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Refraction Dr.Ani, SpM

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RefractionDr.Ani, 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 (-)

Principles Rays coming from distance > 5 m parallel rays Rays coming from distance < 5m divergent rays

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

+2

+2

0

+4

+5

-1

Biconvex

Plano K

Concave K

Minus sphere : Concave Characteristic : makes smaller and farther images0 -4 +1 -5

-2

-2

Bi Concave

Plano K

Convex K

Parallel rays will be centered or diverged from the focus

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+ 2.00 0.00

C + 1.00 D X 90 0+ 2.00 0.00 + 1.00 + 2.00 + 1.00

+ 2.00

+

+ 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 900S + 3.00 C - 1.00 X 1800

Eye as an Optical Instrument

Refraction media : Cornea Humour Aqueous Lens Vitreous body n = 1.33 n = 1.33 n = 1,41 n = 1.33

Haziness on refraction media --> disturbances of vision

Power of refraction of the eye ball Totally Cornea Lens : 60 dioptri : 40 dioptri : 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 > 6.00 D = 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 becontinuously 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 theaccommodation has been paralyzed with cylcopegic agents Latent Hypermetrop : is the diference of the total hypermetrop with the manifest

hypermetrop

Hypermetrop

Latent Hypermetrop

Hypermetrop manifest

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 refractionRight angle to each other

Irregular astigmatism Difference in refraction not only in different meridians, but also in different parts of the same meridian.

Etiology of astigmatism : Corneal curvature disturbances ---> 90% Lens curvature disturbances ---> 10%

Type of Astigmatism : Ast. M. Simplex Ast. H. Simplex Ast. M Compositium Ast. H Compositium Ast. Mixtus

C-2.00 X 90C+2.00 X 45

0 0

S-1.50 C-1.00 X 60 0 S+3.00 C+2.00 X 300 0

S+2.00 C-5.00 X 180

Ast. M. Simplex

Ast. H. Simplex

Ast. M Compositium

Ast. H Compositium

Ast. Mixtus

Presbiopia Physiological changes because accommodation capability is lowering at old ageAccommodation 16

10 6

210 20 40 50 60

Age

Presbiopia correction : 40 years old 45 years old 50 years old 55 years old 60 years old S + 1.00 D S + 1.50 D S + 2.00 D S + 2.50 D 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 :ODS 6/6 I. AVOD 2/60 S - 3.50 = 6/6 headache, eye strain AVOS 3/60 S - 3.00 = 6/6 ODS 6/6 II.AVOD 2/60 S - 3.00 = 6/7 w/o headache, eye strain AVOS 3/60 S - 2.75 = 6/7 read ADD S + 1.50 Give Eye Glasses according to II

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 MM. H. H. M. E. E. H. 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 : Indication :

Hard ---> rigid lens Soft

High anisometropia irregular astigmatism Front asymmetry, orbit Aniridia Descemetocele Sports Cosmetics