OPHTHALMOLOGY: 480-482 Flashcards
How does each branch of the autonomic system mediate pupillary control?
Parasympathetic - miosis, constriction
Sympathetic - mydriasis, dilation
Describe the neuronal pathway for miosis.
1st neuron - Edinger Westphal nucleus to ciliary ganglion via CN III
2nd neuron - short ciliary nerves to pupillary sphincter muscles
Describe the neuronal pathway for mydriasis.
1st neuron - hypothalamus to ciliospinal center of Budge (C8 - T2)
2nd neuron - exit at T1 to to superior cervical ganglion and travels along cervical sympathetic chain (near lung apex and subclavian vessels)
3rd neuron - plexus along internal carotid, through cavernous sinus; enters orbit as long ciliary nerve to pupillary dilator muscles
What is the pupillary light reflex as observed on physical exam?
Illumination of one eye results in bilateral pupillary constriction (consensual reflex)
Describe the pathway of the pupillary light reflex.
Afferent limb: light in either retina sends signal via CN II to pretectal nuclei in midbrain
Efferent limb: Pretectal nuclei signal bilateral Edinger Westphal nuclei which cause pupillary constriction via CN III
Is Marcus Gunn pupil an afferent or efferent pupillary defect?
Afferent
What does a “swinging flashlight test” show in Marcus Gunn pupil?
Decreased BILATERAL pupillary constriction when light is shone in affected eye relative to unaffected eye
What are the two components of CN III and where are they generally located within the nerve?
Central - motor component
Peripheral - parasympathetic component
What type of disease preferentially affects the central motor fibers of CN III first?
Vascular
Why does vascular disease affect the central motor fibers of CN III first?
Decreased diffusion of oxygen and nutrients to the interior fibers from compromised vasculature that resides on the outside of the nerve
What are signs of damage to the central motor fibers of CN III?
Ptosis, down and out gaze
What type of damage preferentially affects the peripheral parasympathetic fibers of CN III first?
Compression from the outside (e.g. posterior communicating artery aneurysm, uncal herniation)
What are signs of damage to the peripheral parasympathetic fibers of CN III?
Diminished or absent pupillary light reflex, blown pupil (often with down and out gaze)
What are the two layers separated in retinal detachment?
Neurosensory layer of retina (that contains all the photoreceptors) from outermost pigmented epithelium (normally shields excess light and supports retina)
What does retinal detachment lead to?
Degeneration of photoreceptors and subsequently vision loss
What can retinal detachment be secondary to?
Retinal breaks, diabetic traction, inflammatory effusions
Retinal breaks are more common in what kind of patient?
Patients with high myopia
What precedes a retinal break and how should this situation be treated?
- Posterior vitreous detachment (flashes and floaters)
- Eventual monocular loss of vision like a “curtain drawn down”
Retinal break = surgical emergency
What are the two things caused by age-related macular degeneration?
- Metamorphopsia - distortion
2. Scotoma - eventual loss of central vision
What are the two types of age-related macular degeneration?
Wet and dry
Which is more common - wet or dry age-related macular degeneration?
Dry (nonexudative) > 80%
Wet (exudative) 10-15%
Describe dry age-related macular degeneration.
Deposition of yellowish extracellular material (drusen) in and beneath Bruch membrane and retinal pigment epithelium leads to gradual decrease in vision.
How can the progression of dry age-related macular degeneration be prevented?
Multivitamin and antioxidant supplements
Which is more acute - wet or dry age-related macular degeneration?
Wet
What causes wet age-related macular degeneration?
Bleeding due to choroidal neovascularization
How do we treat wet age-related macular degeneration?
Anti-VEGF injections or laser
The medial longitudinal fasciculus allows for cross talk between which two nuclei?
CN III and CN VI
What is internuclear ophthalmoplegia?
Lesion in MLF so that eyes have trouble moving in the same horizontal direction
How does the MLF allow for the eyes to move horizontally at the same time?
Highly myelinated - fast communication
What type of patients tend to have lesions in the MLF?
Patients with demyelinating conditions (e.g. multiple sclerosis)
What does right INO mean?
Means the right eye is paralyzed (directional term specifies the eye that cannot move)
Describe what happens in internuclear ophthalmoplegia.
Lack of communication such that when the ipsilateral CN VI activates the lateral rectus, the contralateral CN III does not stimulate the medial rectus to fire
Why does the abducting eye get nystagmus in internuclear ophthalmoplegia?
Ipsilateral CN VI overfires to compensate for contralateral CN III not firing
Is convergence affected in internuclear ophthalmoplegia?
No
