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07 Dec 09

« Neuro-Ophthalmology Lecture 1 (Ophthobook.com)

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ophthalmology

06 Nov 09

Receptive field - Wikipedia, the free encyclopedia

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ophthalmology

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, Brain, and Vision

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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

Basic visual pathway

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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.

04 Nov 09

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.
33 more annotations...
- 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

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clinicalexEYE ophthalmology

27 Oct 09

Conjunctivitis - February 15, 1998 - American Family Physician

great briefing!

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ophthalmology conjunctivitis

Ocular allergy in its many forms is one of the major causes of chronic
conjunctivitis. Blepharitis (inflammation of the eyelid margin), dry eye and
the prolonged use of ophthalmic medications, contact lenses and ophthalmic
solutions are also relatively frequent causes of chronic conjunctival
inflammation.
Differential Diagnosis of a Red Eye
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- thorough
  ocular, medical and medication history. This should establish whether the
  condition is acute, subacute, chronic or recurrent, whether it is unilateral or
  bilateral, and whether it is associated with any specific environmental or
  work-related exposure.
- tearing, irritation, stinging
  and burning are nonspecific.
- Itching is the hallmark of allergic
  conjunctivitis
- recurrent itching or a personal or family history of hay
  fever, allergic rhinitis, asthma or atopic dermatitis is also suggestive of
  ocular allergy
- Mild itching can also be a feature of blepharitis, dry eyes
  and, occasionally, bacterial or viral conjunctivitis.
- serous discharge is most commonly associated with viral or allergic
- mucoid (stringy or ropy) discharge is highly
  characteristic of allergy or dry
- mucopurulent or purulent discharge,
  often associated with morning crusting and difficulty opening the eyelids,
  strongly suggests a bacterial
- Chlamydial
- transmissible by eye-hand contact. Often,
  these infections initially present in one eye
- Algorithm for the differential diagnosis of a red eye.
- keratitis, nasolacrimal duct obstruction, occult
  foreign body and conjunctival neoplasia
- . Sebaceous cell
  carcinoma that is invading the conjunctiva and the superficial cornea
- collagen vascular disease or the use of diuretics or
  antidepressant medications should alert the physician to the possibility of dry
  eyes.
- Viral or chlamydial inclusion conjunctivitis typically presents with a
  small, tender, preauricular or submandibular lymph node. Toxic conjunctivitis
  secondary to topical medications can also produce a palpable preauricular node.
  Palpable adenopathy is rare in acute bacterial conjunctivitis. The exception is
  hyperacute conjunctivitis caused by infection with Neisseria species.
  
  Other facial clues to the etiology of conjunctivitis include the
  presence of herpes labialis or a dermatomal vesicular eruption suggestive of
  shingles.
- cultures should be obtained in patients who have severe inflammation
  (e.g., hyperacute purulent conjunctivitis) or chronic or recurrent
  conjunctivitis. Cultures also should be obtained in patients who do not respond
- copious yellow-green purulent discharge that
  reaccumulates after being wiped
- rapidly progressive
- Infected infants may also have other
  localized gonococcal infections, such as rhinitis or proctitis, or they may
  have disseminated gonococcal infection, such as arthritis, meningitis,
  pneumonia or sepsis.
- eyelids are matted together on
  awakening. Conjunctival swelling and mild eyelid edema may be noted
- S. pneumoniae and H. influenzae are
  more common in children, while S. aureus most frequently affects
  adults
- Cultures should be obtained in certain patients, including young
  children and debilitated
- Since most
  adult cases of acute bacterial conjunctivitis are caused by gram-positive
  organisms, it is best to choose an antibiotic with adequate gram-positive
  coverage (in particular, good staphylococcal coverage).
- Streptococcus
  species
  
  Gram-negative
  organisms
  
  Escherichia coli
  
  Pseudomonas species
  Moraxella species
- ointments are better tolerated by young children, who are less apt to complain
  about associated blurring of vision. Solutions are preferred by most
  adolescents and adults.
- Aminoglycosides, such as gentamicin (Garamycin), tobramycin (Tobrex)
  and neomycin are inexpensive choices for the treatment of acute bacterial
  conjunctivitis. These agents provide good gram-negative coverage, but they have
  relatively poor gram-positive coverage, including incomplete coverage of
  Streptococcus and Staphylococcus species. Furthermore, aminoglycosides are
  associated with a relatively high incidence of toxicity to the corneal
  epithelium (primarily with prolonged use). Neomycin, in particular, can cause
  local oculocutaneous allergic reactions. For this reason, topical ophthalmic
  preparations containing neomycin probably should be avoided as first-line
  therapy.
- sulfacetamide solution (Bleph-10) is still a commonly
  prescribed topical antibiotic for conjunctivitis. This bacteriostatic agent has
  weak to moderate activity against many gram-positive and gram-negative
  organisms
- Stevens-Johnson syndrome.
- Tetracycline is available only
  in an ointment form.
- Although
  chloramphenicol is generally well tolerated, topical application of this agent
  has been associated with a few cases of aplastic anemia
- Given the generally benign, self-limited nature of acute bacterial
  conjunctivitis, the high cost of topical fluoroquinolones, their poor coverage
  of Streptococcus species and the potential for developing resistant pathogens
  with indiscriminate use of this antibiotic class, the fluoroquinolones
  generally should be reserved for use in more severe ocular infections,
  including bacterial keratitis.
- Chronic
  bacterial conjunctivitis is most commonly caused by Staphylococcus species,
  although other bacteria are occasionally involved. This type of conjunctivitis
  often develops in association with blepharitis, which is a common but often
  unrecognized inflammatory condition related to bacterial colonization of the
  eyelid margins. Some cases of chronic bacterial conjunctivitis are also
  associated with facial seborrhea.
- flaky debris, erythema and warmth along
  the lid margins, as well as eyelash loss
- meibomian glands are sebaceous glands that line the posterior lid
  margin behind the eyelashes. These glands secrete an important oily component
  of the tear film. When inflamed, the meibomian glands malfunction, producing
  chronic inflammation of the eyelid margins and the conjunctiva (Figure 6),
  as well as irritating dry-eye symptoms.
- gland
  plugging
- Blepharoconjunctivitis and meibomianitis are common associated
  findings in patients with acne rosacea. This skin disorder typically affects
  adults between 25 and 50 years of age and occurs more commonly in women than in
  men. Diagnostic clues include a history of periodic facial flushing (usually in
  response to the consumption of certain foods or alcohol) and the presence of
  erythematous and telangiectatic skin changes on the forehead, cheeks, chin and
  nose. Some patients also have acneiform lesions and rhinophyma.² Ocular findings include recurrent chalazia and
  styes secondary to chronic blepharitis and meibomianitis, as well as keratitis
  and dry eyes
- Acne rosacea, with a chalazion of
  the left lower
- hygiene using warm compresses and eyelid margin
  scrubs and the application of appropriate topical antimicrobials (e.g.,
  erythromycin).⁵ Patients with meibomianitis
  and acne rosacea often benefit from oral tetracycline therapy. Systemic
  tetracyclines are contraindicated in nursing mothers, pregnant women and
  children. Topical metronidazole (Metrogel) is helpful in some patients with
  acne rosacea.
- Old trachoma, with scarring of the
  superior tarsal
- tearing, conjunctival
  inflammation, moderate discharge and eyelid swelling five to 12 days after
  birth.¹² Ophthalmic referral is essential.
  Neonatal inclusion conjunctivitis usually responds to topical antibiotics.
  However, this condition can be associated with otitis media, and respiratory
  and gastrointestinal tract infections. Such infants should be treated with a
  two-week course of systemic erythromycin.
- subacute or chronic
  infection characterized by unilateral or bilateral redness, mucopurulent
  discharge, a foreign-body sensation and preauricular adenopathy.
- Treatment consists of a two- to three-week course of oral
  tetracycline, doxycycline, minocycline (Minocin) or erythromycin. A single 1-g
  dose of azithromycin (Zithromax) is recommended for adults with lower genital
  tract infection, but a longer course may be necessary in patients with
  chlamydial conjunctivitis
- Adenovirus is by far the most common
- community epidemics, with the virus transmitted
  in schools, workplaces and physicians' offices.
- Occasionally,
  patients also have subconjunctival hemorrhage
- Some patients have an associated upper
  respiratory tract infection.
- contagious for at least seven days,
  patients should be instructed to avoid direct contact with other persons
- Cold
  compresses and topical vasoconstrictors may provide symptomatic relief. Topical
  antibiotics are rarely necessary, because secondary bacterial infection is
  uncommon
- subconjunctival hemorrhage
- follicular reaction
- Herpes simplex virus keratoconjunctivitis can closely mimic the
  presentation of ocular adenovirus infection. In such patients, topical
  corticosteroid therapy can lead to severe ocular complications as a result of
  uncontrolled virus proliferation. Therefore, topical corticosteroids should not
  be used in the management of infectious conjunctivitis unless under the
  direction of an ophthalmologist. Furthermore, viral conjunctivitis is generally
  benign and self-limited. Treatment with corticosteroids can prolong the course
  of the disease and also place the patient at risk for other steroid-induced
  ocular complications, such as glaucoma and cataracts.
- Ocular herpes simplex and herpes zoster are
  often managed with topical and/or systemic antiviral agents. Various topical
  agents, including trifluridine (Viroptic), may be helpful. Useful systemic
  antiviral agents include acyclovir (Zovirax), famciclovir (Famvir) and
  valacyclovir (Valtrex).
- intermittent bouts of itching, tearing, redness and mild eyelid
  swelling. The personal or family history is often positive for other atopic
  conditions, such as allergic rhinitis, asthma or eczema.
- allergen avoidance, cold compresses, vasoconstrictors, antihistamine drops,
  topical nonsteroidal anti-inflammatory agents and mast-cell stabilizers such as
  cromolyn sodium (Crolom) or lodoxamide
- levocabastine (Livostin), which is a topical antihistamine, and with ketorolac
  tromethamine (Acular) and diclofenac sodium (Voltaren), which are topical
  nonsteroidal anti-inflammatory
- severe
  cases, a short course of topical corticosteroids is often required for adequate
  symptomatic relief

Bacterial conjunctivitis: A review for internists - Cleveland Clinic Journal of Medicine

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ophthalmology conjunctivitis

Viral conjunctivitis typically presents as an itchy red eye with mild watery discharge. Many patients have signs and symptoms
of a viral upper respiratory tract infection (eg, cough, runny nose, congestion)
Having both eyes glued shut in the morning had an odds ratio of 15:1 in predicting a positive bacterial culture
22 more annotations...
- In neonates, conjunctivitis is predominantly bacterial, and the most common organism is Chlamydia trachomatis. Chlamydial conjuctivitis typically presents with purulent unilateral or bilateral discharge about a week after birth in
  children born to mothers who have cervical chlamydial infection. Many infants with chlamydial conjunctivitis develop chlamydial
  pneumonitis: approximately 50%
- Neisseria gonorrhoeae is a rare cause of neonatal conjunctivitis. The onset is somewhat earlier than in chlamydial conjunctivitis, ie, in the first
  week of life, and this organism classically causes severe “hyperacute” conjunctivitis with profuse discharge and may result
  in corneal involvement and perforation.
- In children, bacterial conjunctivitis is most often caused by H influenzae or S pneumoniae, which accounted for 29% and 20%
- H influenzae conjunctivitis spreads easily in schools and households. It is associated with concurrent upper respiratory tract infections
  and otitis media (conjunctivitis-otitis syndrome): 45% to 73% of patients with purulent conjunctivitis also have ipsilateral
  otitis media
- S pneumoniae, the second most common cause of bacterial conjunctivitis in children, is a common cause in epidemic
- S pneumoniae is also associated with conjunctivitis-otitis syndrome
- In adults, the most common causes of bacterial conjunctivitis are S aureus and H influenzae. Conjunctivitis caused by S aureus is often recurrent and associated with chronic ble-pharoconjunctivitis (inflammation of the eyelid and conjunctiva). The
  conjunctivae are colonized by S aureus in 3.8% to 6.3% of healthy adults.^9–11 In addition, about 20% of people normally harbor S aureus continually in the nasal passages
- chronic dry eye and lagophthalmos (in which the eye cannot close completely)
  may predispose the eye to frequent infections. Also, an adjacent focus of infection, such as inflammation of the lacrimal
  gland (dacryocystitis), can cause recurrent or chronic conjunctivitis
- Acute bacterial conjunctivitis typically presents abruptly with red eye and purulent drainage without significant eye pain,
  discomfort, or photophobia
- red eye with purulent discharge persisting for longer than a few weeks, is generally
  caused by Chlamydia trachomatis or is associated with a nidus for infection such as in dacryocystitis.
- Viral conjunctivitis is often epidemic and is easily contagious. Several epidemics have been traced to eyecare facilities.
  Adenovirus
- itching and redness of both eyes in response to an allergen exposure. Other allergic
  symptoms may be present, such as allergic rhinosinusitis, asthma, or atopic dermatitis
- gonococcal conjunctivitis with ceftriaxone (Rocephin)
  1 g in a single intramuscular
- same as for pneumonia
  caused by C trachomatis: erythromycin taken orally for 14 days. In adults, it can be treated with a single oral dose of azithromycin
- Other types of bacterial conjunctivitis usually resolve spontaneously: early placebo-controlled studies found that more than
  70% of cases of bacterial conjunctivitis resolve within 8 days
- reduces the chance of rare complications²⁷ and of transmitting
- in the hospital the organisms and their antibiotic resistance patterns
  are more varied, so culturing the conjunctiva before starting broad-spectrum therapy may be warranted
- topical ophthalmic antibiotics can induce resistance among colonizing bacteria
  in nonocular locations.
- fluoroquinolones are still effective against most bacteria that cause conjunctivitis or keratitis, and because they penetrate
  the cornea well, they should be used if clinical features suggest corneal involvement. Remember also that most patients recover
  without treatment even if the organism has appreciable antibiotic resistanc
- Although corticosteroid drops (either alone or combined with antibiotic drops) may quickly relieve symptoms, some conditions
  that present as a red eye with watery discharge, such as herpetic keratitis, worsen
- Contact lenses should be taken out until an infection is completely resolved.
- referral to an ophthalmologist
  include severe eye pain or headache, photophobia, decreased vision, or contact lens use. Patients with hyperacute cases should
  also be referred at once to rule out corneal involvement, although the internist should start treatment for gonorrhea. In
  addition, patients with apparent bacterial conjunctivitis that does not improve after 24 hours of antibiotic treatment should
  also be referred

14 Oct 09

NEJM -- Keratoconus Complicated by Acute Corneal Hydrops -- Figure 1

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case studies ophthalmology

acute onset of foggy vision
5 more annotations...
- bulging, cloudy cornea
- protrusion of the lower eyelid on downward gaze, known as the Munson sign
- edema and opacification of the central cornea (corneal hydrops)
- rupture of the posterior cornea
- resolves in 6 to 10 weeks

13 Oct 09

Interactive Case Series - Index

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ophthalmology case studies

Atlas of Ophthalmology

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ophthalmology medimages

11 Oct 09

fully abducted (away from the nose), only the superior and inferior rectus muscles can elevate and depress the eye. This is purely a mechanical property due to the axis of the eye lining up perpendicular to the superior/inferior muscles. If the eye is looking straight forward, about 50% of vertical motion is due to the inferior/superior oblique muscle combination and 50% is due to the superior/inferior rectus muscle.Cranial nerve III innervate four muscles (medial rectus muscle, superior rectus muscle, inferior rectus muscle, and inferior oblique muscle). Cranial nerve IV innervates the superior oblique muscle. Cranial nerve VI innervates the lateral rectus muscle. damaged cranial nerve will produce the same symptoms that would occur if the associated eye muscle or muscles are damaged.CNIII also innervates the levator palpebrae superioris muscle. This is one of the two muscles that raise the upper eyelid. When CNIII is damaged, the eyelid will demonstrate ptosis (upper eyelid droop). The eyelid is not completely closed because the other muscle partially raises the eyelid.Cervical sympathetic trunk injury will paralyze the superior tarsal muscle and also present with ptosis (one of the signs of Horner Syndrome). The nerve that innervates the sphincter runs along the outside of CNIII. Most compressing lesion that damages CNIII (such as a brain tumor) usually also damages the parasympathetic nerve innervating the sphincter. If CNIII is damaged due to a non compressing lesion then the pupil size should not be affected. best method to test eye motion is ask the patient to follow your finger drawing a large H

check out the quiz in patient cases section.

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ophthalmology case studies med-simulator

04 Oct 09

RedAtlas - Recognizing Eye Disease: A Visual Review of Ophthalmic Disorders

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clinicalmed ophthalmology medimages

09 Jan 09

Clinical Skills::Eye and Vision

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clinicalmed ophthalmology

Ishihara Pseudo-isochromatic
characterised by a
red-green
6 more annotations...
- red-green deficiency
- protan defects the visible range of the spectrum is shorter
  at the red end compared with that of a normal person, and the
  normal blue-green part of the spectrum appears as grey.
- deutan defects the part of the spectrum which appears to the
  normal as green appears as grey.
- 75cm from the subject and tilted so that the
  plane of the plate is at right angles
- 3 or more errors in
  the 1 eye indicates an abnormality.
- Normal skin secretions alter the colours

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clinicalmed ophthalmology

size of both pupils is estimated BOTH in a lighted then a semi-darkened
room, as the pupils may be of equal size in one circumstance and
of unequal size in another.
17 more annotations...
- distant
  target in a semi-darkened room and a bright pentorch
- direct reflex - the constriction of
  the pupil of the illuminated eye
- dark iris. The level of room lighting should
  be sufficient for the examiner to observe the constriction of
  the pupil of the unilluminated eye.
- near reflex, the patient (still
  in semi-darkened illumination) is first asked to fixate a distant
  object and then asked to fixate a near object
- test should be repeated two
  or three
- direct or consensual
  reflex is abnormal, the near
  reflex MUST be assessed and can be either normal (Light-Near Dissociation)
  or abnormal (Argyll Robertson pupil or other midbrain lesion).
- distant object in a semi-darkened room.
  Use the brightest available light source, such as an ophthalmoscope
  set on maximum brightness
- first illuminates the right eye
- then the left, swinging the flashlight from one eye to the other.
  The procedure is repeated several times, each pupil being illuminated
  for about one second
- Normally, the pupil of each eye will stay constricted
- in the
  presence of a relative afferent pupillary defect, the pupils of
  both eyes will dilate when the affected eye is
  illuminated
- by
  a millimetre ruler (a difference of 1mm or more). This condition
  is known as physiological anisocoria and is of
  no consequence
- Relative Afferent Pupillary Defect (RAPD)
  
  The RAPD, previously called the Marcus
  Gunn pupil is detected by means of the swinging flashlight
  test
- message received by the brain during
  light stimulation of the affected eye isn’t as strong
- less stimulus for pupil constriction
- comparison of the direct
  reflex to light, brought about by stimulating the pupil of the
  abnormal eye, with that brought about by stimulating the pupil
  of the normal
- central retinal artery occlusion or
  unilateral or asymmetric optic nerve compression, optic neuritis
  or retrobulbar neuritis

Clinical Skills::Eye and Vision

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clinicalmed ophthalmology

lacrimal gland produces only the water-based,
salty component
tears also contain an oily layer,
produced by modified sebaceous glands (Meibomian glands) contained
in the eyelids. A stye occurs when one of these glands becomes
acutely blocked
5 more annotations...
- third component of tears is mucus, produced
  by goblet cells in the conjunctiva.
- lacrimal punctum on the medial lid margin
  of both lids, drains tears into the lacrimal canaliculus.
  The 2 canaliculi drain into the nasolacrimal sac,
  located behind the medial edge of the bony orbital rim. This then
  drains down the nasolacrimal duct into the nose.
  Movement of tears through the system is largely driven by blinking.
- chronic blockage in the nasolacrimal system results in epiphora
  (constant spilling of tears onto the cheek). Neonates may also
  suffer congenital nasolacrimal duct obstruction. In most cases
  this resolves spontaneously by 1 year of age but in some cases
  the nasolacrimal duct may need to be probed and syringed with
  saline, to encourage drainage. This is done under GA in children
  but a compliant adult
- Infection in the nasolacrimal drainage system is called dacryocystitis
  and usually presents as an extremely tender and painful erythematous
  swelling near the medial canthus of the eye. A firm abscess can
  usually be palpated. Intravenous antibiotics and/or incision and
  drainage of the abscess are required. A secondary complication
  is that of scarring, resulting in chronic nasolacrimal duct obstruction.

Clinical Skills::Eye and Vision

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clinicalmed ophthalmology

optic nerve to chiasm,
from chiasm into the optic tracts to synapse
in the lateral geniculate nucleus and from the
LGN through the optic radiations to the visual
cortex.
“retinotopic” pattern
to the anatomy of the visual pathway that is retained at each
location. That is, the part of the retina from which any optic
nerve fibres originated can be mapped out by knowing whereabouts
4 more annotations...
- “bi-ocular” from the chiasm
  right through to the visual cortex – i.e. one side of the
  brain receives information from both retinas. However, the visual
  pathway is not “binocular” until the striate cortex.
- right visual pathway carries information from the uncrossed
  fibres of the temporal half of the right retina. It also carries
  information from the crossed fibres, arising from the medial half
  of the left
- left half of visual space (i.e. the visual field)
- Binocular
  vision, allowing depth perception, does not occur until the visual
  cortex

Clinical Skills::Eye and Vision

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clinicalmed ophthalmology

tissues and muscles of the orbit can swell causing the eyeball
to move anteriorly, clinically evident as exophthalmos
(proptosis). This results in lid retraction
corneal and conjunctival surface of
the globe can therefore dry out if the eye is proptosed. The conjunctiva
becomes injected (hyperaemic) as the surface
of the globe becomes irritated by dragging of the eyelids across
it with each blink.
6 more annotations...
- Eye symptoms and hyperthyroidism symptoms typically appear within
  18 months of each other. The patient may experience sensitivity
  to light, blurring of vision or grittiness (due to corneal exposure).
  Excess tearing and discomfort may occur in one or both eyes. Corneal
  scarring or corneal infection and permanent visual impairment
  may result from continued dryness.
- Diplopia
  results from a combination of 2 mechanisms occurring in the orbit:-
  
  The swollen muscles are unable to contract as efficiently
  as previously, resulting in reduced or unequal movement of the
  eyes.
  The oedematous tissues within the orbit have a restrictive
- blindness
  due to eventual compression and atrophy of the optic nerve by
  the swollen
- Marked corneal dryness and diplopia, from severe orbital
  tissue swelling, may require orbital decompression surgery, especially
  if a relative afferent pupil defect (previously known as a Marcus
  Gunn pupil) develops, as this is one of the earliest signs of
  optic nerve compression.
- Medications or radiation to shrink the orbital soft tissues
  
  Eyelid surgery or eye muscle surgery

Clinical Skills::Eye and Vision

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clinicalmed ophthalmology

7 bones: Frontal, Maxillary, Zygomatic,
Sphenoid, Ethmoid, Palatine & Lacrimal bones.
9 more annotations...
- medial wall, largely comprised of
  the lamina papyracea of the ethmoid bone, is
  the thinnest. The more exposed lateral wall, comprised of frontal
  and zygomatic bones, is the thickest.
- proximity to the middle cranial fossa.
  This is relevant in conditions such as orbital cellulitis
- facial sinuses surround the orbit. This is relevant
  in both infection & trauma
- A blow-out fracture is a displaced fracture of the orbital floor.
  Because the orbital contents are nearer the floor than any other
  wall of the orbit, a fracture here is more likely to result in
  herniation and entrapment
- If inferior rectus is entrapped (resulting in diplopia and restriction
  of movement of the globe in downgaze and upgaze (think about why
  restriction occurs in upgaze even though inferior rectus only
  depresses the eye), urgent surgical repair is required to prevent
  muscle infarction and persistent diplopia.