Eye Conditions (G - N)

Our list of eye conditions continues here. Look Up makes every effort to ensure the information we provide is correct - however we are not a medical website. We have provided links to other organisations should you need more detailed information about eye health and disease.

Glaucoma
A healthy eye needs to keep its shape to allow it to focus properly and to maintain the health of the structures within the eye. In order to do this it needs to maintain the correct level of internal pressure (intraocular pressure).

The pressure in the eye is maintained by the production of clear fluid (aqueous humour) just behind the iris which then circulates through the pupil into the front part of the eye, providing nourishment for its structures, before draining back in to the blood in a carefully controlled fashion. The balance between the production and drainage of fluid maintains the correct pressure in the eye.

The commonest type of glaucoma occurs when the increased pressure within the eye damages the retina and the optic nerve. The optic nerve carries the nerve fibres of the retina from the back of the eye through to the visual cortex within the brain.

Glaucoma usually develops slowly either due to excess fluid production or poor drainage from the eye and this type of glaucoma is termed chronic glaucoma. Chronic glaucoma is the commonest form of the disease and is usually painless and not noticed by sufferers until late in the disease when they start to become aware of a loss of their peripheral (side) vision and blurring of their central vision. This type of glaucoma is often detected by having routine sight tests.

When glaucoma comes on suddenly due to a rapid rise in the pressure in the eye it is called acute glaucoma. This rapid rise in pressure is often caused by the drainage channels from the eye becoming blocked. This sudden rise in pressure in the eye is usually very painful, causes the pupils to become larger and slightly oval, and the front of the eye to become misty. The vision also becomes misty. Without rapid treatment this type of glaucoma can cause permanent loss of vision or blindness in a matter of days.

If glaucoma is caused by another problem in the eye such as inflammation, surgery or injuries to the eye it is sometimes called secondary glaucoma.

People at higher risk of developing glaucoma include
• People over 40 years of age
• People with a family history of glaucoma
• People from certain racial groups - African, Afro-Caribbean, and South Asian
• People who are myopic (short-sighted)
• People with diabetes


Treatment of Glaucoma
Treatment is usually though medication in the form of eye drops or occasionally tablets – although in some cases surgery or laser treatment might be required to open or improve the drainage mechanism within the eye.

For people with communication difficulties it may be very difficult for them to tell you how they see their world. It requires skilled observation and good knowledge of the person to begin to understand how a person might be seeing their world. A functional vision assessment is an important method of assessing someone’s vision.
Carers and supporters may need to take care to find out if glaucoma is present in a person’s family history.

For more information click here to visit the NHS Choices website

or visit the SeeAbility website to see a simulation of tunnel vision caused by Glaucoma


Keratoconus
Keratoconus affects the cornea. The cornea is the transparent, smooth dome-shaped front of the eye. It is transparent to allow light to enter the eye, and is smooth curved surface provides two thirds of the focussing power of the eye.

Normally the cornea should be equally curved in all directions the central part having a surface like a smooth sphere (like a marble or small ball). Some people may have a cornea where the curvature is not equal in all directions but is still smooth (more like the surface of the back of a spoon or the surface of an egg) – this is known as astigmatism.

Keratoconus is a more serious condition and means "a cone-shaped cornea". Keratoconus occurs when the transparent, dome-shaped cornea becomes more pointed or irregular due to the thinning of the cornea. This thinning normally occurs in the middle or the lower third of the cornea and because the surface becomes distorted the vision becomes difficult to correct with glasses.

Keratoconus is a progressive condition that usually starts in early teenage years but sometimes starts, or is not noticed until the person is older. Its rate of progress varies considerably. It may stabilise after a short time or it may lead to significant sight loss and distortion of vision. Keratoconus does not normally cause blindness.

Sometimes in advanced keratoconus the rear part of the cornea may rupture causing the cornea to become cloudy or hazy. This may cause the eye to be come red, sticky or watery. This complication of keratoconus is called hydrops and needs urgent medical attention if vision is not to be permanently damaged

People with keratoconus commonly report having problems with ‘glare’, having blurred distorted vision, ‘ghosting’ or ‘halos’ and ‘stars’ around lights, and even multiple images of the same object. Often people may have difficulty adapting to changes in lighting levels.

In addition people with keratoconus may find that distortion of vision causes perceptual difficulties such as having difficulties in judging depth and distance, problems on stairs or kerbs or coping with changes of levels underfoot.

People with Down’s Syndrome and other syndromes such as Marfan’s and Turners Syndrome, are more likely to have keratoconus than the general population. In Down’s syndrome up to 15% or one person in six may develop keratoconus. People with keratoconus may also rub or poke their eyes – this may make the condition worse. People may need to wear sunglasses or sun-caps to prevent the affect of glare.

Keratoconus and treatment
The usual treatment for keratoconus is to fit the person with contact lenses. These are usually small rigid gas-permeable (hard) lenses but may also be soft lenses, hard lenses with soft edges, or larger scleral lenses which cover both the cornea and some of the white part of the eye. The way in which all contact lenses for keratoconus work is by covering up the irregular front surface of the keratoconic cornea and providing a smooth artificial front surface for the eye. For some people with learning disabilities it may be difficult to for them or their carers to manage lenses, although quite a number of people will be able to manage with the right help and support. If someone is unable to wear contact lenses either due to an inability in tolerating the physical presence of a lens in their eye or for other reasons such as an inability to handle or care for the lenses then other treatments are available.

Other treatments include:
• Collagen Cross Linking – this is one of the newer treatments for early keratoconus and is showing promise in slowing or even halting the progress of the condition. It works by treating the cornea with a solution of the vitamin riboflavin and then shining ultra violet A (UVA) light onto the eye for a short time. It works by forming more bonds or cross-links between the collagen making up the structure of the clear cornea. This in turn strengthens the cornea and prevents the keratoconus from developing. Because it is not a fully tried and tested method, this treatment is not readily available on the NHS. The treatment does hold exciting possibilities for the management of keratoconus in people with learning disabilities, as it is relatively non-invasive, simple to perform, and does not require the same level of co-operation and aftercare as some of the other treatments currently available.
• Intacs – these devices are thin strips of plastic which are inserted, in a surgical procedure, into the cornea. They provide support for the cornea and have the effect of flattening the distorted central part of the cornea (like tightening the guy ropes of a tent) improving vision. This procedure may be used in conjunction with collagen cross linking.
• Corneal Graft (Keratoplasty) – In this procedure an eye surgeon removes the diseased cornea and replaces it with a healthy one from a donor eye. Sometimes the full thickness of the cornea is replaced and sometimes just a partial thickness graft is used. This procedure is quite complex and requires aftercare for up to a year after the surgery. The graft is sometimes rejected by the eye and to minimise this risk drops are used for some time after surgery. Due to the complex nature of this surgery, in order for the eye to see well afterwards, contact lenses or glasses are often needed.

For people with communication difficulties it may be very difficult for them to tell you how they see their world. It requires skilled observation and good knowledge of the person to begin to understand how a person might be seeing their world. A functional vision assessment is an important method of assessing someone’s vision.

For more information on treatment for Keratoconus see our factsheet or visit the website of the keratoconus-group


Macular Degeneration / Age Related Macular Degeneration
Macular degeneration describes a range of diseases that affects the retina. Age-Related Macular Degeneration (AMD) most commonly occurs in people over the age of 55. It is the leading cause of visual impairment in the UK.

The light sensitive part of the retina is made of up cone and rod cells. Rod cells are responsible for detecting movement, seeing in low light or darkness, and black and white vision. Cone cells are largely responsible for seeing stationary objects in fine detail and for providing information on colour. The macular is the small area in the central part of the retina. It is approximately the size of a grain of pearl barley or a large grain of rice and it has the greatest concentration of cone cells. The very central part of the macula, the fovea, has only cone cells and no rods. This means the macula is the most sensitive part of the retina which is used for all detailed vision. When we see an interesting object in our field of view, our brain directs eye movements to focus this object onto the macula so we can look at it more closely.

The way in which the light sensitive layer of the retina gets its energy and nourishment, and disposes of waste, is via blood circulating in a layer of the eye just under the retina called the choroid. This layer has a very high rate of blood flow and contains specially adapted blood vessels called the choriocapillaris. In between the choriocapillaris and the light receptor cells of the retina is a waterproof layer of cells called the retinal pigment epithelium (RPE). The job of the RPE is to transport nutrients from the blood to the retina, and waste products from the retina back to the blood as well as supporting the light receptor cells and helping them to function efficiently.

Dry Macular Degeneration
In dry macular degeneration the function of the RPE slows down and waste products gradually accumulate between the chorio-capillaris and the RPE. These waste products form plaques called drusen which prevent or slow down the flow of nutrients entering the RPE. In time because this flow of nutrients declines the cells in the RPE start to decay and die and in turn this affects the performance of the light receptor cells in the retina. We think this process selectively affects the macula because it is the busiest and most energy and nutrient hungry part of the retina and in turn produces more waste products. With the gradual decay and death (atrophy) of the RPE and light receptor cells in the retina the central vision is affected, and the ability to discriminate detail declines. This process affects an individual’s ability to perform detailed tasks such as reading, seeing food on their plate, watching TV, or recognising faces. It has less effect on someone’s ability to move about and see large objects.

Wet Macular Degeneration
Wet macular degeneration occurs because in some people when the RPE and other retinal cells start to decline they send out chemical messengers or growth factors into the surrounding tissues. These growth factors stimulate the formation of new blood vessels from the chorio-capillaris. These new blood vessels initially grow under the RPE but eventually break through into the retina (like weeds breaking through fresh tarmac). Unfortunately unlike normal retinal blood vessels which are watertight, these new vessels are leaky and fluid and blood seeps in to the retina and disrupts its normal function. This process of breakthrough and leakage can happen very quickly and often wet macular degeneration comes on very quickly with a devastating effect on central vision.

If wet macular degeneration is suspected, or in any cases of sudden distortion or loss of vision, urgent advice should be sought from an eye-care professional such as an optometrist (optician) or eye doctor (ophthalmologist). If this advice is not readily available then go to eye-casualty at your nearest hospital.

Treatment
There is no proven treatment for the dry form of the disease, but we do know that people who follow a healthy diet rich in anti-oxidant vitamins from leafy vegetables such as spinach and kale, and those who do not smoke have better outcomes and are at reduced risk of developing the condition. There is limited evidence to show that special vitamin and nutritional supplements may also help to slow the progress of the disease in some people with early dry macular degeneration.
Treatments are available for the wet form of the disease, and are most successful when the treatment is given early in the course of the disease. It is therefore important that advice from eye-care professionals is sought if there are any symptoms of distorted vision, or if an individual seems to have problems with their vision. Regular routine sight tests may also detect this condition.

As people with learning disabilities are leading longer lives it is likely that some may also develop macular disease as they grow older. Carers should encourage people to attend regular eye tests and to be vigilant for signs of central vision loss - such as increased anxiety,  loss of colour vision, apprehension when walking, failure to recognise faces, or loss of interest in visual tasks etc.


Macular Disease and Charles Bonnet Syndrome
People who develop macular disease, or other sight losses, may experience visual hallucinations. These hallucinations are called Charles Bonnet syndrome. People who experience Charles Bonnet syndrome may feel very anxious as a result of the hallucinations they perceive. People may fear talking about their hallucinations as they may believe that others may think they are developing mental health difficulties. For more information about Charles Bonnet Syndrome click here

For people with communication difficulties it may be very hard for them to tell you how they see their world. It requires skilled observation and good knowledge of the person to begin to understand how a person might be seeing their world. A functional vision assessment is an important method of assessing someone’s vision.

For more information about Macular disease click here to visit the NHS Choices website.


Microphthalmos / Anophthalmia
Microphthalmos refers to the under-development of the eyes during the development of the child within the womb. It can occur in one or both eyes. The eyeball will be abnormally small and will often appear to be deeply set in the eye socket (orbit). A person with microphthalmos is likely to be severely visually impaired either perceiving only light or being totally blind.

Anophthalmia refers to a rare condition in which a person is born with no eyes.

For people with communication difficulties it may be very hard for them to tell you how they see their world. It requires skilled observation and good knowledge of the person to begin to understand how a person might be seeing their world. A functional vision assessment is an important method of assessing someone’s vision.


Nystagmus
The movement of both our eyes is controlled by the brain and by six muscles that surround the eye. The eye muscles allow the eye to move, in unison, to look at the world around us. Nystagmus is the term for involuntary, uncontrollable and repetitive movement of the eyes. Most commonly the eyes move side to side, or constantly appear to flicker – though other movements can occur.

Nystagmus may occur at birth as result of a problem with the eye, or the visual pathway through the brain. It may be due to damage to the part of the brain controlling eye movements. Sometimes nystagmus starts in early years when the visual system is developing. It can occur in later life with other eye conditions such as cataracts and glaucoma or due to degenerative conditions in the brain such as multiple sclerosis, strokes, tumours or following head injury. In nearly all cases vision will be impaired to a greater or lesser degree

If a person has had nystagmus since birth they usually do not see the world as constantly moving. This is because their brain often adapts to the constant movement of the eye. The amount the eyes wobble or move may vary over a day, in turn affecting vision, and people can be affected by the extra effort involved in using their sight. Many people with Nystagmus may refractive errors such as high myopia or hyperopia (severe short or long sight) or high levels of astigmatism. People may hold their head in positions that helps them see more clearly by reducing the amount the eyes wobble (the null point) or people may move their head, such as nodding or moving their head from side to side to compensate for their nystagmus. People may hold objects, images, print at set length and angles. Depth perception can be affected, as can a person’s balance – this might occur more in unfamiliar or environments that frequently change.

For many people born with Nystagmus the condition does not get better or worse.

For people with communication difficulties it may be very difficult for them to tell you how they see their world. It requires skilled observation and good knowledge of the person to begin to understand how a person might be seeing their world. A functional vision assessment is an important method of assessing someone’s vision.

If Nystagmus occurs in later life medical attention must be sought immediately as it could indicate a serious underlying problem. Spectacles will not prevent Nystagmus. When glasses are prescribed they should be worn as many people will have additional errors of refraction (such as short sightedness or long-sightedness).

For more information about Nystagmus click here.