New Refractive Errors and management · 2019. 7. 5. · • Spectacle lenses • Monofocal lenses :...

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Refractive Errors and management

Transcript of New Refractive Errors and management · 2019. 7. 5. · • Spectacle lenses • Monofocal lenses :...

Page 1: New Refractive Errors and management · 2019. 7. 5. · • Spectacle lenses • Monofocal lenses : spherical lenses , cylindrical lenses • Multifocal lenses • Contact lenses:

Refractive Errors

and management

Page 2: New Refractive Errors and management · 2019. 7. 5. · • Spectacle lenses • Monofocal lenses : spherical lenses , cylindrical lenses • Multifocal lenses • Contact lenses:

Vergence

Parallel Beam Convergence Divergence

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VERGENCE

• All naturally occurring sources of light are

divergent

• Light rays traveling parallel have zero

vergence

• Light rays that focus on a point are

convergent

• The unit of measurement of vergence is

the diopter

D= Vergence (Diopters)=___________1_____________

Distance from the source in meters

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BASIC OPTICS

• Therefore:

• The closer the light is to its source, the

greater the vergence

• The farther the light is from its source, the

lower the vergence, approaching zero as

distance goes toward infinity.

• Diverging light has negative power (-)

• Converging light has positive power (+)

• Lens power is calculated by : using the

biometry by measuring the axis length and

the corneal convexity.

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REFRACTION

• Refraction of light occurs when light

passes from one medium to another of

different refractive index (ie. density)

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Refractive Components of the Eye

• Cornea: responsible for the majority of the

refractive power of the eye (40 D) /

constant.

• Lens: 20 D of refractive power, changes

with accommodation.

• Axial length is constant except under

certain conditions

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• These two refracting elements in the eye

converge the rays of light because:

1-The cornea has a higher refractive index

than air; the lens has a higher refractive

index than the aqueous and vitreous

humours that surround it.

2-The refracting surfaces of the cornea and

lens are spherically convex

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Fovea Light rays

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Emmetropia (normal vision)

• Adequate correlation between axial length

and refractive power.

• Parallel rays of light from a distant object

are brought to focus on the retina with the

eye at rest (no accommodation) ,such an

individual can see sharply in the distance

without accommodation.

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Ametropia (Refractive error)

• Mismatch between axial length and

refractive power.

• Parallel light rays don’t fall on the retina

with the eye at rest (a change in refraction

is required to achieve sharp vision).

• Ametropia may be divided into:

• Nearsightedness (Myopia)

• Farsightedness (Hyperopia)

• Astigmatism

• Presbyopia

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Accommodation

• Emmetropic eye

• object closer than 6 M send divergent light

that focus behind retina , adaptative

mechanism of eye is to increase refractive

power by accommodation

• Helm-holtz theory

• contraction of ciliary muscle -->decrease

tension in zonule fibers -->elasticity of lens

capsule mold lens into spherical shape --

>greater dioptic power -->divergent rays are

focused on retina

• contraction of ciliary muscle is supplied by

parasympathetic third nerve.

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Myopia

• Parallel rays converge at a focal point

anterior to the retina

• Etiology : not clear , genetic factor

• Causes

• excessive long globe (axial myopia) :

more common

• excessive refractive power (refractive

myopia).

• Increase in the curvature of the cornea

or the surfaces of the crystalline lens.

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Uncorrected, light focuses in front of fovea

Corrected by divergent lens, light focuses on fovea

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Myopia

The patient is able to focus on objects near but not far away (blurred distance vision).

Typical complaint is difficulty focusing on road signs or the black board.

Usually detected by the young when they discover they cannot see things at a distance as well as their friends do .

The teacher complains that the child makes too many mistakes copying things from the black-board.

The lens is unable to flatten enough to prevent conversion of images before reaching the retina.

Frequently squinting is compensatory mechanism in an attempt to improve uncorrected visual acuity when gazing into the distance.

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MYOPIA

• Increases with age roughly until the person stops

growing in height.

• A myopic person can still see some objects clearly,

provided the object is closer than the far point

• Pseudomyopia: accomodative spasm.The patient

cannot relax accomodation when looking in the

distance. For example, an over anxious student

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Myopia

• Forms

• Benign myopia (school age myopia): Benign myopia

usually starts in school, develops during adolescence

period and finally stabilizes in the adulthood. It rarely

grows beyond -7.0 D and it is never associated with

any pathologic changes on the eye fundus.

• Progressive and malignant myopia

• interchangeable

• myopia increase rapidly each year

and is associated with vitreous

opacities , fluidity of vitreous and

chorioretinal change.

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Myopia

• Congenital myopia

• Myopia > 10 D

• Increase slowly each year

Special forms cataract nuclear sclerosis , keratoconus , spherophakia

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Myopia

• Symptoms • Typically do not have “eye-strain”, “watering” of the eyes or

headaches as often as hypermetropes do

• Usually detected by the young when they discover they cannot see things at a distance as well as their friends do

• The teacher complains that the child makes too many mistakes copying things from the black-board

• Blurred distance vision

• Squint in an attempt to improve uncorrected visual acuity when gazing into the distance

• Headache

• Amblyopia – uncorrected myopia > 10 D

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Myopia

• Morphologic changes

• deep anterior chamber

• atrophy of ciliary muscle

• vitreous may collapse prematurely -->

opacification

• fundus change : loss of pigment in RPE

,large disc and white crescent-shaped area

on temporal side ,RPE atrophy in macular

area , posterior staphyloma ,retinal

degeneration-->hole-->increase risk of

RD

• Treatment : concave lenses, clear lens

extraction

• *Staphyloma : depression on retina.

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PATHOLOGICAL CAUSES OF

MYOPIA

• KERATOCONUS

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PATHOLOGICAL CAUSES OF

MYOPIA

* Nuclear Cataract *Diabetes

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PATHOLOGICAL CAUSES OF

MYOPIA

Marfan’s Staphyloma

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Complication of myopia

1-RD

2-Macular degeneration.

3-Cataract

4-Open angle glaucoma.

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Hyperopia

• Parallel rays converge at a focal point

posterior to the retina

• Etiology : not clear , inherited

• Causes: • excessive short globe (axial hyperopia) : more

common

• insufficient refractive power (refractive hyperopia)

• Hyperopia forms a stage in normal development of

the eyes—at birth eyes are hypermetropic (2.5 to 3.0

Diopters).

When persists in adulthood it represents an imperfectly

developed eye.

• Lens changes (cortical cataract).

• Special forms : lens dislocation , postoperative aphakia

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HYPEROPIA

• • hyperopic persons must accommodate

when gazing into distance to bring focal

point on to the retina more than normal

people .

• Hyperopia may be partially compensated

for by using the eyes’ accommodative

ability this is possible during the first two to

three decades of life

• • When accommodative ability cannot

keep up with demand, hyperopia is

manifest and images are blurred in the

distance and for near and the need for

reading glasses arises earlier than in the

normal person.

• Typical complaint is difficulty reading.

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Hyperopia

• Symptoms

• Typical complaint is difficulty reading

• visual acuity at near tends to blur relatively early

• nature of blur is vary from inability to read fine print to near

vision is clear but suddenly and intermittently blur

• blurred vision is more noticeable if person is tired , printing

or inadequate light .

• Extremely good distant vision (6/4)

• asthenopic symptoms : eyepain, headache in frontal region,

burning sensation in the eyes, blepharoconjunctivitis.

• Young children with significant hypermetropia can also

develop a convergent squint.

• accommodative esotropia : because accommodation is linked

to convergence -->ET

• Amblyopia – uncorrected hyperopia > 5D

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Hyperopia

• Fundus in axial hyperopia may reveal

pseudooptic neuritis (indistinct disc margin, no

physiologic cup, maybe elevated disc)

• DDx from optic neuritis by :>=4D, no enlarged

blind spot, no passive congestion of vein

• Treatment : convex lenses, keratorefractive

surgery, refreactive lensectomy with IOL, phakic

IOL

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Uncorrected, light focuses behind fovea

Corrected by convergent lens, light focuses on fovea

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PATHOLOGICAL CAUSES OF

HYPEROPIA

DISLOCATED LENS

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PATHOLOGICAL CAUSES OF HYPEROPIA

RETINAL DETACHMENT

1 mm = 3D

RETINAL FLUID

CHOROIDAL TUMOR

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Complication .

They are more susceptible to closed angle glaucoma

because there smaller eyes are more likely to have

shallow A.C and narrow angles.

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Astigmatism

• Parallel rays come to focus in 2 focal lines rather than a

single focal point

• Etiology : hereditary

• Cause : Astigmatism present when the cornea

curvature is irregular (Refractive power of the cornea in

different planes is not equal).

In short, astigmatism occurs whenever the vertical

curvature of the cornea is different from the

horizontal.

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Astigmatism

• Classification

• Regular astigmatism : power and orientation of

principle meridians are constant

• With the rule astigmatism , Against the rule

astigmatism , Oblique astigmatism

• Simple or Compound myopic astigmatism ,

Simple or Compound hyperopic astigmatism ,

Mixed astigmatism

• Irregular astigmatism : power and orientation of

principle meridians change across the pupil.

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• Keratoconus is pathological cause of

irregular astigmatism

• Simple astigmatisum : one focal point on

retina other in front

• Compound astigmatism : 2 points in front

or 2 behind

• Hypermetropic : 2 points behind retina.

• Mixed : 1 point in front other behind.

• With rule astigmatism : when the steeper

meridian is vertical.

• Against rule : when steeper meridian is

horizontal .

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Astigmatism

• Symptoms

• asthenopic symptoms ( headache ,

eyepain)

• blurred vision

• distortion of vision

• head tilting and turning

• Amblyopia – uncorrected astigmatism >

1.5 D

• Treatment

• Regular astigmatism :cylinder lenses with

or without spherical lenses(convex or

concave), Sx

• Irregular astigmatism : rigid CL , surgery

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Treatment of astigmatism

• 1. Laser, Intraocular toric lenses, Limbal

relaxing incision

• Contraindicated to do LASIK as it needs

good thickness of cornea and regular

curvature .

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Pathologic Causes of

Astigmatism

• Corneal: post surgical, traumatic,

infectious

• External pressure on cornea: lid masses

• Lens: pressure on lens from tumors

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Presbyopia

• Physiologic loss of accommodation in advancing age due to age related loss of elasticity of the capsule.

• deposit of insoluble proteins in lens in advancing age-->elasticity of lens progressively decrease-->decrease accommodation.

• Around 45 years of age , accommodation become less than 3 D-->reading is possible at 40-50 cm-->difficultly reading fine print , headache , visual fatigue.

• This occurs earlier in hypermetropes than myopes.

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Presbyopia

• Treatment

• convex lenses in near vision

• Reading glasses

• Bifocal glasses

• Trifocal glasses

• Progressive power glasses

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Anisometropia

• Difference in refractive power between 2 eyes

• refractive correction often leads to different

image sizes on the 2 retinas( aniseikonia)

• aniseikonia depend on degree of refractive

anomaly and type of correction

• closer to the site of refraction deficit the

correction is made-->less retinal image changes

in size ??

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Anisometropia

• Glasses : magnified or minified 2% per 1 D

• Contact lens : change in size less than glasses

• Tolerate aniseikonia ~ 5-8%

• Symptoms : usually congenital and often

asymptomatic

• Treatment

• anisometropia > 4D-->contact lens

• unilateral aphakia-->contact lens or

intraocular lens

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Diagnosis OF refractive errors :

not required

•Diagnosis of refractive errors is made by an

optician or ophthalmologist.

•Instruments used to diagnose refractive errors

include:

- pinhole glasses

- Autorefractor (measures how light changes as

it enters the eye).

-Retinoscope (measures the refractive

condition of the eye).

- Phoropter.

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Pinhole glasses Autorefractor

View through an autorefractor Phoropter

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Pinhole Test

• Light rays that are

perpendicular to the lens

do not refract , but go

straight forward.

• If visual acuity improves

with the pinhole test, then

this is a refractive error; if

it worsens, then this is a

central field defect.

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Types of optical correction • Spectacle lenses

• Monofocal lenses : spherical lenses ,

cylindrical lenses

• Multifocal lenses

• Contact lenses:

• higher quality of optical image and less

influence on the size of retinal image than

spectacle lenses

• indication : cosmetic , athletic activities ,

occupational , irregular corneal

astigmatism , high anisometropia ,

corneal disease.

• Can be: soft, hard, gas-permeable,toric

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• Contact lenses

• disadvantages : careful daily cleaning and

disinfection , expense

• complication : infectious keratitis , giant

papillary conjunctivitis , corneal

vascularization , severe chronic

conjunctivitis

• Intraocular lenses

• replacement of cataract crystalline lens

• give best optical correction for aphakia , avoid

significant magnification and distortion caused

by spectacle lenses

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Hard lenses:

• Plastic polymer.

• Most durable.

• Rigid, therefore may scratch the cornea.

• Not gas permeable corneal hypoxia corneal

ulcers.

• Cannot be worn continuously.

• Difficult to get used to (because they are very rigid).

• Less susceptible to infection and allergy.

• Best for treating astigmatism (smoothes out the

uneven curvature).

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Hard contact lenses are used in orthokeratology: the

fitting of a series of rigid contact lenses to reshape the

cornea. It is an alternative to glasses and surgery

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Soft lenses:

* High water content.

* Less durable.

* Permeable for both gases + liquids.

* Could be worn for long periods.

* Tolerated much better.

* They do correct astigmatism.(MILD ONE )

* Are the most comfortable lenses.

* Are the least durable lenses (must be replaced

more often).

•Susceptible to accumulation of deposits (because

they absorb more water, which binds proteins). This

accumulation of protein deposits leads to allergic

conjunctivitis and other allergies.

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Gas permeable lenses

(Semi-rigid):

•They are permeable only to gases.

•They are more comfortable than hard

lenses, but less than soft ones.

•They are more durable than soft lenses, but

less than hard lenses.

•Allow oxygen to pass, but also allow

proteins to deposit.

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Toric lenses:

Are similar to soft contact lenses, but

have a couple of extra characteristics:

•They have 2 powers in them: 1 for

spherical correction + 1 for astigmatism.

•They are designed to keep the lens in a

stable position even on movement.

They offer the comfort of soft lenses ,and at

the same time they correct astigmatism, but

their disadvantage is that the lens will

sometimes rotate, and this creates a very

irritating change in vision as the lens rotates.

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Contraindications to using

contact lenses:

* History of atopy.

* Dry eyes.

* Previous glaucoma filtration

surgery.

* Inability to handle and cope

with the lenses.

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Refractive Surgery Techniques

• Radial Keratotomy (RK) not used anymore.

• Freeze keratomileusis not used anymore.

• Photorefractive Keratectomy (PRK)

• Laser Epithelial Keratomileusis (LASEK)

• Laser-assisted in-situ Keratomileusis (LASIK)

• Others: • Astigmatic Keratotomy (AK)

• Intracorneal ring segments (Intacs)

• Phakic Intraocular Lens Implants

• Refractive lensectomy

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Surgery classified into :

• Flab : LASIK > and doing a flap needs

good thickness of cornea and regular

surface {so not made for keratoconus nor

astigmatism} and being not susceptible to

trauma after surgery unlike boxer or

solider.

• Surface ablation : SPRK (LASER) ,

LASEK > here we remove part of the

regenerative epithelium .

• LASIK has faster(2-3 days) post op

recovery than Surface ablation(5-7days) .

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Laser technology

• Excimer laser: EXCited dIMER

• AKA “cool laser beam” because little thermal damage to adjacent tissues.

• 193nm wavelength ultraviolet laser with sufficient energy to disrupt intermolecular bonds within the corneal stromal tissue (photoablative decomposition).

• First excimer lasers FDA approved in 1995, with beam width 4-5mm, now available less than 100 microns.

• Each laser pulse removes a given volume of stroma

• Three types of laser application: wide-area ablation, scanning slit, and flying spot lasers.

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Laser technology

• In myopia, laser flattens central cornea to decrease its focusing power to bring secondary focal point back to retina.

• In hyperopia, the laser removes peripheral corneal tissue thereby secondarily steepening the central cornea, increasing the focusing power of the cornea.

• Astigmatism treated with elliptical or cylindrical beams that flatten the steepest corneal meridian.

• To minimize glare and halos, optical zone should be larger than the dilated pupil.

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Myopic photorefractive keratectomy

PRK is recommended for some patients

who cannot undergo LASIK. These

include:

Patients whose corneas are too thin to

have LASIK &Patients whose corneas are

scarred (from infection or trauma).

• PRK can effectively treat low to mod myopia or hyperopia +/- astigmatism.

• Performed as outpt with topical anesthesia.

• First, the corneal epithelium in the area to be ablated is removed to expose Bowman’s layer and the underlying corneal stroma (spatula, laser).

• Excimer laser then applied as directed by the corneal topography-driven computer program.

• Topical antibiotics, steroids, and NSAIDs applied, along with a bandage contact lens (BCTL)

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PRK • In the post-op period, pt may experience tearing,

photophobia, blurred vision, and discomfort due to abrasion of central epithelium.

• This can be controlled with topical steroids and NSAIDs.

• Pts occ. require systemic analgesia for severe pain

• BCTL removed once epithelial defect healed (avg 3-4 days).

• Abx continued several more days, and steroids for up to 3 months post-op.

• Visual acuity improves once the epithelial defect heals, but fluctuates for a few months and finally stabilizes at ~3 months.

• Glare, halos, and dry eye symptoms common in the first month post-op, usually diminishing/disappearing by 3-6 months.

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Laser Sub-Epithelial

Keratomileusis

• LASEK can treat mild to moderate myopia and hyperopia +/- astigmatism.

• Can be performed as an outpt with topical anesthesia

• The corneal epithelium is incompletely incised using a microkeratome with a 70 micron deep blade.

• A hinge is left at the 12 o’clock position.

• Dilute alcohol (20%) drops are applied to the exposed tissue and left for ~30 seconds. The area is then washed with water and allowed to dry. The excimer laser is applied as in PRK to the sub-epithelial stroma.

• The epithelial flap is repositioned afterward.

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LASIK

• The use of the suction ring helps hold the cornea steady and provides for a uniform cut by the microkeratome.

• Flaps can be formed by an automated process involving a blade guide on the suction ring to guide a turbine-driven microkeratome, producing a very smooth, regular cut

• Patients usually sent home on topical antibiotics, steroids, and NSAID drops

• Benefits include little pain, quick recovery of vision, and potential to treat higher levels of myopia. LASIK enhancements are also easily performed.

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LASIK

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LASIK Complications

• Potential complications: • Intra-operative flap complications: microkeratome

complication with a higher rate with surgeon inexperience

• Post-operative flap complications

• Flap-bed interface epithelialization: that epithelial growth at the interface could significantly be reduced by irrigating the stromal surfaces and using a BCTL for one day.

• Irregular astigmatism

• Infection:

• Diffuse lamellar keratitis (DLK): (AKA Sands of Sahara syndrome) Wavy inflammatory reaction at LASIK flap interface 1-3 days post-op of unknown cause. Treatment involved high-dose topical steroids or lifting the flap to irrigating the interface.

• Progressive corneal ectasia: progressive corneal thinning and steepening with worsening irreg. astigmatism thought to result from too thin a stromal bed after LASIK. Most believe stromal bed thickness should be at least 250 microns.

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Implantable Contact Lenses:

-Between iris + lens.

-Preserves accommodation.

-Complications include:

* Over correction.

* Under correction.

* Infection.

* Increased intraocular

pressure.

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Clear lens extraction + IOL:

•IOL: Intra ocular lens.

•Same as cataract extraction.

•Implantation of artificial lens.

•Lose accommodation (patient will need reading

glasses).

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2 contraindications of refractive eye

surgery

Keratoconus. Thin cornea.

Pregnant. SLE, RA. Autoimmune

disorders. Glaucoma. Diabetes.

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• Glasses:

• Advg > comfortable , no risk for infection, or

dryness or allergy.

• Disadvg > cosmatic , poor quality of vision

esp in high degree , not convenient for

some jobs.

• Contact lens :

• Advg : cosmatic , good quality of vision ,

more convenient .

• Disadvg : infection , allergy , dryness.