Download - 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
45 years old S + 1.50 D
50 years old S + 2.00 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