Reza Ferreira Optometrists Pretoria
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| Telephone : +27 12 361 0693 |
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| Telephone : +27 12 361 0695 |
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| Cell : 083 984 0785 |
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| Fax : 086 617 1947 |
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| Email : pta@reza.co.za |
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| Website : www.reza.co.za |
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| Physical Address |
Shop 64-66, Menlyn Retail Park
Cnr Lois & Garsfontein, Menlyn Retail Park - Pretoria, Gauteng |
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| Postal Address |
P.O.Box 234,
Menlyn
0063 |
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 HOW WE SEE
The images we see are made up of light reflected from the objects we look at. This light enters the eye through the cornea. Because this part of the eye is curved, it bends the light, creating an upside-down image on the retina (this is eventually put the right way up by the brain).
What happens when light reaches the retina?
The retina is a complex part of the eye, but only the very back of it is light-sensitive. This part of the retina has roughly the area of a 10p coin, and is packed with photosensitive cells called rods and cones. These allow us to see images in colour and detail, and to see at night.
Cones are the cells responsible for daylight vision. There are three kinds - each responding to a different wavelength of light: red, green and blue. The cones allow us to see in colour and detail.
Rods are responsible for night vision. They are sensitive to light but not to colour. In darkness, the cones do not function at all.
Focusing the image
The lens focuses the image. It can do this because it is adjustable - using muscles to change shape and help us focus on objects at different distances. The automatic focusing of the lens is a reflex response and is not controlled by the brain.
Sending the image to the brain
Once the image is clearly focused on the sensitive part of the retina, energy in the light that makes up that image creates an electrical signal. Nerve impulses can then carry information about that image to the brain through the optic nerve.
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 COMMON EYE PROBLEM
As the most common cause of vision loss among people over the age of 60, macular degeneration impacts millions of older adults every year. The disease affects central vision and can sometimes make it difficult to read, drive or perform other activities requiring fine, detailed vision
short sightedness can be overcome by wearing glasses.
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 THE EYE IN DETAIL
1. Vitreous humour
This fluid preserves the spherical shape of our eyeball, as well as helping to support the retina. Despite having the consistency of egg white it is mainly made of water (99%).
2. Ciliary body
The ciliary body comprises two parts – the ciliary process and the ciliary muscle. It is the latter which causes the lens to change shape. If the eye is focusing on a distant object the muscles relax, causing the ligaments to tighten and the lens to lengthen. When we focus on an object nearby the muscles tighten, the ligaments slacken, and the lens shortens.
The lining of the ciliary body also secretes aqueous humour, the fluid which fills the front of the eye.
3. Lens
The lens is responsible for refracting light. Held in place by ligaments, which connect to the ciliary body, the lens can also change shape to focus on objects at different distances – a reflex known as accommodation. It does this approximately 100,000 times a day.
4. Cornea
Although normally only half a millimetre thick, the cornea is responsible for seventy percent of the total focusing of the eye. It is the most important layer in the refractive procedure and, together with the lens, forms a clear image on the back of the retina.
5. Conjunctiva
The conjunctiva is merely a thin, transparent membrane covering the cornea, and yet its function is vital – it protects the eye from airborne debris. This is actually only one of the protective features of the human eye. Others include the orbit (or eye socket), the eyelashes and, quite surprisingly, the eyebrows – their function being to stop sweat from running into the eye.
Tears, which constantly bathe the surface of the eye, also remove dust and dirt – as well as killing bacteria.
6. Aqueous humour
The watery liquid at the front of the eye, secreted mainly by the ciliary body.
7. Iris
The iris is a thin diaphragm that lies behind - and is visible through - the cornea. The iris contains the pupil, which dilates and constricts to regulate the light that reaches the retina.
8. Choroid
The choroid runs behind the retina and, at the front of the eye, forms the ciliary body. As it contains many blood cells, the choroid supplies the eye with nutrients and oxygen – as well as removing waste.
The choroid also has a high concentration of a pigment called melanin in its cells. It is this pigment that prevents internal reflection within the eye – stopping us from receiving a blurred image.
9. Retina
The back of the retina contains a deep layer of light sensitive cells called rods and cones. This is where the image is projected. Rods are responsible for night vision, while cones are responsible for daytime vision. The cones also allow us to see in colour and detail.
The retina also contains a layer of ganglion cells on the surface. These cells connect the nerve fibres to the optic nerve. This means that the nerve fibres actually pass over the sensitive part of the eye, but, odd as it may seem, no disturbance in vision is caused.
10. Sclera
Basically, this is the white of the eye. Attached to the sclera are six exterior muscles, which enable us to look left, right, up and down. At the front of the eye, the sclera forms the cornea.
11. Optic nerve
The optic nerve is responsible for carrying information about the image to the brain. It contains no sensory receptors itself, and therefore therefore the head of the optic nerve (otherwise known as the Optic Disc) corresponds to the normal blind spot of the eye.
12. Fovea
This area of the retina is packed with cone cells. Because of this, it gives the most acute vision. For example, when we are reading, the word on which we are focusing is being projected onto the fovea.
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 WHAT IS DRY EYES?
Tears serve to lubricate the eye and they are produced around the clock, but when insufficient moisture is produced stinging, burning, scratchiness and other symptoms are experienced and may be referred to as Dry Eye, Keratitis Sicca, Keratoconjunctivitis Sicca (KCS) or Xerophthalmia.
When we blink, tears form a film which spreads over the eye, making the surface smooth and optically clear and enabling good vision.
There are three layers in the thin film of tears: an oily layer, a watery layer and a layer of mucus, each with specific function.
The outermost, oily layer is produced by small glands at the edge of the eyelid (meibomian glands) and the main purpose of this layer is to smooth the tear surface and reduce evaporation.
The middle, watery layer, is produced by small glands scattered through the conjunctiva, (the delicate membrane lining the inside of the eyelid) and by the large lacrimal (tear) gland. This layer cleanses the eye and washes away foreign particles or irritants.
The innermost layer consists of mucus which allows the water layer to spread evenly over the surface of the eye. Without mucus, tears would not adhere to the eye.
What causes it?
Dry eye is caused when the tear gland produces insufficient tears. This can happen as part of the normal ageing process, and is more common among women so although the condition is not common it tends to occur with increasing age when it is not always noticed because the effect of dry eye tends to balance another age-related change; poor tear drainage. The result of this is a balance between not making too much lacrimal fluid (tears) and not being able to drain away much lachrymal fluid.
The main causes of an insufficient film of tears are deterioration of lacrimal tissue, dysfunction of the Meibomian gland destabilizing the film of tears or a blockage in the excretory ducts of the lacrimal gland.
People with Sjogren's syndrome are at risk of dry eye as part of a more systemic problem involving salivary glands and other sites of mucous membrane. Salivary gland involvement produces a dry mouth as well. This syndrome, and dry eyes generally, may be found in people with rheumatoid arteritis .
Effects of the condition
In the early stages there is an increase in mucus strands and as the tear film breaks down, the mucin layer becomes contaminated. Where this contaminated matter cannot be dispersed it tends to move with blinking. Mucin is a substance which dries very quickly and rehydrates very slowly.
People with dry eye rarely have a sensation that the eye is dry but instead experience irritation, burning, a sensation of having a foreign body in the eye, mucus discharge and possible temporary blurring of vision.
Blinking may cause pain to people with severe forms of keratitis.
Treatment
There is a series of tests designed to identify the cause and type of dry eye and these include Rose bengal staining where a dye is used to identify problems and Schirmer's test which involves measuring the amount of wetting of a special filter paper. This can be done with or without topical anaesthetic which may be in the form of eye drops.
The aim of treatment will be to relieve discomfort and prevent corneal damage.
In some situations relief may be found by blinking consciously when doing close or continuous work. It is also helpful to close the eyes for a spell from time to time.
Eye drops may be prescribed or purchased over the counter and since there is a variety, it may be helpful to try others if your present product does not suit you.
Some drops contain preservative which means they are safe to use for a month after opening, but although these drops are cheap and suitable for most sufferers, some people do not tolerate the preservative and may need to get prescription from the hospital pharmacy for a preservative free medication.
Lubricant ointments are also helpful, particularly at night. These are also available without preservative.
Some women benefit from hormone replacement therapy (HRT), especially those whose dry eye problems began around or after the menopause.
Antihistamines or certain types of travel sickness pills, inhibit tear secretion and symptoms can vary from day to day and be affected by general health.
Surgical procedures may be indicated if symptoms are severe despite drops. It involves closing the tear drainage holes in the eyelids permanently. It is a minor operation which is suitable for some patients.
Helping People with Dry Eye
Avoiding the following situations will minimise your risk of Dry Eye. reduce the dry atmosphere caused by central heating by using a humidifier avoid car heaters, particularly at face level
sit away from direct heat such as gas or electric fires
use eyedrops just before activities which cause additional pain or discomfort such as television, reading, sewing and writing remember to blink regularly, particularly when doing close or concentrated work. Blink properly with full lid closure, not "half" blinking. avoid smoky atmospheres.
Prognosis
Prognosis varies considerably and may depend in part upon individual lifestyle choices and overall health as well as the severity and cause of the condition. There is no definite cure, but people can usually be made more comfortable.
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