clinicalrefraction
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This document discusses the basics of clinical refraction and the eye as an optical system. It covers the following key points: 1. Types of corrective lenses include spherical, cylindrical, and prismatic lenses used to treat conditions like hyperopia, myopia, astigmatism, and strabismus. 2. The eye functions as an optical system with refractive media like the cornea and lens contributing diopters of power. Accommodation allows the eye to focus on near objects. 3. Common refractive errors and their treatment are described, such as hyperopia corrected with convex lenses, myopia corrected with concave lenses, and presbyopia treated with reading additions. Astigmatism involves
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clinicalrefraction
- 1. Basics of Clinical Refraction (A).油TYPES油OF油CORRECTIVE油LENSES:油 油油 (a).油Spherical油lenses:油 All油have油equal油curvatures油in油all油meridians.油 (i). Convex, (足F) lenses or convergent lenses are used for the correction of hyperopia, presbyopia and aphakia.油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 They油make油objects油look油larger油in油size.油 (ii). Concave, (足) lenses or divergent lenses are used for the correction of myopia. They make objects look油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 smaller油in油size.油 (b).油Cylindrical油or油toric油lenses:油 One油meridian油is油curved油more油than油all油the油other油ones.油They油are油used油to油correct油astigmatism.油 c油.Prisms:油 A油prism油is油an油optical油device油composed油of油2油refracting油surfaces油that油are油inclined油toward油one油another.油 It has an apex and a base. It refracts light toward its base whereas an object seen through a prism appears油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 deviated油toward油the油apex油of油the油prism.油 It油does油not油change油the油size油of油an油object.油 Prisms油are油used油to油correct油strabismus.油 油 油 (B).油BASIC油PRINCIPLES:油 足油Visible油spectrum油of油light油:油330am油(violet)油油760nm油(red)油 足油Velocity油of油light油in油vacuum:油101 m!sec油 足油Index油of油refraction油of油a油medium:油velocity油of油light油in油vacuum!油that油in油medium油 足 The index of refraction of a medium varies with the wavelength of light traveling through it. Blue light (short油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 wavelength)油is油refracted油more油than油red油light油because油of油its油higher油frequency.油(v油=油f油x油wavelength)油 足油Refraction油of油light:油Snells油Law:油n1油sin叩1油=油n2油sin叩2.油 1. Power油of油a油lens油in油diopters油1/focal油length油in油meters.油 油 油 (C).油REFRACTION:油 油油 Refractive errors are the most common cause of poor vision. They are the easiest to treat. Refraction is a term油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 applied to the various testing procedures employed to measure the refractive error of the eye in order to provide油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 the油proper油correction.油 油油 油 (a)油Subjective油refraction油 (b)油Automated油refraction油 (c)油Cycloplegic油refraction油
- 2. Cycloplegic refraction is done by applying a cycloplegic agent to the eye (atropine, cyclopentolate or油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 tropicamide) to paralyze the ciliary muscle so that the absolute refractive error can be measured. it is helpful to油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 detect油latent油hyperopia油in油children油compensating油their油hyperopia油by油accommodation.油 THE油EYE油AS油AN油OPTICAL油SYSTEM:油 油油 (A).油REFRACTIVE油MEDIA:油 油油 1.油THE油CORNEA:油 The cornea contributes to approximately 2/3 of the refracting power of the eye along with the tear film. It油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 contributes油賊43油diopters.油 油 2.油THE油LENS.油 The lens contributes to 1/3 of the refractive power of the eye (賊 20 diopters). By itself it is more powerful than油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 the cornea as a convergent surface but because of less difference in indices of refraction between the aqueous油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 versus油the油cornea,油less油convergence油exists油at油the油level油of油the油lens.油 The total convergence power of the eye is 58.7d and not 43賊20=63d due to the distance between the cornea and油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 the油lens油(depth油of油the油anterior油chamber)油that油will油subtract油approximately油4d.油 油 3.油THE油PUPIL.油 The油pupil油reduces油the油amount油of油light油that油enters油the油eye.油 It油decreases油the油aberrations.油 It油increases油the油depth油of油focus油when油constricting.油 油 (B).油ACCOMODATION:油 It is the process by which the eye changes its refractive power to focus on near objects. It results from increased油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 curvature of the lens due to contraction of the ciliary muscle. The stimulus to accommodation is a blurred retinal油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 image.油 it油is油part油of油the油Near油Reaction油that油involves油accommodation油along油with油convergence油and油pupillary油constriction.油 油 (C).油REFRACTIVE油ERRORS:油 Emmetropia:油Normal油eye.油No油refractive油error.油 Anisometropia:油A油refractive油error油is油present.油 1.油Hyperopia油 2.油Myopia油 3.油Presbyopia油 4.油Astigmatism油 油 I.油HYPEROPIA油(Hypermetropia,油farsightedness)油 The focused image forms behind the retina. Most children are born with some hyperopia (maximum up to 賊3d. )油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 but油this油usually油resolves油by油12油years油of油age.油 油 油 a.油Structural油or油axial油hyperopia:油 足油It油is油the油most油common油cause油of油hyperopia油 足油AP油diameter油of油the油eye油is油shorter油than油normal.油
- 3. 足油These油eyes油are油more油prone油to油angle油closure油glaucoma油because油of油shorter油 anterior油segment油with油crowding油of油the油angle油structures.油 足油The油optic油nerve油is油also油smaller油 足油It油may油be油associated油with油pseudopapilledema:油 足油usually油occurs油with油more油than油+4d.油 足油swollen油discs油but油no油other油signs油of油true油papilledema油such油as油blurring油 of油the油disc油margins,油hyperemia油of油the油disc,油hemorrhagesμ 油 b.油Curvature油hyperopia:油 When either the lens or cornea has a weaker than normal curvature, lower refractive power or convergence油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 occurs.油 油 c.油Index油of油refraction油hyperopia:油 Occurs油due油to油a油decrease油in油the油index油of油refraction油(and油density)油in油any油part油of油the油optical油system油of油the油eye.油 Latent hyperopia: is that part of the refractive error completely corrected by accommodation. It can only be油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 measured油by油cycloplegic油refraction油and油not油manifest油refraction油 Manifest油or油absolute油hyperopia:油is油the油portion油of油the油hyperopia油not油corrected油by油accommodation.油 With aging, the accommodative power of the eye decreases. This will shift a hyperopic patient from latent油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 hyperopia油to油greater油degrees油of油absolute油hyperopia.油 油 Symptoms油of油hyperopia:油 1.油Blurred油vision油for油distance油 2.油Frontal油headache油aggravated油by油prolonged油use油of油near油vision.油 3. Asthenopia: fatigue, burning eye sensation and periorbital pain when fixing at an object for prolonged油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 periods油of油time.油 4.油Light油sensitivity油 5.油Decrease油in油near油visual油acuity油at油a油younger油age油than油in油emmetropic油eyes.油 油 Treatment油of油hyperopia:油 Convergent油or油(+)lenses.油 油 2.油MYOPIA油nearsightedness)油 The油focused油image油if油formed油in油front油of油the油retina.油 油 a.油Structural油or油axial油myopia:油 The油AP油diameter油is油longer油than油normal.油Patients油may油have油pseudoproptosis油due油to油the油larger油globe.油 油 b.油Curvature油myopia:油 The eye has a normal AP diameter but at the corneal level the curvature may be steeper than normal ex:油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 congenital,油or油keratoconus.油 At油the油lens油level:油lens油curvature油is油increased油ex油in油intumescent油cataract.油 油 c.油Increased油Index油of油refraction:油 Occurs油with油nuclear油sclerosis油making油the油eye油myopic油 油 d.油Anterior油displacement油of油the油lens:油
- 4. Occurs油after油trauma油or油after油glaucoma油surgery.油 油 油 Symptoms油of油myopia:油 I.油Blurred油vision油for油distance油 2.油Squint油(due油to油blepharospasm足like油action油to油act油as油a油pinhole)油 3.油Headache油(rare)油 Myopia is usually detected at the age of 9足10 years and keeps increasing till mid足teens when it stabilizes at 足5d.油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 or油less油 油 Progressive油myopia:油 足油rare油form油of油myopia油 足油may油increase油at油a油rate油of油up油to油足4d.油rare油form油of油myopia油 足油may油increase油at油a油rate油of油up油to油足4d.油per油year油 足油is油associated油with油chorioretinal油degeneration油and油vitreous油floaters油and油liquefaction油 足油usually油stabilizes油at油the油age油of油20油years油but油can油progress油until油mid油30s油 足油may油reach油up油to油10油or油20d.油 足油high油myopes油(more油than油7d)油are油predisposed油to油retinal油detachment油and油POAG.油 油油 Congenital油myopia:油 足油more油than油10d.油in油infants油 足油generally油not油progressive油 足油should油be油corrected油as油soon油as油detected.油 油 Treatment:油 Always油give油full油correction油with油(足)油lenses.油 油 油 油 3.油ASTIGMATISM:油 The curvature of the optical system varies in different meridians thus refracting the incident light differently in油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 those油meridians.油 油Withtherule油astigmatism:油the油vertical油meridian油is油steeper油 Against足the足rule油astigmatism:油the油horizontal油meridian油is油steeper油 油 Regular油astigmatism:油Principal油meridians油are油90油degrees油apart油 Irregular Astigmatism: Principal meridians are not 90 degrees apart. This type of astigmatism cannot be油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 completely油corrected油by油spectacles油and油may油need油contact油lenses油ex:油corneal油scarring油,油keratoconus.油 油 Symptoms油of油astigmatism:油 足油blurred油vision油for油far油and油near油 2足油squint油(for油pinhole油effect)油 3足油asthenopic油symptoms油 4足油frontal油headaches油 5足油tilting油of油the油head油(for油oblique油astigmatism)油 Treatment油is油with油cylindrical油lenses.油
- 6. The power of the intraocular lens to be replaced after cataract surgery is usually calculated according to the SRK油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 (油Sanders足Retzlaff足Kraff)油equation:油 油油 IOL油power油=油A足2.5L足0.9K油 油油 where油A油is油a油constant油particular油to油the油lens油 L油is油the油A足P油diameter油of油the油eye油in油mm油(obtained油from油A油scan)油 K油is油the油measurement油of油the油curvature油of油the油cornea油(obtained油from油a油keratometer)油 油油 油USE油OF油LASERS油IN油OPHTHALMOLOGY:油 油油 油THE油ARGON油LASER:油 It油has油a油thermal油effect油and油is油used油for.油 a.油photocoagulation油of油the油retina油in油diabetic油retinopathy油 b.油macular油degeneration油(if油neovascularization油is油present)油 c.油sealing油of油retinal油holes油and油tears油 d.油trabeculoplasty油in油open油angle油glaucoma油 e.油suture油lysis油 油油 油THE油NEODYMIUM足YAG油LASER:油 It油causes油photodisruption油of油tissues油and油is油used油for:油 a.油iridotomy油in油angle油closure油glaucoma油 b.油capsulotomy:油cutting油a油hole油in油the油posterior油capsule油of油the油lens油which油remains油after油ECCE油and油which油thickens油 c.油cutting油vitreous油bands油and油opacities油 油油 油THE油EXC1MER油LASER:油 it油causes油photoablation油of油tissue油and油is油used油for:油 a.油photorefractive油surgery油to油change油the油surface油of油the油cornea油in油order油to油correct油errors油of油refraction.油 油 油 CLINICAL油&油CASES油 1. A new patient presenting for visual check足up is found to have a vision of 20/40 OU. What test will you do to油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 predict油that油his油vision油will油improve油with油refraction?油 2. A 68 y. old male patient is known to have cataract for the last 3 yrs. His vision 3 yrs ago was 20/50 with油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 +3.50d油eyeglasses.油He油is油now油seeing油better油without油his油correction.油How油do油you油explain油this?油 3. After dilatation and full cycloplegia of a 20 yr old lady whose vision was 20/20, she worsened to 20/50. Does油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 she油have油an油error油of油refraction?油Would油you油prescribe油eyeglasses油for油her?油 4.油What油would油be油the油near油correction油for油a油52油y.old油man油whose油correction油for油far油is:油 足3.50油賊油1.50油X油120油 足1.00油+油2.25油X油85油 油油 5. A 26 y. old patient is presenting for check足up. You find 3.25 +6.00 X 90. However the patient is seeing油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 better油without油any油correction.油How油do油you油explain油this?油
- 7. 油油 6. A 65 y. old male patient with ARMD and mature cataract presents with a vision of CF 1 m. What test would油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 油 you油do油to油predict油what油would油be油his油best油corrected油vision油after油cataract油surgery?油 油油 7.油For油each油of油the油following油patients油presenting油with油low油visual油acuity油20/100,油select油 the油most油likely油cause.油 (a)油6油y油old油girl油operated油several油times油for油strabismus油 (b)油68油y油old油lady油case油of油RA油on油chronic油intake油of油steroids油 (c)油8油y油old油girl油with油the油following油error油of油refraction:油 賊1.50賊0.50X90油20/100油 +5.00油+油3.50油X油100油20/i油00油 (d)油78油y油old油male油patient油with油hard油drusen油in油the油macula油 (e)油12油y油old油boy油with油history油of油recurrent油attacks油of油herpes油simplex油resulting油in油a油disciform油central油scar.油 (f)油15油y油old油male油patient油with油difficulty油reading油the油blackboard.油 油 油 MAYANK油BHARDWAJ油 student油of油Bachelor油of油Optometry油 All油India油Institute油of油Medical油Sciences油 油油油油油油油油油油油油油油油油New油Delhi足29油 油 油 油