At A Glance
- Neurologic visual field loss—the loss of visual field due to a nonocular lesion along the afferent visual pathway—can be accompanied by perceptual, cognitive, and motor dysfunctions.
- The incidence of visual field loss in the general population increases exponentially with age.
- Stroke is the second most common cause of visual field loss in the elderly population, second only to primary open-angle glaucoma.
Eye care providers are often given the daunting task of assessing whether a patient is visually safe to drive. Although every state has definitive guidance regarding visual acuity and driving, recommendations for patients with visual field loss are less specific, and in some states don’t exist at all. This leaves great responsibility with the eye care provider, which is exponentially increased when a patient has neurologic homonymous visual field loss with 20/20 VA.
For the purposes of this article, neurologic visual field loss is defined as the loss of visual field due to a nonocular lesion along the afferent visual pathway. Unlike ocular visual field loss, neurologic visual field loss can be accompanied by and influence perceptual, cognitive, and motor dysfunctions, which must be taken into account.
THE BASIC FACTS
The incidence of visual field loss in the general population increases exponentially with age. Stroke is the second most common cause of visual field loss in the elderly population, second only to primary open-angle glaucoma.1 Depending on the study, 20% to 67% of stroke patients have some type of visual field defect. Of those patients, 50% to 73.5% present with homonymous hemianopsia due to an occipital lobe lesion, 15% to 30% have homonymous quadrinopsia due to parietal and/or temporal lobe lesion, and the remaining patients have other visual field defects due to lesions involving the optic tract or lateral geniculate nucleus.2-5
NEUROLOGIC VISUAL FIELD LOSS AND DRIVER SAFETY
Although we often evaluate the extent of neurologic visual field loss (ie, degrees of visual field lost) and BCVA to determine driver safety, only 31% of patients with neurologic visual field loss present with visual field loss alone. According to Rowe et al, 28.6% of patients after stroke had visual field loss along with reduced vision, 28.2% had visual field loss accompanied by oculomotor abnormalities, and 25% had visual field loss and visual perceptual difficulties.2 These oculomotor and visual perceptual dysfunctions can directly reduce cognitive performance, undermining a patient’s ability to compensate for visual field loss and challenging his or her capacity to interact with the visual environment.
Patients with neurologic visual field loss may complain that their vision is “slow,” that they see objects “too late,” that they get lost in busy, crowded places, or that they are surprised easily, as things such as small children or dogs suddenly appear and disappear in their visual field.
Beyond driving, neurologic visual field loss can affect other tasks of daily living, including reading, writing, cooking, walking, visually guided motor movements such as grasping objects, and more. If patients do not adapt to their visual field loss, they will have an increased risk of falling and may feel unsafe navigating their environment.
TALKING WITH PATIENTS AND CARETAKERS
It is important for eye care providers to survey patients to understand how visual field loss is affecting their daily lives. Don’t be surprised, however, if patients say they are fine or are completely unaware of their visual field loss. Some 10% to 19% of patients may be asymptomatic or unaware of their visual field loss after a stroke.6
Although ocular visual field loss, such as a central scotoma in macular degeneration, may appear as an obvious dark spot to the patient, neurologic visual field loss can be less conspicuous to the patient, even though it is larger and apparent to eye care providers on automated diagnostic testing. In neurologic visual field loss, the brain may try to “fill in” what is missing, and some patients have described the missing area to seem more like a faint blur on the edge of their vision rather than a large scotoma, as our testing may suggest (Figure). This makes it difficult for some patients to recognize just how much visual field has been lost and can be confusing to caretakers or family members who cannot fathom why their loved one is unable to recognize and therefore compensate for their visual field loss.
Figure. A full visual scene without visual field loss (A). What a caretaker may think a patient sees based on visual field test results in the optometrist’s office (B). Patients may think they have a full visual field even though the left side of their vision is missing (C), or they may have a blur zone in their area of visual field loss (D).
Furthermore, patients with damage to areas in the brain involved in visual awareness may even deny the existence of their visual field loss, even when confronted with it in the exam room, a condition known as anosognosia.6 The degree and type of unawareness of visual field defect can vary. In mild presentations, the patient is aware of a visual defect to one side but may consistently misinterpret the visual field loss as missing vision in one eye only. In severe presentations, the patient may be completely unaware of the vision loss and refuse to acknowledge its existence, even when confronted with the test results in the office.7 Therefore, it is important not only to ask patients how they are coping with their visual field loss, but also to ask their family members or caretakers, who may have a different perspective on the impact.
OTHER WORDS FOR VISION LOSS
In addition to awareness of visual field loss, every individual will perceive his or her visual field loss differently.8 Some patients may be able to detect motion in their blind field or scotoma even though they cannot consciously locate or see it, a condition known as blindsight.9 Other patients may experience visual hallucinations in their blind field.8 This can be confusing for patients, as they may feel they are getting their vision back or are seeing things that aren’t really there.
Interestingly, recent studies have documented patients with a condition known as sightblindness, in which the patient experiences visual perceptual processing difficulties in his or her normal intact visual field. Findings in the normal visual fields of sightblind patients include reduced contrast sensitivity, longer reaction times, reduced contour interaction, perceptual distortion, and difficulties with visual search eye movements that can lead to disorientation and difficulty avoiding obstacles.10 Although sightblind patients may have normal visual acuity and a visual field restriction that falls within state guidelines for driving, reduced contrast sensitivity and reaction time may make them unsafe to drive and affect other aspects of their life.
A DUTY TO DO WHAT’S BEST
Eye care providers want to advocate for and empower their patients to see and do the things that they enjoy. It is important, however, to remember that driving is a privilege and not a right. Assessing whether a patient is visually safe to drive affects not only the patient but everyone on the road. With conditions such as anosognosia, blindsight, and sightblindness as possible diagnoses, every case of neurologic visual field impairment must be evaluated beyond visual acuity and visual field testing alone. The more we can educate our patients about their vision, the more we can help them adapt and stay safe.
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- 2. Rowe FJ, Wright D, Brand D, et al. A prospective profile of visual field loss following stroke: prevalence, type, rehabilitation, and outcome. Biomed Res Int. 2013;2013:719096.
- 3. Zhang X, Kedar S, Lynn MJ, et al. Homonymous hemianopias: clinical-anatomic correlations in 904 cases. Neurology. 2006;66(6):906-910.
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- 7. Zihl J. Rehabilitation of Visual Disorders after Brain Injury. New York, NY: Psychology Press; 2011.
- 8. Chokron S, Dubourg L, Garric C, et al. Dissociations between perception and awareness in hemianopia [published online ahead of print 2020 Jan 8]. Restor Neurol Neurosci.
- 9. Goodwin D. Homonymous hemianopia: challenges and solutions. Clin Ophthalmol. 2014;8:1919-1927.
- 10. Bola M, Gall C, Sabel BA. “Sightblind”: perceptual deficits in the “intact” visual field. Front Neurol. 2013;4:80. Published 2013 Jun 25.