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09 Nov 09

Proteinuria: how to evaluate an important finding. — Cleveland Clinic Journal of Medicine

approach to a patient with proteinuria

www.ccjm.org/...535.full.pdf+html - Preview

Is digoxin a drug of the past? — Cleveland Clinic Journal of Medicine

digoxin MOA diagram
digoxin blocks sodium-pot atpase pump & thus prevents removal of sodium ions from cell . this low ECF sodium inturn stops sodium-calcium exchanger to remove calcium from cell.

www.ccjm.org/...821.full.pdf+html - Preview

Skin Lesion Nomenclature Tutorials

www.pediatrics.wisc.edu/...master.html - Preview

clinicalmed dermatology

Demonstrations - Thyroid Exam - Physical Diagnosis Skills - University of Washington School of Medicine

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clinicalmed thyroid

Neurological Examination

great detail

neuroexam.med.utoronto.ca - Preview

clinicalmed Neurology starred

08 Nov 09

Findings - Ethnographic Study Looks at Gossip in the Workplace - NYTimes.com

when going gets tough, when gossip gets mean, one reliable escape line: DON'T WE HAVE SOME WORK TO DO HERE?

www.nytimes.com/...03tier.html - Preview

If, say, an office rival seems poised to trash one of your absent allies, Dr. Hallett suggests you make a “pre-emptive positive evaluation.” A quick “Isn’t she doing a great job?” might be enough to stop the attack.
If your rival tries persisting with indirect sarcasm — “Oh, real great job” — you can force the issue by calmly asking what that means. That simple question, a dare made in a pleasant voice, often silenced the sarcastic gossips observed by Dr. Hallett.
1 more annotations...
- When the going gets tough, when the gossip gets mean, you always have one reliable escape line: “Don’t we have some work to do here?”

07 Nov 09

AUDITORY AND VESTIBULAR PATHWAYS

thalamus.wustl.edu/...audvest.html - Preview

ENT clinicalmed

Endolymph is very similar to intracellular
fluid: it is high in potassium and low in sodium. The ionic composition
is necessary for vestibular and auditory hair cells to function
optimally. The space between the membranous and bony labyrinths
is filled with perilymph, which is very much like normal
cerebral spinal fluid.
27 more annotations...
- As the stapes vibrates the oval window, the perilymph
  sloshes back and forth, vibrating the round window in a complementary
  rhythm. The membranous labyrinth is caught between the two, and
  bounces up and down with all this sloshing
- As with almost all sensory neurons (the exception is in the retina),
  its cell body lies outside the CNS in a ganglion. In this case,
  the ganglion is stretched out along the spiralling center axis
  of the cochlea, and is named the spiral ganglion.
- basilar membrane is actually thinner and narrower
  at the base of the cochlea than at the tip (apex), which seems
  backwards given that the cochlea is widest at the base. The properties
  of the basilar membrane change as its shape changes; just as with
  guitar strings, thin things vibrate to high pitches, and thick
  things vibrate to low pitches. This means that the basilar membrane
  vibrates to high frequencies at the base of the cochlea and to
  low frequencies at the apex. A hair cell at the base of the cochlea
  will respond best to high frequencies, since at those frequencies
  the basilar membrane underneath it will vibrate the most. The
  key idea is that although the hair cells are arranged in order
  along the basilar membrane, from high-frequency to low-frequency,
  it is the properties of the basilar membrane that set up this
  gradient, not the properties of the hair cells.
- outer hair cells help to "sharpen the tuning".
  Outer hair cells can actually move (change length) in response
  to nerve stimulation. If they could push the basilar membrane
  up and down, they could amplify or damp vibrations at will, making
  the inner hair cells more or less responsive. (Just like you
  can push a child higher and higher on a swing or bring her to
  a halt - it's all in when you push.)
- Something about this tight connection allows the timing of the
  signal to be preserved to the microsecond (action potentials are
  on the order of milliseconds, so it is no mean feat). The ventral
  cochlear nucleus cells then project to a collection of nuclei
  in the medulla called the superior olive. In the superior
  olive, the minute differences in the timing and loudness of the
  sound in each ear are compared, and from this you can determine
  the direction the sound came from. The superior olive then projects
  up to the inferior colliculus via a fiber tract called
  the lateral lemniscus.
- The second stream of information starts in the dorsal
  cochlear nucleus. Unlike the exquisitely time-sensitive localization
  pathway, this stream analyzes the quality of sound. The dorsal
  cochlear nucleus, with fairly complex circuitry, picks apart the
  tiny frequency differences which make "bet" sound different
  from "bat" and "debt". This pathway projects
  directly to the inferior colliculus, also via the lateral lemniscus.
- Notice that both pathways are bilateral. The consequence
  of this is that lesions anywhere along the pathway usually have
  no obvious effect on hearing. Deafness is essentially only caused
  by damage to the middle ear, cochlea, or auditory nerve.
- From the inferior colliculus, both streams of information
  proceed to sensory thalamus. The auditory nucleus of thalamus
  is the medial geniculate nucleus. The medial geniculate
  projects to primary auditory cortex, located on the banks
  of the temporal lobes.
- Fibers from the cochlear nuclei
  and the superior olive (not the inferior) travel up the
  lateral lemniscus (not the medial) to the inferior
  colliculus (not the superior), and then to the medial geniculate
  (not the lateral). Try remembering the mnemonic,
  
  "S-L-I-M" .
- You must be able
  to detect rotation, such as what happens when you shake or nod
  your head. In physics, this is called angular acceleration.
  You must also be able to detect motion along a line - such as
  what happens when the elevator drops beneath you, or on a more
  subtle note, what happens when your body begins to lean to one
  side. This is called linear acceleration. The vestibular
  system is divided into two receptor organs to accomplish these
  tasks.
- semicircular canals detect angular acceleration
- continuous endolymph-filled
  hoop. The actual hair cells sit in a small swelling at the base
  called the ampula.
- hair cells are arranged as a single tuft that
  projects up into a gelatinous mass, the cupula. When you
  turn your head in the plane of the canal, the inertia of the endolymph
  causes it to slosh against the cupula, deflecting the hair cells.
  Now, if you were to keep turning in circles, eventually the fluid
  would catch up with the canal, and there would be no more pressure
  on the cupula. If you stopped spinning, the moving fluid would
  slosh up against a suddenly still cupula, and you would feel as
  though you were turning in the other direction.
- Each tuft of hair cells is polarized
  - if you push it one way, it will be excited, but if you push
  it the other way, it will be inhibited. This means that the canals
  on either side of the head will generally be operating in a push-pull
  rhythm; when one is excited, the other is inhibited
- if both sides push at once,
  then you will feel debilitating vertigo and nausea. This is the
  reason that infections of the endolymph or damage to the inner
  ear can cause vertigo. However, if one vestibular nerve is cut,
  the brain will gradually get used to only listening to one side
  - this can actually be a treatment for intractable vertigo.
- semicircular canals exert direct control over
  the eyes, so they can directly compensate for head movements.
  Recall that the eye is controlled by three pairs of muscles;
  the medial and lateral rectus, the superior and inferior rectus,
  and the inferior and superior oblique. You may also remember
  that their directions of motion seemed to be at crazy diagonals.
  Those same crazy diagonals are matched closely by the three planes
  of the semicircular canals, so that a single canal (in general)
  interacts with a single muscle pair. The entire compensatory
  reflex is called the vestibulo-ocular reflex (VOR).
- If you move your head to the left, you will excite
  the left horizontal canal, inhibiting the right. To keep
  your eyes fixed on a stationary point, you need to fire the right
  lateral rectus and the left medial rectus, to move the eyes to
  the right.
- The pathway is as follows: the vestibular nerve
  enters the brainstem and synapses in the vestibular nucleus.
  Cells that received information from the left horizontal canal
  project to the abducens nucleus on the right side, to stimulate
  the lateral rectus. They also project to the oculomotor nucleus
  on the left side, to stimulate the medial rectus. Although not
  shown on the diagram, the same vestibular cells also inhibit the
  opposing muscles (in this case, the right medial rectus, and the
  left lateral rectus).
- right horizontal
  canal is wired to the complementary set of muscles. Since it
  is inhibited, it will not excite its target muscles (the right
  medial rectus and the left lateral rectus), nor will it inhibit
  the muscles you want to use
- A great deal of the VOR axon traffic travels via
  a fiber highway called the MLF (medial longitudinal fasciculus).
  The integrity of this tract is crucial for the VOR to work properly.
  It is occasionally damaged by medial brainstem strokes.
- The utricle and saccule detect linear acceleration.
  Each organ has a sheet of hair cells (the macula) whose cilia
  are embedded in a gelatinous mass, just like the semicircular
  canals. Unlike the canals, however, this gel has a clump of small
  crystals embedded in it, called an otolith (yes, all along you've
  had rocks in your head). The otoliths provide the inertia, so
  that when you move to one side, the otolith-gel mass drags on
  the hair cells. Once you are moving at a constant speed, such
  as in a car, the otoliths come to equilibrium and you no longer
  perceive the motion.
- single
  sheet of hair cells can detect motion forward and back, side to
  side. Each macula can therefore cover two dimensions of movement.
  The utricle lays horizontally in the ear, and can detect any
  motion in the horizontal plane. The saccule is oriented vertically,
  so it can detect motion in the sagittal plane (up and down, forward
  and back).
  
  A major role of the saccule and utricle is to keep
  you vertically oriented with respect to gravity. If your head
  and body start to tilt, the vestibular nuclei will automatically
  compensate with the correct postural adjustments. This is not
  just something that happens if the floor tilts - if you watch
  someone trying to stand still, you will notice constant small
  wavers and rocking back and forth.

Aequanimitas | Life in the Fast Lane

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The title of this page, Aequanimitas, gives due reverence to the great hero of modern clinical medicine, Sir William Osler. Osler enthusiastically encouraged his medical colleagues to embrace interests outside of the profession to protect, preserve and promote their ability to maintain their equanimity despite the daily struggles of being a doctor.
Osler enthusiastically encouraged his medical colleagues to embrace interests outside of the profession to protect, preserve and promote their ability to maintain their equanimity despite the daily struggles of being a doctor
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- “But whatever you do, take neither yourselves nor your fellow-creatures too seriously. There is tragedy enough in our daily routine, but there is room too for a keen sense of the absurdities and incongruities of life, and in the shifting panorama no one sees better than the doctor the perennial sameness of men’s ways
- “It helps a man immensely to be a bit of a hero-worshipper, and the stories of the lives of the masters of medicine do much to stimulate our ambition and rouse our sympathies”

Become a PowerPoint Power User - Wired How-To Wiki

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06 Nov 09

Receptive field - Wikipedia, the free encyclopedia

en.wikipedia.org/...Receptive_field - Preview

There are two types of bipolar cells: "on-center" and "off-center". An on-center cell is stimulated when the center of its receptive field is exposed to light, and is inhibited when the surround is exposed to light. Off-center cells have just the opposite reaction.
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- Stimulation of the center of an on-center cell's receptive field produces depolarization and an increase in the firing of the ganglion cell, stimulation of the surround produces a Hyperpolarization and a decrease in the firing of the cell, and stimulation of both the center and surround produces only a mild response (due to mutual inhibition of center and surround). This prevents an overload of signals to the brain. An off-center cell is stimulated by activation of the surround and inhibited by stimulation of the center
- The center-surround receptive field organization allows ganglion cells to transmit information not merely about whether photoreceptor cells are exposed to light, but also about the differences in firing rates of cells in the center and surround. This allows them to transmit information about contrast.
- The receptive field tends to favor movement (such as a light or dark spot moving over the field, as in center-to-periphery (or vice versa)), as well as contours (due to their nonuniformity in the receptive fields).

Eye and Retina

thalamus.wustl.edu/...eyeret.html - Preview

retina, seven
layers of alternating cells and processes which convert a light
signal into a neural signal ("signal transduction").
The actual photoreceptors are the rods and cones,
but the cells that transmit to the brain are the ganglion cells.
The axons of these ganglion cells make up the optic nerve
pupillary sphincter muscle constricts the pupil like a purse-string, and is under the control of the parasympathetic system. Therefore it is innervated by fibers from the oculomotor nerve which originate in the Edinger-Westphal nucleus of the midbrain.
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- pupillary dilator muscle is composed of radial fibers which pull the pupil open, and is controlled by the sympathetic system. Therefore it is innervated by post-ganglionic sympathetics from the superior cervical ganglion.
- zonule fibers - hold the lens stretched out into
  a more disc-like shape. This shape allows for far-focusing. What
  happens when you need to near-focus? At this point the ciliary
  body, a hoop-like structure that supports the zonule fibers,
  comes into play. Imagine a spiderweb built into the opening of
  a drawstring purse, suspending a disk in the opening. When the
  purse is open, the spiderweb is taut. If you pull the drawstring,
  however, the web will go slack and collapse on itself. The ciliary
  body is the drawstring purse, in this analogy. The ciliary
  muscle within it is the drawstring. When the ciliary muscle
  contracts (this is also under parasympathetic control), the zonule
  fibers go slack, the suspended lens is released from their tension,
  and it is free to round up. This change is necessary for near-focusing.
  The entire process of adjusting the focus to different distances
  is called accommodation.
- retina is a seven-layered structure
  involved in signal transduction. In general, dark "nuclear"
  or "cell" layers contain cell bodies, while pale "plexiform"
  layers contain axons and dendrites.
- In the OPL photoreceptor axons
  contact the dendrites of bipolar cells and horizontal cells. Horizontal
  cells are interneurons which aid in signal processing.
- In the IPL, bipolar axons contact
  ganglion cell dendrites and amacrine cells, another class of interneurons
- The ganglion cells of the GCL send
  their axons through the OFL to the optic disk to make up the optic
  nerve. They travel all the way to the lateral geniculate nucleus.
- fovea defines the center of the retina, and is the region of highest visual acuity. The fovea is directed towards whatever object you wish to study most closely - this sentence, at the moment. In the fovea there are almost exclusively cones, and they are at their highest density.
  The ratio of ganglion cells : photoreceptors is about 2 :1 here, the highest in the eye. In addition, at the fovea all of the other cell types squeeze out of the way to allow the most light to hit the cones. This makes the fovea visible microscopically. The blood vessels also skirt a wide margin around the fovea. The area in and around the fovea has a pale yellow pigmentation that is visible through an ophthalmoscope, and is called the macula.
- ganglion cell axons all leave
  the eyeball at one location, the optic disk. At the optic
  disk all photoreceptors and accessory cells are pushed aside so
  the axons can penetrate the choroid and the sclera. This creates
  a hole in our vision, the blind spot. Normally each eye covers
  for the blind spot of the other, and the brain fills in missing
  information with whatever pattern surrounds the hole. Therefore
  we are not conscious of the blind spot.
- Most cones lie in the fovea, whereas
  peripheral vision is dominated by rods. Overall, rods greatly
  outnumber cones. Review the characteristics of rods (black and
  white vision, very sensitive to low light) and cones (color vision,
  not so sensitive) and explain these phenomena:
  
  1. To see a faint star, you cannot
  look directly at it, but must look slightly to the side.
  
  2. A person with macular degeneration
  can become functionally blind, yet their night vision is not really
  affected. How would their color perception be?
- - The cornea is continuous
  with the sclera, which in turn is continuous with the dura.
  
  - The choroid, a highly vascular,
  highly pigmented layer between the sclera and the retina, is continuous
  with the ciliary body and the iris. Do not confuse it with the
  pigment epithelium.
  
  - The pigment epithelium is
  a single cell layer thick, and comes from the outer layer of the
  original optic cup (a classic embryological "pushed-in
  ball"). In the mature retina it is pushed directly up next
  to the neural retina, which came from the inner layer of the optic
  cup. They are not fused together, however, and can separate along
  the old plane - a "separated" or "detached"
  retina.
- If you were to record from a photoreceptor,
  you would find that it was "ON" (hyperpolarized, paradoxically)
  whenever light shone on it. If you recorded from a ganglion cell
  instead, you would find that diffuse light did little to the cell.
  However, the cell would respond well to a small spot of light,
  a small ring of light, or a light-dark edge. We say that this
  cell has a center-surround receptive field - the center
  must be mainly light and the surround mainly dark, or vice versa.
  What happens between the outer segment and the ganglion cell?
  This complex receptive field is created by the interneurons of
  the retina: the bipolar cells and the horizontal cells, primarily.
- neighbor cones also excite horizontal cells. The horizontal cells send processes laterally and inhibit the center bipolar cell.
  
  So, what does diffuse light do? It excites the central bipolar cell, but also inhibits it via the neighbors. Result - the ganglion cell does not get excited. It continues to tick along at its normal, tonic rate.
- our entire
  visual system exists to see borders and contours. We see the world
  as a pattern of lines, even things as complex as a face. We judge
  colors and brightness by comparison, not by any absolute scale.
  (Don't believe it? Put that teal scarf next to a blue shirt, you'll
  call it green. On a green coat, you'll call it blue.) This system
  of lateral inhibition in the retina is the first step towards
  sharpening contours and picking up on borders between light and
  dark. Diffuse light is ignored by the ganglion cell, but a sharp
  dot will really turn it on. Higher up in the cortex, all these
  dots will be combined into lines, which will be combined into
  curves, etc, etc.

Eye, Brain, and Vision

hubel.med.harvard.edu/b9.htm - Preview

ophthalmology clinicalexEYE

Left:
Four recordings from a typical on-

center retinal ganglion cell. Each record is a

single sweep of the oscilloscope, whose

duration is 2.5 seconds. For a sweep this

slow, the rising and falling phases of the

impulse coalesce so that each spike appears

as a vertical line. To the left the stimuli are

shown. In the resting state at the top, there

is no stimulus: firing is slow and more or

less random. The lower three records show

responses to a small (optimum size) spot, a

large spot covering the receptive-field cen-

ter and surround, and a ring covering the

surround only. Right: Responses of an off-

center retinal ganglion cell to the same set

of stimuli shown at the left.
2 more annotations...
- The
  two main types of retinal-ganglion-cell
  
  receptive fields are on center, with inhibi-
  
  tory surround, and off center, with excita-
  
  tory surround. "+" stands for regions giv-
  
  ing on responses, "—" for regions giving
  
  off responses.
  
  A
  cross section of the retina, about mid-
  
  way between the fovea and far periphery,
  
  where rods are more numerous than cones.
  
  From top to bottom is about one-quarter
  
  millimeter.

Central Visual Pathways

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clinicalexEYE ophthalmology

ganglion cell axons leave the retina, they
travel through the optic nerve
optic tract wraps around the cerebral
peduncles of the midbrain to get to the lateral geniculate
nucleus (LGN). The LGN is really a part of the thalamus,
and remember that nothing gets up to cortex without synapsing
in thalamus first (if the cortex is the boss, the thalamus is
an excellent secretary). Almost all of the optic tract axons,
therefore, synapse in the LGN. The remaining few branch off to
synapse in nuclei of the midbrain: the superior colliculi
and the pretectal area.
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- LGN send their axons directly
  to V1 (primary visual cortex, striate cortex, area 17)
  via the optic radiations. This highway of visual information
  courses through the white matter of the temporal and parietal
  lobes, and can be very vulnerable to strokes.
- What we see can be divided into several categories
  of vision: color, linear pattern, motion, etc.
- rods see only black and white, and can function in dim
  light, whereas cones can see all colors but require full light.
- small ganglion cells that dominate in the fovea: they are
  color sensitive and are "fine-grained", meaning their
  receptive fields are small enough that they can pick up a high
  level of detail. These small cells are called P cells
  (P for parvo for small). The second type of ganglion
  cells have large dendritic arrays, and receive information from
  a wide radius of bipolar cells. They are mostly found in the
  peripheral retina, are not color-sensitive, and are "coarse-grained"
  and relatively insensitive to detail. Their main asset is that
  they are sensitive to motion - you can imagine that due to their
  width they can track a signal flashing across several bipolar
  cells. These are the M cells (M for magno ).
- These two types of information, motion vs. color
  and form, are maintained in separate compartments all the way
  up the visual pathway. They are kept in separate layers in the
  LGN, enter V1 via separate sublayers (4Ca vs. 4Cb), and after
  passing through V2, go on to separate areas of associative cortex.
  In the end, the parietal visual cortical areas (such as
  MT and PP) end up dealing with motion of objects, navigation through
  the world, and spatial reasoning (which is essentially moving
  things around in your head). Temporal visual areas (such
  as V4 and IT) are involved with the complex perception of patterns
  and forms as recognizable objects.
- few optic tract fibers which bypassed the LGN
  entirely, traveling instead to the less glamorous but equally
  essential midbrain. One of their targets in the midbrain is the
  pretectal area, which mediates the pupillary light reflex.
  This reflex can be demonstrated by shining a light in one eye;
  if all is working correctly, both pupils will constrict.
- directly
  to the pretectal area. After synapsing, the information is sent
  to the Edinger-Westphal nuclei on both sides of
  the midbrain - this is the crucial step in ensuring that both
  eyes react to light. The Edinger-Westphal nuclei, via the IIIrd
  nerve, control the pupillary constrictors that narrow the
  pupils

The W.U.S.M. Neuroscience Tutorial

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Basic visual pathway

thalamus.wustl.edu/...basvis.html - Preview

clinicalexEYE ophthalmology

lateral geniculate
nucleus (LGN), where all the axons must synapse. From there,
the LGN axons fan out through the deep white matter of the brain
as the optic radiations, which will ultimately travel to
primary visual cortex
The image projected onto your retina can be cut
down the middle, with the fovea defining the center.
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- right nasal retina and
  the left temporal retina see pretty much the same thing. If you
  drew a line through the world at your nose, they would see everything
  to the right of that line. That field of view is called the right
  hemifield.
- left half of the brain is only interested in visual
  input from the right side of the world. To insure that the brain
  doesn't get extraneous information, the fibers from the retina
  sort themselves out to separate right hemifield from left hemifield.
  Specifically, fibers from the nasal retinas cross over at
  the optic chiasm - whereas the temporal retinas, already positioned
  to see the opposite side of the world, do not cross.
- before the chiasm will affect one
  eye, both hemifields - analogous to closing one eye. Damaging
  the pathway after the chiasm, though, will damage parts of both
  eyes, and only one hemifield. There is no easy way to imagine
  what this would look like. Your field of view would be only 90°,
  from straight ahead to one side.
- strike through a pathway, follow the fibers back
- record a loss of visual field
  is with two circles, called "perimetry charts" as below.
  You can think of these circles as a pair of goggles that the
  patient is looking through, and you blacken those parts of the
  goggles where vision is lost.
- longer loop actually dives into
  the temporal lobe before it heads back to the occipital lobe.
  This group of fibers is called Meyer's loop. Recall that, since
  the lens inverts all images, the lower half of the retina sees
  the upper half of the world. This orientation is preserved through
  the pathway, so that the lower optic radiations, or Meyer's loop,
  are carrying information from the upper visual world.
- calcarine sulcus on the medial surface
  of the occipital lobe. Primary visual cortex, or V1, is
  buried within this sulcus. In a fortuitous section, you may be
  able to see a fine white stripe running within the grey matter
  inside the sulcus. This stripe marks V1, and gives it a third
  name, striate cortex.

Study Hacks » Blog Archive » The Shadow Course: A Simple Technique to Produce Extraordinary Work

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academics starred

…reformat your notes into study guides that are ready for review.
…fill in holes in your knowledge by going to back to the textbook and preparing targeted questions for your TA.
2 more annotations...
- Imagine how much better you would have performed on your last test or paper if you had been able to set aside 15 extra hours to prepare.
- To make things even better, because this time is spread out across an autopilot schedule, these hours all maintain a high intensity of focus — a feat which would be impossible if this time was condensed into a small number of long study session.

04 Nov 09

Welcome to Hansen Nursing

acid-base balance

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Human Embryology Animations

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precinicalmed embryology animation

A Practical Guide to Clinical Medicine

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clinicalexEYE ophthalmology

Damage to the nerves controlling these structures (Cranial Nerves
3 and 7) can cause the upper or lower lids on one side to appear lower then
the other.
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- invisible except for the fine blood vessels that run through
  it. When infected or otherwise inflamed, this layer can appear quite red,
  a condition known as conjunctivitis. Alternatively, the conjunctiva can appear
  pale if patient is very anemic. By gently applying pressure and pulling down
  and away on the skin below the lower lid, you can examine the conjunctival
  reflection, which is the best place to identify this finding.
- minor
  trauma (cough, sneeze, or direct blow), a bleeding disorder or idiopathic.
  The resulting collection of blood is called a subconjunctival hemorrhage.
  While dramatic, it is generally self limited and does not affect vision.
- patient is seated at a height
  such that their eyes are essentially on the same level as your own when you are
  standing next to them.
  Testing Extra-Occular Movements: Instruct the patient to follow your
  index finger with their eyes only (i.e. their head remains in one position)
  as you first move it to either the extreme right or left. Then, once you have
  the patient looking out laterally, have them follow your finger as you move
  it first up, then down. Now move your finger across to the other side and repeat.
  Your path should trace out the letter H. At the end, bring your finger directly
  in towards the patient's nose. This will cause the patient to look cross-eyed
  and the pupils should constrict, a response referred to as accommodation.
  Tracing out this path allows you to test each of the extra-occular muscles
  individually and avoids movements that are dependent on more then one muscle,
  as occurs if you have the patient look up or down while the pupil is oriented
  straight ahead. Assessments of both extra-occular movements and visual acuity
  are actually tests of cranial nerve (CN) function. CNs 3, 4, and 6 control movement
  and CN 2 vision
- Disorders of eye movement can also be due to problems with the extraocular
  muscles themselves. For example, pictured below is a patient who has suffered
  a traumatic left orbital injury. The inferior rectus muscle has become entrapped
  within the resulting fracture, preventing the left eye from being able to
  look downward.
- when the transmitted visual impulse is interrupted at
  some point in its path from the retina to the visual cortex in the back of
  the brain. You would, in general, only include a visual field assessment if
  the patient complained of loss of sight; in particular "blind spots" or "holes"
  in their vision.Visual fields can be crudely assessed as follows:
  
  The examiner should be nose to nose with the patient, separated by approximately
  8 to 12 inches.
  Each eye is checked separately. The examiner closes one eye and the
  patient closes the one opposite. The open eyes should then be staring
  directly at one another.
  The examiner should move their hand out towards the periphery of his/her
  visual field on the side where the eyes are open. The finger should be
  equidistant from both persons.
  The examiner should then move the wiggling finger in towards them, along
  an imaginary line drawn between the two persons.The patient and examiner
  should detect the finger at more or less the same time.
  The finger is then moved out to the diagonal corners of the field and
  moved inwards from each of these directions. Testing is then done starting
  at a point in front of the closed eyes. The wiggling finger is moved towards
  the open eyes.
  The other eye is then tested.
- The normal pupil constricts when either exposed directly to bright light or
  when that same light is presented to the other eye, referred to as the consensual
  response. This is due to the fact that stimulation of the afferent (i.e. sensory,
  carried with CN 2) nerves in one eye will trigger efferent (i.e. motor, carried
  with CN 3) activation and subsequent constriction of the pupils of both eyes.
  Disease affecting either the efferent or afferent limbs will alter these responses
  accordingly. Also, processes which raise intracranial pressure (e.g. brain
  tumors, collections of blood) can cause CN 3 dysfunction, resulting in dilatation
  of the pupils and uresponsiveness to direct stimulation by light. To assess
  pupillary reactions, proceed as follows:
- Instruct the patient to look towards a distant area in the room (e.g.
  the corner where the wall and ceiling meet) while keeping both of their
  eyes open. You may need to gently remind them throughout the exam to continue
  looking in that direction as it is very difficult to examine a roving eyeball.
  Do not ask them to focus on a specific object as this will lead to pupillary
  constriction.
- adjust the light intensity to mid-range
  power. The cone of light produced should be a white, medium sized circle
- assess whether each
  pupil constricts appropriately in response to direct and indirect stimulation
- size and shape of each pupil
- It may be hard to detect the consensual
  response if the lighting in your room is sub-optimal (i.e. if it's too dark,
  you won't be able to see the other eye). Note that you do not need to look
  through the viewing window of the scope to perform this part of the exam
  as you are essentially using it as a flashlight.
- lenses vary in their ability to bend light and are numbered and color coded.
  The specific lens that allows you to see something in focus will vary with
  your distance from that structure as well as the refractive error of both
  your eyes and the patients. To better examine the sclera, conjunctiva, pupil,
  cornea or iris, start with the lens identified by a green 4 or 6.
  
  Now grasp the handle with your right hand (the following instructions
  are for examining the patient's right eye) such that your middle finger
  is resting on the lower, front aspect of the head of the opthalmoscope.
  
  Bring your right eye up to the viewing window. While you can either wear
  or remove your own glasses, the patient's should be taken off. It's OK to
  leave contacts in place.
  
  Take your left hand and place it on the patient's forehead and gently
  apply upward traction on the top lid with your thumb. This will "remind"
  them not to blink and let you know their precise location. Obviously, try
  not to poke them in the eye with this finger! Alternatively, you can place
  your left hand on the patient's shoulder as a means of keeping track of
  their location. Try to keep both of your eyes open when performing the exam
  as you might find it quite tiring to continually squint with the non-examining
  eye.
  
  Start approximately 15 cm from the patient and approach from about 15
  or 20 degrees to the left of center. When you look through the viewing window,
  the outer structures of the eye should come into sharp focus. If not, slowly
  move closer or further from the patient until these structures become clear.
  It takes a bit of experimentation to find the lens that is right for any
  given distance, so make lens changes slowly by rotating the adjustment wheel.
  There is no magic way of guessing which lens will allow the sharpest view.
  
  *Most clinicians don't perform a detailed examination of the outer
  structures of the eye if the patient has neither obvious abnormalities nor
  complaints referable to this region.
- Viewing the Fundus (the retina and associated structures):
- Repeat steps 1 thru 5 as above. Adjust the lens selection wheel
  so that 0 appears in the display window.
- You should see a sparkly, orange-red
  color known as the red reflex. This is caused by light reflecting
  off of the retina
- translucent structures which
  allow light to pass unimpeded from outside the eye to the retina become
  opacified and the red reflex is lost. In adults, this is most commonly
  associated with cataracts
- Your middle finger, the one resting
  on the low front of the head piece, should be on or near the patient's cheek.
  Starting with the 0 lens in place, rotate the adjustment wheel counter clockwise.
  If you change lenses too quickly, you'll probably whizz right by the one
  that gives the sharpest picture, so be patient. In the event that this does
  not bring anything into focus, trying rotating the adjustment wheel in the
  opposite direction. It doesn't really matter what number lens is required
  to achieve the clearest view. Again, this will vary with the refractive
  error of both you and the patient.
- Once you're close in and have the retina
  in clear view, you should only need to change the lens one or two clicks
  in order to keep all structures in focus as you scan across.
  
  You will only be able to see a relatively small segment of the retina
  at any one time. Your initial view will probably be of blood vessels on
  a random patch of retina
- The retina has a refractile, orange-red appearance, varying a bit with the skin
  color and age of the patient. Fundoscopy provides important information as it
  not only enables you to detect diseases of the eyes but is also the only area
  of the body where small blood vessels can be studied with relative ease. There
  are a number of chronic systemic diseases (most commonly hypertension, diabetes
  and atherosclerosis) that affect vessels of this size
- When you first visualize the retina, you will note branching blood vessels.
  The bigger, darker ones are the veins and the smaller, brighter red structures
  the arteries. Changes in the appearance of the arteries (copper wiring)
  as well as alterations in the arterial-venous crossing pattern (a-v nicking)
  occur with atherosclerosis and hypertension respectively (see any text for
  pictures). These vessels are more obvious in the superior and inferior aspects
  of the retina, with relative sparing of the temporal and medial regions.
- Follow them
  in a direction that leads to less branching (i.e. towards the trunk). This
  will direct you towards the optic disc, the point at which the vessels enter
  the retina along with the head of the optic nerve. The edges of this round
  disc are sharp and well defined in the normal state. It should be a bit
  more yellow/orange when compared to the rest of the retina. At the center
  of the disc is the optic cup, a distinct circular area from which the blood
  vessels actually emerge. The disc is not located in the exact center of
  the retina but rather towards its medial/nasal aspect.
- If you are unable to locate the disc after following the vessels
  in one direction, simply head the other way.
- The macula is a region located lateral to the optic disc. It looks somewhat
  darker then the rest of the retina and, as opposed to the disc, has no distinct
  borders. The macula provides the sharpest vision. It can be best visualized
  by asking the patient to stare directly at the light of the opthalmoscope
  while you remain focused on a fixed area of the retina.
- To view different areas, you'll have
  to shift the angle with which you peer through the pupil. This requires
  very small movements. Try to examine the entire structure systematically,
  looking up, down, left and right. You will undoubtedly have to remind the
  patient to continue looking straight ahead, else the fundus will be in continual
  motion and you will have no chance of finding anything.

Eye Simulation Page

cim.ucdavis.edu/...eyesim.htm - Preview

clinicalexEYE ophthalmology

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