. The most common known as a choroidal naevus (pictured) can only be seen by viewing the inside of the eye. Like other naevi a choroidal naevus can develop into a malignant melanoma. Choroidal naevi rarely require treatment. Retinal photography is commonly used to document the size of the naevus. If the choroidal nevus has orange pigmentation, if the nevus is leaking fluid, or has a thickness of 2 mm or more it may be a malignant choroidal melanoma.

Most people with a choroidal nevus should have their eyes examined annually. providing close monitoring for evidence of growth or malignant transformation into a choroidal melanoma.

The optic disc is the visible part of the optic nerve seen when viewing the retina through a dilated pupil. The nerve connects the eye to the brain, and via the central retinal artery and vein which enter and leave the eye via the optic nerve it brings the retina its main blood supply.

There are a wide variety of abnormalities of the optic disc, which are associated with a number of conditions both ocular and involving other parts of the body. However, in diabetic eye screening the most common types of optic disc abnormalities are associated with raised intra ocular pressure and the resulting glaucoma.

The main optic disc abnormalities associated with glaucoma are:

Macular pucker (pictured) is a wrinkling of the part of the eye responsible for central vision, known as the macula. Moderate puckering of the macula can have the appearance of crinkled cellophane and is called cellophane maculopathy. More severe wrinkling is known as a full macular pucker.

Macular puckering occurs when thin transparent scar tissue forms on the surface of the retinal tissue and contracts. The symptoms of macular pucker include varying levels of distortion and reduction of central vision.

In most cases the condition is spontaneous, and it is not thought to be caused by anything an individual has done or failed to do. Sometimes the scar tissue can develop after injury or damage to the eye as well as post operatively. Most people with the condition have minimal to moderate distortion of vision. Surgery is the only treatment for macular pucker and involves peeling the scar tissue from the surface of the retina. In most cases surgery is only offered when vision has been significantly affected.

A retinal vessel occlusion is a blockage in the blood vessels of the eye that can lead to a loss of sight. Both veins and arteries of the retina can be occluded. Retinal arteries deliver the blood supply to the retinal tissue. The main cause of a retinal artery occlusion is atherosclerosis. Atherosclerosis describes a condition which relates to the vessel wall and is sometimes referred to as hardening of the artery.

Eventually arteries may narrow sufficiently to cause a blockage and subsequent haemorrhaging (bleeding). This causes damage to the photosensitive retinal tissue and varying degrees of sight loss depending on where the occlusion occurred.

Retinal veins drain away blood from the retina. When they become blocked the blood cannot drain away properly (retinal vein occlusion pictured). As a result the blood backs up in the vein. This blockage can cause the area to swell and in some cases can lead to haemorrhaging resulting in damage to the retinal tissues and subsequently effecting vision. The extent of the sight loss depends on the location of the blockage.

Asteroid Hyalosis (pictured) is a degenerative eye condition featuring small white or yellowish white opacities (solid non transparent particles) in the vitreous humor (the jelly like material inside the eye which maintains the eyes shape). These opacities appear reflective, giving the appearance of stars or asteroids. Asteroid hyalosis is different from the more common typical vitreous floaters, which are usually fibrous or cellular particles.

The cause of asteroid hyalosis is unknown, but it has been associated with diabetes, hypertension and tumors of the eye.

While asteroid hyalosis does not usually severely affect vision, the floating opacities can be quite annoying, and may occasionally causes visual problems as well as hampering the ability of a physician to clearly view the retina.

Myelin is the insulating layer surrounding neurons (nerves), that dramatically increases the speed at which a signal is transmitted by the nerve.

In the vast majority of people, myelination of the optic nerve fibres stops when it reaches the optic disc (visible part of the optic nerve). This usually occurs shortly after birth. However, in a small proportion of people (approximately. 1%) the process continues and myelination extends into the retina (pictured).

Appearing as a shiny white area of variable extent following the line of the retinal nerve fibre layer myelinated nerve fibre is often continuous with the optic disc margin and has an indistinct edge.

Myelinated nerve fibres are of no significance unless the macula is involved.

AV nipping (pictured) is indicative of hypertension and describes the changes which occur at arteriovenous crossings in the retina where an artery crosses a vein. In patients with hypertension and associated arteriolosclerosis (narrowing of the artery) the artery applies increased pressure on the vein at the point where it passes over the top of the vein.

AV nipping is not necessarily indicative of the severity of hypertension but its presence makes it likely that raised blood pressure has been present for many years.