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VENNILA .C.R. REFRACTION. Refractive Errors. Emmetropia Ametropia. Emmetropia. Emmetropia means no Refractive error It is the ideal condition in which the incident parallel rays come to a perfect focus upon the light sensitive layer of the retina, When accommodation is at rest. - PowerPoint PPT Presentation

Text of VENNILA .C.R


  • Refractive ErrorsEmmetropiaAmetropia

  • EmmetropiaEmmetropia means no Refractive errorIt is the ideal condition in which the incident parallel rays come to a perfect focus upon the light sensitive layer of the retina, When accommodation is at rest

  • AmetropiaAmetropia means Refractive error EyeIt is the opposite condition , wherein the parallel rays of light are not focused exactly upon the retina , When the accommodation is at rest

  • AmetropiaMyopiaHypermetropiaAstigmatism

  • MyopiaPrincipal focus is formed in front of the retina

  • Causes Axial MyopiaCurvature MyopiaIndex MyopiaAbnormal position of the lens

  • Axial MyopiaAxial myopia results from increase in anteroposterior length of the eye ball.Normal Axial length- 23mm to 24mm1mm increase in AL 3Ds of Myopia

  • Curvature MyopiaCurvatural myopia occurs due to increased curvature of the cornea and Lens or both.Anterior surface of the cornea- 7.8mmPosterior surface of the cornea- 6.5mm1mm increases in radius of curvature results in 6 Ds of Myopia

  • Index myopiaIndex myopia results from increase in the refractive index of crystalline lens. Refractive index of normal Lens - 1.42

  • Abnormal position of the lensPositional myopia is produced by anterior displacement of crystalline lens in the eye.

    Accommodative Myopia:. Myopia due to excessive accommodation.

  • Types Congenital myopiaSimple Myopia (or) Developmental myopia Pathological Myopia (or) Degenerative myopiaAcquired myopia

  • Congenital myopiaCongenital myopia is present since birth however, it is usually diagnosed by the age of 2 3 years.

  • Simple myopiaSimple or developmental myopia is the commonest variety. It is considered as a physiological error not associated with any disease of the eye.Power limit less than 6D

  • AetiologyAxial type of simple myopiaCurvatural type of simple myopia

  • Pathological myopiaMyopia associated with degenerative changes in the eye.Myopia more than 6D to25D or More than 25D

  • AetiologyAxial growth(i) Heredity(ii) General growth process

  • Acquired myopiaSome of the causes of acquired myopia* Index myopia* Curvatural myopia* Positional myopia* Consecutive myopia * Pseudo myopia* Space myopia* Night myopia (or) Twilight myopia* Drug induced myopia

  • SymptomsPoor vision for distanceAsthenopic symptomsExophoriaMuscae volitantes (pathological)Night blindness (pathological)

  • SignsLarge eye balldeep Anterior chamber sluggish PupilLarge Disc

  • ComplicationsRetinal tear Vitreous haemorrhageRetinal detachmentDegeneration of the vitreousPrimary open angle GlaucomaPosterior cortical cataractPosterior staphyloma

  • Treatment Optical Spectacle Correction (Concave Lens)Contact lensSurgicalPRKKeratomileusisEpikeratophakiaRedial Keratotomy

  • Optical TreatmentConcave lensMyopic with Exophoria give full correction.Myopic with Esophoria give undercorrection.

  • Hypermetropia

    Principal focus is formed behind the retina

  • Causes Axial HypermetropiaCurvature HypermetropiaIndex HypermetropiaAbnormal position of the lens

  • Axial HypermetropiaAxial hypermetropia is by far the commonest In fact, all the new- borns are almost invariably hypermetropic (approx,+2.50D) This is due to shortness of the globe, and is physiological.Normal axial length 23mm to 24mm1mm decrease in AL 3Ds of hypermetropia

  • Curvature HypermetropiaIn which the curvature of cornea, Lens or both is flatter than the normal resulting in a decrease in the refractive power of the eye.Anterior surface of the cornea- 7.8mmPosterior surface of the cornea- 6.5mm1mm increase in radius of curvature results in 6Ds of hypermetropia

  • Index HypermetropiaIndex hypermetropia occurs due to change in refractive index of the lens in old age. It may also occur in diabetics under treatment.Refractive index of Normal Lens- 1.42

  • ClassificationTotal Hypermetropia may be divided into(a) Latent Hypermetropia(b) Manifest Hypermetropia (i) Facultive Hypermetropia (ii)Absolute Hypermetropia

  • Latent HypermetropiaLH which is corrected physiologically by the tone of ciliary muscle. As a rule latent hypermetropia amounts to only one dioptre. It can be revealed only after atropine cycloplegia.

  • Manifest HypermetropiaMH is made up of two componentsFacultative hypermetropia is that part of hypermetropia which can be corrected by the effort of accommodation.Absolute hypermetropia which can not be overcome by the effort of accommodation.

  • Clinical TypesSimple hypermetropiaPathological hypermetropiaFunctional hypermetropia

  • Simple hypermetropiaIt results from normal biological variation in the development of the eye ball. It includes Axial and Curvatural HM. It may be hereditary.

  • Pathological hypermetropiaPH results due to either congenital or acquired conditions of the eye ball which are out side the normal biological variations of the development.

  • The Normal Age VariationAt birth:- 2D to 3 D Commonly PresentAt the age of 5 Yrs- 90% of Childrens are HypermetropicAt Puberty:- Emmetropic

  • Symptoms Head acheBlurred vision particular near workConvergent squintEarly onset of presbyopiaEye Strain

  • ComplicationsEye appears to be small including cornea and anterior chamber becomes shallowExtreme cases MicrophthalmosRetinal reflex Shot silk-Retina

  • TreatmentOpticalSpectacle ( Convex Lens )Contact lensHypermetropic with Exophoria give under correctionHypermetropic with Esophoria give full correctionSurgicalThermokeratoplasty

  • Astigmatism Astigmatism is that condition of Refraction where the point focus of light cannot be formed upon the Retina

  • CausesCurvature Ex: Keratoconus, Lenticonus etc..Centering error Ex: Sub location of the lensRefractive index Ex: CataractRetinal Oblique placement of macula

  • TypesRegular Irregular

  • Regular astigmatismRefractive typesPhysiological types

  • Refractive typesSimple astigmatismCompound astigmatismMixed astigmatism

  • Physiological typesWith rule astigmatismAgainst rule astigmatismOblique astigmatismBioblique astigmatism

  • SymptomsHead acheBlurring of visionEye tiredEye acheHead TiltHalf-closure of the lids (High astigmatism)Blurring & Itching (Low astigmatism)

  • TreatmentOptical Treatment* Cylindrical lens* Under correction* Contact lens (RGP, Toric)Refractive surgery * Astigmatic Keratotomy* PRK, LASIK

  • Study ReportsPercentage of astigmatism* 0.25-0.50D50%* 0.75-1.00D25%* 1.00-4.00D24%*>4.00D1%Percentage of Types* with rule38%* Against rule30%* Oblique32%

  • Duo chrome test To test if the eye has been under corrected or over corrected or is properly corrected

  • Astigmatic Fan To know the axis and power in Astigmatism

  • Jackson cross cylinder To refine the axis and power of cylinder

  • PresbyopiaThis is a physiological aging process, In which the near point gradually recedes beyond the normal reading or working distance

  • CausesLens matrix is harder and less easily mouldedLens capsule is less elastic Progressive increase in size of the lensWeakening of the ciliary muscle

  • SymptomsPatient holds the book at arms lengthPatient prefers to read in bright lightEye strain Head acheEyes feels tired and ache

  • TreatmentConvex lens Methods of prescription * Occupation * Working distance * Age Surgical * Anterior ciliary sclerotomy * Laser thermal keratoplasty * Small diameter corneal inlays

  • Aphakia Aphakia means absence of the Crystalline lens from the Eye ball

  • Causes Congenital Surgery Traumatic

  • Optics of AphakiaAnterior focal distance 23mm (N-15mm)Posterior focal distance- 31mm (N-24mm)The Nodel point of the eye is thus moved forwardStrong converging (convex) lens- +10D

  • SignsAnterior chamber Deep Iris (i) Iridodonesis (or) Tremulousness(ii) Peripheral button-hole iridectomy markPupil - Jet black reflexAbsence of the 3rd and 4th Purkinje imagesRetinoscopy reveals high hypermetropia and astigmatismOphthalmoscopy As in hypermetropic fundus with a small optic disc

  • DisadvantagesImage magnification of about 25-30%Spherical aberration, Peripheral and PincushionRoving ring scotoma (The scotoma extents from 50- 65 from central fixation)Jack in the boxRestriction of the visual fieldColoured visionInaccurate spectacle correction because of errorneous vertex distance

  • TreatmentSpectacle ( Convex lens )Contact lensSecondary IOLEpikeratophakiaKeratophakia

  • Aphakic formulaP = X / 2 +10.00DP = IOL powerX = Refractive power

  • PseudophakiaPseudophakia means False lens

  • Image magnification

  • Calculation of IOL powerP = A-2.5*L -0.9KP = IOL PowerA= Constant value 2.5= AC depth L = Axial length in mm 0.9= Corneal curvatureK = Corneal diapters

  • Refractive stages of a Pseudophakic eyeEmmetropiaConsecutive myopiaConsecutive hypermetropia

  • AdvantagesImage ma

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