8 - mata sebagai alat optik

8/13/2019 8 - Mata Sebagai Alat Optik

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Mata sebagai

Alat Optik


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Media Refraksi :

Kornea n = 1.33 Humour Aqueous n = 1.33

Lensa n = 1,41

Badan Kaca (Vitreous) n = 1.33

Kekeruhan media refraksigangguan penglihatan


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Kekuatan refraksi bola mata

Total : 60 dioptri

Kornea : 40 dioptri

Lensa : 20 dioptri


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Proses Akomodasi Kemampuan menambah kekuatan refraksi

dengan menambah kecembungan lensa

mata

normal : sinar yang datang dari jarak > 5m

obyek jauh, dianggap memberikan sinar

sejajar - mata dalam keadaan beristirahat,

bayangan akan difokuskan tepat pada

retina (fovea centralis)


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Jika jarak obyek < 5m,

sinar tidak datang

sejajartetapi menyebar(divergen). Jika mata

dalam keadaan beristirahat,

bayangan benda akan jatuh

di belakang retina, sehinggaakan terlihat buram.

Bayangan ini harus digeser

ke depan dan difokuskan di

retina denganmeningkatkan

kecembungan lensa. Proses

ini disebut Akomodasi


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This accommodation

process happens as a result

from the contraction of M.ciliaris in the ciliary body


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These reflexes also happen during theaccommodation process :

Accommodation

MiosisConvergents

Near Reflex/

Trias of Accomodation


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Refraction Anomalies

Normal : Emetropia

Anomalies : (ametropia)

Myopia

Hypermetropia

Astigmatism

Presbiopia


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Emmetropia

Is the condition when the parallel rays focusedexactly on the retina of the eye in relax condition

---> the visual acuity is maximum


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Ametropia

Is the condition when the parallel rays are notfocused exactly on the retina of the eye in relax

condition.

The focal point may be behind or in front of theretina

Hal 47, 4.2 Duke Elder


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Myopia

Refractive condition in which, withaccommodation completely relaxed, parallel

rays are brought to a focus in front of the retina.

Myopic eye : refractive state over plus power


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Factors that causing myopia :

Axial : The antero-posterior axis of the eye ball > normal

in this case, the refraction power of the cornea, lens and the lens

position are normal. The eye usually looks like proptosis

Curvature :

The size of the eye ball ---> normal, but there is a increasing of the

cornea/lens curvature

The change of the lens e.g. : intumescens cataract

Increasing of the refraction index

could occur on Diabetic patient

Changes of the lens location

changes of the lens position to the anterior after glaucoma surgery

lens subluxation


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Clinical findings :

Farsightedness are blurred, nearsightedness are normal

Asthenopia

On high myopia : hemeralopia occurred caused by

periphery retinal degeneration

Floating spots visualization caused by vitreous

degeneration

screw up the eye lids together, in order to get a better

vision

On high myopia ----> proptosis simulation, deep

Anterior Chamber


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Funduscopy : Tigroid fundus ---> thin retina and

the choroid, myopic crescent arround the papillaarea, sthaphyloma posterior


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Complication :

Commonly occurred on high myopia

1. Degenarated and liquefied vitreous

2. Retinal detachment

3. Pigmentation changes + Macular bleeding

4. Strabismus

Myopia classification :

< 3.00 D = low myopia

3.00 - 6.00 D = moderate myopia

> 6.00 D = high myopia/gravis


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Treatment :

Low and moderate myopia : full correction with

weakestspherical lens that give the best visual

acuity

Example :

VOD = 5/60 S -2.50 D = 6/7S -2.75 D = 6/6

S -3.00 D = 6/6

S -3.25 D = 6/7

The glasses are S - 2.75 D

On high myopia, usually full correction are notgiven due to headache that may occurred. Ifnecessary, reading glasses can be given --->

bifocal glasses


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Prognosis :

Simplex/stationer, after puberty will be constant

Progressive myopia, the myopia will be

continuously higher and complication may

occurred


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Hypermetropia

Is a refraction anomaly that without accommodationparallel rays will be focused behind the retina

Divergent rays from near object, will be focused farther

behind the retina


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Etiology :

Axial ---> eye ball diameter < N

Deminished convexity of cornea/lens curvature

Decreasing Refractive index

Changed lens position


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Clinical manifestation :

H. Manifest ---> is detected withoutparalazing accommodation and is represented

by the strongest convex glassneeded , the

patient sees most distinctly. It correspons to the

amount of accommodation which he relaxes

when a convex lens is placed before the eye.

Devided into two types :

Facultative : Can be overcome by an effort ofaccommodation

Absolute : Can not be overcome


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Total Hipermetrop : detected after the

accommodation has been paralyzed with

cylcopegic agents

Latent Hypermetrop : is the diference of the

total hypermetrop with the manifesthypermetrop


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Latent Hypermetrop

Hypermetrop manifest

Hypermetrop


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Clinical finding :

Nearsightness are blurred

High hypermetropia at old age : farsightedness

also blurred

Astenophia accommodative (eye strain)

Children : high hypermetropia usually

occurring convergent strabismus (convergent

squint)


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Treatment :

If foria/tropia not present, apply strongest

positive spherical lens that give the best visualacuity

If foria/tropia present, total hypermetrop

correction. If necessary : bifocal eye glasses


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astigmatism

Refractive condition of the eye in which there is adifference in degree of refraction in diferentmeridian, each will focused parallel rays at adifferent point. The shape of the images :

Line, oval, circle, never a point


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Manifestation :

Regular astigmatism

Difference in the degree of refraction in every

meredian.

Two principles meridian : Maximmum refraction

Minimum refraction

Irregular astigmatism

Difference in refraction not only in different

meridians, but also in different parts of the same

meridian.

Right angle

to each other


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Etiology of astigmatism :

Corneal curvature disturbances ---> 90%

Lens curvature disturbances ---> 10%

Type of Astigmatism :Ast. M. Simplex C-2.00 X 90

Ast. H. Simplex C+2.00 X 45

Ast. M Compositium S-1.50 C-1.00 X 60Ast. H Compositium S+3.00 C+2.00 X 30

Ast. Mixtus S+2.00 C-5.00 X 180

0

0

0

0

0


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Ast. M. Simplex Ast. H. Simplex

Ast. M Compositium Ast. H Compositium

Ast. Mixtus


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Presbiopia

Physiological changes because accommodation

capability is lowering at old age

Accommodation

Age

16

10

6

2

10 20 40 50 60


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Presbiopia correction :

40 years old S + 1.00 D



55 years old S + 2.50 D60 years old S + 3.00 D

Consider the type of previous/history work

TailorArchitect

Weld engineer


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Refraction Examination

Technique

Subjective :

Snellen chart/projector, alphabet , inverse E, picture,Landolt ring

Trial lens

Trial frame

Objective :

Children, incooperative, difficult correction, strabismus : Ophthlamoscopy Retinoscopy

Refractometer


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Subjective

Check firstly just one eye : ODDistance : 5 or 6 meters

VOD : ...(basic right eye visus)

a. Trial and error apply S + 0.50, better visus , add S+ until visus = 6/6

S +0.50, lower visus, change to S -, increase S - until

visus = 6/6

S +/- not working ----> cylindrical With astigmatism dial, stenoplic slit, cross cylinder

astigmatism dial :

Blurred line ----> C negative lens axis


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b. One by one fogging

S + sp. Lens --> blurred vision, step by step distracting

---> best sp.

Near Vision test / reading test

Both eyes at one time at required distance : use jaeger

chart


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Example :I. AVOD 2/60 S - 3.50 = 6/6

AVOS 3/60 S - 3.00 = 6/6

II.AVOD 2/60 S - 3.00 = 6/7AVOS 3/60 S - 2.75 = 6/7

read ADD S + 1.50

Give Eye Glasses according to II

ODS 6/6

headache, eye strain

ODS 6/6

w/o headache, eye strain


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Objective

Use cyclopegic1. Ophthlamoscopy : papilla clearly seen with

which lens

2. Retinoscopy :

Ordinary ---> light source outside

streak -----> light source inside

3. Refactometer

Computerized Lensmeter principal


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Ideally :

Subjective

Objective with cyclopegic

Subjective once more without cyclopegic

Lens meter

Measuring lens power

Measuring focus distance


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Eye Glasses

Monofocal Bifocal

Progressive

Eye Glasses Prescription, the components

are :

Which eye (OD or OS)

Power of the lens ( + or - , Power, axis)

ADDE for reading

Pupil distance far/near

Name of the patient


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Binocular Optical Defects

Anisometropia :

Condition wherein the refractions of the two

eyes are an equal

variation : Myopia M

M. E.

H. E.H. H.

M. H

Antimetropia


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Vision in Anisometrop

difference < 2.50 D : still get fusion + singlebinocular vision

difference > 2.50 D : fusion difficulties ---->

weak eye suppression ---> amblyopic

alternans vision : left and right alternate

Aniseikonia :

The difference of shape and size of the images

between right and left eye


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Limitation of the eye glasses

cannot applied for anisometropia more than 2.50

Dioptri anisometropia causing aniseikonia

Contact lens : Hard ---> rigid lens

Soft

Indication :

High anisometropia

irregular astigmatism

Front asymmetry, orbit

Aniridia Descemetocele

Sports

Cosmetics


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Refraksi

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 distance in meters

D = 1/f

1 D lens, parallel light will be directed into

focal spot in 1 meter distance

2 D = 1/f ----> f = ?

If f = 25 cm , ----> D = ?


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Parallel rays will be converged to the focus

---> Plus lens (+)

or will be diverged as if it comes from the

focus ----> Minus Lens (-)


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Rays coming from distance > 5 m

parallel rays

Rays coming from distance < 5m

divergent rays

Principles


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Spherical lens

Is a lens with the same curvature diameter in

all meridians

Spherical Convex (+) Spherical Concave (-)


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Prismatic Effect that occur on eye glasses

explain :Against motion with (+) Lens

With motion, with (-) Lens

Spherical Lens :Plus sphere : Convex

characteristic : makes larger and nearer images

Biconvex Plano K

+2 +2 0 +4

Concave K

+5 -1


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Minus sphere : Concave

Characteristic : makes smaller and fartherimages

Bi Concave Plano K Convex K

Parallel rays will be centered or diverged

from the focus

-2 -2-40 +1 -5


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Cylindrical Lens

Is a kind of lens that have twomeridians that are perpendicularto each other

The meridian that has no poweris called the axis

The other meridian, has the

power


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Spherocylindrical Lens

Is a combination between spherical lens andcylindrical lens

Example :

S + 2.00 D C + 1.00 D X 90 0

+

+ 2.00

+ 2.00

0.00

+ 1.00

+ 2.00

0.00

+ 2.00

+ 1.00

+ 2.00

+ 3.00


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TranspositionMethods :

Sphere : Sum with algebra ways SPH + CYL

Cylinder : replace power marks (Neg Pos),axis change 90 degrees

Example : S + 2.00 C + 1.00 X 90

S + 3.00 C - 1.00 X 180

0

0

8 - mata sebagai alat optik

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