Eyes Flashcards
Myopia
Near sightedness, where the image forms before the retina because the eyeball is too long or the refractory power is too high
Emmetropia
Correct eyeball size and refractory power such that the image forms appropriately on the retina
Hyperopia
far-sightedness, where the image forms past the retina because the length of the eye is too short or the refractory power is weak
Cornea (content and function)
Avascular w/ highly ordered collagen –> transparent.
* thickness varies across –> best vision @ central, where thinnest.
F(x): main focusing mech. (2/3 of total (60 diopter) converging power); also protective w/ selective permeability.
Corneal layers (3)
- endothelium
- stroma
- epithelium **innervated w/ sensory afferents –> corneal scratch hurts!
Bowman’s Layer
very thin, acellular layer just below the corneal epithelium;
(part of cornea).
* does NOT regernerate, so injury => corneal opacity (vision deficit)
corneal stroma
thickest layer of cornea, contains highly ordered collagen type I
(uniform spacing and thickness).
** collagen & proteoglycan IS regrown after injury, but less orderly => opaque scar & vision deficit.
Corneal endothelium
innermost layer of cornea, transports Na, K, & H ions + removes water from stroma (“deturgescence”) –> to maintain clarity of vision.
- limited regeneration w/ injury.
- ** water removal decreases w/ age –> increased cloudiness.
sclera
most (80%) of eye surface; ~avascular, made of less organized collagen + higher water content than cornea (–> not clear).
w/ sensory & autonomic innervation, extraocular m insertions, & holes for optic nerve, etc.
** slow to heal, but will w/o affecting vision.
anterior & posterior chambers
Both filled w/ aqueous humor to provide O2 & nutrients to cornea, lens, & trabecular meshwork.
Anterior: btwn cornea & iris/lens
Posterior: btwn iris & vitreous chamber
Aqueous humor (flow, content, etc)
Made by ciliary body, flows into anterior chamber, then drains via Schlemm’s canal (trabecular meshwork – main resistance to flow).
- maintains clarity bc NO plasma cells or proteins.
- ** if builds up –> glaucoma! (high intraocular pressure)
3 responsibilities of Ciliary Body
- produce aqueous humor
- regulate aqueous humor outflow
- accommodation (adjust vision using ciliary muscles)
Trabecular meshwork
thin channels of connective tissue, lined w/ epithelium & gap junctions;
= main source of resistance to aqueous humor outflow/drainage.
path of aqueous humor flow
- ciliary body (produced) –> anterior chamber
- –> Schlemm’s canals (trabecular meshwork)
- –> collector canals
- –> episcleral veins
Glaucoma
painless, often unnoticed/”symptomless” disease resulting in blindness.
due to increased intraocular pressures (from reduced aqueous humor outflow) +/- other unknown mechs.
Uvea (contents, function)
Uvea = iris, ciliary body & choroid;
= highly vascular, pigmented cells.
F(x): provide nutrients to lens, cornea & trabecular meshwork
Iris
highly vascular colored segment around pupil, contains:
- iris sphincter muscle: circular fibers, w/ parasymp. innervation.
- iris dilator muscle: radial fibers, w/ sympathetic innervation.
- help w/ visual accomodation
Ciliary muscle
contracts w/ parasympathetic stimulation, ==> lens thickens (for visual accomodation) by releasing pressure.
Presbyopia
loss of visual acuity w/ age due to decreased elasticity of the lens
Lens
Asymmetric, biconcave, avascular & NOT innervated;
Mostly water w/ some protein (crystallin).
– adjusts thickness in order to keep light focused on retina for any object distance.
Cataracts
protein aggregations that decrease visual acuity, caused by conversion of a-crystallin to albuminoid in aging lens.
* preventable & treatable!*
Vitreous body
clear substance filling most of eye past lens,
– 99% water + hyaluronic acid-collagen gel.
lets light pass through eye to retina.
** attached everywhere except anteriorly –> posterior detachment appears like retinal detachment! **
macula & fovea
Macula = central region of retina, w/ high clarity.
Fovea = center of macula, w/ highest density of cones & no blood vessels.
* macular degeneration happens w/ age, not preventable. :(
Oculomotor nerve f(x)
Motor: to levator m. + all Extraocular mm except superior oblique and lateral rectus mm.
Parasympathetic: to ciliary body & iris sphincter m.
Arteritic Ischemic Neuropathy (Temporal Arteritis)
Sx: monocular decreased vision, temporal pain & scalp sensitivity, jaw claudication, fatigue, Aff. pupillary defect;
*age > 60
Tx: Emergency! High dose steroids, biopsy
Non-Arteritic Ischemic Optic Neuropathy
= microvascular insult to optic n.,
Risk factors: HTN, diabetes
Sx: sudden decrease in vision, aff. pupillary defect
Tx: none, assess for risk of temporal arteritis
Central Retinal Artery Occlusion
Sx: very acute monocular vision loss (= embolic occlusion of retinal a.)
Dx: pale retina w/ “cherry red spot,” *rule out temporal arteritis
Tx: if <2 hrs reduce eye P, occular massage, etc. (to improve occular circulation)
Central Retinal Vein Occlusion
= obstruction of venous outflow
Risk factors: HTN, DM, glaucoma, hypercoagulability
Dx: “Blood & Thunder” retina, decreased vision
Tx: laser or injections to prevent neovascularization
Vitreous Hemorrhage
= blood in vitreous cavity
Causes: diabetes, trauma, retinal tear
Tx: observe, laser surgery if diabetic
Ruptured Globe (trauma)
Sx; Subconjunctival hemorrhage, hyphema, peaked pupil
Tx: eye shield, systemic antibiotics, CT to rule out foreign body, surgical repair
Traumatic Hyphema
= blood in anterior chamber,
Complications: risk rebleed @ 3-5 days, risk glaucoma
Tx: NO aspirin, surgical evacuation only if 100% + increased ICP
Endopthalmitis
*often complication of corneal ulcer
= internal infection of eye
Tx: intravitreal antibiotics +/- vitrectomy
Acute Angle Closure Glaucoma
Sx: acute pain & vision loss w/ halos, frontal headache, nausea, cloudy cornea, & Elevated IOP
Pathophys: iris bows to block drainage of aqueous humor
Tx: eye drops to reduce IOP + systemic P lowering meds; laser iridotomy
*IRReversible if not treated in 1st 24 hrs!
Retinal Detachment
Sx: sudden flashes of light & floaters, “curtain over vision,” may have normal acuity
Risk factors: prior surgery, myopia
Tx: surgical repair
Non-proliferative vs. Proliferative Diabetic Retinopathy
General Retinopathy: loss of pericytes -> dot-blot hemorrhage -> microaneurysms, hard exudates, nerve fiber layer infactions, venous beading.
(ischemia => retinal damage)
Proliferative = w/ new blood vessels growing on retina & iris -> vitreous hemorrhage, retinal detachment (w/ scarring).
Treatment for (Proliferative) Diabetic Retinopathy
Laser reduction of peripheral retina to decrease O2 need. (aka: photocoagulation)
Primary Open Angle Glaucoma
= asymtomatic optic n damage due to high IOP,
=> slow, chronic loss of peripheral vision
Dx: increased cup/disk ratio, high IOP, periph.VF loss
Tx: #1 eye drops to suppress aqueous fluid (timolol, a-adrenergics, carbonic anhydrase inhibitors); 2. surgery to increase aqueous outflow
Macular Degeneration: non-exudative vs. exudative
*Macular Degen = loss of deep vascular supply to retina
Non-exudative (“dry”): gradual loss of central vision, (“drussen”/geographic atrophy)
Tx: vitamin supplementation
Cataracts - pathophysiology & etiology
*leading cause of blindness in world (but not in USA bc treatable)
= yellow/clouding of crystalline lens (bc grows inward for entire life);
Causes: #1 Senile, congenital (Emergency!), drug induced, systemic illness
Clinical characterization of Cataracts
may be nuclear sclerotic, cortical or posterior subcapsular of lens.
Sx: decreased visual acuity, monocular diplopia
Tx: surgical extraction & replace w/ new lens
Exudative Macular Degeneration
*Macular Degen = loss of deep vascular supply to retina
Exudative (“wet”): rapid central vision loss, bc of neovascular subretinal membrane (subretinal hemorrhage)
Tx: ant-VEGF meds
