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Clinical Medicine > Intro to eye / Test & tools > Flashcards

Intro to eye / Test & tools Flashcards

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
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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)
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3
Q

Hyperopia

A
  • shorter eyeball

- farsighted

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4
Q

Myopia

A
  • longer eyeball

- nearsighted

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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
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6
Q

Belladonna alkaloids

A
  • anticholinergic
  • cause pupils to be large
  • unable to focus the lens
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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

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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
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9
Q

Extraocular muscles (EOM)

A

-testing can reveal cranial nerve dysfunction or peripheral problems with musculature

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10
Q

Macula

A
  • dark spot in eye
  • highest density of photoreceptors
  • where our central vision is
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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
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12
Q

Tonometry technique

A

-applanation tonometry calculates intraocular indirectly by measuring the force required to flatten a constant area of the cornea

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13
Q

Tonometry shortcomings

A
  • get falsely high measure in pt with thicker corneas

- get falsely low measure in pt with thinner corneas

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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
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15
Q

Color vision testing

A
  • Ishihara test
  • Farnsworth-Munsell Dichotomous D-15 test
  • Lanthony Desaturated color test
  • Gold standard: oculus anomaloscope
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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
Q

Sclera

A

-outermost layer of orbit
-tough and protective
-cornea is the anterior portion of this layer
-Limbus: where the sclera becomes the cornea
-

26
Q

Choroid

A
  • 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
Q

Retina

A
  • inner most layer
  • visual layer
  • exits the orbit as the optic nerve
28
Q

Anterior chamber

A
  • in front of the iris

- contains aqueous humor

29
Q

Posterior chamber

A
  • between iris and lens

- contains aqueous humor

30
Q

Vitreous chamber

A
  • behind the lens

- contains vitreous humor (thick gelatinous substance that gives eyeball its shape)

31
Q

Ciliary Body

A
  • 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
Q

Iris

A
  • 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
Q

Accommodation

A
  • 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
Q

Retinal layers

A
  • Pigment epithelium

- neural retina

35
Q

Pigment epithelium of retina

A
  • 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
Q

Neural rentia

A
  • 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
Q

The optic nerve

A
  • 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
Q

Fovea centralis

A
  • 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
Q

How vision works

A
  • 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

Clinical Medicine (19 decks)

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