·
The distinction
between a preganglionic (i.e., first- and
second-order Horner's syndrome) and a postganglionic (i.e., third-order
Horner's syndrome) lesion can be made pharmacologically. Cocaine drops dilate normal pupils but not
pupils with sympathetic paresis independent of the level of the lesion. Hydroxyamphetamine
does not dilate the miotic pupil in Horner's disease
if it results from a third-order neuron lesion but does dilate normal and
first- and second-order Horner's pupils.
Area
of Nerve Lesions
|
Involved
Cranial Nerves
|
Orbital apex
|
II, III,
IV, VI
|
Superior orbital
fissure
|
III, IV, V1, VI
|
Cavernous sinus
|
III, IV, V1, V2, VI
|
·
Clinically the function of the extraocular eye muscles is tested using the “H” test with the medial rectus tested by
horizontally crossing one’s eyes and the lateral rectus tested by moving the
eye laterally (abducing). From either full adduction or abduction the the eye is then moved in a second direction. When fully adducted, gazing below the horizon
tests the superior oblique muscle. Remember “SO” look like the edge of the nose
“S” forming the ala and “O” the nostril). When fully adducted raising the eye
above the horizon tests the inferior oblique muscle. When fully abduced, gazing below
the horizon tests the inferior rectus muscles. When fully abduced,
raising the eye above the horizon tests the superior rectus muscle.
·
Versions
also known as conjugate movements, are synchronous (simultaneous)
symmetric movements of both the eyes in the same direction. For example:
Dextroversion
is the movement of both eyes to the right.
Levoversion
is the movement of both eyes to the left.
·
Vergences,
also called as disjugate movements, are synchronous
and symmetric movements of both eyes in opposite directions, e.g.:
Convergence is simultaneous inward
movement of both the eyes.
Divergence is simultaneous outward
movement of both the eyes.
·
Synergists
are the muscles which have a similar primary action in the same eye,
e.g., superior rectus and inferior oblique of the same eye act as synergistic
elevators.
·
Antagonists
are the muscles which have opposite actions in the same eye, e.g.,
superior and inferior recti are the antagonists to
each other in the same eye.
·
Yoke muscles (contralateral synergists) are a pair of
muscles (one from each eye) which contract simultaneously during version
movements.
·
Hering’s law of equal innervations: According to it,
an equal and simultaneous innervation flows from the
brain to a pair of muscles which contract simultaneously (yoke muscles) in
different binocular movements, e.g., during dextroversion,
right lateral rectus muscles and left medial rectus muscles receive an equal
and simultaneous flow of innervation.
·
Sherrington’s law of reciprocal innervations:
According to it, during ocular movements an increased flow of innervation to the contracting muscles is accompanied by a
simultaneous decreased flow of innervation to the
relaxing antagonists. For example, during dextroversion
an increased innervational flow to the right lateral
rectus and left medial rectus is accompanied by a decreased flow to the right
medial rectus and left lateral rectus muscles.
·
Suppression
is a temporary active cortical inhibition of the image of an object formed on
the retina of the squinting eye. This phenomenon occurs only during binocular
vision (with both eyes open). It can be tested by Worth’s
four-dot test.
·
Methods by which
angle of squint can be measured:
1. Hirschberg’s
corneal reflex test
2. Prism
bar cover test (PBCT)
3. By
synoptophore (major amblyoscope)
4. Krimsky’s corneal reflex test
5. Perimeter
method
·
Nystagmus
is an abnormal involuntary rhythmic eye movement that
may be induced by having the patient follow a rapid finger movement or can
occur at rest. It consists of a slow component (vestibular) as the eye deviates
in one direction followed by a rapid corrective movement (cerebral) in the
opposite direction. Nystagmus is usually named for
the rapid component. End-point nystagmus occurs when a person is asked to gaze
too far laterally. Asymmetric lateral nystagmus occurs in only one direction of
lateral gaze and is seen in patients with vestibular disease. Up-beating, down-beating, and rotary nystagmus are seen in patients with
brainstem disease, and congenital nystagmus that
typically disappears with convergence is seen in newborns. In pendular nystagmus,
movements are of equal velocity in each direction. In jerk nystagmus, the
movements have a slow component in one direction and a fast component in the
other direction. The direction of jerk nystagmus is
defined by direction of the fast component.
·
·
direct ophthalmoscopy:
1.
Papillitis
2.
Papilloedema
3.
Optic atrophy
4.
Glaucomatous cupping
·
direct/ indirect ophthalmoscopy:
- Diabetic retinopathy
- Hypertensive retinopathy
- Retinal detachment
- Retinitis pigmentosa
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