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C-55410

Homonymous hemianopia following stroke

This article outlines the investigation of patients presenting with homonymous hemianopia following stroke.

Introduction

Acquired brain injury (ABI) is defined as damage to the brain that occurs after birth and is not related to a congenital or degenerative pathology; these deficits may be temporary or permanent and cause partial or functional disability or psychosocial impairment.1 ABI may have several causes including trauma to the brain – traumatic brain injury (TBI), stroke, tumours, infections, exposure to toxins and lack of oxygen to the brain due to a wide variety of causes.

Stroke is the third leading cause of death following heart disease and cancer.2 Stroke is characterised as a neurological deficit due to an acute focal injury of the brain by vascular cause, including cerebral infarction, intracerebral haemorrhage (ICH), and subarachnoid haemorrhage (SAH), and is a major cause of disability and death worldwide.3 There are approximately 152,000 strokes a year in the UK.4 The risk of having a stroke doubles every decade after the age of 55;5,6 by the age of 75, one in five women and one in six men will be affected by stroke.7 Risk factors for stroke include heart disease, high cholesterol, hypertension, diabetes, smoking, alcohol consumption, lack of exercise, poor diet, and ageing.8–10

Table 1

Ischaemic stroke usually produces focal symptoms that persist for at least 24 hours. In transient ischaemic attack (TIA), symptoms and signs resolve after a short period, generally within 30 minutes. With haemorrhagic stroke, the main causes include: vascular intracranial malformations; aneurysms, haemangiomas, atrial venous malformations; cerebral amyloid angiopathy; hypertension, coagulation disorders; and illicit drugs.8 Once the haemorrhage occurs, blood might reach other brain sites through the arachnoid spaces resulting in global cerebral dysfunction. One of the common symptoms in a patient with haemorrhagic stroke is severe headache. Tables 1 and 2 highlight the main general and visual effects of stroke, respectively.

Homonymous hemianopia (HH) is a frequent visual consequence in patients suffering from stroke as a result of postchiasmal damage. Evidence suggests that 8–10% of stroke patients have permanent HH, and 52–70% of hemianopias are caused by stroke.9–10 Other types of visual field deficits resulting from stroke include: inferior and superior quadrantanopia; constricted visual fields; scotomas, and altitudinal defects.11–12 In terms of site location, 40% of HH involve lesions in the occipital lobe, 30% in the parietal lobe, 25% in the temporal lobe, and 5% arising in the optic tract and lateral geniculate nucleus (LGN).13–14 The more posterior the lesion is, the more congruous the HH will be. However, most lesions involving the occipital lobe characteristically produce congruent HH, with at least 50% of lesions arising in other brain sites also resulting in congruent HH.15 HH may occur in different forms:16 complete hemianopia, affecting both the upper and lower areas of the visual hemifield; quadrantanopia, affecting a visual quadrant; or a paracentral scotoma which does not exceed 10°and lies on the immediate edge of the central vision. Homonymous visual defects are usually accompained by foveal sparing of 0.5° to 1°; sparing above 1° is rarely seen.19

Table 2

Homonymous hemianopia (HH) is a frequent visual consequence in patients suffering from stroke as a result of postchiasmal damage. Evidence suggests that 8–10% of stroke patients have permanent HH, and 52–70% of hemianopias are caused by stroke.9–10 Other types of visual field deficits resulting from stroke include: inferior and superior quadrantanopia; constricted visual fields; scotomas, and altitudinal defects.11–12 In terms of site location, 40% of HH involve lesions in the occipital lobe, 30% in the parietal lobe, 25% in the temporal lobe, and 5% arising in the optic tract and lateral geniculate nucleus (LGN).13–14 The more posterior the lesion is, the more congruous the HH will be. However, most lesions involving the occipital lobe characteristically produce congruent HH, with at least 50% of lesions arising in other brain sites also resulting in congruent HH.15 HH may occur in different forms:16 complete hemianopia, affecting both the upper and lower areas of the visual hemifield; quadrantanopia, affecting a visual quadrant; or a paracentral scotoma which does not exceed 10° and lies on the immediate edge of the central vision. Homonymous visual defects are usually accompained by foveal sparing of 0.5° to 1°; sparing above 1° is rarely seen.19

Patients with HH may have mobility and navigational impairment and frequently complain of bumping into obstacles on the side of the affected visual field. Furthermore, patients with HH often cannot readily/spontaneously scan into the blind area and reading ability may be significantly impaired. In right HH, when the patient tries to read text, the scotoma of the field loss moves with the patient down the line of text like a curtain hiding what the patient is reading. Where the scotoma involves the macula, it may block the end of the line of text, which makes it difficult to recognise the end of the line, or the end of long words. In left HH, the patient may find it difficult to return to the start of the next line.

Figure 1

HH due to stroke may occur with or without unilateral neglect (UN). UN is characterised by reduced awareness of objects on one side of space, even though there may not be sensory loss.17 The reported incidence of UN varies from 10%18 to 82%19 following right hemisphere stroke and from 15%20 to 65%21 following left hemisphere stroke. The differential diagnosis between a visual field defect and UN is an important clinical consideration. UN like visual impairment, comes in varying densities; a dense UN will appear as a hemianopia. In the case of UN, the primary visual pathway is usually intact.

It is the patient’s ability to attend to, and, therefore, perceive and respond to, the stimulus that has been damaged.21 However, UN is more than a visual condition as the patient may not respond to a voice when the person is standing on the affected side.

Optometric examination

Providing care to stroke patients with HH can be challenging but is an important aspect of optometric practice. Eye care in these patients includes:
  • Taking a careful history
  • Distance and near visual acuity assessment
  • Refraction
  • Visual field assessment
  • Tests for UN
  • Ocular motility assessment
  • Ocular health assessment.

History taking

Taking a history with a patient suffering from HH often requires more time than routine cases. These individuals often have complicated medical histories and may be taking numerous medications due to their condition(s). In addition, they may have self-awareness deficits and consequently may not have a full understanding of their visual problems.22 Patients with stroke may also have cognitive impairment, affecting speech and hearing, which can slow the processing of information exchange.23 Naturally, this will affect both the ability of the patient to cooperate with the optometrist and the amount of time required to perform the examination. It is imperative to understand the patient’s visual needs through careful questioning in order to understand: if the patient can be considered legally severely sight impaired (blind) or sight impaired (partially sighted); establish lifestyle and hobbies; decide if optical or non optical aids can potentially be useful for the patient; and determine if the patient is motivated to carry out a neuro-optometric rehabilitation programme.

Figure 2

Visual acuity assessment

Visual acuity is usually normal in patients with HH except in cases where the optic tract is affected, while reading impairment (hemianopic alexia) occurs by a loss of parafoveal field (parafoveal scotoma).24 LogMar charts provide the visual acuity assessment for distance and reading as logarithm of the minimum angle of resolution. Thus the size of letters change in steps of 0.1 log units between one row and the next with the same degree of legibility. Each letter has a value of 0.02 log units and each letter read correctly by the patient is scored as 0.02 log units; these charts provide a better visual acuity quantification than traditional Snellen charts, even at low visual acuities. Charts designed with Lea symbols may be useful for patients with communication difficulties or aphasia (see Figure 1: LogMAR chart designed with Lea symbols may be useful in patients with communication difficulties or aphasia).

Refraction

Retinoscopy is a procedure to establish objectively the patient’s refractive status. In patients with cloudy optical media and/or small pupils, radical retinoscopy (refracting closer than the usual distance) should be performed and then refined subjectively. It is sometimes useful, especially in patients with low visual acuity, to determine the sphere power by a bracketing technique using large steps according to the following recommendations: +/-1.00D in individuals with visual acuity of 6/30; +/-2.00D in those with visual acuity of 6/60; and +/-4.00D in those with visual acuity of 6/120 or worse. Cylindrical power and its axis can be established with a Jackson cross cylinder (JCC) using a +/-1.00D JCC for visual acuities of 6/60 or worse and +/-0.75D for those with visual acuities of around 6/48.

Visual field

Visual field assessment and management must be included during a neuro-optometric rehabilitation program in any patient with brain injury, as visual field impairment is common following brain damage. A variety of methods can be considered to estimate the patient’s visual field, from gross methods such as confrontation visual field testing to computerised procedures.

Figure 3

Confrontation visual field testing

Eye care practitioners are very familiar with using this method to evaluate the patient’s visual field. The examination is undertaken monocularly and does not require special equipment. The patient’s visual field is compared to the examiner’s visual field, assuming of course, the examiner has a normal visual field in each eye. For instance, performing the count finger procedure, the practitioner presents the fingers of their hand as a stimulus in each of the patient’s visual sectors at a distance of 1m. The patient indicates the number of fingers seen (see Figure 2: Confrontation visual field testing using the count finger method). An Amsler grid can also be used, not only for delineating potential macular defects, but as a miniature tangent screen for determining the boundary of a hemianopic defect.23

Automated visual field analysis

The use of automated instrumentation is an excellent method for evaluating the patient’s visual field. Light stimuli with different intensities are shown in various areas of patient’s visual field. The visual field assessment determines the threshold level in each area of the visual field.

Tests for unilateral neglect

The Behavioural Inattention Test (BIT) is useful to identify patients with UN.25 The BIT contains six pen and paper tasks and nine behavioural assessments. Pen and paper assessments include star and letter cancellation, line crossing, line bisection, free drawing and shape copying tasks.

In the star and letter cancellation and in line tasks, subjects are presented with an array of target symbols that they are asked to mark. A patient with UN is likely to miss symbols toward the contralesional side and more often begin to search from the ipsilesional side of the page. When the line bisection task is used, patients are required to mark the mid-point of several horizontal lines. In the case of left UN the patient tends to mark the mid-point further to the ipsilesional side. Using shape copying and free drawing tasks, the patient is instructed to reproduce geometric shapes or simple objects. Patients with UN are more likely to miss the contralesional side of these images when drawing.

Ocular motility

Patients suffering from stroke with or without HH may have vertical and/or horizontal gaze palsy, diplopia, or even nystagmus. Due to the high incidence of ocular motor dysfunction, which can affect ocular fixation, pursuit, and saccades, careful assessment of these functions should be undertaken (see Figure 3: Assessment of pursuit movements. The patient is asked to follow a stimulus on the horizontal and vertical plane, and then oblique directions, and Figure 4: Assessment of saccadic movements. The patient is instructed to look at the examiner's finger on the left hand (A) and then the finger on the right hand (B)). The corneal light reflex test can be helpful in assessing ocular alignment in uncooperative patients. The examiner is seated about 40cm in front of the patient while they fixate a spotlight. The practitioner notes the position of the corneal reflections in respect to the centre of the pupils. For an esotropia and exotropia deviation, the corneal reflex in the deviated eye appears displaced temporally and nasally, respectively. Each millimeter of displacement of the corneal reflex is equivalent to 22Δ of ocular misalignment.26 A prism from the trial set or a prism bar is usually held in front of the patient’s fixating eye. The magnitude of prism required to neutralise the ocular deviation is reached when the position of the corneal reflex in the deviated eye is symmetrical to the corneal reflex in the fixating eye. The cover/uncover and alternating cover test with prism bar often do not require significant patient cooperation so that can also be performed.

Ocular health

The assessment of the anterior segment of the eye in a clinical setting is usually performed using a slit lamp. A handheld slit lamp might be used instead of a traditional instrument in patients with lack of cooperation. Assessment of intraocular pressure with an applanantion tonometer should be undertaken with caution to avoid potential corneal injury due to sudden and uncoordinated head movements in patients with cognitive decline. The assessment of the posterior segment of the eye can be conducted after the patient’s pupils are dilated with either binocular indirect ophthalmoscopy or direct ophthalmoscopy depending upon the patient’s ability to cooperate.

Figure 4a and 4b

Conclusion

Assessing patients suffering from stroke with visual field impairment can be challenging for an eye care practitioner. Patients with ischaemic or haemorrhagic stroke might have a constellation of visual and neurological clinical signs. Stroke along with other acquired brain injuries may cause HH. In addition to loss of half of the visual field, HH can result in ocular motion disturbances affecting visual scanning and visual searching of the environment, including reading ability, so taking a thorough ocular history and clinical assessment is paramount when seeing these patients.

About the author

Fabrizio Bonci Dip Optom, MCOptom is the clinical optometry lead at Ocular-Optikus Clinic in Kecskemét, Hungary. He has mostly worked in eye clinics in Italy and was also a clinical research fellow at the Department of Clinical Neuroscience and Mental Health, Imperial College London, Charing Cross Hospital.

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