Sir,

Alzheimer’s disease (AD) is a degenerative neurological condition of unknown aetiology affecting approximately 10% of the UK population aged 65 or over.1 Clinical features include disturbances of memory, language, praxis and conceptual abilities. We describe a case of Alzheimer’s disease presenting, unusually, with visual field loss.

Case report

A 52-year-old female teacher presented to her optometrist with an 18-month history of difficulty in writing. Optometric examination showed visual acuities of 6/5 in each eye. No abnormality of the anterior segments or fundi was detected and intraocular pressures were 20 mmHg bilaterally. Automated perimetry revealed a left inferior field defect in both eyes. These findings prompted referral to the glaucoma clinic, where a more detailed history was elicited. She first noticed problems with poor spelling and spidery handwriting. More recently she had become aware of an impaired ability to iron, orientate her dress, interpret the time on a clock and to read the schoolchildrens’ handwriting. Occasionally her mind would go blank in mid-conversation and she had problems remembering the plot of a film.

She denied headache or other neurological symptoms. Her general health was good and she was not on medication.

The findings recorded by the optometrist were confirmed. In addition, Goldmann intraocular pressures were 16 mmHg in each eye and the optic disc appearances were normal (cup:disc ratio 0.4). A slightly incongruous left inferior homonymous quadrantanopia was clearly defined by Goldmann and Humphrey full threshold visual field testing (see Figure 1). An MRI scan showed severe cerebral atrophy, most pronounced in relation to the temporal and parietal lobes bilaterally (see Figure 2). Apkarian flash visual evoked responses were normal from the left occipital lobe and reduced and delayed from the right. An electroencephalogram showed non-specific changes reflecting generalised cerebral dysfunction, suggesting the possibility of Jacob–Creutzfeld disease to be unlikely. On the basis of the long history, the nature of the presenting symptoms and the striking MRI findings a diagnosis of Alzheimer’s disease was made after consultation with a neurologist.

Figure 1
figure 1

(a) Full threshold 24–2 perimetry. (b) Goldmann perimetry.

Full size image

Comment

Disturbances of the visual system in Alzheimer’ disease (AD) are well documented, and importantly, can predate other manifestations of dementia.2 Unfortunately, because of characteristically vague symptomatology and normal examination findings at presentation, the diagnosis may be overlooked.

Patients with AD usually seek an ophthalmic consultation because of disturbances of pattern processing and recognition. The commonest example of this is difficulty with reading which may present as skipping of words or lines on a page, ‘dancing print’ and blurred vision, and can progress to alexia in advanced disease.2,3 Other well-documented difficulties include an inability to recognize faces (prosopagnosia), to pick out individual objects in a group, or disorders of visuospatial processing,4 eg inability to grasp objects within the field of view (optic ataxia), neglect of objects to one side of the object of regard (simultanagnosia), dress disorientation (optic apraxia), and becoming lost in familiar surroundings.

Conventional examination findings are often unremarkable in patients with AD.4 Central visual acuity generally remains normal, at least early in the disease. Colour vision disturbances are not uncommon but may not always be apparent on formal testing. Optic disc pallor has been reported, but is not a characteristic finding. Subtle ocular motility disturbances have been demonstrated, but patients are usually asymptomatic.

Visual fields, though sometimes difficult to assess in AD patients, are usually full in the early stages.4 Abnormal perimetry measurements have been identified by Trick et al during apparently reliable automated field testing.5 However, the reported defects were mainly generalised loss of sensitivity or arcuate scotomata, and none had a clearly defined homonymous quadrantanopia. Our patient was young, with no cardiovascular risk factors, and there was no sign on neuroimaging of a lesion in the contralateral optic radiation, parietal lobe or optic tract such as thromboembolic infarction, cerebral hemorrhage or a space-occupying lesion. However, histopathological studies have shown AD patients may exhibit significant selective loss of neural elements within the visual cortex, which could account for the pattern of field loss in this case.6

Although not applicable here, one should consider that hemisensory visual deficits have also been described in patients with corticobasal degeneration or a mixed corticobasal degeneration – AD picture.7 In addition, some patients with AD have ‘simultanagnosia’ involving a defect of visual attention, in which hemifield loss or disorientation may be apparent rather than genuine.3

Given the diagnostic limitations of standard examination techniques, attention has focused on ‘higher visual function’. Studies have shown that patients with AD have impaired form-identification and visuospatial skills in spite of preserved visual acuity and color vision.8,9 Several tests have been designed to look for visually symptomatic patients with as yet undiagnosed AD, who may be passed as ‘normal’ on standardised cognitive screening tests.9