Eye and visual pathway

orbit has … bones

7 bones

7 bones of the eye orbit

1. frontal bone
2. zygomatic bone
3. sphenoid bone
4. lacrimal
5. ethmoid
6. palatine
7. maxilla

3 basic functions of eyelid

1. distribute tears across eye surface
2. limit light that enter eye
3. together with eyelashes, protect from FB (blinking mechanism)

tarsal plates

band of CT

* houses meibomian glands

palpebral fissue

area btw upper lid and lower lid

* should be sim bilateral
* normal if cover some iris, not normal if cover pupil

what do meibomian glands produce

oily lubricant for surface of the eye

levator palpebrae

elevate eyelid

what innervates levator palpebrae

CN III- occulomotor

3 chambers of the eye

1. anterior- btw cornea and iris
2. posterior- btw iris and lens
3. vitreous- btw lens and retina

anterior chamber (5)

1. conjunctiva
2. sclera
3. cornea
4. iris
5. pupil

conjunctiva

* vascular, clear mucous membrane
* 2 parts
* bulbar- cover anterior eye / sclera
* palpebral- lines eyelid

sclera

white of eye

opaque, fibrous, protective, outer layer

cornea

* transparent and avascular
* cover iris and pupil
* limbus = where conjunctiva meets cornea

iris

* colored, circular muscle
* control diameter of pupil and amount of light entering

pupil

* eyes aperture
* allows light to travel btw eye to retina

tear function

1. prevent excessive drying
2. provide nutrition and oxygen
3. possess antibacterial properties

3 layers of tears and lacrimal aparatus

1. inner mucous layer- conjunctival cells
2. outer lipid/ oil later- meibomian glands
3. watery later- lacrimal glands

tear production pathways

lacrimal glands → sweep across eye to punctum medially

drain into lacrimal sac → down nasolacrimal duct → into inferior nasal turbinate

posterior chamber (2)

1. lens
2. aqueous humor

lens

* suspended by ligaments
* muscles of ciliary body control thickness of lens
* allows eye focus on near/distant objects

accommodation

allows eye focus on near/distant objects

aqueous humor

* produced by ciliary body
* fills anterior and posterior chambers
* circulates from posterior chamber to anterior chamber via pupil
* drains out through canal of schlemm
* control the intraocular pressure

vitreous chamber (2)

1. vitreous body
2. optic fundus

vitreous body

* gelatinous material
* posterior to lens
* maintains the shape of eye

optic fundus

1. retina
2. choroid
3. macula
4. fovea
5. optic disc
6. physiological cup
7. retinal vessels

retina

rods and cones

macula

functional center of retina

fovea

center of macula; central vision

optic disc

where optic nerve exist & retinal vessels enter

physiologic cup

white, cup-like area in center of optic disc

size of physiologic cup

should be no more than 1/2 diameter of disc

less than 0.5

area with largest amount of cones and clearest vision

fovea

extraocular muscles and innervation

1. superior rectus - CN III
2. inferior rectus - CN III
3. medial rectus - CN III
4. lateral rectus - CN VI
5. superior oblique - CN IV
6. inferior oblqiue - CN III

(LR6SO4)R3

why is 15 degree significant

optic disc - 15 degree temporal from central vision

light reflected into optic disc

visual field

entire area seen by eye when it looks at a central point

blind spot

15 degree temporal to lines of gaze

* no rods or cones

binocular vision

overlap of visual field

why do fields extend farther on temporal side?

nose limits medial vision

visual pathways

1. cornea
2. anterior chamber
3. pupil
4. lens
5. vitreous body
6. retina

projected imagine on retina is ….

upside down and revered R and L

light reflected from visual pathways must pass through …. and be focused on photoreceptors in the …

pupil

retina

T/F anything seen nasally will stay on same side

True

pupil change size in response to …

light and focus on near object

pupillary reaction: light reaction

1. direct


1. pupillary constriction of stimulated eye
2. consensual reaction


1. constriction of opp pupil
3. oculomotor nerve (CN III)

pupillary reaction: Near reaction

1. pupil constriction when shifting gaze far to near objects


1. CN III
2. occurring coincidentally


1. convergence- medial rectus movement
2. accommodation- increased convexity of lenses due to contraction of ciliary muscle

what brings near objects into focus

change in lens

vision testing- visual acuity

Tests central vision

OD

Right eye

OS

left eye

OU

both eyes

testing far vision steps

1. test at 20 ft with standard size snellen chart
2. corrective lenses should be worn if other than for reading
3. records as fraction (20/20 = normal), and if corrected


1. larger denominator, poorer vision

myopia

nearsightedness

* difficulty seeing distant objects clearly
* most common cause of impaired vision

near vision test step

1. test at 14 in with pocket chart
2. can be used bedside
3. identify need for reading glasses or bifocals in pt >45 years

hyperopia

farsightedness

* dif seeing close

presbyopia

age related, gradual loss of ability to focus on near objects

* loss of elasticity of lens of eye

visual testing- visual fields by confrontation

estimates peripheral vision

\*static finger wiggle

static finger wiggle

1. use own visual field as referene
2. screen with both eye together


1. if defect found, refer for definitive testing

\*just screening test

what lives in optic chiasm

pituitary gland

horizontal defect

occulsion of a branch of central retinal a may cause horizontal defect

* ischemia of optic n can produce sim defect

Blind R eye (r optic n)

lesion of optic n and eye itself, produce unilateral monocular blindness

bitemporal hemianopsia (optic chiasm)

lesion at optic chiasm (pituitary tumor), may involve only fibers crossing over opposite side. Since fibers originate in nasal half of each retina, visual loss involves the temporal half of each field

Left homonymous hemianopsia (R optic tract)

a lesion of optic tract, interrupts fibers originating on same side of both eyes. Visual loss in the eyes is, therefore, similar (homonymous) and involves half of each field (hemianopsia)

Homonymous Left superior quadrantic defect (R optic radiation, partial)

partial lesion op optic radiation in the temporal lobe, may involve only a portion of the nerve fibers, producing, for example a homnoymous quadrantic (pie in the sky) defect

Left homonymous hemianopsia (R optic radiation)

a complete interruption of fibers in the optic radiation, produces visual defect similar to that produces by a lesion of the optic tract

examination of the eye- external eye (5)

1. ocular symmetry
2. eyebrow
3. eyelids
4. bony orbit
5. lacrimal apparatus

examine ocular symmetry

note position and alignment of eye

examine eyebrows

fullness/thinning, hair distribution, scaliness

examine eyelids

width of palpebral fissure, edema, color, lesions, eyelashes, closure of eyelids, drooping of retracted

examine bony orbit

pain, trauma, bruising, crepitus (ricecrispy crunching)

palpate

examine lacrimal apparatus

swelling, excessive tearing or dryness, nodules, discharge, tenderness

examination of eye- conjunctiva and sclera

1. conjunctiva - bulbar/palpebral
2. sclera

examination of the eye- cornea, lens and iris

1. cornea and lens
2. iris

examine conjunctiva

look at color, vascular pattern

* injection/hemorrhage
* foreign bodies /growth
* discharge
* nodularity
* edema
* every upper eyelid

examine sclera

perform in combo with conjunctiva- color/vascular pattern

examine cornea and lens

inspect with oblique lighting from temporal side

* clarity
* opacities
* scars
* irregularities

examine iris

inspect at same time as cornea and lens

* crescent shadow
* iridectomy scars- complete or peripheral irregularities from trauma

examination of the eye- pupils (6)

1. inspect


1. size (diameter)
2. shape


1. round, oval, irregularity
3. symmetry
2. miosis- constriction of pupils
3. mydriasis- dilation of pupils
4. aniscoria


1. pupils inequality > .4mm
2. can be normal variant


1. approx 35% of population
2. size difference rarely exceed 1 mm
3. Horners CN III paralysis
5. check reaction to light (direct and consensual)


1. block light between eyes
6. check accommodation / near reaction

miosis

constriction of pupils

mydriasis

dilation of pupils

examination of eye- extraocular muscles

1. alignment
2. extraocular movements
3. check for convergence

nystagmus

* can be normal ossulation that at very end lateral portion visual field
* can be abnormal

convergence

keep object stagnant as move it closer to face

steps of fundoscopic exam

1. remove glasses unless you have marked nearsightedness or severe astigmatism
2. darken room
3. 15 inches away from patient and 15 degree lateral
4. note red reflex
5. examine optic disc and retina


1. inspect outline of disc, color, size of physiologic cup
6. inspect retinal vessels and fovea/macula

what is fundoscopic exam looking at

retina- arteries, veins, arteriovenous crossings, fovea, and macula

disc: orange

cup: light, and less than half diameter

\*vessels get bigger as closer to disc and cup

distinguish arteries and veins on fundoscopic exam

arteries light red, smaller, bright

veins: dark red, larger, inconspicuous or absent

seborrheic dermatitis of eyebrow

scaliness

absence of lateral 1/3 of eyebrow

hypothyroidism

exophthalmos

protrusion of eyeball

lid retraction: rim of sclera visible btw upper lid and iris

hyperthyroidism

ptosis

drooping of eyelid

cause:

• myasthenia gravis, oculomotor nerve damage, horner syndrome, senile ptosis, congenital

blepharitis

inflammation of eyelid at base of hair follicle

MC chronic, S. aureus

red inflamed lid margin often crusting

xanthelasma

benign, raised, yellow well circumscribed cholesterol-filled plaque

hyperlipidemia and primay biliary

entropion

inward turning lid margin

lashes abrade cornea

ectropion

outward turning of lid margin

dry eyes

stye (hordeolum)

painful, tender red lump at inner or outer margin of eyelid

points out (like pimple)

chalazion

nontender, painless nodule on eyelid caused by blocked meibomian gland

usually points inside the lid

darcycystitis

infection or inflammation of lacrimal sac usually due to blockage in nasolacrimal duct

painful, red, swollen, tearing

pressure applied to lacrimal sac may push tick material through punctum

raccoon eye

periorbital ecchymosis

• may be unilat or bilat

basilar skull fracture

• facial / orbital bone fracture

conjunctivitis

inflammation of conjunctiva

viral, bacterial, allergic, chemical

discharge, vision blurry

cornea clear, pupil not affected

pingecula

benign yellowish, raised nodule of bulbar conjunctiva

nasal side, can be tempral

does not cross limbus

potentially due to combination of dry eye and exposure to dust or light

pterygium

sufers eye

triangular, fleshy tissue growth of bublbar conjunctiva

can progress to cover part of cornea (vision affected)

causes can be dry eyes, wind, dust, UV light