Eyes

The ageing eye

Vision is a complex activity which involves eye function, cognition, reasoning, and memory. With increasing age the chance of visual impairment increases because of:

Changes due to senescence
Changes due to cumulative exposure to environmental toxins
Changes in associated functions (cognition, hearing, etc.)
Increasing incidence of many eye diseases

Visual impairment is not inevitable—there is considerable diversity both in visual decline and in compensatory adaptations. There is a tendency for patients to blame failing vision on age, and so not to seek help. However some changes may be age related (but corrective action may be available, eg glasses) or else impairment may herald the onset of treatable disease. Prompt identification and treatment may make all the difference between independence and dependence. Distinguishing what is ‘normal’ and when to refer to a specialist is key.

Changes in vision with age

Visual acuity often decreases

Multifactorial—changes in macula, lens, and cornea
May be corrected (eg glasses)
Consider eye disease if deterioration is rapid

Visual fields—peripheral vision less sensitive

Although formal field-testing normal—consider cerebrovascular disease if distinct homonymous field defect
Multifactorial—pupil smaller, lens cloudier, and peripheral retina less sensitive

Near vision decreases

Accommodative power diminishes due to increasingly rigid lens
Presbyopia (a lack of accommodation range) is part of normal ageing, begins in middle age and can be corrected with glasses

Colour vision

Retinal receptors unchanged
Alterations in colour perception may relate to yellowing of the lens altering the light reaching the retina

Light adaptation slower

Rods and cones may be slower to react to changes in illumination, and the pupil may let in less light, requiring brighter lighting for good vision
Causes difficulty with night driving in particular
Glare may be a problem as the lens, cornea, and vitreous become less clear, and minute particles scatter light

Contrast sensitivity decreases

Due to changes in cornea, lens, and retina

Floaters

Due to aggregation of collagen fibrils in vitreous
Usually normal, but if sudden onset, or large quantity, may indicate retinal detachment or vitreous haemorrhage

Visual impairment

2.5% of the UK population has visual impairment not amenable to correction by glasses alone. There is considerable social and psychological impact, yet it is underreported and optimal help is often not delivered.

Causes

(From blind registration data):

Macular degeneration (49%)
Glaucoma (15%)
Diabetes (6%)
Cardiovascular disease (5%)

83% of people who register are >65 years old. Low-vision clinics are available in most hospitals.

Interventions

Include:

Change glasses prescription (benefits 10-20%)
Explain the disease (often does not cause total blindness, eg with macular degeneration; improve understanding of future)
Psychological support (often combined with hearing loss in older people—beware social withdrawal. Acknowledge problem, discuss fears)
Discuss blind registration
In some cases, consider guide dogs and learning Braille
Take specific history of certain activities and provide practical advice:
- Reading—what do they actually need to read? Advise about good light, magnifiers, large print books, photocopy recipes to larger size.
- Writing—use black pen on white paper, consider a Millard writing frame or bold line paper, discuss specific tasks such as cheques and pension books.
- Television—sitting closer, black and white sets may improve contrast
- Telling the time—talking watches and clocks
- Cooking—improving lighting in kitchen by removing net curtains, tactile markers for cookers, electronic fullness indicators on cups
- Telephoning—large button telephones
- Social interaction—sit with back to the window to improve light on a visitor’s face, discuss accessible holidays

Further reading

Royal National Institute for the Blind online:

www.rnib.org.uk.

SENSE online:

www.sense.org.uk.

Blind registration

Done by ophthalmologists. Copy of the form goes to social services, GP and the office for national statistics.

Generally there is under-registration—probably due to stigma and a sense that this is the end of the fight, rather than the start of new help and opportunity.

Benefits to individual

Financial—including personal income tax allowance, disability living allowance or attendance allowance, working tax credit or pension credit, extra housing or council tax benefits, carers’ allowance, help towards care home fees, free NHS sight test, free NHS prescriptions, lower television licence fee, car parking and public transport concessions, exemption from directory enquiries fees
Easier access to help from social services
Loan of cassette recorder and talking books and newspapers (also available without registration)

HOW TO … Optimize vision

Bigger

Magnifiers (glasses or contacts, hand magnifiers, stand magnifiers, illuminated magnifiers, reading telescopes). Consider portability, cosmetic aspects, and posture required to use
Larger print (books, enlarge frequently used items with photocopier)

Bolder

Contrasting colours—eg black on white
Use to emphasize written word, door handles, stair edges, etc.
Use white cups for dark drinks
Put contrasting strips round light fittings

Brighter

Remove net curtains
Use high power bulbs (eg 150W not 60W incandescent; a wider range of high luminescence ‘low energy’ lamps is now available)
Use directable light sources (eg angle poise lamps)

Visual hallucinations

Management varies with the cause.

Organic brain disease

Lewy body dementia (occur in 50-80%; usually well formed, eg animals). Also occurs in dementia of Parkinson’s disease. Can respond dramatically to cholinesterase inhibitors
Anoxia, migraine and delirium—treat the underlying cause
Focal neurological disease (especially occipital and temporal lobe—range from unformed lines and lights, etc. to complex)
Occipital lobe seizures—treat with anticonvulsants

Psychiatric disease

Visual hallucinations occasionally occur with schizophrenia (auditory more common).

Charles Bonnet syndrome

Diagnosis of exclusion
No other psychiatric symptoms or diseases present
Occurs with bilateral visual loss (typically secondary to cataracts or glaucoma) as a ‘release phenomenon’
These are usually well formed, vivid, and occur in clear consciousness
Insight is usually present
Duration is usually seconds to a minute or so
May be simple (flashes, shapes) or complex (recognisable images)
Non-threatening—the patient’s reaction is often one of curiosity or amusement
Probably under-estimated as patients reluctant to tell doctors for fear of being labelled as ‘mad’
Not related to psychiatric problems
Reassurance is often all that is required, but symptoms may be improved by enhancing vision

Cataract

Term used to describe any lens opacity. The most common cause of treatable blindness worldwide. In the UK it is largely a disease of the older population: 65% of people in their 50s and everyone >80 have some opacification. This is probably caused by cumulative exposure to causative agents rather than senescence per se.

Causes

Exposure to environmental agents (eg UV light, smoke, blood sugar)—more exposure with increasing age
Ocular conditions (trauma, uveitis, previous intraocular surgery)
Systemic conditions (eg diabetes, hypocalcaemia, Down’s syndrome)
Drugs (especially steroids—ocular and systemic)