first aid eye section Flashcards
hyperopia (farsightedness)
-eye too short for refractive power of cornea and lens–> light focused behind retina
myopia (nearsightedness)
eye too long for refractive power of cornea and lens–> light focused in front of the retina
presbyopia
decrease in focusing ability during accomodation due to scleoris and decreased elasticity
Aqueous humor pathway
ciliary epithelium produce aqoeus humor (Beta)–> travels to anterior chamber–> the trabecular meshwork collects the aqueous humor–> the canal of schlemm collects the humor from the trabecullar meshwork
glaucoma
- optic disk atrophy with characteristic cupping
- increased intraocular pressure IOP
- progressive peripheral visual field loss
cataract
- painless, often bilateral, opacification of lens
- decrease in vision
- risk factors: increased age, smoking, EtOH, excessive sunlight, prolong corticosteroid use, classic galactosemia, galactokinase deficiency, diabetes (sorbitol), trauma and infection
Open angle glaucoma
assoc: increase age, black, fx painless primary cause unclear secondary: blocked trabecular meshwork from WBC (uveitis), RBC (vitreous hemorrahage), retinal elements (retinal detachement) --> increased intraocularpressure
closed/narrow angle glaucoma
primary:
enlargement or forward movement of the lens against the iris leads to obstruction of the normal aqous flow through pupil–> fluid back up behind the iris–> pushing the peripheral iris agianst the cornea and impeding flow through the trabecular network.
secondary:
hypoxia from retinal disease (diabetes, occlusion) induces vasoproliferation in the irsis that contracts the angle
chronic closed/narrow angle glaucoma
Chronic: often aysmptomatic with damage to optic nerve and peripheral vision
acute closed/narrow angle glaucoma
acute: EMERGENCY increased IOP pushes the iris forward and the angle closes ABRUPTLY. very painful, sudden vision loss, halos around lights, rock hard eye, frontal headache. DO NOT give epi because of its mydriatic effect
CN III damage
eye looks down and out, ptosis, pupillary dilation (loss of parasympathetic), loss of accomodation
CN VI abducens lesion
medially directed eye that cannot abduct
CN IV trochlear lesion
superior oblique (normall moves eye down and out) eye moves upward, particulalty with contralateral gaze .
Miosis (constriction, parasympathetic)
1st neuron edinger westphall nucleus to ciliary ganglion via CN III
2nd neuron: short ciliary nerves to pupillary sphincter muscles
Mydriasis (dilation, sympathetic)
1st neuron: hypothalamus to ciliospinal center of budge (C8-T2)
2nd neuron: exit T1 to superior cervical ganglion (travels talong cervical chain sympathetic chain near lung apex and sublcavian vessels)
3rd neuron: plexus along internal carotid, though cavernous sinus and enters orbit as long ciliary nerve to pupillary dilator muscles—- interupt this chain and you can get horners syndrome
pupillary light reflex
afferent: CN II to retectal nuclei in midbrain that activate bilateral edinger westphal nuclei –> CN III efferent –> pupil contract bilateally consensual reflex
what can cause compression of parasympathetic output fibers of CN III?
Pcomm artery aneurism, uncal herniation
lesion at optic nerve before chiasm
one eye anopia
lesion at optic chiasm
bitermporal hemianopia
lesion at optic tract
homonymous hemianopia all left or all right
lesion in meyer loop (temporal lobe) inferior retina; loops around inferior horn of lateral ventricle
left or right UPPER quandrantic anopia
Lesion in dorsal optic radiation - superiror retina ,takes shortest path via internal campsues –> parietal lesion, MCA
LOWER quandrantic anopia
PCA infarct
hemianopia with macular sparing
central scotoma
macular degerenation
Medial longitudinal fasiculus MLF
Cross talk between CN VI and CN III
When looking left, the left nucleus of CN Vi fires, which contracts the left lateral rectus muscle and stimulates the contralateral right nucleus of CN II via the right MLF to contract the medial rectus.
Internuclear opthalmoplegia INO
Lesions of demyelination of the MLF
-MS
So the CN Vi fires, but it cant communicated with CN III via MLF, and the CN VI overfires to stimulated CN III and it gets abduction with nystagmus.
