Severe and partial sight impairment

The difficulties caused by visual impairment vary from one individual to the next depending on their age, circumstance and their personality. For one, there may be the fear of social isolation; for another, not being able to do the crossword. There may also be concerns regarding:

• Maintaining independence (mobility, driving).

• Activities of daily living (reading, writing, television).

• Issues surrounding financial support.

In the case of children and younger people, there is also the important element of education and finding or keeping a job.

Early detection of eye disease by regular screening can enable earlier diagnosis and treatment of underlying causative factors, which may then prevent or slow the progression of visual impairment.¹

Definition²

There is no legal definition of sight impairment or partial sight. However, convention is that partial sight involves:

• A visual acuity from 3/60 to 6/60 with a full field.

• Up to 6/24 with moderate restriction of visual field, opacities in the media or aphakia.

• 6/18 or better with a gross field defect (eg, hemianopia) or a marked constriction of the field (eg, glaucoma or retinitis pigmentosa).

Severe visual impairment is defined as:³

• A best corrected visual acuity below 3/60 or 1/18.

• A best corrected visual acuity better than 3/60 but below 6/60 with a very restricted visual field.

Epidemiology⁴

Over two million people in the UK are living with sight loss. All ages are affected but there is an increased prevalence in the elderly, black and minority ethnic groups, and adults with learning difficulties.³

Globally, uncorrected refractive errors are the main cause of visual impairment. Cataracts remain the leading cause of loss of vision in middle- and low-income countries. The other main global causes of visual impairment are age-related macular degeneration, diabetic retinopathy and glaucoma.

The number of people visually impaired from infectious diseases has greatly reduced in the last 20 years. About 50% of all visual impairment can be avoided or cured.

Among children, the causes of vision impairment vary considerably across countries. For example, in low-income countries congenital cataract is a leading cause, whereas in middle-income countries it is more likely to be retinopathy of prematurity. Uncorrected refractive errors remain a leading cause of vision impairment in all countries amongst children.

Causes of visual impairment⁴

There are a great number of causes of visual impairment ranging from congenital or hereditary conditions through to the more frequently encountered acquired diseases. The most common cause of gradual-onset bilateral loss of vision in the developed world is macular degeneration. Diabetic retinopathy is the second most common cause. Other causes include:

• Uncorrected refractive errors.

• Hypertensive retinopathy.

• Cataracts.

• Chronic glaucoma.

• Chiasmal or bilateral optic nerve compression.

• Bilateral optic nerve damage - eg, tobacco amblyopia.

• Worldwide, chlamydial infection causing trachoma is still a common cause.

See also the separate article Gradual Loss of Vision.

Sudden bilateral loss of vision is rare and is an ophthalmological emergency which requires immediate referral to the eye emergency department. Possible causes of acute loss of vision include:

• Bilateral occipital lobe ischaemia or infarction.

• Bilateral occipital lobe trauma.

• Severe bilateral papilloedema.

• Rapidly progressive chiasmal compression.

• Bilateral optic nerve damage - eg, methyl alcohol poisoning.

More commonly, a new problem may develop in one eye on the background of sight impairment due to pre-existing disease in the fellow eye.

Treatment and management

Managing initial reactions

Patients will come to learn about their visual impairment in a variety of ways. Some will be a part of the significant proportion who never seek help and who bear the weight of their disease alone. You may never meet them.

Many others will have had a formal diagnosis by an ophthalmologist. These patients will have had to take on board the reality of what the problem is, what the treatment options are (and are not) and any other associated information in a very short space of time - maybe a matter of minutes.

You may be left with the consequences of managing the subsequent reactions as the news sinks in. It is tough facing a person who has been told that they or their relative is irretrievably sight impaired.

There are no perfect solutions to managing this and it will depend on your time, your knowledge of the patient and of the condition. It may be helpful to be aware of the following:

• Patients often go through a series of initial reactions to news of a chronic disease:
  

  • Shock - this is most pronounced if the diagnosis comes without warning. It is characterised by a feeling of bewilderment, behaving in an automatic fashion and having a sense of detachment. It may last from hours to weeks.

  • Encounter reaction - the individual is overwhelmed by the reality and seems unable to think clearly or plan effectively.

  • Retreat - the health problem or its implications may be denied.

• Over time, adaptation will occur whereby the individual will make constructive changes in their life to accommodate the new state of being.

• There are few conditions where the sight completely goes to no perception of light. Most retain some sort of visual perception. For example, even in severe macular degeneration, peripheral vision will be maintained.

Practical support

• What visual acuity remains needs to be optimised by good, up-to-date refraction. Encourage the patient to see an optician.

• Remind the patient of good lighting: use brighter bulbs, more lights round the house and use a good reading light.

• Enhance contrast where possible such as using large print books (don't forget talking books, the radio).

• Encourage the patient or relatives to find local support groups - these may be found through the Royal National Institute of Blind People's (RNIB) generic website (see below) or by looking up specific conditions.

• Consider referral to a low visual aids clinic (contact your Eye Department for local arrangements) where further advice can be given especially with regard to optical devices. These may include magnifiers, telescopes, close circuit TV, computers, talking watches, writing guides, liquid level indicators, talking scales, etc.

Visual impairment registration²

Each local authority keeps a register of people with visual impairment living in its area. The register is held by the social services department or by the local voluntary society for people with sight problems acting as agents for the local authority.

The register is confidential. Registration is voluntary but it is helpful in getting extra support.⁵ However, anyone having difficulties because of poor sight, is entitled to ask their local social services department to assess their needs, even if not yet registered.

Referral forms for people who are visually impaired
There are several possible forms, the last of which (CVI) is the only one conferring a status of registration as visually impaired:

• Form LVI: self-referral letter which a person with problems of sight loss can send to social services if they wish to be contacted for help and advised on what services are available locally and nationally. The form is available to be given by optometrists/opticians to appropriate patients.

• Form RVI: may be issued by staff in the hospital eye service to refer the patient (with consent) for a social care assessment. It should be used as soon as social needs become apparent but where certification is not appropriate at this time or cannot be carried out (for instance, they are not being seen by a consultant). Hospital eye services are able to download it from the GOV.UK Department of Health website.

• Form CVI has replaced the previously used form BD8. It formally certifies someone as sight impaired (partially sighted) or as severely sight impaired so that the local council can register him or her. The signature of a consultant ophthalmologist certifying eligibility to be registered is required on a CVI before registration can be offered. Registration is voluntary but entitles people to various benefits and concessions.

Benefits of registering as severely sight impaired or sight impaired
The purpose of the register is to help local authorities provide the best service they can for people who have sight problems. To do this, they need a record of all the severely sight impaired and sight impaired people in their area and what kind of services they need. The statutory requirements are that:

• An assessment of needs is carried out.

• Information about services for visually impaired people is provided in a format accessible to the individual.

On receipt of the appropriate form, social services contact the person who is sight impaired about being added to the register. Social services assess the person's needs and any support that would help.

The social services department should arrange a community care assessment, with input from a worker for severely sight impaired and sight impaired people.

Registration will confer a number of benefits, the extent and exact nature of which depend on whether the person is registered as severely sight impaired or sight impaired (ie partially sighted). These include:

• Tax relief and allowances - eg, disability living allowances, additional income support/pension credit, council tax reduction, etc.

• Community care services - eg, trained staff who can provide support for a range of activities, including safe mobility indoors and out, skills for daily living such as cooking and leisure activities

• Referral to other local services for collateral help.

• Financial support - eg, free prescriptions and low visual aids, railcard and other travel concessions, free postage on 'articles for the visually impaired', car park blue badge, reduction in TV licence fee (50%), free loan of radio, etc.

Other considerations

Driving⁶

Visual acuity

• Group 1 (car or motorcycle): the law requires that all licensed drivers meet the following eyesight requirements (including drivers aided by prescribed glasses or contact lenses):
  

  • In good daylight, able to read the registration mark fixed to a vehicle registered under current standards:

    • At a distance of 20 metres with letters and numbers 79mm high by 50mm wide on a car registered since 1 September 2001, or

    • At a distance of 20.5 metres with letters and numbers 79mm high by 57mm wide on a car registered before 1 September 2001, and

  • The visual acuity must be at least Snellen 6/12 with both eyes open or in the only eye if monocular.

  Any driver unable to meet these standards must not drive and must notify DVLA, which will refuse or revoke a licence.

  The law also requires all drivers to have a minimum field of vision (see below).

  
  

  Bioptic telescope devices are not accepted by DVLA for driving.

• Group 2 (lorry or bus):
  

  • Drivers must have a visual acuity, using corrective lenses if necessary, of at least 6/7.5 (0.8 decimal) in the better eye and at least 6/60 (Snellen decimal 0.1) in the other eye.

  • Where glasses are worn to meet the minimum standards, they should have a corrective power not more than +8 dioptres in any meridian of either lens.

  • It is also necessary for all drivers of Group 2 vehicles to be able to meet the prescribed and relevant Group 1 visual acuity requirements.

Visual fields

• Group 1: the minimum field of vision for safe driving is defined as a field of at least 120° on the horizontal; the extension should be at least 50° left and right. In addition, there should be no significant defect in the binocular field which encroaches within 20° of fixation above or below the horizontal meridian.

• Group 2: the horizontal visual field should be at least 160°, the extension should be at least 70° left and right, and 30° up and down. No defects should be present within a radius of the central 30°.

Professional standards

• Pilots - there are strict rules set out that involve visual acuity, degree of refractive error and correction, colour vision, visual fields and a number of other factors. Standards are marginally different for commercial and private pilots but they are all beyond the visual means of the visually impaired individuals considered in this article.

• UK armed forces - this depends on the area of work as each military section has specific requirements. Standards should be checked at the local forces career advice centre. Pilots and navigators or observers have higher visual standards imposed on them.

Complications

The difficulties experienced by anyone with significant sight loss can have a devastating effect if they are not properly advised and supported. In the provision of support, the needs, views and independence of the person with sight loss are of paramount importance. The list of possible complications is very long but includes:

• Social isolation.

• Falls.

• Accidents.

• Restriction of activities, and the requirement for supervision.

• Education difficulties.³

• Reduced employment possibilities.³