By Marcello Cherchi, MD PhD
For patients
The brain needs correct visual information in order for a person to maintain equilibrium, so some patients with impaired vision may notice that their balance is “off.” Patients in this situation should be evaluated by an eye doctor. It is also reasonable to check for other common causes of disequilibrium (besides the visual problem). For cases in which the visual problem seems to be the only factor causing disequilibrium, it is reasonable to try treating that visual problem. If that fails, then a trial of physical therapy for balance is reasonable.
For clinicians
Overview
Vision is one of the three main sensory modalities involved in maintaining equilibrium (the other two are somatosensory input and vestibular input). Visual input can be abnormal in many ways (reduced acuity, reduced contrast sensitivity, impaired stereopsis and depth perception) from a range of diseases (refractive errors, cataracts, glaucoma, retinopathy, macular degeneration). Ophthalmologic visual deficits interfere with visual input, and can thereby cause disequilibrium. Studies have shown that ophthalmic visual deficits can lead to impaired postural stability and increased fall risk at any age. Most (though not all) studies show that treatment of the ophthalmologic visual deficit brings about improvement in postural stability and reduces fall risk. If treatment of the ophthalmologic visual deficit is not possible, or if it is unsuccessful, then a trial of physical therapy is medically reasonable; a basic mechanism of such therapy is to decrease reliance on visual input, and increase reliance on other (intact) sensory modalities. Although ophthalmic visual deficits may be the main or only cause of disequilibrium, it is medically reasonable to check for common otovestibular diseases by undertaking a screening workup.
Introduction
It has frequently been observed that patients who fall are found to have higher rates of visual impairment. For example, Schwartz and colleagues (Schwartz et al. 2005), citing work by Lord and colleagues (Lord et al. 1994) comment that, “Elderly patients admitted to hospitals, especially those who have fallen, have a high prevalence of visual impairment.”
This observation of this associative relationship (falling is associated with visual impairment) raises the question of whether there is also a causal relationship (visual impairment causes an increase in falls). Schwartz and colleagues comment that, “Vision is one of the three basic input channels controlling balance, together with the vestibular and somatosensory subsystems. It is not surprising therefore that visual dysfunction has been reported to be associated with an increased risk of falling” (Schwartz et al. 2005).
How would one study the relationship between visual problems and disequilibrium? Two broad considerations are relevant.
- Many factors can adversely impact visual function; the most commonly studied visual deficits include reduction in visual acuity, reduction in contrast sensitivity, and impaired depth perception (Abdelhafiz and Austin 2003; Harwood 2001; Lord and Dayhew 2001). The effects of each type of deficit may differ; for example, Lord (Lord 2006) reported that impaired depth perception and reduced contrast sensitivity may have more of an impact than poor visual acuity. A variety of ocular diseases can cause these visual deficits, including refractive errors, cataracts, glaucoma, diabetic retinopathy, macular degeneration, and others (Kamel et al. 2000; Kotecha et al. 2013).
- The presence and degree of disequilibrium can be studied by a variety of methods. A common approach is to infer the presence of disequilibrium from an increased rate of falls — in other words, use reported falls as a proxy quantitative biomarker for disequilibrium. Another approach is to use a specific measure of equilibrium; these types of studies commonly analyze instrumented assessments of postural sway (such as static or dynamic computerized dynamic posturography). It must also be kept in mind that disequilibrium can result from a very broad range of other problems (vestibular, neurologic, orthopedic, cardiovascular and others).
Thus, there is a many-to-many relationship between types of visual impairment, and measures of disequilibrium. Consequently, it would be ideal if:
- Studies of the relationship between visual impairment and disequilibrium should, at minimum, begin by observing correlations between a particular measurable visual deficit and a particular measurable assessment of equilibrium.
- In studies of the relationship between visual impairment and disequilibrium, each group of patients should be studied against carefully matched healthy individuals to control for age and medical histories.
Most studies are not ideally designed. Nevertheless, below we review several broad categories of observations.
Visual impairment increases fall risk
Visual dysfunction (of undifferentiated etiologies) has been repeatedly reported to be associated with increased fall risk (Felson et al. 1989; Harwood 2001; Ivers et al. 1998; Klein et al. 1998).
Other studies focus on particular ocular diseases. For example:
- Reduced visual acuity has been reported to increase the rate of falls (Coleman et al. 2004).
- Cataracts have been reported to increase fall risk in the elderly, even independent of visual acuity (McCarty et al. 2002).
- Alexander and colleagues (Alexander et al. 2014) report that age-related macular degeneration, especially in conditions of low lighting, may increase fall risk.
Visual impairment decreases postural stability
Visual dysfunction (of undifferentiated etiologies) has been shown to correlate with decreased postural stability (Anand et al. 2003; Black et al. 1982; Manchester et al. 1989; Turano et al. 1994).
Other studies focus on particular ocular diseases or specific visual functions. For example:
- Reduced visual acuity and reduced contrast sensitivity have been associated with decreased postural stability (Lord et al. 1991).
- Cataract simulation (via refractive blur) has been reported to have an adverse impact on postural stability (Anand et al. 2003).
- Black and colleagues (Black et al. 2008) report that in older adults with glaucoma, greater visual field loss and thinner retinal nerve fiber layer thickness are associated with reduced postural stability.
- Chatard and colleagues (Chatard et al. 2017) report that age-related macular degeneration (whether unilateral or bilateral) causes increased postural instability. Other studies report similar findings (Dev et al. 2021; Turano et al. 1996).
- In the pediatric population, visual impairment from strabismus (Ezane et al. 2015; Lions et al. 2014; Papalia et al. 2022), with or without amblyopia (Zipori et al. 2018), has been reported to impair postural stability.
Improved vision reduces fall risk
Some studies report that treatment of cataracts reduces fall risk (Brannan et al. 2003). Other studies do not find such improvement in fall risk (McGwin et al. 2006). Some studies report that cataract surgery improved the symptom of dizziness, but did not affect fall risk (Supuk et al. 2016). Some studies even report an increased risk of falls after vision-improving interventions (Cumming et al. 2007).
In view of the mixed results, Desapriya and colleagues (Desapriya et al. 2010) conducted a systematic review of the literature and performed a meta-analysis that included 737 participants from 22 studies. They reported that, “Pooling of data from 2 RCTs [randomized controlled trials] of 535 participants showed a nonsignificant reduction in the incidence of falls after expedited cataract surgery.”
Improved vision increases postural stability
Some studies report improvement in postural stability following cataract surgery (Durmus et al. 2011; Schwartz et al. 2005).
Some studies of strabismic children report improvement in postural stability after correction (Legrand et al. 2012; Lions et al. 2016).
The role of stereopsis
A factor often overlooked in studies is whether the visual impairment in question is monocular or binocular. This is important because inter-ocular disparities in visual function can impair stereopsis, and thereby adversely impact depth perception. Impaired depth perception can, in turn, cause or worsen disequilibrium.
Some studies are sufficiently astute to recognize this. For example, Felson and colleagues (Felson et al. 1989) observed that patients with good vision in one eye and poor vision in the other eye actually had a higher fall risk than in patients with comparably poor vision in both eyes; they stated, “This suggests that good stereoscopic vision may be necessary to prevent falls.”
Epidemiology
The relationship between visual problems and disequilibrium is worth studying in all age groups. The prevalence of visual impairment, on average, increases with age (Abdelhafiz and Austin 2003) due to age-related changes such as cataracts and macular degeneration. Vision in the pediatric population can be adversely affected as well, although the etiologies of visual impairment may be different, such as strabismus and amblyopia (Ezane et al. 2015; Zipori et al. 2018).
Pathophysiological mechanism of disease
At a basic level, as mentioned earlier, vision is one of the three main sensory modalities upon which the brain draws in order to maintain equilibrium, so impaired vision is likely to interfere with a person’s stability and may increase fall risk.
Clinical presentation
Many of the ophthalmological diseases we have discussed tend to develop gradually (macular degeneration, glaucoma, cataracts, diabetic retinopathy). Some may be congenital (e.g., strabismus). Often when these patients are referred to otoneurology their ophthalmologic disease has already been diagnosed, and the clinical query is whether some other (non-ophthalmologic) factor is causing the symptom of disequilibrium.
Differential diagnosis
In some cases a patient’s visual deficit may be the main contributor, or even the exclusive cause, of the symptom of disequilibrium. However, in order to reach that conclusion it is medically reasonable to undertake a screening workup at least for the more common otovestibular etiologies of disequilibrium. Depending on the clinical scenario, we usually consider checking audiometry, cervical and ocular vestibular evoked myogenic potentials, video head impulse testing, videonystagmography, rotatory chair testing and computerized dynamic posturography. If a patient has discrete visual complaints and has not yet had a thorough eye examination, then referral to ophthalmology is appropriate.
Treatment
If a visual deficit is believed to be contributing to disequilibrium, then that visual deficit (if treatable) is a reasonable therapeutic target. Some (though not all) of the studies cited earlier describe improvements in postural stability and falls after treatment aimed at improving vision.
If the visual deficit is untreatable, or treatment is unsuccessful, then other approaches can be considered.
Physical therapy is a reasonable, low-risk intervention for patients in whom visual deficits appear to be contributing to disequilibrium.
How does such an intervention work? In general, if a patient has disequilibrium due to deficient input of one sensory modality, the patient may unconsciously develop compensatory strategies that place greater reliance on other (intact) remaining sensory inputs. For example, Lions and colleagues (Lions et al. 2014) compared postural stability in strabismic children and healthy controls, and observed that strabismic children “use proprioceptive information more than control age-matched children to control their posture.”
It is possible to leverage this ability — in other words, develop a treatment strategy whose purpose is to increase reliance on intact sensory inputs and reduce reliance on deficient ones. For example, Radvay and colleagues (Radvay et al. 2007) studied 54 patients with age-related macular degeneration and 55 healthy control subjects. They commented that:
“Sixteen of these patients and 14 controls subsequently received balance training sessions on a postural platform (Multitest) stressing sensorimotor coordination by selectively inhibiting or disturbing either, visual, vestibular or somatosensory input. Producing a conflict between two inputs reinforces the use of the third” (Radvay et al. 2007).
In other words, physical therapy can be configured to increase a patient’s reliance on intact sensory modalities and rely less on impaired sensory modalities.
Prognosis
Prognosis of disequilibrium from visual deficits will depend on the underlying etiology.
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