Visual aids 29/09/2014

What is low vision?

The latest advances in ophthalmology and the frequency of preventative eye check-ups mean that a large number of pathologies affecting the eyes do not result in total sight loss.

However, some illnesses cause a loss of vision that cannot be restored by means of surgery, other pharmacological treatments or even conventional glasses. Such vision, which can be useful but insufficient, is called low vision.

The most frequent symptoms are a loss of vision of detailed objects, a reduction in the visual field (peripheral sight, steps, etc.) or both at the same time.

The most frequent illnesses causing low vision are age-related macular degeneration (AMD), retinitis pigmentosa, cataracts, diabetic retinopathy (DR) and glaucoma.

What are the symptoms?

— Loss of central vision: patients may suffer from a loss of vision that prevents them from reading, watching television or recognising people's faces but does not make movement impossible. This happens to those suffering from age-related macular degeneration.

— Loss of visual field: patients suffer from limited peripheral vision (lateral, superior, inferior or tunnel vision). They have mobility problems because, for example, they can't see obstacles or steps. This is a classic symptom of glaucoma and retinitis pigmentosa.

— Glare, loss of contrast and colour confusion.

— Image distortion.

— Blurred vision.

The team specialising in low vision carries out a study to assess each patient's vision, used to determine visual acuity, contrast sensitivity, the visual field and colour vision.

When should you see a low vision specialist?

When the ophthalmologist has diagnosed an ocular illness (AMD, glaucoma, non-operable cataracts, etc. ) that stops you from carrying out everyday tasks involving near or far sight and which conventional optical solutions (glasses, contact lenses, etc.) can't improve. In many cases the ophthalmologist will recommend visual rehabilitation.

Visual aids

Anyone with severely limited sight who is keen and interested in continuing to carry out their usual activities and prepared to work to achieve this can notably improve their condition with the help of different optical adaptations and aids, personalised optical systems and non-optical aids.

Types of aid

1) Optical aids

There are different types of aid depending on the task to be carried out. For example, magnifying glasses; microscopes and telemicroscopes for close-up tasks such as reading, sewing, writing, puzzles, painting, DIY, board games, etc.; telescopes to watch television, read a blackboard, information panels, follow sports, visit museums, appreciate landscapes, attend concerts, etc. Special filters are another important optical aid as they help with solar radiation; i.e. to prevent glare and improve contrast.

Magnifying glasses

Magnifying glasses are positive lenses that enlarge the objects viewed through them. The more powerful the magnifying glass, the larger the image, albeit with a smaller visual field and requiring closer focus.

This is the first aid people normally resort to independently when they lose visual acuity. It's used as an initial prescription to help children as well as a complementary device and is the most economical and widely used aid on the market.

Microscopes

This is a positive lens or system of lenses that can be used at very close distances and is normally used at a distance of less than 25 cm. Microscopes make use of the principle of magnification by approximation, providing a clear image by getting closer to the object. The greater the magnification, the smaller the visual field and the shorter the working distance. Compared with magnifying glasses, these products are more aesthetic and their visual field is larger. They're also practical as they leave the hands free to be able to work more easily and independently. With sufficient distance, microscopes can aid writing and are widely used for long periods of reading.

Telescopes

Telescopes are suitable for aiding far sight as they enlarge the image of the object without having to get any closer to it. In this case they must be used with the appropriate lens for distance required by the patient. Telescopes are suitable for those people who need static vision at a specific distance, such as watching television at 2.5 metres.

This is the only instrument for distance vision and can magnify the image substantially. Telescopes can be very useful with the right rehabilitation and if used properly.

Telemicroscopes

This is a telescope with a focal range for different distances, normally close vision. It offers a larger working distance than a microscope and can therefore be considered as an optical aid prescribed for intermediate distances. The greater the distance, the smaller the visual field and depth of field. Essentially, this is a telescope focused at a specific distance via an approximation lens. It's used for a range of close-up activities depending on the patient's requirements and objectives.

It can be used for the theatre, cinema, sports events, etc., as well as in everyday tasks such as watching television at a normal distance and other tasks carried out at an intermediate distance. Other possible uses are painting, reading music and working with a computer. It's also very useful for carrying out manual tasks that require moving the hands between the visual plane and the optical aid. A lot of patients use telemicroscopes to read without having to be too close to the object in question.

 Filters

Special filters help with solar radiations; i.e. to prevent glare and improve contrast. The sun emits ultraviolet rays, the visible spectrum and infrared rays. Ultraviolet rays are filtered by the ozone layer and infrared rays are filtered by the water droplets contained in the atmosphere. However, the visible spectrum has the shortest wavelength and can be absorbed by the eye. It has been proven that the toxicity of blue light on the retina results in photochemical lesions, this being scattered in all directions, both in the atmosphere and in the human eye.

Patients with low vision suffer from solar radiations every day; the greater amount and intensity of the light, the better patients with low vision can perceive stimuli but other factors are also involved: more ultraviolet rays and therefore more fluorescence, glare and dispersion. Light is controlled and interference reduced by selectively absorbing the wavelength using different types of filters, chosen after a thorough analysis.

These selective filters filter the ultraviolet, violet and blue rays from 400 to 585 nanometres in wavelength, effectively reducing the glare caused by ocular devices that scatter the rays.

These selective filters, which are becoming increasingly widespread, provide greater contrast and comfort and prevent glare for those suffering from low vision.

2) Non-optical aids

These are all those aids that are not optical enlargement systems but which nevertheless help patients to carry out their everyday tasks more easily, such as eating, cleaning, sewing or ironing, working in the kitchen, handling money, using the telephone, etc.

Here are some examples of non-optical aids:

— Lecterns: 20° for writing and 90° for reading.
— Watches and clocks: speaking, large text, tactile.
— Audio books: cassettes.
— Typoscopes.
— Large print games, such as cards and dominoes.
— Special purses and wallets.
— Cooking utensils for low vision.
— Adapted telephones.

Advice is fundamental for our patients as they can substantially improve their quality of life with the right aids, both optical and non-optical, and with guidance on their pathology and requirements. This advice, in addition to the prescription of visual aids, can improve the lives of those suffering from low vision.

3. Electronic aids

When conventional aids are not enough, the image can also be enlarged using electronic devices, which are particularly useful for reading and writing. These aids are more convenient, such as: electronic magnifying glasses, television, closed circuit TV, etc. They also magnify substantially, thereby maintaining the normal reading distance, as well as having a larger reading field than with optical aids, in excess of 8×-12× (magnification).

Electronic aids also provide greater depth of field than optical aids which means that users normally have enough space to turn over the pages of a book, to write, etc. Another feature is that they allow binocular vision (if possible) and patients can move forwards, backwards, left and right without losing focus. In general, the image is projected in black and white although devices have now started to appear in different colours with varying contrast.

How can we choose the right aid?

 The best aid for each patient is determined based on a range of variables:

 — Visual acuity.
— Visual field (central and peripheral field).
— The patient's objectives (reading, watching television, sewing, cooking, etc.).
— Motivation (psychologically motivated, in line with their objectives, age, profession, etc.).