Vision and dementia: Ocular effects and examination

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Dementia is a loss of mental function in two or more areas such as language, memory, visual and spatial abilities, or judgment severe enough to interfere with daily life. Dementia itself is not a disease but a broader set of symptoms that accompanies certain diseases or physical conditions. Well known diseases that cause dementia include Alzheimer's disease, multi-infarct dementia and Creutzfeldt-Jakob disease.

Alzheimer's disease is the most common cause of dementia among older people, affecting many millions of people. It is a degenerative disease that attacks the brain. It begins gradually, and progresses at a variable rate, and results in impaired memory, thinking and behaviour. It lasts an average of eight years from the time of onset of symptoms, but it can last from three to 20 years.

In Alzheimer's disease, there is a deposit of abnormal protein outside nerve cells in the form of amyloid (Figure 1). These are called diffuse plaques, and the amyloid also forms the core of more organised plaques called senile or neurotic plaques (Figure 2). There is also an accumulation of abnormal filaments of protein inside nerve cells in the brain. This protein accumulates as masses of filaments called neurofibrillary tangles (Figure 3). There can also be atrophy of the affected areas of the brain and enlargement of the ventricles (Figure 4), as well as loss of the neurotransmitters serotonin, acetylcholine, norepinephrine and somatostatin.

There have been attempts to try to slow the progress of the disease by replacing these neurotransmitters with cholinesterase inhibitors, such as donepezil (Aricept), rivastigmine (Exelon), galantamine (Reminyl) and memantine (Namenda). These drugs temporarily increase levels of cell-to-cell chemical transmitters, which become deficient in Alzheimer's disease. In March 2005, however, the National Institute for Clinical Excellence (NICE) said that none of these drugs produced sufficient benefit to justify their cost, and recommended against their use in the National Health Service. However, the Department of Health later reversed this ruling.

In fact, Alzheimer's disease can only be firmly distinguished from other forms of dementia by detailed examination of the brain, which can only be done after the patient's death. Nevertheless, it seems that experienced doctors can identify Alzheimer's disease correctly in about 90% of cases.

The disease usually begins after the age of 60, although in can occur earlier in some individuals. A genetic link to the early onset of Alzheimer's disease has been demonstrated. Early onset or familial Alzheimer's disease are rare forms of the disease, affecting less than 10% of Alzheimer's patients. This is caused by gene mutations on chromosomes 1, 14 and 21.

Although a specific gene has not been identified as the cause of late-onset Alzheimer's disease, genetic factors do appear to play a role in its development. Only one risk factor gene has been identified so far. Researchers have identified an increased risk of developing late onset Alzheimer's disease related to the apolipoprotein E gene found on chromosome 19.

About 5% of people aged between 65 and 74 have Alzheimer's, and the proportion rises to nearly half of those aged over 85.


Three stages of Alzheimer's

Three stages of the disease have been identified.

Stage 1 is characterised by a loss of recent memory, an impaired ability to acquire new information, mild anomia (the inability to find the right word) and agnosia (the inability to recognise and name objects). The difference between the normal memory reduction of ageing and the earliest stages of Alzheimer's disease cannot necessarily be distinguished. This can be followed by slight visuo-spatial impairment and mild personality change. This is a difficult period because the patient still has insight into his or her condition, and they can become quite upset by their new limitations.

In Stage 2, memory loss becomes more profound and the long-term memory is now affected as well as the short-term. The patient demonstrates a significant impairment of their other cognitive functions as apraxia and aphasia (the failure to comprehend either spoken, or written, language) begin to manifest themselves, together with severe loss of judgment, and a reduced attention span. The patient now has no insight into his or her condition and is unmoved by the obvious distress of relatives.

In Stage 3, there is a severe impairment of all cognitive functions, with complete disorientation of time, place and other individuals. The patient cannot now look after even their most basic needs, nor recognise their loved ones (prosopagnosia). Spontaneous speech deteriorates; the patient may exhibit echolalia, a tendency to repeat words and questions without making any effort to answer. Further deterioration follows with parallelia, when the same words get repeated over and over again. In the advanced stage of the disease, speech becomes unintelligible and eventually complete mutism may set in.

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Figure 1
Deposits of abnormal protein (amyloid) outside brain cells in the cerebral cortex (immunostain for b-amyloid)

Figure 2
A more organised senile plaque with a condensed central core of amyloid (H/E stain)

Figure 3
Neurons in the cerebral cortex containing abnormal threads called neurofibrillary tangles (silver impregnation stain)

Figure 4
Coronal slice of an Alzheimer brain showing atrophy of the gyri and enlarged ventricles

Figure 5
Arcus senilis
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Physical difficulties, such as muscle rigidity and a complete loss of mobility, can manifest themselves and the patient becomes bedridden and incontinent. They lose the ability to care for themselves; there is gross intellectual impairment and they are unable to recognise even very familiar faces.

The onset of Alzheimer's disease is insidious and the progress is slow but relentless. In 1988, Reisenberg[1] produced a scale of progression, described as (FAST) -- Functional Assessment Staging of Alzheimer's Disease (Table 1).

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Table 1: FAST scale of Alzheimer's disease progression

STAGE SKILL LEVEL

1 No difficulties, either subjectively or objectively

2 Complains of forgetting location of objects. Subjective word finding difficulties

3 Decreased job functioning evident to co-workers; difficulty in travelling to new locations. Decreased organisational capacity

4 Decreased ability to perform complex tasks (e.g. planning dinner for guests), handling personal finances (forgetting to pay bills), difficulty marketing, etc

5 Requires assistance in choosing proper clothing to wear for the day, season or occasion

6 a. Difficulty putting on clothing properly without assistance
b.Unable to bathe properly, e.g. difficulty adjusting bath water temperature, occasionally or more frequently over the past weeks
c. Inability to handle mechanics of toileting (e.g. forgets to flush the toilet, does not wipe properly or properly dispose of toilet tissue) occasionally or more frequently over the past weeks
d.Urinary incontinence, occasional or more frequent
e. Faecal incontinence (occasional or more frequently over the past week)

7 a. Ability to speak limited to approximately a half dozen different words or fewer, in the course of an average day or in the course of an intensive interview
b.Speech ability limited to the use of a single intelligible word in an average day or in the course of an interview (the person may repeat the word over and over)
c. Ambulatory ability lost (cannot walk without personal assistance)
d.Ability to sit up without assistance lost,e.g. the individual will fall over if there are no lateral rests (arms) on the chair
e. Loss of the ability to smile
f. Loss of the ability to hold up head independently
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Visual changes in Alzheimer's patients

Vision loss among the elderly is a major healthcare problem. Approximately one person in three has a vision reducing eye disease by the age of 65. Alzheimer's patients are subject to the same conditions as other elderly patients.

Some of the main changes that can occur in the eye with age include[2]:

- The crystalline lens increases in thickness, volume and weight and decreases in transparency and elasticity, and thus there is a tendency for cataracts to appear

- The iris may atrophy, and the pupils become constricted and their responses sluggish. This can reduce the capacity of the eye to adapt to light or dark

- The conjunctiva may become thinner and wrinkled, and subject to deposits such as pinguecula

- The refractive index of the cornea decreases and it becomes less transparent and less permeable. Arcus senilis (Figure 5) and dystropia may appear. Corneal sensitivity reduces significantly. This can be an advantage in air-puff tonometry

- The ocular globe, eyelids and surrounding tissues can shrink leading to conditions such as entropion, ectropion and trichiasis, and while lachrymal production is reduced, the puncta lachrymalis can become stenosed and provide less drainage, which gives rise to chronic watering of the eye

- The anterior chamber tends to become more shallow, and the sclera more rigid, increasing the prospects for glaucoma

- There are often opacities floating in the vitreous, and the retina can be affected by cysts and degeneration, atrophy and haemorrhages - in particular, of course, age-related macular degeneration and diabetic retinopathy

- A generally reduced muscle tone will tend to increase exophoria, recess the near point of convergence and lower the ductions in all directions

- In truth, nothing gets better as we get older. Accommodation is long gone, and so there is no stimulus to accommodate. Consequently, there is no accommodative-convergence manifested, and the convergence effort rests entirely on the fusional convergence, which makes a large exophoria likely. This can possibly be helped by prisms, but these should be used with caution


All these changes not only reduce the expected quality of vision, many of them also make the examination of the eye more difficult.

As well as the general problems of ageing, Alzheimer's patients can also suffer from visual disturbances caused by the brain rather than the visual system. That is, their problem can be having difficulty perceiving what they see rather than how sharply they see it. Problems most commonly occur in four areas -- motion, depth, colour and contrast. Visual hallucinations have been reported to increase with loss of visual acuity in some Alzheimer's patients[3]. Like other Alzheimer's symptoms, not everyone with the disease will experience visual and perceptual problems to the same degree. Spectacles improve the outcome, as does cataract surgery. It has also been reported that the patient can appear to be confused and lost due to a form of motion blindness, as if the world is seen in a series of still frames[4]. This, it is argued, can cause patients to appear lost even in familiar surroundings.

Selective degeneration of large ganglion cell axons has been observed in the optic nerves of Alzheimer's patients, which suggests an impairment of broadband channel visual function. However, studies show that broadband visual capabilities are not selectively impaired in Alzheimer's disease. Dorsal LGN studies have shown that both the magno and parvocellular neurons were greatly affected in Alzheimer's patients.

The geniculostriate projection system is divided both anatomically and functionally into two parts: that incorporating the parvocellular layers of the lateral geniculate body (the 'parvo' system); and that incorporating the magnocellular layers (the 'magno' system). These systems are largely segregated in the primary visual cortex, undergo further segregation in the visual association cortex, and ultimately terminate in the temporal and parietal lobes, respectively. The parvo system neurons have smaller, more centrally located receptive fields that exhibit high spatial resolution (acuity), and they respond well to colour. They do not, however, respond well to rapid motion or high flicker rates. The magno cells, by comparison, have larger receptive fields and respond better to motion and flicker, but are relatively insensitive to colour differences. Magno neurons generally exhibit poorer spatial resolution, although they seem to respond better than parvo neurons at low luminance contrasts. In general, the parvo system is better at detecting small, slowly moving, coloured targets located near the centre of the visual field, while the magno system is more capable of processing rapidly moving and optically degraded stimuli across larger regions of the visual field.

What is important about these two components of the geniculostriate system is that the parvo system projects ventrally to the inferior temporal areas, which are involved in visual search, pattern recognition, and visual object memory, while the magno system projects dorsally to the posterior parietal and superior temporal areas, which are specialised for motion information processing. The cerebral cortical areas to which the parvo system projects receive virtually no vestibular afferents; the areas to which the magno system projects, on the other hand, receive significant vestibular and other sensory inputs, and are believed to be highly involved with maintaining spatial orientation. Symptoms suggest that the magnocellular system is more affected in Alzheimer's disease.

Strangely, these patients were impaired at low frequencies instead of the high frequencies, as in old age. This implies that regions controlling the low spatial frequency processing in the primary visual cortex would be affected more than those for high frequency processing[5]. The neuropathologic examination of the brains with visual impairment in a 1997 study by Hof et al revealed cortical atrophy dominating on the posterior parietal cortex and occipital lobe[6].

Vision is important in the maintenance of postural stability[7], particularly in the aged who may have decreased vestibular and proprioceptive input[8]. It is therefore not surprising to discover that decreased visual acuity and contrast sensitivity are factors, which predict falling in the elderly. Thus, some Alzheimer's patients fall or bump into things when the problem is not visual at all. As already stated, there is also a form of motion blindness, as reported by Tetewsky and Duffy[4], who claimed that there was damage to the area of the brain concerned with the perception of motion. Colour perception diminishes with age, and for people with Alzheimer's, there seems to be even greater deficits in the ability to see colours in the blue-violet range.

Optometric examination of patients with dementia

The patient with dementia causes special problems for the optometrist. During the ocular examination, the patient is in an unfamiliar environment surrounded by unusual equipment and is subject to a history taking that taxes their defective memory for details that cannot be recalled. The patient is required to maintain a fixed posture and attention while unfamiliar procedures are performed. During subjective refraction, the patient is expected to remember and follow complex sequential instructions and make many fine discriminatory judgements in rapid succession.

These requirements are all severely limited by the disease process, so it is hardly surprising that patients with even a minor degree of dementia retreat into an apathetic state, fail to provide answers, or provide quite unreliable responses to the questions directed to them in subjective refraction.

During the clinical evaluation of patients with mild to moderate dementia of the Alzheimer's type, visual difficulties such as topographic agnosia, visual agnosia, alexia without agraphia and prosopagnosia are detected. These symptoms, such as difficulty describing the individual components of a picture, are consistent with the severity of cytochrome oxidase deficits in the associated cortical areas. Other deficits experienced by Alzheimer's patients can be texture discrimination, and blue-violet discrimination. When Alzheimer's patients were compared to other age-matched controls, they showed specific deficits in contrast sensitivity; deficits in colour vision were found to be only age-related[5].

The more people can see, the easier it is for them to make sense of their world. Many people with dementia give the impression of having poor sight when, in fact, they need spectacles. Carers may assume that the patient will automatically reject spectacles, but there are ways of helping people get used to them.

When examining a confused elderly patient, there are two conflicting requirements. On the one hand, their responses are slow and they can be easily intimidated, so they need gentle consideration and should not be rushed. On the other hand, their attention span is often limited and they can get tired easily, so the examination should not be prolonged. Balancing these two requirements is not easy.

Most often, patients with dementia cannot give you coherent information themselves. They can be rambling and confused, so you need either a professional carer or a member of the family present who can give you a medical, ocular and family history. You need to be aware of any major medical condition and how long it has been present, and what medication the patient is taking. Is the carer aware of any visual problems? If so, how long has the patient suffered with them? Has the patient previously seen an eyecare professional? What was the result of the examination? Does he or she have spectacles? Does the patient wear them? Can you examine them?

Ask the carer if the patient can recognise people? Does he or she make eye contact? Does he or she gaze into the distance, or hold objects close to their eyes? Do they fall?

External examination

Make general observations of the patient, which can indicate visual problems such as their head position and whether they close one eye. They may have an unsteady gait, which may be caused by other medical or neurological disorders, or possibly visual loss from cataracts. You should be able to check pupillary reflexes, but biomicroscopy may be difficult depending on the patient's behaviour.

When performing the external examination, be aware that some patients can find a light in their face, and a stranger approaching too closely, very intimidating. You may need to move towards the patient slowly, perhaps from one particular side, to avoid causing alarm.

Internal examination

Ophthalmoscopy may be difficult in elderly patients because of constricted pupils and opacities in the media. In patients with dementia, there is also the problem of lack of cooperation and poor fixation. Pupil dilation may help but there can also be a very poor reaction to the insertion of eye drops.

A Goldmann or a Perkins contact tonometer can be quite dangerous with an uncooperative patient, as they may make sudden uncoordinated head movements. A hand-held air-puff tonometer, such as a Keeler Pulsair (Figure 6), is probably better for these patients than trying to get them to put their head in a head-rest. But again, it can be very difficult for uncontrolled patients with poor fixation and sudden head movements.

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Figure 6
Keeler EasyEye Pulsair hand-held NCT
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Objective examination

With constricted pupils, opacified media, poor fixation and lack of concentration, retinoscopy can be very difficult to perform. However, the new hand-held optometers, such as the Nikon Retinomax, are ideal for obtaining an objective refraction in these patients even with cloudy media[9] and constricted pupils, as long as they are prepared to fixate.

Of course, measuring the visual field with an unresponsive patient, or one who cannot understand instructions, is very difficult. One technique that can be tried is for one examiner to sit in front of the patient and try to keep his or her attention, while a second examiner stands behind the patient and slowly brings round a light into the line of sight, until the patient turns his or her eyes or head towards the object. Obviously, this will not work if the patient is totally unresponsive.

The quality of the response in Alzheimer's patients can vary from a keen reading of a Snellen chart to no response whatsoever. In the former case, a visual acuity can be recorded, but it is very difficult in the latter.

The standard Snellen chart is often useless for patients with moderate to severe dementia. Even the newer tests of visual dysfunction utilising glare testing, contrast sensitivity testing[10], potential vision tests, and specular photographic microscopy, have not been well studied, nor do they appear appropriate for patients with significant dementia and poor vision.

There is no way to consistently record an objective visual acuity in the unresponsive elderly. In young people with active curiosity, preferential looking techniques, such as the Cardiff Acuity Test where patterns with various spatial frequencies are moved in front of the infant and the eye response noted, are extremely useful. They do not work, however, for the elderly mentally infirm, as there is no interest and no response at all.

Various opto-kinetic nystagmus systems have been tried[11,12] but none has produced consistent results, and this has not been found to be a useful method of clinically finding the objective visual acuity.

It has been reported[13] that there is a drop in contrast sensitivity at all spatial frequencies in Alzheimer's disease, but this becomes impossible to measure once subjective responses are gone.

It has also been reported[14,15] that the degree of visual impairment is related to increased severity of dementia. However, the majority of studies have failed to find any changes in visual acuity, as measured by the traditional Snellen chart, in Alzheimer's disease beyond those found in ordinary ageing[16-19].

Kahn et al (1976)[11] found that opto-kinetic nystagmus methods of visual acuity testing did not appear useful for general clinical purposes, especially with the unresponsive patient.

Conclusion

Dementia should not be considered a contraindication to surgery or prescribing spectacles. On the contrary, the presence of cognitive dysfunction, such as that seen in dementia, should be considered a co-morbid factor that might increase the need to consider cataract removal or an optical correction to improve sensory input, which opens another communication channel for the patient. Nursing home physicians and nurses should be encouraged to consider the possible quality-of-life improvements gained by cataract surgery and optical correction in patients with dementia.


About the author

Dr Howard Solomons is a former senior lecturer in the Department of Optometry and Visual Science at City University, London.

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References

1. Reisberg B (1988) Functional Assessment Staging (FAST). Psycho-pharmacology Bulletin 24: 653-659.

2. Solomons H (1992) Examination of the elderly patient. Optician 205: 15-18.

3. Chapman F, Dickinson J, McKieth I, Ballard C (1999) Association between hallucinations, visual acuity and specific eye pathology in Alzheimer's disease: treatment implications. Am. J. Psychiatry 156: 1983-5.

4. Tetewsky SJ and Duffy CJ (1999) Visual loss and getting lost in Alzheimer's disease. Neurology 52: 958-965.

5. Wong-Riley M et al (1997) Cytochrome oxidase in Alzheimer's disease: biochemical, historical, and immunohistochemical analyses of the visual and other systems. Vision Research 37: 3593-3607.

6. Hof PR, Vogt BA, Bouras C and Morisson JH (1997) Atypical form of Alzheimer's disease with prominent posterior cortical atrophy: a review of lesion distribution and circuit disconnection in cortical visual pathways. Vision Research 37: 3609-3622.

7. Milner DA and Goodale MA (1995) The Visual Brain in Action. Oxford University Press, Oxford.

8. Lord SR, Ward JA, Williams P and Anstey KJ (1993) An epidemiological study of falls in older community dwelling women: the Randwick falls and fractures study.

Australian J. Pub. Hlth. 17: 240-245. 9. Cordonnier M, Dramaix M, Kallay O, de Bideran M (1998) How accurate is the hand-held refractor Retinomax in measuring cycloplegic refraction: a further evaluation. Strabismus 6: 133-142.

10. Koch DD (1989) Glare and contrast sensitivity testing in cataract patients. J. Cataract Refract. Surg. 15: 158-164.

11. Khan SG, Chen KF and Frenkel M (1976) Subjective and objective visual acuity testing techniques. Arch. Ophthalmol. 94: 2086-2091

12. Fukai S, Hayakawa T, Tsutsui J (1990) Objective visual acuity testing by optokinetic nystagmus suppression. Jpn. J. Ophthalmol. 34 (2): 239-44.

13. Cormack FK, Martin M and Ballard C (1998) Contrast sensitivity and visual acuity in patients with Alzheimer's disease. Int. J. Geriatric Psychiatry 04: 503-519.

14. Uhlmann RF, Larson EB, Koespell TD, Rees TS and Duckert LG (1991) Visual impairment and cognitive dysfunction in Alzheimer's disease. J. Gen. Int. Med. 5: 015-021.

15. Lakshiminarayanan V, Lagrave J, Keane ML, Dick M and Shankle R (1996) Vision in dementia: contrast effects. Neurolog. Res. 18: 9-15.

16. Mendez MF, Mendez MA, Martin R, Smyth KA and Whitehouse PJ (1990) Complex visual disturbances in Alzheimer's disease. Neurology 40: 439-443.

17. Katz B and Rimmer S (1989) Ophthalmologic manifestations of Alzheimer's disease. Surv. Ophthalmol. 34: 31-43.

18. Schlotterer G, Moscovitch M and Crapper-Mclachlan D (1983) Visual processing deficits assessed by spatial frequency contrast sensitivity and backwards masking in normal ageing and Alzheimer's disease. Brain 107: 308-75.

19. Cronin-Golomb A (1991) Visual dysfunction in Alzheimer's disease: relation to normal ageing. Ann. Neurol. 29: 41-52.

Further reading

Shua-Haim JR, Joel S and Ross JS (1998) Cataract and dementia. Annals of Long-Term Care 6: 1524.



Acknowledgements

Figures 1-4 by courtesy of Richard Armstrong and Figure 5 by courtesy of Professor Roger Buckley.



27 | October 7 | 2005 OT