Download - VENNILA.C.R REFRACTION Refractive Errors Refractive Errors Emmetropia Emmetropia Ametropia Ametropia
VENNILA .C.RVENNILA .C.R
REFRACTIONREFRACTION
Refractive Refractive ErrorsErrors•EmmetropiEmmetropiaa
•AmetropiaAmetropia
EmmetropiaEmmetropia
• Emmetropia means no Refractive Emmetropia means no Refractive errorerror
• It is the ideal condition in which the It is the ideal condition in which the incident parallel rays come to a incident parallel rays come to a perfect focus upon the light sensitive perfect focus upon the light sensitive layer of the retina, When layer of the retina, When accommodation is at restaccommodation is at rest
AmetropiaAmetropia
• Ametropia means Refractive error Ametropia means Refractive error EyeEye
• It is the opposite condition , wherein It is the opposite condition , wherein the parallel rays of light are not the parallel rays of light are not focused exactly upon the retina , focused exactly upon the retina , When the accommodation is at rest When the accommodation is at rest
AmetropiaAmetropia
• MyopiaMyopia
• HypermetropiaHypermetropia
• AstigmatismAstigmatism
MyopiaMyopia• Principal focus is formed in front of Principal focus is formed in front of
the retinathe retina
Causes Causes
• Axial MyopiaAxial Myopia
• Curvature MyopiaCurvature Myopia
• Index MyopiaIndex Myopia
• Abnormal position of the lensAbnormal position of the lens
Axial MyopiaAxial Myopia
• Axial myopia results from increase in Axial myopia results from increase in anteroposterior length of the eye anteroposterior length of the eye ball.ball.
• Normal Axial length- 23mm to Normal Axial length- 23mm to 24mm24mm
• 1mm increase in AL – 3Ds of Myopia1mm increase in AL – 3Ds of Myopia
Curvature MyopiaCurvature Myopia
• Curvatural myopia occurs due to Curvatural myopia occurs due to increased curvature of the cornea and increased curvature of the cornea and Lens or both.Lens or both.
• Anterior surface of the cornea- 7.8mmAnterior surface of the cornea- 7.8mm
• Posterior surface of the cornea- 6.5mmPosterior surface of the cornea- 6.5mm
• 1mm increases in radius of curvature 1mm increases in radius of curvature results in – 6 Ds of Myopiaresults in – 6 Ds of Myopia
Index myopiaIndex myopia
• Index myopia results from increase in Index myopia results from increase in the refractive index of crystalline the refractive index of crystalline lens.lens.
Refractive index of normal LensRefractive index of normal Lens - - 1.42 1.42
Abnormal position of the Abnormal position of the lenslens
• Positional myopia is produced by Positional myopia is produced by anterior displacement of crystalline anterior displacement of crystalline lens in the eye.lens in the eye.
Accommodative Myopia:. Accommodative Myopia:. Myopia Myopia due to excessive accommodation.due to excessive accommodation.
Types Types
• Congenital myopiaCongenital myopia
• Simple Myopia (or) Developmental Simple Myopia (or) Developmental myopia myopia
• Pathological Myopia (or) Pathological Myopia (or) Degenerative myopiaDegenerative myopia
• Acquired myopiaAcquired myopia
Congenital myopiaCongenital myopia
• Congenital myopia is present since Congenital myopia is present since birth however, it is usually diagnosed birth however, it is usually diagnosed by the age of 2 – 3 years.by the age of 2 – 3 years.
Simple myopiaSimple myopia
• Simple or developmental myopia is Simple or developmental myopia is the commonest variety. It is the commonest variety. It is considered as a physiological error considered as a physiological error not associated with any disease of not associated with any disease of the eye.the eye.
• Power limit less than 6DPower limit less than 6D
AetiologyAetiology
• Axial type of simple myopiaAxial type of simple myopia
• Curvatural type of simple myopiaCurvatural type of simple myopia
Pathological myopiaPathological myopia
• Myopia associated with degenerative Myopia associated with degenerative changes in the eye.changes in the eye.
• Myopia more than 6D to25D or More Myopia more than 6D to25D or More than 25D than 25D
AetiologyAetiology
• Axial growthAxial growth
(i) Heredity(i) Heredity
(ii) General growth process(ii) General growth process
Acquired myopiaAcquired myopia
Some of the causes of acquired myopiaSome of the causes of acquired myopia* Index myopia* Index myopia* Curvatural myopia* Curvatural myopia* Positional myopia* Positional myopia* Consecutive myopia * Consecutive myopia * Pseudo myopia* Pseudo myopia* Space myopia* Space myopia* Night myopia (or) Twilight myopia* Night myopia (or) Twilight myopia* Drug induced myopia* Drug induced myopia
SymptomsSymptoms
• Poor vision for distancePoor vision for distance
• Asthenopic symptomsAsthenopic symptoms
• ExophoriaExophoria
• Muscae volitantes (pathological)Muscae volitantes (pathological)
• Night blindness (pathological)Night blindness (pathological)
SignsSigns
• Large eye ballLarge eye ball
• deep Anterior chamber deep Anterior chamber
• sluggish Pupilsluggish Pupil
• Large DiscLarge Disc
ComplicationsComplications
• Retinal tear – Vitreous haemorrhageRetinal tear – Vitreous haemorrhage
• Retinal detachmentRetinal detachment
• Degeneration of the vitreousDegeneration of the vitreous
• Primary open angle GlaucomaPrimary open angle Glaucoma
• Posterior cortical cataractPosterior cortical cataract
• Posterior staphylomaPosterior staphyloma
Treatment Treatment
• Optical Optical
Spectacle Correction (Concave Lens)Spectacle Correction (Concave Lens)
Contact lensContact lens
• SurgicalSurgical
PRKPRK
KeratomileusisKeratomileusis
EpikeratophakiaEpikeratophakia
Redial KeratotomyRedial Keratotomy
Optical TreatmentOptical Treatment
• Concave lensConcave lens
Myopic with Exophoria give Myopic with Exophoria give full full correction.correction.
Myopic with Esophoria give Myopic with Esophoria give underunder
correction.correction.
HypermetropiaHypermetropia
Principal focus is formed Principal focus is formed behind the retina behind the retina
Causes Causes
• Axial HypermetropiaAxial Hypermetropia
• Curvature HypermetropiaCurvature Hypermetropia
• Index HypermetropiaIndex Hypermetropia
• Abnormal position of the lensAbnormal position of the lens
Axial HypermetropiaAxial Hypermetropia
• Axial hypermetropia is by far the Axial hypermetropia is by far the commonest commonest
• In fact, all the new- borns are almost In fact, all the new- borns are almost invariably hypermetropic (approx,+2.50D) invariably hypermetropic (approx,+2.50D) This is due to shortness of the globe, and This is due to shortness of the globe, and is physiological.is physiological.
• Normal axial length – 23mm to 24mmNormal axial length – 23mm to 24mm
• 1mm decrease in AL – 3Ds of 1mm decrease in AL – 3Ds of hypermetropiahypermetropia
Curvature Curvature HypermetropiaHypermetropia• In which the curvature of cornea, Lens In which the curvature of cornea, Lens
or both is flatter than the normal or both is flatter than the normal resulting in a decrease in the resulting in a decrease in the refractive power of the eye.refractive power of the eye.
• Anterior surface of the cornea- 7.8mmAnterior surface of the cornea- 7.8mm• Posterior surface of the cornea- Posterior surface of the cornea-
6.5mm6.5mm• 1mm increase in radius of curvature 1mm increase in radius of curvature
results in – 6Ds of hypermetropiaresults in – 6Ds of hypermetropia
Index HypermetropiaIndex Hypermetropia
• Index hypermetropia occurs due to Index hypermetropia occurs due to change in refractive index of the lens change in refractive index of the lens in old age. It may also occur in in old age. It may also occur in diabetics under treatment.diabetics under treatment.
• Refractive index of Normal LensRefractive index of Normal Lens - - 1.421.42
ClassificationClassification
•Total HypermetropiaTotal Hypermetropia may be may be divided intodivided into
• (a) Latent Hypermetropia(a) Latent Hypermetropia
• (b) Manifest Hypermetropia(b) Manifest Hypermetropia
(i) Facultive Hypermetropia(i) Facultive Hypermetropia
(ii)Absolute Hypermetropia(ii)Absolute Hypermetropia
Latent HypermetropiaLatent Hypermetropia
• LH which is corrected physiologically LH which is corrected physiologically by the tone of ciliary muscle. As a by the tone of ciliary muscle. As a rule latent hypermetropia amounts to rule latent hypermetropia amounts to only one dioptre. It can be revealed only one dioptre. It can be revealed only after atropine cycloplegia.only after atropine cycloplegia.
Manifest HypermetropiaManifest HypermetropiaMH is made up of two MH is made up of two componentscomponents
•Facultative Facultative hypermetropiahypermetropia is that part of is that part of hypermetropia which can be corrected hypermetropia which can be corrected by the effort of accommodation.by the effort of accommodation.
•Absolute hypermetropiaAbsolute hypermetropia which can not be overcome by the which can not be overcome by the effort of accommodation.effort of accommodation.
Clinical TypesClinical Types
• Simple hypermetropiaSimple hypermetropia
• Pathological hypermetropiaPathological hypermetropia
• Functional hypermetropiaFunctional hypermetropia
Simple Simple hypermetropiahypermetropia
• It results from normal biological It results from normal biological variation in the development of the variation in the development of the eye ball. It includes Axial and eye ball. It includes Axial and Curvatural HM. It may be hereditary.Curvatural HM. It may be hereditary.
Pathological Pathological hypermetropiahypermetropia
• PH results due to either congenital or PH results due to either congenital or acquired conditions of the eye ball acquired conditions of the eye ball which are out side the normal which are out side the normal biological variations of the biological variations of the development.development.
The Normal Age VariationThe Normal Age Variation
• At birth:- 2D to 3 D Commonly At birth:- 2D to 3 D Commonly PresentPresent
• At the age of 5 Yrs- 90% of Children’s At the age of 5 Yrs- 90% of Children’s are Hypermetropicare Hypermetropic
• At Puberty:- EmmetropicAt Puberty:- Emmetropic
Symptoms Symptoms
• Head acheHead ache
• Blurred vision particular near workBlurred vision particular near work
• Convergent squintConvergent squint
• Early onset of presbyopiaEarly onset of presbyopia
• Eye StrainEye Strain
ComplicationsComplications
•Eye appears to be small Eye appears to be small including cornea and anterior including cornea and anterior chamber becomes shallowchamber becomes shallow
•Extreme cases – MicrophthalmosExtreme cases – Microphthalmos
•Retinal reflex – Shot silk-RetinaRetinal reflex – Shot silk-Retina
TreatmentTreatment
• OpticalOpticalSpectacle ( Convex Lens )Spectacle ( Convex Lens )Contact lensContact lensHypermetropic with Exophoria give Hypermetropic with Exophoria give
under correctionunder correctionHypermetropic with Esophoria give Hypermetropic with Esophoria give
full full correctioncorrection• SurgicalSurgical
ThermokeratoplastyThermokeratoplasty
AstigmatismAstigmatism Astigmatism is that condition ofAstigmatism is that condition of Refraction where the point focus Refraction where the point focus of light cannot be formed upon of light cannot be formed upon the Retina the Retina
CausesCauses
• CurvatureCurvature Ex: Keratoconus, Lenticonus etc..Ex: Keratoconus, Lenticonus etc..• Centering errorCentering error
Ex: Sub location of the lensEx: Sub location of the lens• Refractive indexRefractive index
Ex: CataractEx: Cataract• RetinalRetinal Oblique placement of maculaOblique placement of macula
TypesTypes
• Regular Regular
• IrregularIrregular
Regular astigmatismRegular astigmatism
• Refractive typesRefractive types
• Physiological typesPhysiological types
Refractive typesRefractive types
• Simple astigmatismSimple astigmatism
• Compound astigmatismCompound astigmatism
• Mixed astigmatismMixed astigmatism
Physiological typesPhysiological types
• With rule astigmatismWith rule astigmatism
• Against rule astigmatismAgainst rule astigmatism
• Oblique astigmatismOblique astigmatism
• Bioblique astigmatismBioblique astigmatism
SymptomsSymptoms
• Head acheHead ache
• Blurring of visionBlurring of vision
• Eye tiredEye tired
• Eye acheEye ache
• Head TiltHead Tilt
• Half-closure of the lids (High Half-closure of the lids (High astigmatism)astigmatism)
• Blurring & Itching (Low astigmatism)Blurring & Itching (Low astigmatism)
TreatmentTreatment
• Optical TreatmentOptical Treatment
* Cylindrical lens* Cylindrical lens
* Under correction* Under correction
* Contact lens (RGP, Toric)* Contact lens (RGP, Toric)
• Refractive surgeryRefractive surgery
* Astigmatic Keratotomy* Astigmatic Keratotomy
* PRK, LASIK* PRK, LASIK
Study ReportsStudy Reports
• Percentage of astigmatismPercentage of astigmatism* 0.25-0.50D* 0.25-0.50D 50%50%* 0.75-1.00D* 0.75-1.00D 25%25%* 1.00-4.00D* 1.00-4.00D 24%24%*>4.00D*>4.00D 1%1%
• Percentage of TypesPercentage of Types* with rule* with rule 38%38%* Against rule* Against rule 30%30%* Oblique* Oblique 32%32%
Duo chrome testDuo chrome test To test if the eye has been To test if the eye has been under corrected or over under corrected or over corrected or is properly corrected or is properly correctedcorrected
Astigmatic FanAstigmatic Fan To know the axis and power in To know the axis and power in
Astigmatism Astigmatism
Jackson cross cylinderJackson cross cylinder To refine the axis and power To refine the axis and power of of cylinder cylinder
PresbyopiaPresbyopia
• This is a This is a physiological aging physiological aging process, In which process, In which the near point the near point gradually recedes gradually recedes beyond the normal beyond the normal reading or working reading or working distancedistance
CausesCauses
• Lens matrix is harder and less easily Lens matrix is harder and less easily mouldedmoulded
• Lens capsule is less elastic Lens capsule is less elastic
• Progressive increase in size of the Progressive increase in size of the lenslens
• Weakening of the ciliary muscleWeakening of the ciliary muscle
SymptomsSymptoms
• Patient holds the book at arms lengthPatient holds the book at arms length
• Patient prefers to read in bright lightPatient prefers to read in bright light
• Eye strain Eye strain
• Head acheHead ache
• Eyes feels tired and acheEyes feels tired and ache
TreatmentTreatmentConvex lensConvex lens
Methods of prescriptionMethods of prescription
* Occupation* Occupation
* Working distance* Working distance
* Age* Age
SurgicalSurgical
* Anterior ciliary sclerotomy* Anterior ciliary sclerotomy
* Laser thermal keratoplasty* Laser thermal keratoplasty
* Small diameter corneal inlays* Small diameter corneal inlays
Aphakia Aphakia
• Aphakia means Aphakia means absence of the absence of the Crystalline lens Crystalline lens from the Eye ballfrom the Eye ball
Causes Causes
• Congenital Congenital
• Surgery Surgery
• Traumatic Traumatic
Optics of AphakiaOptics of Aphakia
• Anterior focal distance – 23mm (N-Anterior focal distance – 23mm (N-15mm)15mm)
• Posterior focal distance- 31mm (N-Posterior focal distance- 31mm (N-24mm)24mm)
• The Nodel point of the eye is thus The Nodel point of the eye is thus moved forwardmoved forward
• Strong converging (convex) lens- Strong converging (convex) lens- +10D+10D
SignsSigns
• Anterior chamber – Deep Anterior chamber – Deep • Iris Iris
(i) Iridodonesis (or) Tremulousness(i) Iridodonesis (or) Tremulousness(ii) Peripheral button-hole iridectomy (ii) Peripheral button-hole iridectomy
markmark• Pupil - Jet black reflexPupil - Jet black reflex• Absence of the 3Absence of the 3rdrd and 4 and 4thth Purkinje images Purkinje images• Retinoscopy – reveals high hypermetropia Retinoscopy – reveals high hypermetropia
and astigmatismand astigmatism• Ophthalmoscopy – As in hypermetropic Ophthalmoscopy – As in hypermetropic
fundus with a small optic discfundus with a small optic disc
DisadvantagesDisadvantages
• Image magnification of about 25-30%Image magnification of about 25-30%• Spherical aberration, Peripheral and Spherical aberration, Peripheral and
PincushionPincushion• Roving ring scotoma (The scotoma extents Roving ring scotoma (The scotoma extents
from 50°- 65° from central fixation)from 50°- 65° from central fixation)• Jack in the boxJack in the box• Restriction of the visual fieldRestriction of the visual field• Coloured visionColoured vision• Inaccurate spectacle correction because of Inaccurate spectacle correction because of
errorneous vertex distanceerrorneous vertex distance
TreatmentTreatment
• Spectacle ( Convex lens )Spectacle ( Convex lens )
• Contact lensContact lens
• Secondary IOLSecondary IOL
• EpikeratophakiaEpikeratophakia
• KeratophakiaKeratophakia
Aphakic formulaAphakic formula
P = X / 2 +10.00DP = X / 2 +10.00D
P = IOL powerP = IOL power
X = Refractive powerX = Refractive power
PseudophakiaPseudophakia
• Pseudophakia Pseudophakia means False lens means False lens
Image magnificationImage magnification
Calculation of IOL powerCalculation of IOL power
P P = A-2.5*L -0.9K= A-2.5*L -0.9K
P P = IOL Power= IOL Power
AA = Constant value= Constant value
2.52.5 = AC depth= AC depth
L L = Axial length in mm= Axial length in mm
0.90.9 = Corneal curvature= Corneal curvature
K K = Corneal diapters= Corneal diapters
Refractive stages of a Refractive stages of a Pseudophakic eyePseudophakic eye
• EmmetropiaEmmetropia
• Consecutive myopiaConsecutive myopia
• Consecutive hypermetropiaConsecutive hypermetropia
AdvantagesAdvantages
• Image magnification is only 0- 2%Image magnification is only 0- 2%
• No spherical and prismatic aberrationsNo spherical and prismatic aberrations
• Minimum (or) No Anisokonia with rapid Minimum (or) No Anisokonia with rapid return of binocularityreturn of binocularity
• Normal Peripheral field of vision and Normal Peripheral field of vision and eccentric visioneccentric vision
• Freedom from handling of the optical Freedom from handling of the optical devicesdevices
• Cosmetically it is well acceptedCosmetically it is well accepted
DisadvantagesDisadvantages
• Risks and complications may be Risks and complications may be moremore
• Initially, the cost is moreInitially, the cost is more
• PCOPCO
• CMECME
• IOL related complicationsIOL related complications
Thank “U”Thank “U”