2: intro into ret

intro into retinoscopy 

what is retinoscopy

it is means of objectively determining the size of refractive error

can determine if the eye has astig,atism and can correct it

millodots definition of retinoscopy

the determination of the refractive state of the eye by means of a retinscope

why is retinscopy objective 

patient is not required to respond as no questions are being asked 

why do we ask pateints to look into the distance

to relax their eyes focusing myscles (ciliary muscles), making it easier to read the true prescription. Eyes stop accomodating giving a more accurate measurement

what does retinscope look like

light emitted by streak ret shows rectangle beam, spot ret is circle

sleeve/ collar must always be at lowest position, turning the collar changes the orientation of the streak

what does changing orientation of streak using sleeve mean 

tells us that the eye has diff focusing powers in diff directions - astigmatism

streak of light moves differently depending on the axis of astig 

by rotating sleeve and watching how light relfex changes doctor can figure out:

axis of astig 

amount of astig 

advantages of retinoscopy

objective means establishing refractive error

speeds up refractive error determination

quick to perfomr

accurate

in some patients specs can be prescribed directlty ffrom retinoscopy

disadvantages

can be difficult to learn

basic set up for retinoscopy 

patient wears trial frame to hold lenses 

patient views distant target 6m, so refractive eror can be determined when accom is relaxed 

direct them to spotlight target needed toholf eyes steady and ensure looking a fixed distance away 

fairly level with the eyes 

dim lights 

observe relfex of one eye using BOTH eyes 

working distance

should take under a minute

how ca we generate different amounts of myopia or hyperopia

by rotating/ pulling back the back of the eye

the scale is usually calibrated :

e.g. -4 to+4 unit in D

minus signs 

simulated myopia 

if scale reads -3.00  Dt he model eye is myopic by -3.00 D 

plus signs

simulated hyperopia e.g if the cale reads +2.00 D the model eye is hyperopic by +2.00 D

how do you alter axial length

pull retina away from the front of the eye or by pushing it towards the front of the eye

long eyes are myopic

short eyes are hyperopic

leses are placed in front of the eye

dioptre 

a unit proposed by monoyer to evalate the refractive power of the lens or of an optical system 

duochrome 

a subjective refraction test in which the sibject compares the sharpness of black targets of similar sizes on a red background on one side and a green on the other 

what are we doing when we alter axiallength

we are generating axial ametropia

• when light located at E light from the distant object is fomred on the retina

• when retina is moved further away from the front of the eye ( longer axial length) eye becomes myopic M

• when retina moved closer then eye becomes hyperopic H

how does retinoscopy work

involves you comparing the movement of retinal reflex with the movement of light outside the patients eye, when the retinoscopy light is moved

whats retinal reflex 

the light that bouncs back from the eye of patient youre examining relfex might move with or againts you 

with and against movements

if you move light to th right:

if relfex moves left its against: myopic; means far point is in front of infinity - somehwere closer to examiner

if behind the far point during retinoscopy (usually are unless really close) the light leaving eye diverges and moves in opp direction

if reflex moves right its with; hyperopic, youre in front of the far point 

always move the light at right angles to the prientation of streak e.g if streak is vertical, move the light horizontally

in myopia the far point is closer to the eye so you end up being behind it causing against movement 

speed of relfex

shows how fast light moves across the pupil

fast reflex: eye is closer to emmetropia

slow reflex: eye is far from focused, high myopia or hyperopia

tells how weak the refractive error is

brightness of reflex 

bright reflex: eyes focusing is stronger or closer to neutral , easy to see

dim reflex: may indicate high refractive error , small pupil or media opacity like cataracts 

how does dim reflex indicate cataracts

catarcats is clouding of the lens

cloudy lens scatters and absorbs some of the light, so less light reaches the retina and reflected back

what are we trying to achieve in retinoscopy

we are trying to identify the lens power where the relfex movement is neither with or against but instead flashes ( reversak) .

shows an endpoint of retinoscopy