VISION - THE EYE Flashcards by Ellie Williams

name the 3 layers of the eye?

outer = cornea and sclera
middle = uveal tract
inner = retina

How well did you know this?

Not at all

Perfectly

explain the function of the eye?

transmits light to the sensitive tissue
metabolic functions mentioning the eye
direction and focus of gaze
protection of the delicate features
the conversion of light to a nerve impulse

How well did you know this?

Not at all

Perfectly

state the requirements for vision?

transparency
refractive power
direction of gaze
metabolic functioning
brain capable of perceiving image

How well did you know this?

Not at all

Perfectly

describe refractive power as a function of vision?

-the eye acts as a set of lenses focusing light onto the retina (macula).
—this is known as refraction
-this is mainly a function of the cornea and the length of the eyeball (e.g. position of the macula)
—the lens only makes adjustments for near vision

How well did you know this?

Not at all

Perfectly

define myopia and how it is corrected?

too much refractive power (short sightedness)

-requires a minus spherical lens (concave) to reduce focusing power

How well did you know this?

Not at all

Perfectly

define hypermetropia and how it is corrected?

not enough focussing power

-plus lenses (convex) are used to add focussing power to the eye

How well did you know this?

Not at all

Perfectly

define presbyopia?

describes the changes which occur to the lens resulting in loss of accommodating power

How well did you know this?

Not at all

Perfectly

define astigmatism?

a curvature in the eye that causes blurred distance and near vision
-measured along one axis as a cylinder

How well did you know this?

Not at all

Perfectly

state which structures of the eye allow vision through transparency?

tear film
cornea
anterior chamber and aqueous
lens
vitreous
transparent layers of the retina

How well did you know this?

Not at all

Perfectly

explain the functions of the transparent media (cornea and lens).

transmission of light to the sensitive tissues
focus of gaze
protection of delicate structures

How well did you know this?

Not at all

Perfectly

what is the tear film and lacrimal gland?

produces by various glands in the eye lids

- the lacrimal gland produces excess tears seen in injury or times of emotion

How well did you know this?

Not at all

Perfectly

state the role of the tear film?

protection

- transparency

How well did you know this?

Not at all

Perfectly

what are the 3 layers to tear film?

oily outer layer
watery middle layer
inner mucin layer

How well did you know this?

Not at all

Perfectly

what is the cornea, and what are its 2 main functions?

it covers the anterior one-fifth of the eye ball
it is a dome shaped oval consisting of 5 distinct layers
these are all transparent, allowing protection and refraction

How well did you know this?

Not at all

Perfectly

describe the functions of the cornea and the lens?

-they are transparent and the main refractive media of the eye
-aqueous and vitreous have very low refractive power
-overall power of the eye is 58 dioptres
—lens contributes about 15 D (range of about 8D before presbyopia)
—cornea contributes to about 43D

How well did you know this?

Not at all

Perfectly

describe the structure and function of the pupil?

-the pupil is a hole in the centre of the thin, contractile circular iris muscle
-regulates the amount of light entering the posterior segment of the eye
—avoiding bleaching of the retinal pigments
-pupil dilates in dark and constricts in bright light

state the difference between the dilator and sphincter pupillae muscles of the iris?

*dilator pupillae
-when contracted = dilated pupil, sympathetic reflex follwoing 3rd nerve pathway (mydriasis)
*sphincter pupillae
-when contracted, moves pupil inwards
—e.g. constricts via parasympathetic reflex following blood vessel pathway (miosis)

list the 9 positions of gaze?

forward gaze
elevation
depression
left and up
left gaze
left and down
right and up
right gaze
right and down

describe binocular single vision (BSV)?

-each eye sees a slightly different image
-the brains ability to see this as one image is BSV
—simultaneous perception
—fusion
—stereopsis
-corneal light reflexes to assess alignment

describe the 3 factors required for BSV development?

reasonable clear vision in both eyes
the ability of the visual areas in the brain to promote fusion of the two slightly dissimilar images
the precise coordination of the two eyes for all directions of gaze

what is amblyopia?

-until the age of 8, the visual process has not matured
—if the eye is not used it may lose the ability to see
— this results in reduced visual acuity and is a condition called amblyopia (lazy eye)

list the structures if the retina?

-ora serrata anterior
-optic disk posterior
-macula
-retinal artery arcades
-retina
—inner neurosensory
—outer pigmented

what is the choroid and retinal blood supply?

-all branch from the ophthalmic artery: first branch off internal carotid
*central retinal artery supplies the inner 2/3 if retina and optic nerve = extraocular part
-anatomical idiosyncrasy = the posterior ciliary artery supplies optic nerve head including optic disk
= intraocular part
*the choroid supplies the other 1/3 (from ciliary artery too)

name and describe the metabolic functions in the eye?

*tear film production 
—goblet cells, meibomian glands, krausse + wolfring, lacrimal gland 
*cornea
—oxygen, deturgesence (Na pump)
*uveal tract 
—aqueous production 
*lens
—epithelial pump mechanism, glucose metabolism
*retina
—photoreceptor activity

explain the uveal tract in the metabolic functioning of the eye and vision?

``` *uveal tract form —iris, ciliary body, choroid *uveal tract functions —protection (iris) —metabolic functioning (aqueous formation by ciliary body, blood supply to retina) —absorption of excess light (choroid) ```

describe intraocular pressure (IOP)?

- the fluid pressure inside the eye | - achieved by glance between production and drainage of aqueous humour

what are the 4 parts if the anterior lid structure?

- skin - lashes - greyline - orbicularis muscle

describe how eyelids open?

*levator muscle —arises from lesser wing of sphenoid bone of the orbit —follows superior rictus and shares its muscle sheath —divides into: aponeurosis which inserts into obicularis and skin müllers muscle to tarsal plate —enervated by CN 3

list the 12 cranial nerves and their function?

1) olfactory = smell 2) optic = sight 3) oculomotor = moves eye, pupil 4) trochlear = moves eye 5) trigeminal = face sensation 6) abducens = moves eye 7) facial = moves face, salivate 8) vestibocochlear = hearing, balance 9) glossopharyngeal = taste, swallow 10) vagus = heart rate, digestion 11) accessory = moves head 12) hypoglossal = moves tongue

how many cranial nerves are involved with the eye?

6 - optic - oculomotor - trochear - trigeminal - abducens - facial

explain the visual pathway (CN2)?

- the retina and optic nerves - the chiasma - the optic tracts - the lateral geniculate bodies - the optic radiations - visual cortex and other areas if the brian

describe the roles of cranial nerves 4 to 7 in the eye?

*4th = trochlear nerve —supplies motor impulse to superior oblique muscle which moves the eye down and out *5th = trigeminal nerve (has 3 divisions) —1st sensory from conjunctiva, sclera, cornea, iris, eyelid, scalp, forehead, nose *6th = abducent nerve —supplies the lateral recuts muscle which moves the eye laterally *7th = facial nerve —has parasympathetic supply to lacrimal gland + motor supply to orbicularis muscle for lid closure

describe visual perception in the brain as a function of vision?

- visual pathway | - other contributing factors

describe the 3 stages of perception?

1) the visual system analyses info from external world derived from a range of possible signals —all of which are captured captured by the retina —fixation/ attention, discrimination from surroundings 2) this info is integrated with input from other sensory systems and memory 3) the final stage is perception- involves brain editing to ensure normality and constancy, involves: —form perception followed by —object recognition, which depends on capacity to acquire + store info + accumulate experience

what is vision?

the end profit if processing, by the cerebral cortex, of sensory responses made by the retina to light stimulation -some degree of processing is thought to take place in the retina —also includes appreciation of spatial perception or appreciation of size, distance and depth

state the components of vision?

- orientation perception (measuring by eye) - motion perception (BSV) - colour perception - shale detection (element of memory involved) - brightness discrimination (luminance/ contrast sensitivity) - image stabilisation