RefractionDr. Saskia N Mokoginta,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 images -2 -2 0 -4 +1 -5 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 . 00 + 2.00 D X 90 0 + 2.00 + 1.00 + 2.00 D 0.00 + + 1.00 + 2. Spherocylindrical Lens Is a combination between spherical lens and cylindrical lens Example : + 2.00 .00 S + 2.00 C + 1.00 0.00 + 3. Transposition Methods : Sphere : Sum with algebra ways SPH + CYL Cylinder : replace power marks (Neg Pos).00 X 90 0 S + 3.00 C + 1.00 X 180 0 .00 C .1. axis change 90 degrees Example : S + 2. Eye as an Optical Instrument Refraction media : Cornea Humour Aqueous Lens Vitreous body n = 1.33 n = 1.41 n = 1.33 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 . the eyes are in relax position. the images are focused right on the retina (fovea centralis) . by increasing the convexity of the lens normal : rays that come from > 5 m . Accommodation Process Capability of adding the refraction power of the eye.distance object regarded as parallel light. the images will be focused behind the retina. 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. the rays do not come parallel but divergent. So the object will be seen blurred. If the eyes are still in relax position. For object at less than 5 meters distance. . ciliaris in the ciliary body . This accommodation process happens as a result from the contraction of M. 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 . 4. The focal point may be behind or in front of the retina Hal 47. Ametropia Is the condition when the parallel rays are not focused exactly on the retina of the eye in relax condition.2 Duke Elder . with accommodation completely relaxed. Myopic eye : refractive state over plus power . parallel rays are brought to a focus in front of the retina. Myopia Refractive condition in which. but there is a increasing of the cornea/lens curvature Curvature : The change of the lens e. : intumescens cataract could occur on Diabetic patient changes of the lens position to the anterior after glaucoma surgery lens subluxation Increasing of the refraction index Changes of the lens location . The eye usually looks like proptosis The size of the eye ball ---> normal. lens and the lens position are normal. the refraction power of the cornea. Factors that causing myopia : Axial : The antero-posterior axis of the eye ball > normal in this case.g. 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. Clinical findings : Farsightedness are blurred. deep Anterior Chamber . in order to get a better vision On high myopia ----> proptosis simulation. Funduscopy : Tigroid fundus ---> thin retina and the choroid. myopic crescent arround the papilla area. sthaphyloma posterior . Pigmentation changes + Macular bleeding 4. Complication : Commonly occurred on high myopia 1. Retinal detachment 3.6. Degenarated and liquefied vitreous 2.00 D = high myopia/gravis .00 D = moderate myopia > 6.00 . Strabismus Myopia classification : < 3.00 D = low myopia 3. usually full correction are not given due to headache that may occurred.2.25 D = 6/7 The glasses are S .50 D = 6/7 S -2.00 D = 6/6 S -3. If necessary. Treatment : Low and moderate myopia : full correction with weakest spherical lens that give the best visual acuity Example : VOD = 5/60 S -2.75 D = 6/6 S -3. reading glasses can be given ---> bifocal glasses .75 D On high myopia. after puberty will be constant Progressive myopia. Prognosis : Simplex/stationer. the myopia will be continuously higher and complication may occurred . will be focused farther behind the retina .Hypermetropia Is a refraction anomaly that without accommodation parallel rays will be focused behind the retina Divergent rays from near object. Etiology : Axial ---> eye ball diameter < N Deminished convexity of cornea/lens curvature Decreasing Refractive index Changed lens position . It correspons to the amount of accommodation which he relaxes when a convex lens is placed before the eye. Manifest ---> is detected without paralazing accommodation and is represented by the strongest convex glass needed . Devided into two types : Facultative : Can be overcome by an effort of accommodation Absolute : Can not be overcome . Clinical manifestation : H. the patient sees most distinctly. 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 . 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) . apply strongest positive spherical lens that give the best visual acuity If foria/tropia present. total hypermetrop correction. Treatment : If foria/tropia not present. If necessary : bifocal eye glasses . The shape of the images : Line.astigmatism Refractive condition of the eye in which there is a difference in degree of refraction in diferent meridian. circle. never a point . each will focused parallel rays at a different point. oval. Manifestation : Regular astigmatism Difference in the degree of refraction in every meredian. Two principles meridian : Maximmum refraction Minimum refraction Right angle to each other Irregular astigmatism Difference in refraction not only in different meridians. . but also in different parts of the same meridian. 00 C+2. Mixtus C-2.00 X 30 S+2.00 X 60 Ast. Simplex Ast. M Compositium Ast. H Compositium S+3. Etiology of astigmatism : Corneal curvature disturbances ---> 90% Lens curvature disturbances ---> 10% Type of Astigmatism : Ast. Simplex Ast.00 X 45 0 0 0 0 0 S-1. M.00 C-5. H.50 C-1.00 X 90 C+2.00 X 180 . M. Simplex Ast.Ast. Simplex Ast. H. M Compositium Ast. H Compositium Ast. Mixtus . Presbiopia Physiological changes because accommodation capability is lowering at old age 16 Accommodation 10 6 2 10 20 40 50 60 Age . 50 D S + 3. Presbiopia correction : 40 years old 45 years old 50 years old 55 years old 60 years old S + 1.00 D S + 2.50 D S + 2.00 D Consider the type of previous/history work Tailor Architect Weld engineer .00 D S + 1. Refraction Examination Technique Subjective : Snellen chart/projector. difficult correction. incooperative. alphabet . inverse E. strabismus : Objective : Ophthlamoscopy Retinoscopy Refractometer . Landolt ring Trial lens Trial frame Children. picture. . Subjective Check firstly just one eye : OD Distance : 5 or 6 meters VOD : …. increase S .50.until visus = 6/6 S +/.not working ----> cylindrical With astigmatism dial.50.(basic right eye visus) a.. cross cylinder astigmatism dial : Blurred line ----> C negative lens axis . lower visus. stenoplic slit.. change to S -. better visus . Trial and error apply S + 0. add S+ until visus = 6/6 S +0. step by step distracting --> best sp. One by one fogging S + sp. Lens --> blurred vision. Nearsightedness/read Both eyes at one time at required distance : use jaeger chart . 2.00 = 6/6 II. eye strain ODS 6/6 w/o headache. eye strain I.50 = 6/6 AVOS 3/60 S .3. Example : ODS 6/6 headache.50 Give Eye Glasses according to II .3.75 = 6/7 read ADD S + 1.3.AVOD 2/60 S .00 = 6/7 AVOS 3/60 S . AVOD 2/60 S . Ophthlamoscopy : papilla clearly seen with which lens 2. Refactometer Computerized Lensmeter principal . Objective Use cyclopegic 1. Retinoscopy : Ordinary ---> light source outside streak -----> light source inside 3. Ideally : Subjective Objective with cyclopegic Subjective once more without cyclopegic Lens meter Measuring lens power Measuring focus distance . the light is coming from in front of the patient. Add 3 mm ---> for pupil distance more than 60 mm . Measuring Pupillary Distance drop the flashlight light onto both eyes. 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. the components are : Which eye (OD or OS) Power of the lens ( + or . Eye Glasses Monofocal Bifocal Progressive Eye Glasses Prescription.. axis) ADDE for reading Pupil distance far/near Name of the patient . Power. M. Antimetropia E. H.Binocular Optical Defects Anisometropia : Condition wherein the refractions of the two eyes are an equal variation : Myopia M M. H. E. H. H . 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. orbit Aniridia Descemetocele Sports Cosmetics .50 Dioptri anisometropia causing aniseikonia Contact lens : Hard ---> rigid lens Soft Indication : High anisometropia irregular astigmatism Front asymmetry.