ERROR OF REFRACTIONERROR OF REFRACTION

OutlineOutlineI. IntroductionI. Introduction

A. OpticsA. OpticsB. RefractionB. RefractionC. Emmetropia and AmetropiaC. Emmetropia and Ametropia

II. General Symptomatology II. General Symptomatology III. Errors of RefractionIII. Errors of Refraction

A. HyperopiaA. Hyperopia B. MyopiaB. Myopia C. AstigmatismC. Astigmatism D. EOR secondary to AgingD. EOR secondary to Aging E. Congenital EORE. Congenital EOR F. Iatrogenic EORF. Iatrogenic EOR

IV. Measurement of EORIV. Measurement of EORV. ManagementV. Management

LENS - a device LENS - a device which causes which causes light to either converge and

concentrate or to diverge, usually formed from a

piece of shaped glass

OPTICSOPTICS

OPTICSOPTICS

POSITIVE OR CONVERGING LENSPOSITIVE OR CONVERGING LENS

If the lens is If the lens is biconvex or plano-convexbiconvex or plano-convex, a collimated or parallel , a collimated or parallel beam of light travelling parallel to the lens axis and passing beam of light travelling parallel to the lens axis and passing through the lens will be converged (or focused) to a spot on through the lens will be converged (or focused) to a spot on

the axis, at a certain distance behind the lens. the axis, at a certain distance behind the lens.

NEGATIVE OR DIVERGING LENSNEGATIVE OR DIVERGING LENSIf the lens is biconcave or plano-concave, a collimated beam If the lens is biconcave or plano-concave, a collimated beam

of light passing through the lens is diverged (spread)of light passing through the lens is diverged (spread)

The beam after passing through the lens appears to be The beam after passing through the lens appears to be emanating from a particular point on the axis in front of the emanating from a particular point on the axis in front of the

lenslens

Diopter Diopter - is the standard unit to express - is the standard unit to express the refractive power of optical lenses. the refractive power of optical lenses. It is the reciprocal of the distance, It is the reciprocal of the distance, expressed in meters, between a lens expressed in meters, between a lens and its focus (its focal length)and its focus (its focal length)

D = 1D = 1

ff

D: diopterD: diopter f: focal length (in f: focal length (in meters)meters)

OPTICSOPTICS

Focal length = 1 meter D = 1/1

D = 1 diopter

Focal length = 0.5 meterD = 1/0.5

D = 2 diopters

Focal length = 0.25 meterD = 1/0.25

D = 4 diopters

Example:

D = 1/f

OPTICSOPTICSMAIN OPTICAL MAIN OPTICAL

COMPONENTS COMPONENTS OF THE EYE:OF THE EYE:

Cornea 43 DCornea 43 D

Lens 17 DLens 17 D

The anterior surface of the cornea is the major refractive surface of the eye

DEFINITION OF TERMS:DEFINITION OF TERMS:Emmetropia Emmetropia

optical condition in which an eye does optical condition in which an eye does not have an error of refractionnot have an error of refraction

Light from a distant object is focused on Light from a distant object is focused on the retina.the retina.

AMETROPIAAMETROPIA

optical condition in which parallel rays of optical condition in which parallel rays of light from an object an infinite distance light from an object an infinite distance from the eye does not come to focus from the eye does not come to focus (form an image) exactly at the retina(form an image) exactly at the retina

Three general types: HYPEROPIA, MYOPIA AND Three general types: HYPEROPIA, MYOPIA AND ASTIGMATISMASTIGMATISM

Ammetropia

Axial ametropiaAxial ametropia - Abnormal length of - Abnormal length of the globethe globe

Curvature AmetropiaCurvature Ametropia - Abnormal - Abnormal curvature of the cornea or the lenscurvature of the cornea or the lens

Index AmetropiaIndex Ametropia - Abnormal - Abnormal refractive indices of the mediarefractive indices of the media

Abnormal position of the lensAbnormal position of the lens

GENERAL SYMPTOMATOLOGYGENERAL SYMPTOMATOLOGY

Decreased visual acuity

Pin hole test

Ocular discomfort

increased sensitivity to light, decreased efficiency, various aches and fatigue

Headache

HYPEROPIAHYPEROPIA

FarsightednessFarsightedness

The refractive power of the The refractive power of the cornea and lens are weak, or a cornea and lens are weak, or a relatively short eyeballrelatively short eyeball

light from distant objects focus light from distant objects focus behind the retina behind the retina

Axial Hyperopia - the eyeball is Axial Hyperopia - the eyeball is shorter than averageshorter than average

Hyperopia

Accomodation increases the Accomodation increases the refractive power of the lens and refractive power of the lens and may compensate for hyperopiamay compensate for hyperopiaHeadache – due to excessive Headache – due to excessive sustained accomodation required sustained accomodation required for clear visionfor clear vision

Corrected by: Corrected by: Convex lensesConvex lenses

HyperopiaHyperopia

MYOPIAMYOPIANearsightednessNearsightedness

The refractive power of the cornea The refractive power of the cornea and lens are too strong, or a and lens are too strong, or a relatively long eyeballrelatively long eyeball

light from distant objects focus in light from distant objects focus in front of the retina front of the retina

Axial myopiaAxial myopia - The eyeball is longer - The eyeball is longer than averagethan average

Curvature MyopiaCurvature Myopia – due to abnormal – due to abnormal curvature of the cornea curvature of the cornea (Keratoconus)(Keratoconus)

MYOPIA

Corrected by: Concave lenses

AstigmatismAstigmatism Abnormalities in corneal shapeAbnormalities in corneal shape

A condition wherein the light rays entering A condition wherein the light rays entering the eye focus on two or more separate the eye focus on two or more separate lines instead of one pointlines instead of one point

This happens when the refractive power is This happens when the refractive power is not uniform in all meridiansnot uniform in all meridians

Principal symptom: Principal symptom: inability to have clear inability to have clear imageimage

Usually accompanied by myopia or Usually accompanied by myopia or hyperopiahyperopia

TREATMENT: Cylindrical LensTREATMENT: Cylindrical Lens

TYPES OF REGULAR ASTIGMATISMTYPES OF REGULAR ASTIGMATISM

1. Compound myopic1. Compound myopicBoth anterior and posterior focal lines are in front of the

retina2. Simple Myopic2. Simple Myopic

Anterior focal line is in front of the retina while posterior focal line is on the retina

3. Mixed3. MixedAnterior focal line is in front of retina while posterior focal

line is at the back of the retina

4. Simple Hyperopic4. Simple HyperopicAnterior focal line is on the retina while posterior focal line

is behind the retina

5. Compound hyperopic5. Compound hyperopicBoth focal lines are behind the retina

1.1. Compound myopicCompound myopic

2. Simple Myopic2. Simple Myopic

3. Mixed3. Mixed

4. Simple Hyperopic4. Simple Hyperopic

5. Compound hyperopic5. Compound hyperopic

ERRORS OF REFRACTION 2ERRORS OF REFRACTION 2OO TO AGINGTO AGING

AccomodationAccomodation

- As object comes closer to the eye, lens As object comes closer to the eye, lens increases its power by altering its shape to increases its power by altering its shape to become more convexbecome more convex

- Accommodation = oculomotor nerve Accommodation = oculomotor nerve stimulation (parasympathetic fibers)stimulation (parasympathetic fibers)

PresbyopiaPresbyopia

- manifest in 5- manifest in 5thth decade decade

- overcome by convex lens (Reading - overcome by convex lens (Reading glasses)glasses)

PRESBYOPIAPRESBYOPIAloss of accommodation due to agingloss of accommodation due to aging

Inability to read small printInability to read small print

Due to a reduction in the deformability of the lensDue to a reduction in the deformability of the lens

Corrected by: Corrected by: convex lenses (reading glasses), convex lenses (reading glasses), bifocals or progressive lensesbifocals or progressive lenses

ERRORS OF REFRACTION 2ERRORS OF REFRACTION 2OO TO AGINGTO AGING

““Second Sight” – Myopic shiftSecond Sight” – Myopic shift

↑ ↑ density of lens nucleus (nuclear density of lens nucleus (nuclear sclerosis)sclerosis)

↑ ↑ refractive power → myopiarefractive power → myopia

distant vision → blurred and out of focusdistant vision → blurred and out of focus

near vision→ improvesnear vision→ improves

AnisometropiaAnisometropia

difference in refractive power difference in refractive power between the two eyesbetween the two eyes

major cause of amblyopia due to major cause of amblyopia due to failure of both eyes to failure of both eyes to accommodate independentlyaccommodate independently

cause complications in refractive cause complications in refractive correction due to:correction due to:

differences in size of retinal images differences in size of retinal images (aniseikonia)(aniseikonia)

CONGENITAL ERRORS OF CONGENITAL ERRORS OF REFRACTIONREFRACTION

Hyperopic at birth (+1.50 D)Hyperopic at birth (+1.50 D)

Corneal curvature is much steeper (6.59 mm Corneal curvature is much steeper (6.59 mm radius) at birth and flattens to adult curvature radius) at birth and flattens to adult curvature (7.71 mm) by about 1 y/o(7.71 mm) by about 1 y/o

Cornea and lens grow and eyes elongate with Cornea and lens grow and eyes elongate with child growth thus,child growth thus,

HYPEROPIA --> EMMETROPIA OR MYOPIAHYPEROPIA --> EMMETROPIA OR MYOPIA

IATROGENIC ERRORS IATROGENIC ERRORS OF REFRACTIONOF REFRACTION

Cataract Surgery:Cataract Surgery:

a. Tension in suture astigmatisma. Tension in suture astigmatism

Reduced by suture removalReduced by suture removal

Induced astigmatism may persistInduced astigmatism may persist

b. Removal of lensb. Removal of lens

Artificial lens replacementArtificial lens replacement

MEASUREMENT OF EORMEASUREMENT OF EOR

1. Subjective method1. Subjective method

- utilizes the ability of the individual to choose the lens that - utilizes the ability of the individual to choose the lens that gives him the best imagegives him the best image

- a set of trial lenses is usually used- a set of trial lenses is usually used

2. Objective method2. Objective method

Retinoscopy Retinoscopy •• makes use of an instrument (retinoscope) that catches makes use of an instrument (retinoscope) that catches the rays of light reflected at the patient’s retina whose the rays of light reflected at the patient’s retina whose source comes from a mirror near the examiner’s eyesource comes from a mirror near the examiner’s eye•• useful in children, the low intelligent, semiconscious or useful in children, the low intelligent, semiconscious or unconsciousunconscious

MEASUREMENT OF EORMEASUREMENT OF EOR

3. Cyclopegic Refraction3. Cyclopegic Refraction

drugs that paralyze accommodation are used to measure accurately the refractive error the individual has by the objective method

usually performed in children

4. Keratometry4. Keratometry measurement of the corneal astigmatism

the curvature of the cornea is measured in various meridians by reflected light on the cornea coming from

plates with various transparent configurations

CORRECTION OF EORCORRECTION OF EORSpectacle lensesSpectacle lenses

- safest method of refractive correction- safest method of refractive correction

- correct low degrees of ametropia- correct low degrees of ametropia

- bifocals: lens for both near and distant - bifocals: lens for both near and distant vision in single framevision in single frame

- progressive: graduated lens for objects - progressive: graduated lens for objects at any at any distancedistance

- may be cosmetically unacceptable for - may be cosmetically unacceptable for high degrees of ametropiahigh degrees of ametropia

Limitation of Limitation of Spectacles:Spectacles:

Most spectacles are worn successfully. Most spectacles are worn successfully. Problems occur with increasing refractive Problems occur with increasing refractive power.power.

Cosmesis : convex magnify,concave minifyCosmesis : convex magnify,concave minify

Distortion of objects in peripheral visionDistortion of objects in peripheral vision

Magnification of objects by highly convex Magnification of objects by highly convex lenseslenses

WeightWeight

Cannot correct severe astigmatismCannot correct severe astigmatism

Contact LensesContact Lenses

DISADVANTAGES:DISADVANTAGES: worn beneath the eyelids anterior to the cornea

May be hard or soft

Used to neutralize ametropia

To protect the healing cornea

To conceal unsightly damaged eyes

not appropriate for children

Maintenance

Size

Irritation

infection

TYPES OF CONTACT LENSES:TYPES OF CONTACT LENSES:

1. Hard contact lenses1. Hard contact lenses

Offer clear, crisp vision and are durable

Correct major errors of refraction

Indicated for correction of irregular

astigmatism

Correct by changing the curvature of the

anterior surface of the eye

2. Soft contact lenses2. Soft contact lenses

More comfortable

Require little adjustment to their use

Easier to insert and remove than hard lenses

little correction of astigmatism

Provide poorer corrected vision than do hard lenses

Contact Lens CareContact Lens Care

Do not exceed the recommended Do not exceed the recommended wearing timewearing timeObserve meticulous hygieneObserve meticulous hygieneDo not clean with tap water or salivaDo not clean with tap water or salivaRemove if the eye becomes sore or Remove if the eye becomes sore or inflammedinflammedRemove soft lenses while Remove soft lenses while administering preservative administering preservative containing dropscontaining drops

Complications of Contact Lens use

Giant papillary conjunctivitis – a condition in which wearers of (usually) soft contact lenses develop increasing ocular discomfort and itching

Corneal vascularization - more common in soft lens due to larger surface area covering the part of the sclera and limbus

Corneal ulceration

Corneal infection

CORRECTION FOR EORCORRECTION FOR EOR

Keratorefractive SurgeryKeratorefractive Surgery

Radial KeratotomyRadial Keratotomy

Photorefractive Keratectomy (PRK)Photorefractive Keratectomy (PRK)

Laser Assisted Intrastromal Laser Assisted Intrastromal Keratomileusis (LASIK)Keratomileusis (LASIK)

Keratorefractive Keratorefractive surgerysurgery

Radial keratotomyRadial keratotomy

incisional technique incisional technique to alter corneal to alter corneal curvaturecurvature

Cornea becomes Cornea becomes flatter as incision flatter as incision healsheals

Excimer laserExcimer laser: shaves off ultra-thin : shaves off ultra-thin discs of corneal tissue to reduce discs of corneal tissue to reduce refractive power in myopiarefractive power in myopia

PRK (photorefractive PRK (photorefractive keratectomy)keratectomy)

LASIK (laser assisted in-situ LASIK (laser assisted in-situ keratomileusis)keratomileusis)

Photorefractive Keratectomy Photorefractive Keratectomy (Excimer laser)(Excimer laser)

Uses an excimer laser to reshape the Uses an excimer laser to reshape the outer surface of the corneaouter surface of the cornea

Benefits:Benefits:

- reliable correction of low to moderate - reliable correction of low to moderate myopia (-2 to -6 diopters)myopia (-2 to -6 diopters)

- improvement in unaided visual acuity- improvement in unaided visual acuity

Complications:Complications: - corneal haze- corneal haze - post op pain- post op pain - loss of best-corrected visual acuity- loss of best-corrected visual acuity - regression of effect- regression of effect

LASIKLASIKcorneal flap is created --- Excimer laser corneal flap is created --- Excimer laser reshapes the corneareshapes the cornea

reliable correction of low to high myopia (-2 to reliable correction of low to high myopia (-2 to -12 diopters)-12 diopters)

BenefitsBenefits

Clear vision in 24 hoursClear vision in 24 hours

Minimal post-op painMinimal post-op pain

LimitationLimitation

Additional surgical stepAdditional surgical step

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CORRECTION OF CORRECTION OF EOREOR

Intraocular lenses- phakic IOLsIntraocular lenses- phakic IOLs

Clear lens extraction for myopiaClear lens extraction for myopia

- extraction of non-cataractous lenses- extraction of non-cataractous lenses

- eyes must be highly myopic in order for - eyes must be highly myopic in order for the operation to be a success.the operation to be a success.

LensLens

LensLenstransparent, transparent, avascular, biconvexavascular, biconvex

Held in position by Held in position by zonules zonules

Surrounded by the Surrounded by the lens capsulelens capsule

1 of the main 1 of the main refracting surfaces of refracting surfaces of the eyethe eye

Has inherent Has inherent elasticityelasticity

LensLensCross sectionCross section

Causes of CataractCauses of CataractAge relatedAge related

50 % in 65 – 74 yo50 % in 65 – 74 yo

70 % in > 75 yo70 % in > 75 yo

3 main types3 main types

Subcapsular Subcapsular CataractCataract

Nuclear CataractNuclear Cataract

Cortical CataractCortical Cataract

CataractCataract

Subcapsular cataractSubcapsular cataract

May be anterior or posteriorMay be anterior or posterior

Anterior type is associated with Anterior type is associated with fibrous metaplasia of the fibrous metaplasia of the anterior epithelium of the lensanterior epithelium of the lens

Posterior type is associated Posterior type is associated with posterior migration of the with posterior migration of the epithelial cells of the lensepithelial cells of the lens

CataractCataractNuclear CataractNuclear Cataract

Sclerosis and yellowing of the lens Sclerosis and yellowing of the lens nucleusnucleus

Myopic shift “second sight”Myopic shift “second sight”

Advanced cases, nucleus becomes Advanced cases, nucleus becomes opaque and brown (brunescent opaque and brown (brunescent nuclear cataract)nuclear cataract)

CataractCataractCortical cataractCortical cataract

Hydropic swelling of the lens fibersHydropic swelling of the lens fibers

Due to ionic changes in the lens fibersDue to ionic changes in the lens fibers

Formation of radial cortical spokes.Formation of radial cortical spokes.

Mature CataractMature Cataract – Entire cortex becomes – Entire cortex becomes opaqueopaque

Hypermature CataractHypermature Cataract – Leakage of – Leakage of degenerated cortical material through the degenerated cortical material through the lens capsule leaving the capsule wrinkled and lens capsule leaving the capsule wrinkled and shrunken.shrunken.

Morgagnian CataractMorgagnian Cataract – further liquefaction of – further liquefaction of the cortex allows free movement of the the cortex allows free movement of the nucleusnucleus

CataractCataractMature Cortical CataractMature Cortical Cataract

CataractCataractHypermature CataractHypermature Cataract

CataractCataractMorgagnian CataractMorgagnian Cataract

Traumatic CataractTraumatic CataractDirect Penetrating Injury - Direct Penetrating Injury - lens capsule ruptured lens capsule ruptured with hydration of lens fiberswith hydration of lens fibers

Blunt injuryBlunt injury

stellate or rosette shaped opacificationstellate or rosette shaped opacification

Vossius ring – imprinting of iris pigment onto Vossius ring – imprinting of iris pigment onto the anterior lens capsulethe anterior lens capsule

Electric shockElectric shock – causes protein coagulation and – causes protein coagulation and cataract formationcataract formation

Ionizing radiation Ionizing radiation - damage to actively growing - damage to actively growing lens cells, younger patients more susceptiblelens cells, younger patients more susceptible

Traumatic CataractTraumatic CataractSevere penetrating traumaSevere penetrating trauma

Traumatic cataractTraumatic cataractVossius ringVossius ring

Metabolic CataractMetabolic CataractDiabetes MellitusDiabetes Mellitus

Inc. glucose in aqueous humor

Glucose enters lens by diffusion

Glucose converted to sorbitol

Influx of water in the lens

“Snow flake” Cataract

Metabolic CataractMetabolic CataractGalactosemiaGalactosemia

Autosomal recessiveAutosomal recessive

Inability to convert galactose to glucoseInability to convert galactose to glucose

Symptoms of Malnutririon,hepatomegaly, Symptoms of Malnutririon,hepatomegaly, jaundice and mental deficiencyjaundice and mental deficiency

75 % develops cataract few weeks after birth75 % develops cataract few weeks after birth

Inc. galactose and glactiol in the lens cellsInc. galactose and glactiol in the lens cells

Nucleus and deep cortex opacifiedNucleus and deep cortex opacified

““Oil dropletOil droplet” cataract” cataract

Metabolic CataractMetabolic Cataract

Wilson’s diseaseWilson’s disease

Autosomal recessiveAutosomal recessive

Disorder in copper metabolismDisorder in copper metabolism

Cuprous oxide (reddish brown pigment) Cuprous oxide (reddish brown pigment) is deposited in the anterior lens capsuleis deposited in the anterior lens capsule

““sunflower cataractsunflower cataract””

Toxic CataractToxic CataractSteroid induced cataractSteroid induced cataract

Posterior subcapsular cataractPosterior subcapsular cataract

PhenothiazinesPhenothiazines

Yellow brown granules on the anterior capsuleYellow brown granules on the anterior capsule

Visually insignificantVisually insignificant

Miotics - cholinesterase inhibitorsMiotics - cholinesterase inhibitors

Anterior subcapsular vacuolesAnterior subcapsular vacuoles

Amiodarone Amiodarone

anterior subcapsular lens opacitiesanterior subcapsular lens opacities

Visually InsignificantVisually Insignificant

Secondary CataractSecondary Cataract

Chronic Anterior UveitisChronic Anterior Uveitis

Most common cause of secondary cataractMost common cause of secondary cataract

Formation of posterior synechiaeFormation of posterior synechiae

Thickening of anterior lens capsuleThickening of anterior lens capsule

Formation of fibrovascular membraneFormation of fibrovascular membrane

Chronic Anterior Uveitis

Secondary CataractSecondary CataractAcute angle closure glaucomaAcute angle closure glaucoma

glaukomfleckenglaukomflecken

Congenital Cataract

lens opacity present at birth

Rubella

Maternal infection with rubella virus

Cardiac defects, deafness, mental retardation

Cataracts are characterized by pearly white nuclear opacification

Abnormalities of Lens Shape Abnormalities of Lens Shape and Positionand Position

Coloboma-congenital absence of an eye Coloboma-congenital absence of an eye structurestructure

Lenticonus-cone formation in the anterior Lenticonus-cone formation in the anterior or posterior pole of the lensor posterior pole of the lens

Microphakia-lens with a smaller than Microphakia-lens with a smaller than normal diameternormal diameter

Microsherophakia-not only small but Microsherophakia-not only small but sphericalspherical

Ectopia LentisEctopia LentisMarfan Syndrome’sMarfan Syndrome’s

Widespread abnormality of connective tissue

Autosomal Dominant

Cardiac anomalies - aneurysm of the ascending aorta.

Skeletal anomalies – limbs are inappropriately long.

Arachnodactyly - excessively long fingers

Muscular underdevelopment

Zonular attachment of the lens usually are intact but become stretched and elongated

Marfan’s SyndromeMarfan’s Syndrome

Marfan’s SyndromeMarfan’s SyndromeOcular featureOcular feature

Bilateral lens subluxation – 80 % of Bilateral lens subluxation – 80 % of casescases

Ectopia Lentis

HomocystinuriaAutosomal recessive

Error of methionine metabolism

Lenses are usually subluxated inferiorly

Zoules have high levels of cysteine and tend to be brittle

Management of Management of CataractCataract

Cataract SurgeryCataract Surgery

Intracapsular Cataract SurgeryIntracapsular Cataract Surgery

Extracapsular Cataract SurgeryExtracapsular Cataract Surgery

PhacoemulsificationPhacoemulsification

Extracapsular Cataract Extracapsular Cataract ExtractionExtraction

PhacoemulsificationPhacoemulsification

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After CataractAfter Cataract

YAG laser capsulotomy

Complications of Cataract Complications of Cataract SurgerySurgery

EarlyEarly

Inc intraocular pressureInc intraocular pressure

Iris prolapseIris prolapse

Wound leakWound leak

Acute Bacterial EndophthalmitisAcute Bacterial Endophthalmitis

Pupil BlockPupil Block

Iris ProlapseIris Prolapse

Wound LeakWound Leak

Bacterial Bacterial EndophthalmitisEndophthalmitis

Complications of Cataract Complications of Cataract SurgerySurgery

LateLate

Toxic suture syndromeToxic suture syndrome

Corneal DecompensationCorneal Decompensation

Irvine-Gass SyndromeIrvine-Gass Syndrome

Toxic Suture Toxic Suture SyndromeSyndrome

Corneal Corneal DecompensationDecompensation

Irvine-Gass SyndromeIrvine-Gass Syndrome

Cystoid Cystoid macular edemamacular edema

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