12-refraksi

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Refraction

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Refraction

• Consists of :

– General Optics

– The optical system of the eye

– Clinical anomalies : refractive errors

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Optic

• Dioptri (D) : Lens power unit, is an inverse

of focal istance in meters

D ! "#f

• " D lens, parallel li$ht will %e irecte into

focal spot in " meter istance

& D ! "#f '''' f !

*f f ! &+ cm , '''' D !

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• arallel rays will %e conver$e to the focus ''' lus lens (-)

• or will %e iver$e as if it comes from the focus '''' .inus

Lens (')

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• /ays comin$ from istance + m

parallel rays

• /ays comin$ from istance 0 +m

iver$ent rays

rinciples

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• 1pherical lens

– *s a lens with the same curvature iameter in

all meriians

1pherical Conve2 (-) 1pherical Concave (')

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• 3 conve2 lens may %e re$are as a series

of prisms %ases towar the mile of the

lens• 3 concave lens may %e re$are as a series

of prisms ape2 towar the mile of the

lens

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• rismatic 4ffect that occur on eye $lasses

e2plain : – 3$ainst motion with (-) Lens

– 5ith motion, with (') Lens

• 1pherical Lens : – lus sphere : Conve2

• characteristic : ma6es lar$er an nearer ima$es

7iconve2 lano 8

-& -& 9 -

Concave 8

-+ '"

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• .inus sphere : Concave

– Characteristic : ma6es smaller an farther ima$es

7i Concave lano 8 Conve2 8

• arallel rays will %e centere or iver$e

from the focus

'& '& '9 -" '+

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Cylindrical Lens

• *s a 6in of lens that have twomeriians that are perpenicularto each other

• The meriian that has no poweris calle the a2is

• The other meriian, has the

power

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• 1pherocylinrical Lens

– *s a com%ination %etween spherical lens ancylinrical lens

– 42ample :

• 1 - &;99 D C - ";99 D < =9 9

-

- &;99

- &;99

9;99

- ";99

- &;99

9;99

- &;99

- ";99

- &;99

- >;99

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• Transposition – .ethos :

• 1phere : 1um with al$e%ra ways 1? - C@L

• Cyliner : replace power mar6s (Ae$ os),a2is chan$e =9 e$rees

• 42ample : 1 - &;99 C - ";99 < =9

1 - >;99 C ' ";99 < "B9

9

9

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Eye as an Optical Instrument

• /efraction meia :

– Cornea n ! ";>> – ?umour 3ueous n ! ";>>

– Lens n ! ","

– itreous %oy n ! ";>>

• ?aEiness on refraction meia '' istur%ances of vision

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• ower of refraction of the eye %all

– Totally : F9 ioptri

– Cornea : 9 ioptri

– Lens : &9 ioptri

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• 3ccommoation rocess – Capa%ility of ain$ the refraction power of the

eye, %y increasin$ the conve2ity of the lens

– normal : rays that come from + m ' istance

o%ect re$are as parallel li$htH the eyes are in

rela2 position, the ima$es are focuse ri$ht on

the retina (fovea centralis)

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• For object at less than 5 meters

distance, the rays do not come

parallel but divergent. If the eyes

are still in relax position, the

images will be focused behind the

retina. So the object will be seen

blurred. These images must be

moved forward so it will be

focused on the retina by increasing

the convexity of the lens. This

process is called accommodation

process.

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• This accommoation

process happens as a

result from the

contraction of .; ciliaris

in the ciliary %oy

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• These refle2es also happen urin$ theaccommoation process : – 3ccommoation

– .iosis – Conver$ents

Aear /efle2

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Refraction Anomalies

• Aormal : 4metropia

• 3nomalies : (ametropia)

• .yopia

• ?ypermetropia

• 3sti$matism

• res%iopia

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• 4mmetropia

– *s the conition when the parallel rays focusee2actly on the retina of the eye in rela2 conition

''' the visual acuity is ma2imum

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• 3metropia

– *s the conition when the parallel rays are notfocuse e2actly on the retina of the eye in rela2

conition;

– The focal point may %e %ehin or in front of theretina

?al I, ;& Du6e 4ler

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• .yopia

– /efractive conition in which, withaccommoation completely rela2e, parallel

rays are %rou$ht to a focus in front of the retina;

– .yopic eye : refractive state over plus power

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• Jactors that causin$ myopia :

– 32ial : The antero'posterior a2is of the eye %all normal

• in this case, the refraction power of the cornea, lens an the lens

position are normal; The eye usually loo6s li6e proptosis

– Curvature :

• The siEe of the eye %all ''' normal, %ut there is a increasin$ of the

cornea#lens curvature

• The chan$e of the lens e;$; : intumescens cataract

– *ncreasin$ of the refraction ine2

• coul occur on Dia%etic patient

– Chan$es of the lens location

• chan$es of the lens position to the anterior after $laucoma sur$ery

• lens su%lu2ation

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• Clinical finin$s :

– Jarsi$hteness are %lurre, nearsi$hteness are normal

– 3sthenopia

– On hi$h myopia : hemeralopia occurre cause %y

periphery retinal e$eneration

– Jloatin$ spots visualiEation cause %y vitreous

e$eneration

– screw up the eye lis to$ether, in orer to $et a %etter

vision

• On hi$h myopia '''' proptosis simulation, eep

3nterior Cham%er

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• Junuscopy : Ti$roi funus ''' thin retina an

the choroi, myopic crescent arroun the papillaarea, sthaphyloma posterior

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• Complication :

– Commonly occurre on hi$h myopia

"; De$enarate an liuefie vitreous

&; /etinal etachment

>; i$mentation chan$es - .acular %leein$

; 1tra%ismus

• .yopia classification :

– 0 >;99 D ! low myopia

– >;99 ' F;99 D! moerate myopia

– F;99 D ! hi$h myopia#$ravis

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• Treatment :

– Low an moerate myopia : full correction with

wea6est spherical lens that $ive the %est visual acuity• 42ample :

OD ! +#F9 1 '&;+9 D ! F#I

1 '&;I+ D ! F#F

1 '>;99 D ! F#F

1 '>;&+ D ! F#I

The $lasses are S !."5 #

– On hi$h myopia, usually full correction are not $iven

ue to heaache that may occurre; *f necessary,reain$ $lasses can %e $iven ''' %ifocal $lasses

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• ro$nosis :

– 1imple2#stationer, after pu%erty will %e constant – ro$ressive myopia, the myopia will %e

continuously hi$her an complication may

occurre

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Hypermetropia

• *s a refraction anomaly that without accommoation parallel rays will %e focuse %ehin the retina

• Diver$ent rays from near o%ect, will %e focuse farther

%ehin the retina

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•4tiolo$y : – 32ial ''' eye %all iameter 0 A

– Deminishe conve2ity of cornea#lens curvature

– Decreasin$ /efractive ine2

– Chan$e lens position

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• Clinical manifestation :

– ?; .anifest ''' is etecte without paralaEin$ accommoation an is represente

%y the stron$est conve2 $lass neee , the

patient sees most istinctly; *t correspons to the

amount of accommoation which he rela2es

when a conve2 lens is place %efore the eye;

Devie into two types :

• Jacultative : Can %e overcome %y an effort ofaccommoation

• 3%solute : Can not %e overcome

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– Total ?ipermetrop : etecte after the

accommoation has %een paralyEe with

cylcope$ic a$ents

– Latent ?ypermetrop : is the iference of the

total hypermetrop with the manifest

hypermetrop

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Latent ?ypermetrop

?ypermetrop manifest

?ypermetrop

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• Clinical finin$ : – Aearsi$htness are %lurre

– ?i$h hypermetropia at ol a$e : farsi$hteness

also %lurre

– 3stenophia accommoative (eye strain)

– Chilren : hi$h hypermetropia usually

occurrin$ conver$ent stra%ismus (conver$ent

suint)

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• Treatment :

– *f foria#tropia not present, apply stron$est

positive spherical lens that $ive the %est visual

acuity

– *f foria#tropia present, total hypermetrop

correction; *f necessary : %ifocal eye $lasses

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astigmatism

• /efractive conition of the eye in which there is aifference in e$ree of refraction in iferentmeriian, each will focuse parallel rays at aifferent point; The shape of the ima$es :

– Line, oval, circle, never a point

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• .anifestation :

– /e$ular asti$matism

• Difference in the e$ree of refraction in every

mereian;

• Two principles meriian : – .a2immum refraction

– .inimum refraction

– *rre$ular asti$matism

• Difference in refraction not only in ifferent

meriians, %ut also in ifferent parts of the same

meriian;

/i$ht an$le

to each other

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• 4tiolo$y of asti$matism :

– Corneal curvature istur%ances ''' =9K – Lens curvature istur%ances ''' "9K

• Type of 3sti$matism :

– 3st; .; 1imple2 C'&;99 < =9

– 3st; ?; 1imple2 C-&;99 < + – 3st; . Compositium 1'";+9 C'";99 < F9

– 3st; ? Compositium 1->;99 C-&;99 < >9

– 3st; .i2tus 1-&;99 C'+;99 < "B9

9

9

9

9

9

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3st; .; 1imple2 3st; ?; 1imple2

3st; . Compositium 3st; ? Compositium

3st; .i2tus

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Presbiopia

• hysiolo$ical chan$es %ecause accommoation

capa%ility is lowerin$ at ol a$e

3ccommoation

3$e

"F

"9

F

&

"9 &9 9 +9 F9

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• res%iopia correction :

– 9 years ol 1 - ";99 D

– + years ol 1 - ";+9 D

– +9 years ol 1 - &;99 D

– ++ years ol 1 - &;+9 D

– F9 years ol 1 - >;99 D

• Consier the type of previous#history wor6

– Tailor

– 3rchitect

– 5el en$ineer

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Refraction Examination

Techniue• 1u%ective :

– 1nellen chart#proector, alpha%et , inverse 4, picture,Lanolt rin$

– Trial lens

– Trial frame

• O%ective :

– Chilren, incooperative, ifficult correction, stra%ismus :• Ophthlamoscopy

• /etinoscopy

• /efractometer

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• 1u%ective

– Chec6 firstly ust one eye : OD – Distance : + or F meters

– OD : ;;;(%asic ri$ht eye visus)

a; Trial an error

• apply 1 - 9;+9, %etter visus , a 1- until visus ! F#F

• 1 -9;+9, lower visus, chan$e to 1 ', increase 1 ' until visus

! F#F

• 1 -#' not wor6in$ '''' cylinrical

• 5ith asti$matism ial, stenoplic slit, cross cyliner

• asti$matism ial :

– 7lurre line '''' C ne$ative lens a2is

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• One %y one fo$$in$

– 1 - sp; Lens '' %lurre vision, step %y step istractin$

''' %est sp;

• Aearsi$hteness#rea

– 7oth eyes at one time at reuire istance : use ae$er

chart

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– 42ample :*; 3OD &#F9 1 ' >;+9 ! F#F

3O1 >#F9 1 ' >;99 ! F#F

**;3OD &#F9 1 ' >;99 ! F#I3O1 >#F9 1 ' &;I+ ! F#I

rea 3DD 1 - ";+9

Give 4ye Glasses accorin$ to **

OD1 F#F

heaache, eye strain

OD1 F#F

w#o heaache, eye strain

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• O%ective

– Mse cyclope$ic"; Ophthlamoscopy : papilla clearly seen with

which lens

&; /etinoscopy :

• Orinary ''' li$ht source outsie

• strea6 ''''' li$ht source insie

>; /efactometer

• ComputeriEe• Lensmeter principal

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• *eally :

– 1u%ective

– O%ective with cyclope$ic

– 1u%ective once more without cyclope$ic

• Lens meter

– .easurin$ lens power

– .easurin$ focus istance

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• .easurin$ upillary Distance

– rop the flashli$ht li$ht onto %oth eyes, theli$ht is comin$ from in front of the patient,The patient loo6 at the o%server forehea orthe li$ht '''' measure the istance of li$ht

spot %etween OD an O1 '''' as near pupilistance

– Jar istance :

• a & mm ''' for pupil istance less than F9mm;

• 3 > mm ''' for pupil istance more than F9mm

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• 4ye Glasses• .onofocal

• 7ifocal

• ro$ressive

• 4ye Glasses rescription, the components are :

– 5hich eye (OD or O1)

– ower of the lens ( - or ' , ower, a2is)

– 3DD4 for reain$

– upil istance far#near

– Aame of the patient

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!inocular Optical "efects

• 3nisometropia :

– Conition wherein the refractions of the two eyes are

an eual – variation : .yopia .

.; 4;

?; 4;

?; ?;.; ?

3ntimetropia

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• ision in 3nisometrop

– ifference 0 &;+9 D : still $et fusion - sin$le %inocular vision

– ifference &;+9 D : fusion ifficulties ''''

wea6 eye suppression ''' am%lyopic

– alternans vision : left an ri$ht alternate

• 3nisei6onia :

– The ifference of shape an siEe of the ima$es

%etween ri$ht an left eye

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• Limitation of the eye $lasses – cannot applie for anisometropia more than &;+9

Dioptri – anisometropia causin$ anisei6onia

• Contact lens : ?ar ''' ri$i lens

1oft – *nication :

• ?i$h anisometropia

• irre$ular asti$matism

• Jront asymmetry, or%it

• 3niriia• Descemetocele

• 1ports

• Cosmetics

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