11

OCULAR OCULAR REFRACTIONREFRACTION

22

Visual analVisual analyyser ser performancesperformances

Phisical status of Phisical status of refractive refractive components (correct components (correct focus on the retina);focus on the retina);

Retinian neurons Retinian neurons quality;quality;

Brain neurons Brain neurons quality.quality.

33

Ocuar refraction Ocuar refraction is defined is defined by the anatomical components by the anatomical components which contribute on light array which contribute on light array optical modulation optical modulation

44

transparenttransparent medimediumsums

lacrimal layerlacrimal layer ccorneaornea aquaqueouseous humour humour lens lens vitriousvitrious

55

Ocular refraction Ocular refraction

static refraction static refraction dinamic refraction dinamic refraction

SubjectsSubjects

1.1. AmetropiaAmetropia

2.2. HyperopiaHyperopia

3.3. MyopiaMyopia

4.4. AstigmatismAstigmatism

5.5. AnizometropiaAnizometropia

6.6. AccomodationAccomodation

7.7. PresbyopiaPresbyopia 66

EMETROPIAEMETROPIA

emetropia is that optical condition in emetropia is that optical condition in which there is no refraction error so which there is no refraction error so that rays of parallel to the visual axis that rays of parallel to the visual axis appear entering the eye are brought appear entering the eye are brought to a focus on the fovea centralis to a focus on the fovea centralis when no accommodation is usedwhen no accommodation is used

77

AMETROPIA AMETROPIA classificlassificationcation

spherical or stigmic disorders in spherical or stigmic disorders in which enter: which enter: myopiamyopia hyperopiahyperopia

88

asferical or astigmic disorders in asferical or astigmic disorders in which we include astigmatisms:which we include astigmatisms: regularregular iregulariregular

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HYPEROPIAHYPEROPIA

refractive condition of the eye in refractive condition of the eye in which which (with accommodation (with accommodation suspended) suspended) parallel rays of light are parallel rays of light are intercepted by the retina before intercepted by the retina before coming to focuscoming to focus

1010

Clasification of Clasification of hyperopiahyperopia

AxialAxial = when the globe is too short = when the globe is too short to the amount of the refractive power to the amount of the refractive power present;present;

RefractiveRefractive = when the power of the = when the power of the cornea and lens is inadequate for the cornea and lens is inadequate for the length of the globelength of the globe

1111

TType of ype of hyperopiahyperopia

Total hyperopia Total hyperopia = amount of the hyperopia = amount of the hyperopia with all accommodation suspended (by with all accommodation suspended (by using the cycloplegic drugs);using the cycloplegic drugs);

Manifest hyperopia Manifest hyperopia = is the maximum = is the maximum hyperopia that can be corrected with a hyperopia that can be corrected with a convex lens when accommodation is active;convex lens when accommodation is active;

Latent hyperopia Latent hyperopia = is the difference = is the difference between total and manifest hyperopia.between total and manifest hyperopia.

1212

Signs and symptomsSigns and symptoms

Visual acuity Visual acuity is reduced when accommodation is reduced when accommodation is not able to fully substitute the hyperopia;is not able to fully substitute the hyperopia;

Vision is blurredVision is blurred, especially after near work;, especially after near work; The increased of the accommodation may The increased of the accommodation may

stimulate an excessive degree of convergence, stimulate an excessive degree of convergence, manifested as a tendency of for the eyes to manifested as a tendency of for the eyes to deviate inward (deviate inward (esodeviationesodeviation););

The The corneacornea is smaller than normal, and even the is smaller than normal, and even the globe itself may be smaller;globe itself may be smaller;

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OftalmoscopyOftalmoscopy

optic disk congestive, with indistinct optic disk congestive, with indistinct margins and the absence of the margins and the absence of the physiologic cup (physiologic cup (pseudopapiledema)pseudopapiledema)

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TreatmentTreatment

convex lenses (glases or contact lenses)convex lenses (glases or contact lenses) corneal refractive surgery:corneal refractive surgery:

Laser thermal keratoplastyLaser thermal keratoplasty Lamellar keratoplastyLamellar keratoplasty Photorefractive keratectomyPhotorefractive keratectomy Laser in situ keratomileusis (LASIK)Laser in situ keratomileusis (LASIK)

phakic intraocular lenses using iris-claw IOL;phakic intraocular lenses using iris-claw IOL; clear lens extraction with posterior chamber lens clear lens extraction with posterior chamber lens

implantation.implantation.1515

LASIKLASIK

1616

MYOPIAMYOPIA

optical condition in which rays of light optical condition in which rays of light entering the eye parallel to the visual axis entering the eye parallel to the visual axis come to focus in front of the retinacome to focus in front of the retina

1717

Clasification of Clasification of myopiamyopia

AxialAxial = because the refractive power of = because the refractive power of the cornea and lens is too great for the the cornea and lens is too great for the length of the eye;length of the eye;

RefractiveRefractive = because the eye is to long = because the eye is to long for the refractive power presentfor the refractive power present

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physiologicphysiologic myopia myopia refractive (refractive (lenticular lenticular myopia – is refractive myopia – is refractive

myopia related to the lens power)myopia related to the lens power) axialaxial

pathologicpathologic or degenerative myopia – is or degenerative myopia – is axial myopiaaxial myopia

1919

physiologicphysiologic myopia myopia

is the most common typeis the most common type onset usually between 5 and 10 years of onset usually between 5 and 10 years of

age but may begin as late as 25 years ageage but may begin as late as 25 years age gradually increase until the eye is fully gradually increase until the eye is fully

grown about 18 years of agegrown about 18 years of age seldom exceeds 6 diopters.seldom exceeds 6 diopters.

2020

pathologicpathologic or degenerative myopia or degenerative myopia SymptomsSymptoms

decreased visiondecreased vision axial length of the eye is excessive, axial length of the eye is excessive,

primarily because of overgrowth of primarily because of overgrowth of the posterior two thirds of the globethe posterior two thirds of the globe

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oftalmoscopyoftalmoscopy

crescent of the optic disc that begins at the crescent of the optic disc that begins at the temporal side and progresses to surround the disc.temporal side and progresses to surround the disc.

Staphyloma of the posterior pole .Staphyloma of the posterior pole . hyperpigmented spot in the macula (Fuchs spot).hyperpigmented spot in the macula (Fuchs spot). degeneration of the retinal pigment epitheliumdegeneration of the retinal pigment epithelium choroidal sclerosis.choroidal sclerosis. peripheral retinal thinning with lattice peripheral retinal thinning with lattice

degeneration and retinal breaks.degeneration and retinal breaks.2222

Treatment Treatment

is neutralized by concave lensesis neutralized by concave lenses contact lenses (in high myopia, contact lenses (in high myopia,

anizometropia); highly fitted contact anizometropia); highly fitted contact lenses may temporarily reduce the corneal lenses may temporarily reduce the corneal curvature and thus may show an apparent curvature and thus may show an apparent decrease in myopiadecrease in myopia 2323

Refractive surgeryRefractive surgery

radial keratotomy acts through peripheral radial radial keratotomy acts through peripheral radial incision that flatten the central corneaincision that flatten the central cornea

photorefractive keratectomy (PRK) ablates tissue photorefractive keratectomy (PRK) ablates tissue directly from central cornea. directly from central cornea.

laser in situ keratomileusis (LASIK) excimer laser in situ keratomileusis (LASIK) excimer application (PRK) after creation of a hinged flapapplication (PRK) after creation of a hinged flap

posterior chamber phakic intraocular lens posterior chamber phakic intraocular lens (implantable ocular lens)(implantable ocular lens)

intracorneal implantsintracorneal implants2424

2525

For high myopiaFor high myopia

laser photocoagulation for symptomatic retinal laser photocoagulation for symptomatic retinal breaksbreaks

extrafoveal or juxtafoveal laser extrafoveal or juxtafoveal laser photocoagulation therapyphotocoagulation therapy

combination between LASIK and phakic combination between LASIK and phakic intraocular lens = “BIOPTIC”intraocular lens = “BIOPTIC”

scleral enforcement to stop or to retard the scleral enforcement to stop or to retard the progression of disease (controversial and under progression of disease (controversial and under investigationinvestigation

2626

ASTIGMATISMASTIGMATISM optical condition in which the refractive optical condition in which the refractive

power of the eye is not the same in all power of the eye is not the same in all meridians. meridians.

variation in the curvature of the cornea or variation in the curvature of the cornea or lens at different meridians induces light lens at different meridians induces light rays focusing to more than one point.rays focusing to more than one point.

2727

ClassificationsClassifications irregular irregular = when the meridian are not at right angle = when the meridian are not at right angle

to each otherto each other regular regular = when the meridian of minimal and = when the meridian of minimal and

maximal refraction are at right angle to each other. maximal refraction are at right angle to each other. Regular astigmatism can be:Regular astigmatism can be:

with the rule with the rule – when the vertical meridian is steepest and a – when the vertical meridian is steepest and a correcting plus cylinder should be placed at axis 90°correcting plus cylinder should be placed at axis 90°

against the rule against the rule – when the horizontal meridian is steepest and a – when the horizontal meridian is steepest and a correcting plus cylinder should be placed at axis 180°correcting plus cylinder should be placed at axis 180°

oblique astigmatism oblique astigmatism – the principal meridian do not lie at or – the principal meridian do not lie at or close to 90° and 180°close to 90° and 180°

2828

Classifications IIClassifications II

simplesimple: when one meridian is emetropic and : when one meridian is emetropic and other is ametropic (myopic and hypermetropic)other is ametropic (myopic and hypermetropic)

composedcomposed: when both meridian are ametropic: when both meridian are ametropic myopicmyopic = both meridian are in front of the retina = both meridian are in front of the retina hypermetropichypermetropic = both meridian are intercepted by = both meridian are intercepted by

retina before coming to a focusretina before coming to a focus mixed astigmatism: mixed astigmatism: one meridian is myopic and one meridian is myopic and

other is hypermetropicother is hypermetropic

2929

Classifications IIIClassifications III

congenitalcongenital astigmatism astigmatism acquiredacquired astigmatism: astigmatism:

surgical incision o the corneasurgical incision o the cornea trauma and scarring of the corneatrauma and scarring of the cornea tumors of the eyelid pressing upon the globetumors of the eyelid pressing upon the globe

3030

Pathogenic aspectsPathogenic aspects parallel rays of light do not focus at a point. Each parallel rays of light do not focus at a point. Each

meridian has a focal line; the distance between meridian has a focal line; the distance between these focal lines is the “interval of Sturm”. these focal lines is the “interval of Sturm”. Between the focal lines, in the circle of least Between the focal lines, in the circle of least diffusion (conffusion), the diverging and diffusion (conffusion), the diverging and converging tendency of the light rays is the same. converging tendency of the light rays is the same. In this area the image is clear enough to satisfy the In this area the image is clear enough to satisfy the patientpatient

3131

Symptoms and signsSymptoms and signs

the image is not clearthe image is not clear the accommodation is interferedthe accommodation is interfered severe astigmatism may cause the optic severe astigmatism may cause the optic

disc to appear oval rather then near disc to appear oval rather then near circularcircular

3232

TreatmentTreatment MinorMinor degree of astigmatism with good VA degree of astigmatism with good VA

and without symptoms – correction is not and without symptoms – correction is not indicatedindicated

Simple astigmatism Simple astigmatism – cylindrical lens placed – cylindrical lens placed in the meridian 90 degrees away from the axis in the meridian 90 degrees away from the axis of the ametropic meridianof the ametropic meridian

ComposedComposed and and mixed astigmatism mixed astigmatism – sphero-– sphero-cylindric lenses (combination of a sphere and a cylindric lenses (combination of a sphere and a cylinder -plus or minus- )cylinder -plus or minus- )

3333

Hard contact lenses Hard contact lenses may be used to correct may be used to correct regular astigmatism and especially the regular astigmatism and especially the irregular astigmatismirregular astigmatism

SurgerySurgery incisional surgery incisional surgery (relaxing incisions, block (relaxing incisions, block

resection, compressive suture) is indicated in resection, compressive suture) is indicated in congenital regular astigmatismcongenital regular astigmatism

excisional surgery excisional surgery (excimer laser – PRK and (excimer laser – PRK and LASIK) is recommended both in regular and LASIK) is recommended both in regular and irregular astigmatismirregular astigmatism

3434

ACCOMMODATIONACCOMMODATION

process by which the refractive process by which the refractive power of the anterior lens power of the anterior lens segment increases so that a near segment increases so that a near object may be distinctly imaged object may be distinctly imaged upon the retinaupon the retina

3535

complex reflexcomplex reflex

the stimulus is a blurred retinal imagethe stimulus is a blurred retinal image this is coming to brainthis is coming to brain different area of the brain send order to the different area of the brain send order to the

peripheryperiphery stimulation of the short ciliary branch of the stimulation of the short ciliary branch of the

oculomotor nerve constricts or relaxes the oculomotor nerve constricts or relaxes the circular ciliary muscle circular ciliary muscle

the eye almost instantly adjust to provide clear the eye almost instantly adjust to provide clear vision. vision.

3636

For near visionFor near vision

contraction of the ciliary muscle causescontraction of the ciliary muscle causes the zonulae fibers to relax the zonulae fibers to relax then lens become more convex then lens become more convex the power is increasedthe power is increased the focal line is projected onto retina.the focal line is projected onto retina.

3737

For long distanceFor long distance

ciliary muscle relaxesciliary muscle relaxes the zonulae fibers are pull and the zonulae fibers are pull and

tensioned tensioned the convexity of the lens surface the convexity of the lens surface

becomes minimalbecomes minimal

3838

amplitude of accommodationamplitude of accommodation

is distance between far point of the is distance between far point of the eye and nearest point at which the eye and nearest point at which the eye can maintain focuseye can maintain focus

amplitude of accommodation is amplitude of accommodation is properly a monocular expression and properly a monocular expression and is measured for each eye is measured for each eye independentlyindependently

3939

accommodation associated accommodation associated reactionsreactions

convergence of the eyesconvergence of the eyes pupilary constriction (miosis)pupilary constriction (miosis)

4040

presbyopiapresbyopia

with ageing with ageing lens capsule becomes less elasticlens capsule becomes less elastic nucleus becomes harder and less compressible nucleus becomes harder and less compressible

this causes a gradual loss of accommodation this causes a gradual loss of accommodation

4141

SymptomesSymptomes

inability to see near work distinctlyinability to see near work distinctly patient places reding mater farther away patient places reding mater farther away

from the eyes than previouslyfrom the eyes than previously ocular discomfortocular discomfort

4242

Evolution of accomodationEvolution of accomodation

10 years age - 14Dpt.10 years age - 14Dpt.

45 years age45 years age - 1Dpt., - 1Dpt., 50 years age50 years age - - 2Dpt. , 2Dpt. , 55 years age55 years age - - 2.5Dpt. , 2.5Dpt. , 60 years age60 years age - - 3Dpt. , 3Dpt. , 70 years age70 years age - - 3.5Dpt 3.5Dpt

4343

Special situationsSpecial situations

Myopic Myopic patients may compensate for patients may compensate for presbyopia by removing the lens that presbyopia by removing the lens that corrects the distance vision.corrects the distance vision.

Presbyopia is aggravated in a Presbyopia is aggravated in a hypermetropichypermetropic patients if the lens that patients if the lens that corrects the hypermetropia is removedcorrects the hypermetropia is removed

4444

TreatmentTreatment

convex lenses added to the distance correction;convex lenses added to the distance correction; Rules:Rules:

the weakest possible convex to permit the the weakest possible convex to permit the individual to carry an vocational and avocational individual to carry an vocational and avocational tasks;tasks;

if a subject requires lenses for distance, bifocal, if a subject requires lenses for distance, bifocal, trifocal or multifocal lenses should be worn as trifocal or multifocal lenses should be worn as soon as are indicatedsoon as are indicated

4545

Convergence insufficiency (CI)Convergence insufficiency (CI) the inability to maintain fusion at near as a result of a the inability to maintain fusion at near as a result of a

reduced amplitude of fusional convergence power. reduced amplitude of fusional convergence power. Symptomes: Symptomes:

eye discomforteye discomfort headacheheadache blurred vision from reading or doing near workblurred vision from reading or doing near work

Signs: Signs: reduced amplitude of accommodationreduced amplitude of accommodation exoforiaexoforia

4646

Accomodative insufficiency (AI)Accomodative insufficiency (AI)

symptoms develops after 20-40 min of reading symptoms develops after 20-40 min of reading (same as CI) but:(same as CI) but:

these patients have normal fusion capacities these patients have normal fusion capacities when a 4 diopters base in prism is placed in when a 4 diopters base in prism is placed in front of the eye while redingfront of the eye while reding

patients with AI benefit from reading glasespatients with AI benefit from reading glases

4747

Accomodative spasm (AS)Accomodative spasm (AS) inability to relax ciliary muscle (involuntary) inability to relax ciliary muscle (involuntary) is associated with stressful situations or functional nevrosesis associated with stressful situations or functional nevroses Symptoms:Symptoms:

bilateral blurred distance visionbilateral blurred distance vision headache,headache, fluctuating visionfluctuating vision

Sings: Sings: cycloplegic refraction reveals hyperopiacycloplegic refraction reveals hyperopia abnormally close near point of focusabnormally close near point of focus miosismiosis

4848

ANISOMETROPIAANISOMETROPIA

condition in which the refractive error of each condition in which the refractive error of each eye is differenteye is different

the different is more than 2 diopter there is a the different is more than 2 diopter there is a different in image size of the two eyes named different in image size of the two eyes named anizeiconiaanizeiconia

total amount of aniseiconia suported by patient total amount of aniseiconia suported by patient must be less then 8%must be less then 8%

4949

several problemsseveral problems the difference of the power of the two lenses (bifocal the difference of the power of the two lenses (bifocal

lenses) induce a vertical prism, so that the image lenses) induce a vertical prism, so that the image from each eye is on a different level (anisophoria);from each eye is on a different level (anisophoria);

severe anisometropia may cause ambliopia because severe anisometropia may cause ambliopia because of the developing infant`s failure to use the eye with of the developing infant`s failure to use the eye with greater refractive error;greater refractive error;

failure of central vision leads to strabismus, to failure of central vision leads to strabismus, to absence of binocular vision or to deficiency of absence of binocular vision or to deficiency of binocular visionbinocular vision

5050

Treatment Treatment must be done in the first year of lifemust be done in the first year of life must to equalize the size of the retinal image.must to equalize the size of the retinal image.

When:When: the refractive difference between two eyes is the refractive difference between two eyes is

smaller then 4D = full corection with glasessmaller then 4D = full corection with glases this difference is greater we can use:this difference is greater we can use:

contact lens corectioncontact lens corection specific surgical procedure for each type of refractive specific surgical procedure for each type of refractive

errorerror

5151