Download Physiological-clinical importance of the eye.

Physiologicalclinical
importance of
the eye.
Prof James Ker
MBChB, MMED, MRCP,
FRCP, PhD, FESC, FACC,
L.Akad.SA
12012
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Physiological purpose of the
visual system:
 The
visual system provides a supremely
efficient means for the rapid assimilation
of information from the environment to
aid in the guidance of behavior.
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The act of seeing:

Begins with the capture of images focused
by the cornea and lens upon the retina.

Retina—a light sensitive membrane in the
back of the eye. Actually a part of the brain,
banished to the periphery to serve as a
transducer for the conversion of patterns of
light energy into neuronal signals.
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 Light
is absorbed by photopigment in 2
types of receptore: Rods and cones.
 100
million rods
 5 million cones
 The rods operate in dim conditions and
the cones under daylight conditions
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 The
cones is specialized for color
perception and high spatial resolution.
 The
majority of cones are located in the
macula, the portion of the retina serving
the central 10 degrees of vision.
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The fovea:
 This
is a small pit in the middle of the
macula, packed exclusively with cones
and provides the best visual acuity.
 Photoreceptors
hyperpolarize in response
to light and activates bipolar, amacrine
and horizontal cells in the inner nuclear
layer.
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 The
flow of sensory information converges
upon a final common pathway: the
ganglion cells.
 The
ganglion cells translate these into
action potentials that propagates along
the primary optic pathway to visual
centers in the brain.
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 There
are a million ganglion cells in each
retina and thus a million fibers in each
optic nerve.
 The
majority of fibers synapse upon cells in
the lateral geniculate body, a thalamic
relay station. Cells from the lateral
geniculate body then projects to the
visual cortex.
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 This
massive retinogeniculocortical sensory
pathway provides the neural pathway for
visual perception.
 The
lateral geniculate body is the main
target of the retina, however some
gangion cells project to other subcortical
visual nuclei , involved in different
functions.
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 These
include:
 Pupillary
reflexes
 Circadian rhythms
 Visual orientation and eye movements
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Clinical importance:


Primary disease processes affecting the eye
Systemic disease assessment: Hypertension and
diabetes, vasculitis


Cardiac disease: Infective endocarditis


Morphine: miosis
Optic neuritis: Toxins (ethambutol, methanol)


Skew deviation
Drug intoxications


Arcus cornealis; Hollenhorst plaque
Brainstem disorders


Roth Spots
Hypercholesterolemia


Hypertension: hard/soft exudates
Pallor of disc
Optic neuritis due to MS
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 Intracranial
hypertension
 Papilloedema

Without hypertension: Hypercarbia
 Primary
metabolic disorders, such as
Wilson`s disease: Kayser-Fleischer ring
 Copper
 Circadian
blind
deposition around eyes
rhythm implications for the
 Endocrinopathy:
cortisol & GH
hormone disturbances: