Lenses FOR PRESBYOPIA

The tiny lens inside the human eye changes its shape to let us see clearly at different distances. As we get older, the lens begins to lose its flexibility, which makes it increasingly more difficult and tiring for us to change our focus and to see close objects clearly. The difficulty in focusing when reading, sewing and performing other close tasks are affected becomes noticeable around the ages of 40 to 45 years.

This condition is called presbyopia. It can be corrected by spectacle lenses that restore our power to see at near range.

Reading spectacles are prescribed to help people see close up. These spectacles cannot be used to see in the distance, so the wearer will continually find it necessary to remove the reading spectacles when looking at people when talking to them, when viewing television while knitting or looking across the room or the street. While driving, it is necessary to constantly scan the road and the instrument panel and a single vision lens will not permit this.

Multifocal Lenses

Multifocal lenses enable the wearer to focus on both near and distance and, depending on the lens type, on middle distances, without removing his or her spectacles.

There are three main kinds of multifocal lenses: bifocal, trifocal and progressive.

Bifocal Lenses

There are two distinct areas to a bifocal lens. In most cases the top portion is used for distance viewing and the lower portion for reading and other close work such as sewing.

The lower portion may be semi circular, D shaped, a narrow band or simply divided from the upper portion by a straight line..

If spectacles are already worn for distance vision, the onset of presbyopia means you will need either a second pair of spectacles for reading range or bifocal lenses, incorporating prescriptions for both distance and near ranges.

For people who need near range correction only, bifocals are still an excellent alternative to single vision lenses because they will avoid the inconvenience of removing the spectacles for distance vision.

Trifocal Lenses

It is important for some people to be able to focus clearly at mid range between distance and near. For example, musicians may need to see their instruments close up and read music at arm’s length while still being able to see the conductor in the distance, Someone with these needs will require trifocals, which give clear vision at three distances: for distance, middle distance and near.

There are three portions to a tri focal lens. The top, which is usually the largest portion, is for distance; the middle section is for seeing at intermediate distances, such as at arms length; and the lowest part is for reading and other close work. The dividing lines between the three portions may be curved or straight, just as with bifocals. Trifocal lenses have these portions in different positions to cater for particular needs.

Progressive Lenses

In progressive lenses, or varifocals as they are also called, the lens power changes gradually from distance correction through the intermediate powers to the reading prescription.

Unlike a trifocal, progressive lenses do not have definite dividing lines between the different portions of the lens-they merge into each other. Instead of distinct segments, there is a gentle change from distant to intermediate to near focus parts of the lens.

The wearer has an infinite number of focusing distances, the nearest one can get to having natural sight with prescription spectacles. All distances are sharp and clear.

Most people think that the progressive lenses look better than bifocals or trifocals because, like ordinary single vision lenses, there are no obvious lines across the lenses. Some people are reluctant to wear multifocal lenses because they associate them with older people. Progressives offer them the best of both worlds: the benefits of multifocals and a young appearance.

Another advantage of progressive lenses is that because there is no sharp line dividing portions of the lens, there is no obstruction to vision through image jump, which makes it safer to use stairs and escalators.

Generally, people find that adapting to progressives is fast and easy. Some people are aware of distortion at the sides of the lenses when first wearing progressives but adapt readily, as with any new pair of glasses.

Australian safety glasses standard

In 1986 Australia and New Zealand published a joint standard for protective eyewear used in industry AS/NZS 1337:1992 ‘Eye protectors for industrial applications’. In 2010 a revised protective eyewear standard AS/NZS 1337:2010:

All of our safety glasses supplied by Dapto Optical meet these standards

Ultraviolet light and your eyes

Sunglasses are not a fashion fad. They are essential in preventing eye damage caused by the sun’s ultraviolet (UV) radiation. While most of us are aware that sunburn can lead to premature ageing of the skin and, ultimately skin cancer, medical evidence shows that our eyes too can suffer from ‘sunburn’, which can lead to cataracts: a leading cause of blindness as well as other problems outlined below.

The long-term effects of excessive amounts of UV radiation happen slowly and painlessly, yet can impair vision. Short and long-term damage to the eye includes inflammation of the cornea, cancer, cataracts and pterygium (a fleshy growth on the cornea).

Children and young adults are especially at risk. Parents should make sure their children wear sunglasses, particularly when levels of UV radiation are high, such as on the beach, in water and on snow, where there is additional danger due to reflection.

What is Ultraviolet Radiation?

UV radiation is a component of solar energy as are visible light and infrared radiation (heat). Other sources of UV radiation include welding arcs, high intensity mercury vapour lights and tanning lamps.

UV radiation consists of three main types: UVA, UVB and UVC. You need to be concerned mainly with UVB that causes sunburn and is largely responsible for causing skin cancer.

Most solar UV radiation striking the Earth is absorbed by the ozone layer but it has been calculated that a one per cent decrease in the amount of atmospheric ozone will increase UVB levels by about two per cent.

According to predictions of the Australian National Health and Medical Research Council, more than 36,000 additional cases of eye problems a year will occur as a result of ozone depletion. A one per cent rise in UV radiation levels would increase the annual incidence of pterygia in Australia by 26,000 cases.

Effects of UV Radiation on the Cornea

Most UV radiation striking the eye is absorbed by the cornea and high UV levels such as those encountered in the snow or on the beach can cause it to become inflamed. The condition is extremely painful and causes the eye to be highly sensitive to any light source. Although extremely uncomfortable, the condition usually resolves itself in about 48 hours, but it is advisable to have an eye examination by an optometrist or ophthalmologist (eye surgeon) to ensure that no other damage has occurred.

Effects of UV Radiation on the Conjunctiva

Short-term exposure to UV radiation can damage the conjunctiva, while long term exposure can cause it to thicken, forming a fleshy growth known as a pterygium. Progress of this condition is usually slow, with the pterygium growing until it starts to cover part of the cornea when it can interfere with vision and become unsightly. The only treatment is surgical removal, which is a relatively minor procedure. The eye should be examined by an expert to differentiate between pterygia and other more serious growths.

Effects of UV Radiation on the Lens

UV radiation, particularly UVB, is associated with the formation of cataracts. These are opacities that form in the lens of the eye and interfere with vision, as though you were looking through a dirty window. In severe cases, cataracts can be removed surgically and the old clouded lens replaced by an artificial one. Cataracts have always been more common among elderly people and were thought to be a natural result of ageing. Recent research suggests that while this may be partly true, they are much more likely to be caused by prolonged exposure to UV radiation, which can also damage the eye’s retina the delicate nerve rich lining of the eye used for seeing. Most forms of retinal damage are irreversible.

How to Avoid the Effects of UV Radiation

The simplest way of protecting your eyes from UV radiation is to limit your exposure to it. The best ways of doing this are to:

AVOID THE SUN

In summer, three-quarters of outdoor UV exposure occurs between 10 am and 4 pm, staying out of the sun between those times will significantly reduce your U V exposure.

WEAR A HAT

A broad brimmed hat will protect your head from sunburn and reduce the amount of UV radiation reaching your eyes by at least half

WEAR SUNGLASSES

A good pair of sunglasses will reduce the amount of UV reaching your eyes and cut the amount of glare.

Which Sunglasses Should you Choose?

All sunglasses on sale in Australia must meet an Australian Standard that specifies how much UV radiation the sunglasses must block.

Sunglasses should have a tag stating that they meet AS 1067 and we recommend Category levels 2 & 3.

Category 2  is for sunglasses designed for use in everyday situations, where exposure to the sun is not prolonged. While Category 3 units are intended for people exposed to high levels of UV radiation and provide maximum protection in various sports such as skiing, Cycling ,Golf or in special occupations such as flying or prolonged  outdoor Work situations.

Wrap-around models are excellent & with the latest free-form Prescription technology, they are now available in multifocals & distance precscriptions for a clearer more comfortable field of view.

Contact us today to inquire if your prescription is suitable.

Should Children Wear Sunglasses?

Children are particularly at risk from UV radiation because they spend so much of their time outdoors and are not aware of the danger it poses. It is up to parents to protect their children’s eyes by ensuring that children wear hats and good quality sunglasses.Be careful when choosing sunglasses for children. Sometimes models that appear to be sunglasses are ‘toys’ that provide no protection. Always check to make sure the sunglasses comply with the Australian Standard.