Download - Myopia refractive error-M.B
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Myopia
DR. MEENANK
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1. Definition
2. Etiology
3. Optics
4. Classification
5. Clinical varieties in detail
6. Treatment
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Definetion
Myopia ( short sight ) condition where parallel rays come to focus in front of the sentient layer of retina when accommodation is at rest
Muopia (Greek) = To close the eye
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History
Kepler (1611), Plempius (1632) - lengthening of posterior part.
Donders (1866) est.. Pathological basis, and detail clinical manifestation's
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Etiology Axial : most commonest
1mm = 3D
Curvatural : cornea thickness causes astigmatism
1mm = 6D
eg : ectasies
conical cornea
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lenticular curvature
eg : ant/post lenticonus – marked
Positional : dislocation of lens
Myopia due to excessive accommodation - spasm of accommodation,
suspensory lig. Rupture
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Index myopia : change in the R.I of the crystalline lens
eg : Nuclear Sclerosis,
Incipient Cataract,
Diabetes.
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Buphthalmos : cong/ infantile glaucoma.
Defective development – A.P diameter enlarged and
myopia not in ratio
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Optics
Optical system – eye too powerful for axial length
Image of distant object on retina are circles of diffusion form by divergent beam
Far point is finite pt in front of eye – object at far pt focused without acc.
Angle of alpha –ve resulting in convergent squint
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Accommodation- uncorrected- not developed , as not needed for Nv. Thus may develop exophoria, convergence insufficiency and presbyopia
Enlarged image is cause of nodal pt being far away from retina
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Classification
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myop
ia
Congenital myopia
Simple (or) Developmental
myopia
Pathological (or) Degenerative myopia
Acquired myopia
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Congenital myopia
Since birth
Diagnosed – 2 -3 yrs.
Associated – prematurity, birth defects, congenital squint, and axial length
Unilateral or bilateral
Unilateral – manifest as anisometropia
diagnosed - after squint- amblyopia
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Associated – cataract, microphthalmas, cong. Retinal separation, megalo-cornea
Prognosis – early detection
no 6/6 uni-ocular
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Simple Myopia
Physiological / developmental / school
Biological variation in development
Limited progression no disease
Factors associated : Axial – A.P diameter (or) neurological
Curvatural – underdevelopment of eye ball
Diet – poor nutriention
Genetic influence – one (or) both parents
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Simple Myopia
Physiological – A/S normal along with normal fundus
Intermittent – early signs of globe enlargement temporally
Sever category of intermittent – crescent with super-traction of disc
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course
Born hyper metropic Emmetropic
• overshoot
Myopic
• 7-10 yrs
Stabilized at teens
• -5D to -8D
symptom's :
Poor distance vision – beyond far point impaired
Asthenopic sympt – eye strain due to difference b/w convergence and accommodation
Nv -No accommodation – convergence weakness – exophoria – suppression of one eye
Nv –convergence – excessive accommodation – ciliary spasm
Physiological out-look – myopic child behavior
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Signs Eye – large and prominent
A.C. – deep
Pupil – large and sluggish
Fundus – normal
Error - -5.00 D to -8.00D
Diagnosis –visual acuity
subjective testing
retinoscopy
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Pathological Myopia
Degenerative / progressive
2-3 %
More marked, high degree
Hereditary
Postnatal
Inc. progressive
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Prevalence –
earlier and higher in females
higher – Asians, Arabs, Jews
lower – Africans, Caucasians
more in urban populations
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Etiology
Results from rapid growth of eye out side its biological variation
2 theories
- Hereditary
- General growth Genetic factors
Retinal growth Scleral
stretchingIncrease in axial length
Pathological myopia• Degeneration – choroid, retinae,
vitreous
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Symptoms Diminished Vn – progressive due to degeneration
Muscae volitantes – deg. lig. Vitreous
Night blindness – high myopes with choroidi-retinal changes
Signs Prominent, elongated(post), unilateral, stimulating
exophthalmos
Cornea – large; A.C – deep; pupil – large, sluggish
Refractive error – by -4D/yr up to 20-30yrs
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Fundus – Generalized atrophy of choroid and retinae
Loss of RPE- fundus tugroid- prominent choroidal vessels
Choroid disappears – visible sclera – atrophic patch - post. Pole – macula (common)
Foster – Fuchs's spots – rare, sudden, dark pig.
sub-retinal neovascularization and choroidal hx.
Cystoid degeneration at periphery
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Advance cases – total retinal atrophy, central
Lattice degeneration/ snail track lesion
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Optic disc Myopic crescent – from elongation of disc
separation of retina and choroid from temp
may be annular
Super traction crescent – nasal retina extending over the disc – blur margin
Posterior staphyloma – higher degree,
herniation of post. Pole – sudden kinking of vessels at margin as in glaucoma
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Vitreous – degeneration, PVD-Wiess reflex, liquefaction, opacities
Visual field – ring scotoma
Electo-retinograph – chorioretinol atrophy
Complications retinal tears, detachment, Hx (high myopia)
vitreous detachment, degeneration
complicated cataract –↓ lenticular metabolism
Nuclear sclerosis – common, effects refraction
Choroidal Hx – sever Vn loss if in fovea
POAG – not common but seen
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acquired index – nuclear sclerosis, incipient cataract, diabetic myopia
Curvatural – true inc. in corneal curvature (or) lenticular
Positional – subluxation(ant) of lens
Consecutive – surgical overcorrection(cataract/ hypermetropia)
Pseudo-myopia – due to excessive accommodation and spasm of accommodation
Space myopia – no stimulus for Nv, its variable, trouble in flying and in fog
Night/twilight – shift from photic to scotopic vn is associated with inc. sensitivity to shorter wavelength viz myopic
Drug induced - Cholinergic – pilocarpine, echothiosulphate
Steroid – show changes in crystalline lens
Sulplanamides – changes the refractive indices in media
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Diagnosis
presentation Simple – blurred Dv, constant/ transient, Nv may be normal, co-existing condt.
Nocturnal – blurred Dv in dim illumination, difficulty in driving
Pseudo myopia – transient Dv blur, inc after near work
Degenerative - considerable Dv blur, flashes/ floaters, Vn loss
Induced – transient Dv blur until drug effect, pupils constricted – cholinergic antagonist
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Ocular examination
Visual acuity – both unaided Nv and Dv should be measured-mean gives reduced V.A
Refraction – retinoscopy or and A.R. , but A.R not qualitativeretinoscopy – diagnosis for nocturnal myopia with cyclopegics
Ocular motility, binocular Vn, accommodation – heterophoria, versions, accommodative facility test
systemic and ocular health – IOP, SLB, post-segment
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Special test Fundus Photography
A and B scan
Visual field
Fasting blood sugars
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Treatment
Optical Correction Proper correction with concave lens for image to fall on retina
Myopia up to -6.00D Children – full correction
Young adults – prevent over correction
Adults - ↓ 30 yrs. – full correction
↑ 30 yrs. – under corrected – ciliary muscles fail to accommodate
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Spectacle's
Economical, safe
Allow incorporation
Better correction of astigmatism
Less acco- near pt. blur in presbyopia
Contact lens
Larger retinal image
Better Vn in Sr. myopia
Better visual field
Dec. prismatic effect
Rigid lens dec. progressive myopia
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Surgical Treatment
Incisional – Radial Keratotomy
Lamellar corneal refractive Sx
Freeze keratomileusis of Barraque for myopia obsolete
Non-freeze keratomileusis
Keratomileusis insitu
Automated lamellar keratoplasty
Laser-based corneal refractive Sx
Photorefractive keratectomy (PRK)
Laser insitu keratomileusis (LASIK)
Custom Laser insitu keratomileusis (C-LASIK)
Epithelial Laser insitu keratomileusis (E-LASIK)
Miscellaneous corneal refractive Sx
Orthokeratology
Intracorneal contact lens
Intra stromal corneal ring segment
Intra ocular refractive procedure's
Phakic refractive lens
Refractive lens exchange
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Radial keratotomyPhotorefractive keratectomy LASIK
Intraocular refractive procedure's
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Radial keratotomy Deep radial incisions (90% thickness) sparing central 4mm –
cornea flatter's on healing
Disadvantages – globe rupture, irregular astigmatism, glare, bullous keratopathy
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Photorefractive keratectomy (PRK)
De-epithelialzation – photo ablative0.5.1.0mm morePrevent extreme drying or wetting of cornea and residual islands
Ablation – 6mm for myopiaHand held ring for centration Laser should be coaxial with pupilToric photoabalation
corneal curvature shifts as ant stroma collapse and thins
Intrastromal PPk – double NdYAG Plasmamediated photodistribution shock wave
Complications – decentationCorneal haze, infiltrates, ulcersNight glare , halosDelayed epi healingIslands, Hx, IOP↑
First refractive procedure to use the excimer laser Max success in myopia Good for -2.00D to -6.00D Photoabalation of central optical zone of ant.
Corneal stroma
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Combination – Incisional & Ablative Procedure
LASIK - Laser In Situ Keratomileusis
Microkeratome to make a corneal flap – excimer to ablate the refractive error
adv – bilateral, PRK healing risks avoided, stable results
Dis-adv – flap related, striae, diffuse lamellar keratitis, under (or) over correction
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LASEK – LASER Epithelial Keratomileusis Similar to PRK – epithelium is removed and replace post Sx
Alcohol to store the epithelium
For large pupils and thin corneas
For > -8.00 D
Adv – no risk of flap dislocation (LASIK)
Thin flap
Less chance of ectasia
Dis- adv – visual recovery slower than LASIK
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Epi LASIK Newer version of LASEK- advantage on LASIK
Cleaves epi from bowmen's – structural integrity maintained
More thin flap, less haze, faster recovery
Custom LASIK Customized for each eye
Less halos and glare, More chance of 6/6
Wave front aberrometer - corneal topography
Ablation – flexible laser system
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Intra ocular refractive Sx
Refractive lens exchange Existing cataract and cornea unfit for refractive
Sx
For -16.00D to -30.00D
PCO reduced
Accommodation retained thrgh ‘hinges’
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Phakic IOLs Patients not qualified for refractive Sx
Ant / Post chamber lens with out removing crystalline lens
Made of plastic (or) silicone
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Management flow chart
Patient history and examination
Supplemental testing Assessment and diagnosis
Patient counseling and education
Treatment and management
Simple myopia
Correction
Infants and toddlers – no correction < 3DPre-school/early-school – correct if
>1-2DAdolescent's/
adults – correct significantly
Controlplus lens for NvRigid contact
lensVisual hygiene
ReductionCorneal
modification – refractive
Sx
Nocturnal myopia
Myopia correction for night
time seeing only
Pseudo-myopia
Reduction of accommodative
response – vision therapy,
plus lens for Nv, cycloplegic
agents, visual hygiene
Degenerative myopia
Correction and
management of retinal
changes
Induced myopia
Identification and
treatment of causative
agent
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If a man is called to be a street sweeper,
he should sweep street so well that all the
host of heaven and earth will pause to
say, here lived a great street sweeper
who did his job well.
- Martin Luther King, Jr.