?This paper accompanied a lecture to the North American
Neuro-Ophthalmology Society [NANOS] in March 1999 by Dr.
Jacqueline Winterkorn. Her office address is Neuro-Ophthalmology, Suite
210, 900 Northern Blvd., Great Neck, NY 11021.
NEURO-OPHTHALMOLOGIC MANIFESTATIONS OF PARKINSON'S DISEASE
© 1999 Jacqueline M.S. Winterkorn, Ph.D., M.D.
New York, New York
1. INTRODUCTION - DEMOGRAPHICS
Parkinson's disease [PD] is known to affect over 1 million Americans and
its diagnosis is
becoming increasingly common, including 50,000 new patients per year26.
Some epidemiologic
studies involving door-to-door canvassing suggest underdiagnosis by as
much as 25%14. In the
over-60 population, the incidence is 1-2%. Despite the common myth that
Parkinson's affects
only the elderly, in fact the average age of symptom onset is 57, with
over a third of all victims
starting symptoms in their 20's, 30's, and 40's. PD is characterized by
tremor, rigidity,
bradykinesia, and impaired balance26. Most patients with Parkinson's
disease [PD] develop some
ophthalmic complaints, e.g. blurred vision, double vision,
photophobia, asthenopia, or trouble
reading. As many as 75% of PD patients have been reported to show
oculomotor signs10. PD is
mainly a motor disorder, caused by death of dopaminergic neurons in the
substantia nigra
compacta, leading to loss of dopamine in the putamen. The depletion of
dopamine from the other
regions of the brain, especially from the visual cortex6 and from
amacrine and interplexiform cells
of the retina16, 30 in patients with PD has prompted studies looking for
visual perceptual
abnormalities19.
It behooves us as neuro-ophthalmologists to know the eye signs of PD,
which ones the patients
complain about, and what relief or management can be offered.
2. NEURO-OPHTHALMIC DEFICITS
Lawton Smith described an acrostic for PD problems 36, 37, which I
present here with
modifications.
Pareses of gaze-- Clinical observations of patients with PD have
described slow, hypometric
saccades and incomplete upgaze10. A differential response to an
optokinetic stimulus in the
horizontal and vertical plane has been described, with OKN present in
the horizontal plane, but
absent or poorly-formed vertically 36, 37. These old studies may reflect
the high prevalence of post-
encephalitic PD at that time. Although vertical gaze abnormality has
been associated with PD,
limited upgaze to command is common in older people33 and may be a
non-specific defect.
Moreover, the eye movement disorder characteristic of idiopathic PD is
mild and may not be
apparent in the early stages of PD or in patients well-controlled by
levodopa39.
Pursuit gain is decreased, leading to jerky pursuit, referred to as
“cogwheel,” since
reminiscent of the ratchety limb movements in PD10, 41. Saccades to
novel stimuli usually remain
unaffected, with normal latency, peak velocity and duration 11.
However, saccades that are made
not to an actual visual stimulus, but rather to a remembered location,
or repeated predictive
saccades tend to be dysmetric11. These saccades are hypometric, show
delayed initiation, and may
be slowed34. In patients with hypometric saccades, saccadic amplitude
has been shown to
normalize after a dose of L-dopa. In patients having Levodopa-induced
dyskinesias, eye
movements may become more frequent and saccades hypermetric.
Imbalance and postural instability are reflected in poor stabilization
of images and
impaired eye-head coordination 38, 41. Head movements may also become
smaller and slower than
normal.
Despite their visual complaints, examination of patients with idiopathic
PD often shows only
minor impairment of ocular motility. If saccades are dramatically slow
or downgaze is severely
impaired, the diagnosis of idiopathic PD should be questioned39.
Parkinson's Plus syndromes
should be differentiated from idiopathic PD, by severity of eye
movements abnormalities.
Disorders such as Progressive Supranuclear Palsy [PSP], cortical-basal
ganglionic [corticobasal]
degeneration, olivopontocerebellar atrophy, and nigrostriatal
degeneration show far more severe
eye movement deficits. For example, the eye movements of PSP are
characterized by interruption
of fixation by numerous square wave jerks, very slowed saccadic speeds,
and supranuclear vertical
ophthalmoplegia, with early absence of downgaze12, 13. These signs do
not respond to L-dopa.
Accommodative paresis -- Accommodative insufficiency is a common problem
in people with PD,
causing double vision and difficulty with reading1, 33. Difficulties
with accommodation also can
result from medications, especially the anticholinergics [e.g. Artane,
Cogentin, benedryl] given to
control tremor. Despite normal convergence amplitudes, a distant near
point can be
demonstrated. Convergence insufficiency has been described as a
consistent abnormality,
contributing to asthenopia or diplopia at near33. Less often,
divergence insufficiency leads to
diplopia in the distance.
Reflex Blepharospasm and Blepharoplegia-- Eyelid abnormalities including
blepharospasm and
apraxia of eyelid opening and low blink rate are typical in PD1.
Inability to open the eyes in a
person with PD may be caused by [1] blepharospasm, either reflexive or
essential, [2] apraxia of
eyelid opening, [3] diplopia avoidance, or [4] dry eyes. Both
Essential Blepharospasm and
apraxia of eyelid opening have been associated with
postencephalitic-PD42 and PSP. Frontal lobe
activity may be abnormal35.
Having PD does not exempt a patient from common eye diseases such as
glaucoma,
cataract, macular degeneration, refractive errors and presbyopia.
However, blepharospasm makes
examination for these conditions especially difficult, for example, by
interfering with obtaining
intraocular pressure by applanation.
Keratitis Sicca -- Dryness of the cornea is the result of autonomic
dysfunction, exacerbated by
medications1. Seborrheic dermatitis affecting the lids and face is
common, especially in patients
with compromised hygiene. Tear secretion is reduced with abnormal
composition, and chalazia
[styes] may develop. A poor tear film also results from infrequent
blinking24. Eye pain and
blurred vision frequently are caused by corneal surface abnormalities.
Infrequent Blinking -- Infrequent blinking contributes to the wide-eyed
expressionless stare
characteristic of PD. Hypokinesia of the levator make the lids appear
retracted. The blink rate
may be as low as 1-2 per minute [nl 16-18 per minute]24. This
complicates management of the dry
eye syndrome.
No hemianopsia-- except after pallidotomy. Visual fields have not been
shown to be abnormal in
patients with PD, except after surgical procedures, such as
pallidotomy. In the early years of this
surgery, as many as 40% of patients were left with contralateral
homonymous hemianopsias
resulting from involvement of the optic tract in the lesion intended for
the adjacent ansa
lenticularis. Today, even with advanced neurosurgical methods of
recording VEPs in order to
avoid lesioning the optic tract, pallidotomy surgery still results in
contralateral superior
quadrantanopsias in 5-10% of patients4.
Sensory Abnormalities -- Although many studies of visual perception have
documented
abnormalities, few clinical correlates are apparent 28. [See TABLE]
Visual acuity may be slightly
decreased in PD patients compared with controls 23 ,33 but more often it
is normal after careful
refraction and corneal wetting. Performance has been impaired on some
more complex sensory
tests. Contrast sensitivity [CS] is abnormal 8, 25, especially the form
of the CS curve 6, 7, 8. This
reflects diminished CS at intermediate and high frequencies, with
relative absence of the low
frequency drop-off. Similarly, latency of the VER is delayed to
sinusoidal gratings of medium to
high spatial frequency 5, 25. This has been interpreted as an indication
that retinal dopaminergic
cells are involved in refinement of center-surround receptive field
organization7. The finding that
the CS abnormality is greater for horizontal than for
vertically-oriented gratings was interpreted
to implicate cortical function, since orientation selectivity is a
property of cells in the visual cortex
40. However, this might also reflect paucity of eye movements affecting
viewing of the gratings.
The degree of delay is correlated with motor impairment, with
improvement shown after L-Dopa
20, 25, 29.
Poor performance on color discrimination has been reported, not
improved by medication
2, 9, 32. Color vision in the blue/yellow axis seems particularly
affected18. Pattern ERG's show
decreased amplitudes17, 29, 31.
Temporal functions have been ascribed to amacrine cell abnormalities.
Flicker thresholds
are impaired 7. Decreased motion detection has been reported. Simple
visual attention is normal,
but more complex tasks may be affected3.
Hallucinations are common in patients with PD, occurring in 25-40% of
patients. Patients who
experience hallucinations are usually older, have poor vision, or are
receiving medications. As
many as 10% may also have auditory hallucinations21 .
Oculogyric Crises -- This unusual ocular deviation was a hallmark of
postencephalitic Parkinson's
(common after the pandemic influenza outbreak of 1916-1930) and is
rarely seen nowadays
