Eye Flashcards
what are the 3 layers of the eye ?
sclera, choroid and retina
sclera
Outermost layer
Tough and protective
Cornea is the anterior portion of this layer
choroid
Highly vascular layer - supplies to rods and cones w/ blood
The ciliary body, with its lens, and the iris are a continuous layer with the choroid (aka the uvea)
retina
Visual layer
Exits the orbit as the optic nerve
limbus
The point at which the sclera becomes the cornea
what is the cornea? what does it do?
anterior portion of the sclera and makes the eyeball “not round”. The steep curvature of the cornea makes it ideal for refraction (bending and focusing) the light that enters the eye. (the lens helps too but only fine adjustments to focus).
what part of the eye is known for vascular function which supplies the eye with nourishment.?
choroid
what are the three chambers of the eye? where are they and what do they contain?
Anterior Chamber: In front of the iris. Contains aqueous humor
Posterior Chamber: Between the iris and lens. Contains aqueous humor
Vitreous Chamber: Behind the lens. Contains vitreous humor (thicker gelatinous substance that gives the eyeball its shape).
what does the ciliary body produce? what process does it do?
Produces aqueous humor
Process of accommodation which changes the shape of the lens to fine tune vision- accommodation for near vision
what is aqueous humor?
Watery substance that bathes the anterior and posterior chambers. It exits at the Canal of Schlemm which is at the angle between the cornea and iris. The Canal of Schlemm communicates with the venous system.
how does contraction of the ciliary body work?
surrounds the lens supporting it by the zonular fibers that attach to the lens capsule. When the muscle of the ciliary body contract they release the tension on the zonular fibers and allow the lens to become more convex thereby focusing the image on the retina.
what nerve controls contraction of the ciliary body muscles?
controlled mainly by the parasympathetic fibers of the Oculomotor cranial nerve (CN III).
what does a curved lens mean for refraction and focal point? flat lens?
more curve in lens= more refraction= closer focal point
flatter lens= less refraction =further focal point
muscles of the iris
The iris contains circular muscle fibers (sphincter) that constrict the pupil and radial muscle fibers (straight) that dilate the pupil iris constricts (scrunches up) into the angle - this will be painful if you have closed-angle glaucoma b/c theres no angle for it tot scrunch into
____ accounts for 2/3 of focusing ability of the eye, ____ for 1/3
cornea: 2/3 lens: 1/3
what is the lens responsible for in terms of viewing images?
small adjustments when viewing items up close (accomodation is for near vision) - pupil shrinks and eye converge together
blurred image activates what?
Blurred image activates parasympathetic preganglionic neurons in Edinger-Westphal nuclei sending signal to the sphincter muscle (of the Iris) .
what are the two layers of the retina?
pigment epithelium and neural retina
pigment epithelium
Dark layer lies on top of choroid
Bruch Membrane- Absorbs light so there is no reflection of light around the eye
Pigment epithelium- Stores large quantities of Vit A a precursor of the photosensitive visual pigments
what three type of cells does the neural retina contain?
photoreceptors, bipolar cells, and ganglion cells
what are the two photoreceptor types?
Rods- distinguish black and white
Cones- distinguish color
bipolar cells of the neural retina? what cells connect them together?
receive information (synapse) with rods and cones Horizontal cells connect bipolar cells together
ganglion cells of the neural retina? what cells connect them together?
- the end neuronal cell whose axon becomes the cranial nerve II- The Optic Nerve
Amacrine cells connect the ganglion cells together
how do you distinguish retinal arteries from veins?
The arteries are light red and smaller than the veins.
Veins are dark red and larger
where do retinal arteries come from and where do they drain?
branches of the central retinal artery which enters through the orbital papilla
drained through the central retinal veins.
supply: bipolar, ganglion & photoreceptors
what cranial nerve takes in vision?
CN 2 -optic nerve
optica papilla
“tunnel” in the optic nerve through which the central retinal artery and central retinal vein travel
cup and saucer
The nerve is seen as the optic disc in the back of the eye and the papilla is seen as the cup
The cup should be less than half the diameter of the
saucer (optic disc).
papilledema
increased intracranial pressure = pressure of the globe of the eye pushes on the papilla and all of the axons of CN2 (vision)- decrease ability to see
increase intracranial pressure - travels force through the optic nerve into the eye - can cause papill-edema
fovea centralis
rod free area of thinned retina with no overlying vessels that has a one to one cone to ganglion ratio producing great focus and therefore the best visual acuity.
path of vision
enters eye- focused on retina (passes through its layers)
- rods & cones synapse w/ bipolar cells–> synapse w/ ganglion cells
- come together = optic nerve
- -> optic chiasm –> optic tract –> lateral genticulate body (in thalamus)
- -> visual cortex on occipital lobe
what are the 4 vision fields in an eye
lateral top: upper temporal
lateral low: lower temporal
medial top: upper nasal
medial low: lower nasal
convex lens causes light beams to ____ while a concave lens causes beams to ____
convex: converge
concave: diverge
higher diopter # = ?
with increasing convexity (more curved out) - the higher the diopter # - the focal point is closer/more forward in the eye - closer to the cornea
diopter number for glasses tells you what?
for glasses tells you how far back or close up the focal point on your retina is (distance from your cornea)
where is the focal point in the normal eye? myopia? hyperopia?
normal: hits retina w/ macula & fovea on retina
myopia- long eye : in front of retina
hyperopia- short eye: behind retina
myopia
long eyeball
Uses a biconcave lens
Would use a negative diopter to push the focal point back toward the retina
hyperopia
+ diopters shorten the eye’s focal length to account for a shorter eyeball
diopters
the measure of refractive power; the number is the inverse of the lens focal length in meters
1 diopter is a lens with a 1 m focal length, 3 diopters is a lens with ⅓ m focal length, etc.)
positive diopters magnify (convex lens), negative minify (concave lens)
spectacles with + diopters shorten the eye’s focal length to account for a shorter eyeball (hyperopia), those with – diopters lengthen focal length to account for a longer eyeball (myopia)
refractive errors
The closer an object is to a convex lens, the more the image is focused (the bigger the angle). Hence, for myopes (nearsighted), near objects are focused closer to the retina than far objects and are seen best. For hyperopes (farsighted), far objects focus closer to the retina and are seen best.
5 parts of the PE for eye
Visual Acuity (does it work and how well?)
Visual Fields (binocular- middle, peripherals)
External Eye Exam
Extraocular Movements
Fundoscopy
visual fields by confrontation
Will screen for lesions of anterior and posterior pathway
Static Finger Wiggle Test
Kinetic Red Target Test (if they have a defect in visual field- you not figure out where it is in their field of vision)
pupillary reaction test
shine light in one eye, both sides contrsict b/c they talk to both eddinger-westphal nucleus (CN 3- oculomotor tested)
4 ways to test extraocular movement
Resting gaze (pupils should be looking parallel)
Six cardinal gazes (“H” shape - 3 spots on each side of head, then the middle)
Lid lag (if the globe is too big, the lid lags, see the sclera above the iris)
Convergence
right up & left up gaze : nerve and muscles
CN 3 superior rectus and inferior oblique
right & left gaze: nerve and muscles
CN6- lateral rectus CN3- medial rectus
right down & left down gaze: nerve and muscles
CN 3- inferior rectus CN4- superior oblique
cover, uncover test
ver, uncover test- looking for weak eye. (in terms of its muscles)
cover right, left moves inward, uncover right, left moves back outward (looking for the swing of the non-dominant eye)
PE of retina
color clarity teacup and saucer (cup- nerve, saucer- disc) vessels- arteriovenous crossings asymm (both eyes the same) edema of disc
three measurements within the eye
clock face (to describe where something is in the eye)
disc diameters
diopters
6 pieces of equipment used in eye exam
Ophthalmoscope Slit Lamp (biomicroscope) Snellen Chart Fluorescein dye Mydriatic drops Proparicaine drops
