Transcript
Refraction
Dr. Edia Asmara Soelendro, SpM
Dr. Pandji A. Akbar, SpM
Refraction
• Consists of :
– General Optics
– The optical system of the eye
– Clinical anomalies : refractive errors
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 = ?
• Parallel rays will be converged to the focus ---> Plus lens (+)
• or will be diverged as if it comes from the focus ----> Minus Lens (-)
• Rays coming from distance > 5 m
parallel rays
• Rays coming from distance < 5m
divergent rays
Principles
• Spherical lens– Is a lens with the same curvature diameter in
all meridians
Spherical Convex (+) Spherical Concave (-)
• A convex lens may be regarded as a series of prisms bases toward the middle of the lens
• A concave lens may be regarded as a series of prisms apex toward the middle of the lens
• 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
• Minus sphere : Concave– Characteristic : makes smaller and farther images
Bi Concave Plano K Convex K
• Parallel rays will be centered or diverged from the focus
-2 -2 -40 +1 -5
Cylindrical Lens• Is a kind of lens that have two
meridians that are perpendicular to each other
• The meridian that has no power is called the axis
• The other meridian, has the power
• Spherocylindrical Lens– Is a combination between spherical lens and
cylindrical lens– Example :
• S + 2.00 D C + 1.00 D X 90 0
+
+ 2.00
+ 2.00
0.00
+ 1.00
+ 2.000.00
+ 2.00+ 1.00
+ 2.00
+ 3.00
• Transposition– Methods :
• 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
Eye as an Optical Instrument
• Refraction media :– Cornea n = 1.33– Humour Aqueous n = 1.33– Lens n = 1,41– Vitreous body n = 1.33
• Haziness on refraction media --> disturbances of vision
• Power of refraction of the eye ball– Totally : 60 dioptri– Cornea : 40 dioptri– Lens : 20 dioptri
• Accommodation Process– Capability of adding the refraction power of the
eye, by increasing the convexity of the lens
– normal : rays that come from > 5 m - distance
object regarded as parallel light; the eyes are in
relax position, the images are focused right on
the retina (fovea centralis)
• 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.
• This accommodation
process happens as a
result from the
contraction of M. ciliaris
in the ciliary body
• These reflexes also happen during the accommodation process :– Accommodation– Miosis– Convergents
Near Reflex
Refraction Anomalies
• Normal : Emetropia
• Anomalies : (ametropia)• Myopia
• Hypermetropia
• Astigmatism
• Presbiopia
• Emmetropia– Is the condition when the parallel rays focused
exactly on the retina of the eye in relax condition ---> the visual acuity is maximum
• Ametropia– Is the condition when the parallel rays are not
focused exactly on the retina of the eye in relax condition.
– The focal point may be behind or in front of the retina
Hal 47, 4.2 Duke Elder
• Myopia– Refractive condition in which, with
accommodation completely relaxed, parallel rays are brought to a focus in front of the retina.
– Myopic eye : refractive state over plus power
• 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
• 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
• Funduscopy : Tigroid fundus ---> thin retina and the choroid, myopic crescent arround the papilla area, sthaphyloma posterior
• 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– > 6.00D = high myopia/gravis
• Treatment :– Low and moderate myopia : full correction with
weakest spherical lens that give the best visual acuity• Example :
VOD = 5/60 S -2.50 D = 6/7
S -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 not given due to headache that may occurred. If necessary, reading glasses can be given ---> bifocal glasses
• Prognosis :
– Simplex/stationer, after puberty will be
constant
– Progressive myopia, the myopia will be
continuously higher and complication may
occurred
Hypermetropia• Is a refraction anomaly that without accommodation
parallel rays will be focused behind the retina
• Divergent rays from near object, will be focused farther behind the retina
• Etiology :
– Axial ---> eye ball diameter < N
– Deminished convexity of cornea/lens curvature
– Decreasing Refractive index
– Changed lens position
• Clinical manifestation :– H. Manifest ---> is detected without
paralazing accommodation and is represented by the strongest convex glass needed , 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 of accommodation
• Absolute : Can not be overcome
– Total Hipermetrop : detected after the
accommodation has been paralyzed with
cylcopegic agents
– Latent Hypermetrop : is the diference of the
total hypermetrop with the manifest
hypermetrop
Latent Hypermetrop
Hypermetrop manifest
Hypermetrop
• 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)
• Treatment :
– If foria/tropia not present, apply strongest
positive spherical lens that give the best visual
acuity
– If foria/tropia present, total hypermetrop
correction. If necessary : bifocal eye glasses
astigmatism• Refractive condition of the eye in which there is a
difference in degree of refraction in diferent meridian, each will focused parallel rays at a different point. The shape of the images :– Line, oval, circle, never a point
• 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
• 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 60
– Ast. 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
Ast. M. Simplex Ast. H. Simplex
Ast. M Compositium Ast. H Compositium
Ast. Mixtus
Presbiopia
• Physiological changes because accommodation capability is lowering at old age
Accommodation
Age
16
10
6
2
10 20 40 50 60
• 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 D– 60 years old S + 3.00 D
• Consider the type of previous/history work– Tailor– Architect– Weld engineer
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
• Subjective– Check firstly just one eye : OD– Distance : 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
• One by one fogging
– S + sp. Lens --> blurred vision, step by step distracting
---> best sp.
• Nearsightedness/read
– Both eyes at one time at required distance : use jaeger
chart
– 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 = 6/7
AVOS 3/60 S - 2.75 = 6/7
read ADD S + 1.50
Give Eye Glasses according to II
ODS 6/6headache, eye strain
ODS 6/6w/o headache, eye strain
• Objective– Use cyclopegic
1. Ophthlamoscopy : papilla clearly seen with which lens
2. Retinoscopy : • Ordinary ---> light source outside
• streak -----> light source inside
3. Refactometer• Computerized
• Lensmeter principal
• Ideally :– Subjective– Objective with cyclopegic– Subjective once more without cyclopegic
• Lens meter– Measuring lens power– Measuring focus distance
• Measuring Pupillary Distance– drop the flashlight light onto both eyes, the
light is coming from in front of the patient, The patient look at the observer forehead or the light ----> measure the distance of light spot between OD and OS ----> as near pupil distance
– Far distance : • add 2 mm ---> for pupil distance less than 60
mm. • Add 3 mm ---> for pupil distance more than
60 mm
• 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
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
• Vision in Anisometrop– difference < 2.50 D : still get fusion + single
binocular 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
• Limitation of the eye glasses– cannot applied for anisometropia more than 2.50
Dioptri– anisometropia causing aniseikonia
• Contact lens : Hard ---> rigid lensSoft
– Indication :• High anisometropia• irregular astigmatism• Front asymmetry, orbit• Aniridia• Descemetocele• Sports • Cosmetics
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