Intro to eye / Test & tools Flashcards
(39 cards)
1
Q
Refraction
A
- bending of light
- images are brought to a focus on the retina by the structures of the eye
- most comes for your cornea
- lens fine-tunes it
- in older age lens stops fine-tuning
- diopters measure refractive power
2
Q
Diopters
A
- measure of refractive power
- number is the inverse of the lens focal length
- 3 diopter is a lens with 1/3 m focal length
- positive (convex lens)
- negative (concave lens)
- glasses with + diopters shorten the eye’s focal length to account for a shorter eyeball (hyperopia)
- glasses with - diopters lengthen focal length to account for a longer eyeball (myopia)
3
Q
Hyperopia
A
- shorter eyeball
- farsighted
4
Q
Myopia
A
- longer eyeball
- nearsighted
5
Q
Autonomic motor control
A
- via ciliary ganglion
- cholingergic
- causes ciliary body to squeeze lens (+ diopters)
- constricts pupils when you focus on a near object
6
Q
Belladonna alkaloids
A
- anticholinergic
- cause pupils to be large
- unable to focus the lens
7
Q
Pinhole test
A
- used to see if poor vision is refractive
- your brain will interpolate data to where it should be even if we can’t really see it
8
Q
Aqueous humor
A
- produced by ciliary body
- watery substance that bathes the anterior and posterior chambers
- exits at the Canal of Schlemm which is at the angle between cornea and iris
- if there is a blockage in canal of Schlemm the aqueous humor cannot drain from eye causing glaucoma
- maintains the shape of the eye
9
Q
Extraocular muscles (EOM)
A
-testing can reveal cranial nerve dysfunction or peripheral problems with musculature
10
Q
Macula
A
- dark spot in eye
- highest density of photoreceptors
- where our central vision is
11
Q
Tonometry indications
A
- pt with abnormal cupping on funduscopic exam
- risk factors: over 40, African-American, family hx, DM, HTN, high cholesterol, long term statin use
- pt with IOP detected during community-based screening
12
Q
Tonometry technique
A
-applanation tonometry calculates intraocular indirectly by measuring the force required to flatten a constant area of the cornea
13
Q
Tonometry shortcomings
A
- get falsely high measure in pt with thicker corneas
- get falsely low measure in pt with thinner corneas
14
Q
Snellen / Rosenbaum chart
A
- part of a comprehensive eye exam
- technique: have pt stand 20ft away, cover one eye, and have pt read as far down as they can
- cheap
- shortcomings: children might not be familiar with the alphabet or someone can memorize the chart
- The gold standard for pt who can identify the alphabet
15
Q
Color vision testing
A
- Ishihara test
- Farnsworth-Munsell Dichotomous D-15 test
- Lanthony Desaturated color test
- Gold standard: oculus anomaloscope
16
Q
Ishihara test
A
- cheap
- pt must identify an object in the background of another color
- shortcomings: only tests for red/green deficiencies
- need additional testing to test for blue/yellow deficiencies
17
Q
Farnsworth-Munsell Dichotomous D-15 test
A
- detects red/green and blue/yellow deficiencies
- pt need to place the color caps in order of hue (gradient)
18
Q
Lanthony desaturated color test
A
- discs are desaturated (lighter in hue)
- pt has to discriminate between subtle color variations
- can distinguished between normal color perception and mild deficiency in red/green or blue/yellow
19
Q
Oculus Anomaloscope
A
- Gold standard
- pt matches color/brightness together
- can grade the diagnosis
20
Q
Fluorescein stain
A
- Indications: FB, corneal abrasions, any suspected minor ocular trauma
- technique: wet fluroescein strip and apply drops to eye, illuminate with blue light, abrasions show up green
- very cheap
- risk: infection, scarring, vision loss, recurrent corneal erosion, stinging, stains everything
21
Q
Pupillary dilation
A
- indications: allows visualization of interior of the eye and more accurate measurement of refractive error
- technique: pull out lower lid, place 1-2 drops, close eye, lacromal occlusion
- risks: light sensitivity, blurry vision, slight burning
- DOA 4-24 hours
- Atropine has systemic anticholinergic effects and can last 2 weeks
22
Q
Slit lamp
A
- Indications: cataracts, ulcers, macular degeneration, retina detachment, blockages, injuries to cornea
- Technique: use a bioicroscope. Pt places chin on bar and forehead against bar. Light shines into pt’s eye to illuminate structures
- risk: infection, scarring, vision loss, recurrent corneal erosion
- Gold standard
23
Q
Clarity
A
- structures within the eye (aquueous, vitreous, lens) are clear to allow light passage
- poor clarity results in poor vision
- This CANNOT be corrected with lenses
24
Q
Layers of the orbit
A
- Scleara
- Choroid
- Retina
25
Sclera
-outermost layer of orbit
-tough and protective
-cornea is the anterior portion of this layer
-Limbus: where the sclera becomes the cornea
-
26
Choroid
- middle layer of orbit
- highly vascular
- supplies the eye with nourishment
- ciliary body, lens, and the iris are continuous layer within the choroid (uvea)
- Photoreceptors (rods and cons) get blood supply from the choroid not the retinal arteries
27
Retina
- inner most layer
- visual layer
- exits the orbit as the optic nerve
28
Anterior chamber
- in front of the iris
| - contains aqueous humor
29
Posterior chamber
- between iris and lens
| - contains aqueous humor
30
Vitreous chamber
- behind the lens
| - contains vitreous humor (thick gelatinous substance that gives eyeball its shape)
31
Ciliary Body
- surronds the lens supporting it by the zonular fibers that attach to the lens capsule
- produces aqueous humor
- Process of accommodation (changes the shape of the lens to fine tune vision - changes for close vision)
- muscles of the ciliary body contract they release the tension on the zonular fibers and allow the lens to become more convex - focus on the image on the retina
- contraction of ciliary muscles is contronlled by parasympatethic fibers of the oculomotor cranial nerve (CN III)
32
Iris
- contains circular muscles fibers (sphincter) that constricts the pupil
- radial muscle fibers that dilate the pupil
- Pupillary sphincter contraction decreases pupil size - parasympathetic
- dilator muscle contraction: increases pupil side - sympathetic
33
Accommodation
- cornea accounts for 2/3 of focusing ability of the eye
- lens accounts for 1/3
- when an object is viewed close up the refraction of the image entering the eye has to change in order for it to focus on the retina
- lens is responsible for this small adjustment (lens changes shape) when viewing items up close
34
Retinal layers
- Pigment epithelium
| - neural retina
35
Pigment epithelium of retina
- dark layer that lays 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
- Albinism: have no pigment
36
Neural rentia
- contains photoreceptors: rods (black/white) and cons (color)
- bipolar cells: receive information with rods and cones
- ganglion cells: end neuronal cell whose axon becomes the cranial nerve II (optic nerve)
37
The optic nerve
- leaves through the back of the eye through the optic papilla (tunnel)
- contiguous with the brain and is surrounded by subarachnoid space
- subject to changes with increased intracranial pressure
- optic disc: the nerve
- optic cup: the papilla
- cup should be less than half the diameter of the disc
38
Fovea centralis
- macula lutea is found lateral to the optic disc
- yellowish area of pigmentation at the center is the fovea centralis
- rod free area of thinned retina with no overlying vessels
- has one to one cone to ganglion ratio producing great focus
- best visual acuity here
39
How vision works
- light enters eye
- must pass through the layers of the neural retina as the photoreceptors are at the bottom
- rods and cons synapse with the bipolar cells who turn synapse with the gangalion cells
- axons gather together to become the optic nerve
- nerve travels through the optic chiasm and become the optic tract and on to the lateral geniculate body that resides in the thalamus
- they synapse there and go on to the visual cortex on the occipital lobe by the way of the Geniculocalcarine tract
