Basic Anatomy and Fundamentals Flashcards
Anterior Segment Contains
Anterior & Posterior Chambers w/ Cornea, aqueous humor, iris/ciliary body, lens
Posterior Segment Contains
Sclera, Choroid, Retina, Vitreous humor
Uveal Tract contains
Iris, Ciliary Body, Choroid
Meibomian glands
produce oil to mix with tears
Aqueous Humor Production
Continually being produced by cilary body (2-3 microliters/minute)
Intraocular Pressure (IOP)
Balance between formation and reabsorption of aqueous humor determines volume & pressure of IOP. Amount leaving usually = amount formed so pressure usually remains constant.
Elevated = Glaucoma
Aqueous Humor Outflow
Pupil –> anterior chamber –> trabeculae meshwork –> Canal of Schlemm –> Empties into extraocular veins & systemic circulation
Normal IOP
12-20mm Hg
Main determiner of IOP
Resistance to outflow of aqueous humor
Rods
Retinal receptors associated w/ peripheral vision and vision in low light (less concentrated in macula)
Cones
Retinal receptors associated w/ central vision and color vision
5 Corneal Layers
External to Internal: Epithelium (5-6 layers) Bowman's Layer Stroma (90% of corneal thickness) Descement's membrane Endothelium
Corneal Stroma
90% of corneal thickness
Composed of collagen fibrils
Stromal edema causes decreased corneal clarity
Descemet’s membrane
Specialized basement membraine for endothelial layer
Endothelium
Maintains desiccatio of the stroma by actively removing water
Anterior cornea provides how much refractive power of eye?
2/3
Lens provides how much refractive power of eye?
1/3
Accomodation
lens increases curvature in response to nervous signals from brain
Anterior suface of cornea can be modified to overcome refractive errors how?
Various types of surgeries
Myopia
Nearsightedness
EYEBALL is too LONG so FOCAL POINT is in FRONT of retina
(can’t relax ciliary muscle any more to extend focal point back further BUT when object comes ear, gets close enough that image can be focused onto retina)
Hyperopia
Farsightedness
EYEBALL is too SHORT so FOCAL POINT is BEHIND retina
(lens can focus distant objects on the retina initially by accommodation. Accomodative power of the lens is eventually maxed out & lens can’t focus on close objects)
Errors of Refraction
Emmetropia (20/20)
Hyperopia (Farsighted)
Myopia (Nearsighted)
Myopia Correction
“Minus” concave numbers (e.g. -3.75 diopters)
Hyperopia Correction
“Plus” convex numbers (e.g. +2.75 diopters)
Presbyopia
Elasticity of lens declines w/ age
Lens loses ability to change shape to accommodate for near objects
Corrected w/ cheaters or bifocals
Astigmatism
Non-spherical cornea
Corneal images focus at different distances
Accomodation manipulates the entire lens, so can’t correct for astigmatic refractive error in the cornea
How the lens works
W/out tension, eye would assume spherical shape
Suspensory ligaments (zonules) attach radially around lens, pulling edges outward to flatten lens
Constant tension causes the lens to remain relatively flat in the normal state
Ciliary muscle attaches to zonules (lens ligaments) & causes contraction and relaxation of lens
Ciliary muscle contraction
Zonules & Lens relax
Lens becomes more spherical to focus on NEAR OBJECT
Ciliary muscle relaxation
Tension on zonules & lens increase
Lens flattens to focus on DISTANT OBJECTS
Ciliary muscle control
Primarily Parasympathetic under CN III
Sympathetic –> minimal effect/almost no role in accomodation
Pupillary Response
Direct & consensual pupillary light reflex
Sensory –> CN II
Motor –> CN III
Consensual response via Edinger-Westphal nucleus
Parasympathetic pupillary response
stimulation causes pupillary muscle contraction & decreases in size
Miosis
Decreasing pupil size
Sympathetic pupillary response
dilates the pupil
Mydriasis
Increasing pupil size
Horner’s Syndrome
Lesion of sympathetic pathway
Miosis, ptosis, absence of sweating on ipsilateral face/neck if preganglionic (sweating preserved if post-ganglionic)
Marcus Gunn
Decreased direct reaction to light
Consensual response intact
RAPD with “swinging flashlight test”
Argyll Robertson
Pupillary constriction w/ near accomodation but NOT to light stimulation
Hx in pt w/ eye sx
- Any change in VA?
- Any Hx of trauma?
OLDCARTS
PMH: Comorbidities, Meds
FH
Pt. Profile: Occupation, Hobbies
PE in pt w/ eye sx
VA (best corrected) VF/confrontation Inspect: lids, lashes, brows, conjunctiva, sclera EOMS PERRLS Ispect cornea/iris Anterior Chamber Depth (IOP) Lens clarity Fundoscopic Exam - disc, vessels, retina, macula *IOP if indicated
Ocular Vital Signs
VA VF EOMs Pupillary Response IOP
Red Reflex
Cornea/aqueous/lens/vitreous must be clear
Eye arteries
lighter in color than veins, 2/3 size of veins, have brighter light reflex
Eye veins
larger, darker w/ less bright light reflex
Disc Margins
sharp or blurred, elevated?
Cup/Disc ratio: normal is <1:2
Retinal Background
Normal is uniform
Abnormal? Hemorrhages, “drusen,” “cotton wool spots”
Macula
Temporal to disc; NO VESSELS = macular degeneration