Opthamology Flashcards
(38 cards)
Pupil basics
Is a hole in the middle of the iris and is made up of the circular muscles and radial muscles
- circular = pupillary sphincter
- radial = pupillary dilator
What controls the circular and radial muscle contractions?
Circular (constriction of pupil)
- parasympathetic response
- occurs in bright light
- occurs when calm/relaxed
- occurs when high on opioids
Radial (dilation of pupil)
- sympathetic response
- occurs in dim light
- occurs when afraid
- occurs when high on cocaine/ amphetamines
What is anisocoria
Unequal pupils
in bright light:
- the larger pupil = loss of parasympathetics ipsilaterally
In dim light:
- the smaller pupil = loss of sympathetics ipsilaterally
What tumor is most common in causing horners syndrome?
Pancoast tumors
Anatomy of the sympathetics for the eyes
First order = hypothalamus
- runs down the brainstem and into spinal cord where it synapses at C8-T2
Second order = exits out C8-T2 and goes to the inferior cervical ganglion
- ruins over the apex of the lung around the subclavian artery and synapses on the superior cervical ganglion
Third order = exits off superior cervical ganglion and ascends along the carotid artery
- runs through cavernous sinus and innervates muscles via CN3 tract
Most common causes of ipsilateral Horner syndrome in ophthalmology
Brainstem stroke (usually medullary syndrome)
Cord hemisection (brown-sequard syndrome)
Pancoast tumors at apex of lung
Carotid artery dissections
Damage at the cavernous sinus
Anatomy of parasympatheticsof the eye
Afferent:
- Light signals are received through CN 2 and travels along the nerve
- Hemi-decussates at optic chiasm
- Synapses onto E-W nuclei bilaterally in the rostral midbrain near the superior colliculi
Efferent:
- travels along CN 3 from E-W nucleus
- synapses in the ciliary ganglion and runs along short ciliary nerves to innervate the iris sphincter
What is the most sinister etiology for a blown pupil?
3rd nerve palsy
- caused by aneurysm of the circle of wills or herniation of the uncus impinging on the CN 3
Classic clinical signs are
- ptosis
- mydriasis
- eye is down and out
Relative afferent pupillary defect (RAPD)
Results from a lesion in the CN2 nerve or some sort of damage.
- the pupils are always the same size but respond differently to light
(I.e shining light in the left eye = 100% constriction in both. Shining light in the right eye = 50% constriction in both)
Common causes are optic neuritis, MS, retinal artery occlusions
can cause red color dislocation (where red looks like orange)
What is a quick and easy way to differentiate 3rd nerve palsy from chemical mydriasis?
Use 1% pilocarpine eye drops on the dilated pupil.
- if it DOES NOT constrict = NOT 3rd nerve palsy
- if it DOES constrict = 3rd nerve palsy
What does a blurred optic disc signify?
A blockage of the axoplasmic flow from the optic nerve
Causes:
- ischemia to the nerve
- high cranium pressure
- optic neuritis
- metabolic dysfunctions (toxic ODs, hereditary mitochondrial diseases
what is OD vs OS abbreviations mean?
OD = right eye
OS = left eye
Papilledema
Swelling of the optic nerve at the retina which causes a swollen blurry optic disc which is CAUSED BY INCREASED INTRACRANIAL PRESSURE
if it is not caused by increased intracranial pressure, it is an “optic nerve disease” not papilledema
Idiopathic intracranial hypertension (IIH)
also known as Pseudotumor cerebri
Classic risk factors:
- use of tetracyclines
- over use of vitamin A
- obesity (especially rapid and recently)
Classic signs:
- transient visual obscurations
- pulsation tinnitus
- occasional horizontal diplopia
Diagnosis:
- increased CSF pressure > 25mmHg
- NO ABNORMALITIES IN CSF counts
What is a classic MRI sign for MS?
Bright finger-like projections of brain tissue that are just superior to the corpus callosum in the sagittal view.
Optic neuritis
More common in ages 20-40s
Very common with MS patients
Classic signs:
- pain in the eye that is losing vision
- eye movement causes pain in the eye
- red colors are less saturation (dissociation)
- requires brain and orbit MRI/CT to confirm*
When should your never LP a patient with papilledema or blurred optic disc?
If you have not ruled out a tumor yet.
if a tumor is present, LP will cause herniation of brain tissue to the medulla and impinge on it, causing respiratory and cardiac failure
Bitemporal hemianopia
Caused by lesion to the optic chiasm in sagittal fashion
- knocks out the lateral aspects of both eyes
common in pituitary tumors
Where does the fibers of the optic tract travel to?
The lateral geniculate ganglion (LGG) of the thalamus
- from here it becomes optic radiations and splits into an upper (parietal) and lower (temporal) pathways
The radiations travel directly to the visual cortex in the occipital lobe
Upper quadrantanopia
Damage to the lower (temporal part) of the optic radiations
Causes upper 1/4 visual blindness in either the right side of both eyes (left optic radiations) or the left side of both eyes (right optic radiations)
Lower quadrantanopia
Damage to the upper (parietal part) of the optic radiations
Causes lower 1/4 visual blindness in either the right side of both eyes (left optic radiations) or the left side of both eyes (right optic radiations)
What does damage tot he occipital lobe itself cause?
Causes similar defects to optic tract lesions
- mild subtly different though, but not important to know now
What is the general rule for visual fields?
Everything is flipped
Dorsal stream dysfunction
The “where” stream
Causes the following:
- stimultanagnosia: cant pay attention to more than one object at a time
- astereognosis: inability to perceive the depth perception of objects
- akinetopsia: inability to detect motion
