Patients with Alzheimer’s or Parkinson’s disease may present with visual processing complaints that predate significant cerebral neuro degeneration.
Mark E. Wilkinson, O.D., Iowa City, Iowa
A 56-year-old white male presents with difficulty in both clarity and tracking when reading. In recent months, he loses his place when reading from one line to the next. Best-corrected visual acuity is 20/20 in each eye, and he can read 0.4M single word sat 16 inches. The ocular health exam is unremarkable. He responds, “But I can’t read.”
Now what? When faced with functional visual complaints incommensurate with a normal structural eye exam in an older patient (age 55 and older), your differential diagnosis should include possible dementia. Alzheimer’s disease accounts for 50%-to-80% of dementia cases.1 Some 5.4 million Americans have the condition.2 Also, consider Parkinson’s disease, the second-most common neurodegenerative condition, affecting nearly one million Americans.3
Both diseases can produce complex visual disorders often sans identifiable ocular findings. Therefore, you, the optometrist, may be the first to detect the signs and symptoms of Alzheimer’s disease, of which an estimated half to two-thirds of cases go undetected.1 Likewise, the subtle early signs of Parkinson’s disease often predate a neurological clinical diagnosis, so you may be the first to pick up its nascent signals.
Particularly in light of an aging population, it’s imperative you’re prepared to diagnose and possibly treat the visual sequelae of dementia.
Alzheimer’s disease: an overview
Alzheimer’s disease is a neurodegenerative disorder involving an insidious onset of progressive dementia often beginning in a person’s 60s. Typically, the most prominent and earliest symptom is memory loss. As the disease progresses, visuospatial, linguistic and executive functions (e.g. problem solving, organizational skills, selective attention, etc.) deficits emerge.
Early neuropathological and neuroimaging abnormalities derive mostly from the brain’s temporoparietal regions. A definitive diagnosis requires a pathological brain exam.
Alzheimer’s disease incidence increases with age. An estimated 10% of Americans who have it are younger than age 65, while almost half of those age 85 and older have the condition.1
The good news: Treatments, such as cholinesterase inhibitors, are emerging to slow the worsening of Alzheimer’s disease dementia symptoms, improving the patient’s and their caregiver’s quality of life.
Visual symptoms commonly associated with Alzheimer’s disease: reduced visual acuity secondary to loss of retinal ganglion cells, decreased contrast sensitivity and difficulty perceiving motion, which can affect walking and driving.2,4,5,6 (See “The Aging Driver,” page 54.)
Alzheimer’s visual variant
An atypical form of Alzheimer’s disease is its visual variant, also called posterior cortical atrophy. First described in 1988, the condition’s neurodegenerative changes (greatest in the occipitoparietal and occipitotemporal regions) disrupt higher-order visual processing.7
Posterior cortical atrophy patients may complain of seeing but not recognizing, affecting reading and driving. A telltale chief complaint: “I can’t interpret what I see.” An eye exam will reveal normal visual acuity and fields.
Compared with typical Alzheimer’s disease, those who have its visual variant often present without dramatic neurocognitive deficits or dementia and tend to possess better language skills, memory and more insight into their illness.8 Therefore, these patients may suffer from concomitant clinical depression, perhaps requiring referral for diagnosis and treatment.
Parkinson’s disease: an overview
Parkinson’s disease is a progressive neurodegenerative condition that impairs cognitive, motor and sensory function due to the malfunction and death of dopaminergic neurons in the cerebral substantia nigra. Some of these dying neurons produce the neurotransmitter dopamine, which is needed by the brain to control movement and coordination.3,9
As the disease progresses, the brain produces decreasing amounts of dopamine and, in turn, the patient becomes unable to control movement. Symptoms vary from one person to the next. The primary motor signs indicating a Parkinson’s disease diagnosis: tremors of the hands, arms, legs, jaw and face; slow movements (bradykinesia); rigid limbs and trunk; and unstable posture or impaired balance and coordination.3 Incidentally, a recent study reveals persistent oscillatory fixation instability.10
The Aging Driver
As many as half of Alzheimer’s disease patients continue to drive up to three years after diagnosis.17 They have been known to get lost on familiar routes — sometimes, for days —and cause accidents. One such accident occurred in 2003 when an elderly man killed 10 and injured 63 in a farmer’s market because he applied the gas, thinking it was the brake.
As you provide eye care to an increasing number of elderly drivers, remember that many may have early undiagnosed (or already diagnosed) neurodegenerative disorders. To promote the safety of older drivers and the public, recommend your older patients who drive undergo a formal assessment of their vision, cognition and motor skills. Typically, a multidisciplinary team consisting of a gerontologist, an occupational therapist and an eyecare provider will perform the assessment. Also, refer these patients for a behind-the-wheel driving assessment when appropriate.18 These assessments can be performed by the state department of transportation, rehab professionals trained to assess driving safety, such as occupational therapists, and adult driver’s education instructors.
Eyecare practitioners or rehab centers who/that deal with driving typically perform Useful field of view (UFOV) testing. While conventional measures of visual field testing assess sensory sensitivity, UFOV evaluates higher-order visual processing skills, such as selective or divided attention and visual processing speed under increasingly complex visual displays. UFOV therefore more closely approximates driving’s complexity. Following testing, the UFOV software provides an assessment of the patient’s risk for a car accident.
I assess the safety of older drivers by asking them these questions:
► Do you drive? If so, what type of driving do you do? Specifically, I’m interested to know whether the patient restricts driving to certain speeds, times of day or distances from home.
► Do you have vision problems that make you fearful when driving? Anyone with such fear should not continue driving until its cause is identified and eliminated. Also, consider asking the patient’s spouse whether he feels safe in the car while the patient drives.
► Have you made any driving errors in the last six months? Depending on the error, it may indicate that the person is no longer safe to drive.
► Does your vision affect your mobility? If someone has difficulty with ambulation because of their vision, they are no longer safe to drive.
If you have concerns about the patient’s safety when driving, discuss the possibility of restricting the person’s driving or having him retire from driving altogether. The Physician’s Guide to Assessing and Counseling Older Drivers, which can be accessed at www.ama-assn.org/ama1/pub/upload/mm/433/older-drivers-guide.pdf, can assist you with these difficult conversations.
Altered retinal visual processing in Parkinson’s disease is believed to stem from dopamine deficiency, due to a change in the receptive field properties of ganglion cells in the lateral geniculate nucleus and visual cortex.11 Common Parkinson’s disease visual problems: reduced visual acuity and impaired ocular motility, which can lead to diplopia. Epiphora and dry eye syndrome may develop secondary to reduced blinking. Further, reduced contrast sensitivity, motion perception, color vision, impaired depth perception (which can create walking/driving difficulties), blepharospasm and complex visual hallucinations commonly occur in Parkinson’s disease patients.11-13
The condition usually is partially treatable — primarily with dopamine-replacement therapy — for a few years after diagnosis. Unfortunately, this generally is followed by years of decline, culminating in premature death.9
Dementia and ophthalmic findings
An attentive and thorough patient history is critical when evaluating someone who has visual complaints yet a normal eye exam. Listen carefully to the patient’s complaints. Remain especially vigilant when patients report difficulty interpreting scenes or pictures, with depth perception, reading, recognizing faces or objects, color vision abnormalities, difficulty walking or getting lost in familiar places.
These complaints could be early signs of an undiagnosed neurodegenerative disorder. Homonymous visual field defects with normal MRI likewise should raise your suspicion of Alzheimer’s disease or other neurodegenerative conditions.
Numerous researchers have recommended OCT to evaluate retinal thinning, a suspected biomarker for neurodegenerative changes in both Alzheimer’s and Parkinson’s disease.2’5’6’8’14’15 For now, however, protocols for OCT as a diagnostic biomarker are not well-established.12
Complex visual disorders
The following complex visual disorders occur commonly with dementia, particularly with the visual variant of Alzheimer’s disease.16:
► Agnosia. Inability to recognize familiar people and objects.
► Spatial/environmental agnosia. Getting lost in familiar surroundings.
► Visual object agnosia. Inability to recognize an object by sight, but able to do so by touch or sounds. This is usually worse with drawings vs. three-dimensional objects.
► Simultagnosia. Difficulty locating and identifying objects by sight with increasing complexity and the number of items in the visual field. Roughly half of simultagnosia patients exhibit hemispatial neglect (hemianopia), primarily involving the inferior quadrant on either side. Simultagnosia patients have difficulty seeing more than one object at a time.
Clinicians commonly use the Cookie Theft Picture (www.ling.ohio-state.edu/~hana/x201m/other/11-cookieTheft.jpg) to test for simultagnosia. Simultagnosia patients usually cannot identify all items in the picture, nor can they describe accurately the situation depicted. Simultagnosia has been called shaft vision because of piecemeal perception when a patient cannot attend to extrafoveal targets.
Impaired reading unrelated to language or visual field deficits commonly accompanies simultagnosia. Despite normal visual acuity, these patients often can read only one letter or word at a time and may require the letter or word to be isolated from the other text. Besides trouble reading, these patients often have difficulty driving.
► Prosopagnosia. Inability to recognize familiar or famous faces, although able to identify someone by their voice.
Ocular motility defects
The neurodegenerative deficits of dementia may also produce ocular motility problems:
► Ataxia. Inability to coordinate muscle movement.
► Optic ataxia. Defective visual control of hand movements sans visual field changes, reduced visual acuity or motor/somatosensory dysfunction.
► Apraxia. Loss of the ability to execute or carry out learned purposeful movements, despite having the desire and physical ability to perform such movements.
► Ocular apraxia. Defective saccades. When asked to look at an object, these patients may initially stare straight ahead, then gaze around the room erratically until, as if by chance, their eyes fall on the object.
Tests for complex visual/motility defects
You can identify those who have complex visual disorders or ocular motility defects, possibly caused by early neurodegenerative disease, through asking the patient to:
► identify photos of familiar faces.
► name and sort colors.
► reach for objects both away from or near him, including touching his nose — a test for optic ataxia.
► read a newspaper or other text.
► draw a clock face, labeling its hours, and place its hands to indicate a specified time. This is statistically sensitive and specific for dementia. (See www.alz.org/professionals_and_researchers_14306.asp.)
A test of vigilance
Remember that neurodegenerative diseases may present with visual problems. Especially consider posterior cortical atrophy in light of functional visual complaints and a structurally normal eye exam.
If you suspect a neurodegenerative disorder, refer the patient to his primary care provider, geronotologist or a neuro-psychologist. Remember: With prompt diagnosis and proper treatment, the patient’s quality of life may be greatly enhanced. OM
1. alz.org. alzheimer’s association. What Is Alzheimer’s? Alzheimer’s and dementia basics. www.alz.org.(Accessed 5/22/12’).
2. Frost S, Klunk WE: Alzheimer’s Asssociation International Conference 2011. Paris, July 2011.
3. National Parkinson Foundation. Parkinsons Disease Overview. www.parkinson.org. (Accessed 5/22/12’)
4. Kirby E, Bandelow S, Hogervorst E. Visual impairment in Alzheimer’s disease: a critical review. J Alzheimers Dis. 2010;21(1):15-34. Review.
5. Valenti DA. Alzheimer’s disease: visual symptom review. Optometry 2010 Jan;81(1):12-21. Review.
6. Paquet C, Boissonnot M, Roger F, et al. Abnormal retinal thickness in patients with mild cognitive impairment and Alzheimer’s disease. Neurosci Lett 2007 Jun 13;420 (2):97-9.
7. Benson DF, Davis RJ, Snyder BD. Posterior cortical atrophy. Arch Neurol. 1988 Jul;45(7):789-93.
8. Mendez MF, Ghajarania M, Perryman KM. Posterior cortical atrophy: clinical characteristics and differences compared to Alzheimer’s disease. Dement Geriatr Cogn Disord. 2002;14(1):33-40.
9. The Scientist: Magazine of the Life Sciences. The Genes of Parkinson’s Disease. Thomas B, Beal MF. http://the-scientist.com/2011/02/01/the-genes-of-parkinson’s-disease. (Accessed 5/22/12’)
10. Gitchel GT. Wetzel PA, Baron MS. Pervasive Ocular Tremor in Patients With Parkinson disease. Arch Neurol. 2012 Apr 9.
11. Armstrong RA. Visual symptoms in Parkinsons disease. Parkinsons Dis. 2011;2011:908306. Epub 2011 May 25.
12. Archibald NK, Clarke MP, Mosimann UP, Burn DJ. Retinal thickness in Parkinson’s disease. Parkinsonism Relat Disord. 2011 Jul;17(6):431-6.
13. Huang YM, Yin ZQ. Minor retinal degeneration in Parkinson’s disease. Med Hypotheses. 2011 Feb;76(2): 194-6.
14. Guo L, Duggan J, Cordeiro MF. Alzheimer’s disease and retinal neurodegeneration. Curr Alzheimer Res. 2010 Feb;7(1):3-14. Review.
15. Moschos MM, Tagaris G, Markopoulos I, et al. Morphologic changes and functional retinal impairment in patients with Parkinson disease without visual loss. Eur J Ophthalmol. 2011 Jan-Feb;21(1):24-9.
16. Lee AG, Martin CO. Neuroophthalmic findings in the visual variant of Alzheimer’s disease. Ophthalmology. 2004 Feb;111(2):376-81.
17. Driving with Alzheimer’s disease: Comprehensive Information About Safe Driving & Dementia. www.alzheimers.about.com/cs/diagnosisissues/a/driving.htm. (Accessed 5/22/12’)
18. Physician’s Guide to Assessing and Counseling Older Drivers. www.ama-assn.org/ama1/pub/upload/mm/433/older-drivers-guide.pdf. (Accessed 5/22/11).
||Dr. Wilkinson, a clinical professor of ophthalmology, also works in the Vision Rehabilitation Service at the University of Iowa Carver College of Medicine in Iowa City. Email him at firstname.lastname@example.org, or send comments to email@example.com.|
Optometric Management, Volume: 47 , Issue: June 2012, page(s): 52 - 57